final draft urban polder guidelines volume 1: general aspects

FINAL DRAFT

Urban Polder Guidelines

Volume 1: General Aspects

Bandung, January 2009

Preface

1

Preface

Four Guidelines on Urban Polder Development have been prepared within the framework of the

Banger Polder Pilot Project (2007 - 2009). This was one of the projects under the Memorandum

of Understanding between the Indonesian Ministries of Public Works and of Environment and

the Netherlands Ministries of Transport, Public Works and Water Management, and of Spatial

Planning, Housing and Environment. The themes of the guidelines are: General Aspects,

Institutional Aspects, Technical Aspects, and Case Study Banger Polder, Semarang. Support to

this project was given by the programme Partners for Water and Rijkswaterstaat.

The guidelines were prepared by a joint working group, consisting of:

• Indonesia:

∗ Dr. Arie Setiadi Moerwanto, MSc, Research Centre for Water Resources;

∗ Ir. Joyce Martha Widjaya, MSc, Research Centre for Water Resources;

∗ Dr. William Putuhena, MSc, Research Centre for Water Resources;

∗ Dr. Ibnoe Fajar Poernomosidhi Poerwo, MSc, Directorate General of Spatial

Planning, Dept. of Public Works;

∗ Dr. Benny D. Setianto MSc, Catholic Univ.of Soegijapranata, Semarang

∗ Mr. Nurkholis, Municipal of Semarang Planning Board

∗ Mr. Suhardjono, Municipal of Semarang Planning Board

∗ Mr. Fauzi, Local Public Works Municipal of Semarang

∗ Dr. R.W. Triweko, MSc, Catholic Univ.of Parahyangan, Bandung.

• the Netherlands:

∗ Prof. Bart Schultz, PhD, MSc, Rijkswaterstaat

∗ F.X. Suryadi PhD, MSc, UNESCO-IHE

∗ Mr. Martijn Elzinga, Rijkswaterstaat

Substantial input to the guidelines has been obtained from the Banger Pilot Polder Project team.

Drafts of the guidelines have been presented and discussed in two workshops with Central,

Provincial and Municipal government staff. The comments made during these workshops have

been incorporated in these guidelines.

Urban polder guidelines, Volume 1: General

2

The authors like to thank the Ministry of Public Works, the Municipality of Semarang, the

Principle Water-board of Schieland and the Krimpenerwaard, Witteveen + Bos, and all others

that have given input during the preparation of these guidelines.

We hope that the guidelines may contribute to an improved development and management of

urban polders in Indonesia.

Contents

3

Contents

Preface 1

Contents 3

1 Introduction 5

1.1 Definition of a polder 9

1.2 Background and scope of the guidelines 12

1.3 Purpose and objectives of the guidelines 14

2 Polder development in Indonesia 16

2.1 Historical development 16

2.2 Urban polders in Indonesia 16

3 Polder perspectives 23

3.1 Overall process cycle 24

3.2 Socio-economic aspects 25

3.3 Policy, legal and institutional aspects 25

3.4 Environmental impacts 25

3.5 Spatial planning 25

3.6 Technical aspects 26

4 Planning 28

4.1 Identification of potentials and constraints 28

4.2 General planning framework 28

4.3 Land and water development framework 30

4.4 Spatial planning approaches 30

4.5 Water resources aspects 32

4.6 Geo-technical aspects 34

4.7 Environmental aspects 35

4.8 Policy, social, economic aspects 35

4.9 Community involvement 36

4.10 Institutional and legal aspects 37

4.11 Procedures 37


4

5 Design aspects of urban polders 40

5.1 Urban polders in the river basin context 40

5.2 Local parameters and conditions 40

5.3 Impoldering principles 43

5.4 Polder infrastructure 44

5.5 Feasibility aspects of urban polder development 46

5.6 Landscape and land use planning 47

5.7 Design criteria 47

5.8 Design approaches 50

5.9 Impacts of subsidence and sea level rise 50

5.10 New technologies 51

6 Construction aspects of urban polders 52

6.1 Dikes, outlets and inlet structures 52

6.2 Urban drainage systems 53

7 Operation, maintenance and management of urban polder water management and

flood protection systems 56

7.1 Operation of structures 57

7.2 Maintenance of urban polder water management and flood protection systems 58

7.3 Laws, regulations and permits 59

7.4 Institutions in charge 59

7.5 Stakeholder participation 60

References 61

Annex I. Glossary 67

1 Introduction

5

1 Introduction

In 1950 30% of the world’s population lived in cities, in 2000 it was 47% and it is envisaged

that it will be 60% by 2030 (Figure 1.1). Such a rapid urbanization, particularly in the emerging

countries, creates many opportunities and challenges (Schultz, 2006 and 2008). Figure 1.1 also

shows that the urbanisation in Indonesia goes even faster than in Asia, where the urbanisation is

already faster compared to the world scale. Especially in South and South-East Asia we see in

addition the development of ‘mega cities’. Mega cities are defined as urban areas with more

than five million inhabitants. It is estimated that by 2015 the world may contain as many as 60

mega cities, including Jakarta and Bandung, together housing more than 600 million people.

They are located where much of the worldwide process of urbanization is taking place (Figure

1.2) (UNDP Population Reference Bureau, 2007).

0

10

20

30

40

50

60

70

80

90

100

1950 1960 1970 1980 1990 2000 2010 2020 2030

Year

Per

cen

tag

e u

rban

po

pu

lati

on

Indonesia Asia World Netherlands

Figure 1.1. Development of percentage of the urban population living in Indonesia, Asia, the

world and the Netherlands

In the emerging countries, urban areas grow faster than their infrastructure, water management

and flood protection provisions. This is the more important while the major part of the

urbanisation takes place in flood prone lowland areas in the coastal zone, in river flood plains

and in deltas. While generally the good land has already been urbanised increasingly new urban

areas have to be developed in flood prone lowland areas, which often may imply polder

development (Oudshoorn et al., 1999).


6

Figure 1.2. Location of the mega cities by 2015 (UNDP Population Reference Bureau, 2007)

In the last three decades, the rapid development of Indonesia and the growing population

required excessive conversions of mainly agricultural land and land reclamation mainly for

industrial and urban development (human settlements) (Figure 1.1). Expansion of large cities

takes place at a very high speed, especially of Jakarta (Figure 1.3), Semarang and Surabaya.

In these large cities, polder development is done for the development of new areas with up to

date technology by project developers and in the existing urbanised areas by government and

the local people. Unfortunately, in the second case, so far, this development was often not

carried out based on a well-balanced approach between resources utilization and valuation of

ecological functions as called for in the principles of conservation. As a result urban drainage

and flooding1 problems, salinity intrusion in the groundwater and land subsidence have

increased significantly, both in the urban areas themselves as in the surrounding areas.

1 The terms ‘flood’ and ‘flooding’ are often used in different ways. In these guidelines the words will be

based on the following definitions:

• a flood is a temporary condition of surface water (river, lake, sea), in which the water level and/or

discharge exceed a certain value, thereby escaping from their normal confines. However, this does

not necessarily result in flooding (Munich-Re, 1997);

• flooding is defined as the overflowing or failing of the normal confines of a river, stream, lake,

canal, sea or accumulation of water as a result of heavy precipitation by lacking or exceedance of

the discharge capacity of drains, both affecting areas which are normally not submerged (Douben

and Ratnayake, 2006).

1 Introduction

7

Figure 1.3. Growth of Jakarta from 1972 - 2005

To improve this situation, a systematic approach to urban polder development and the related

water management and flood protection schemes would need to be applied, taking into account

technical, socio-economic and environmental aspects. An illustration of a polder system in

relation to urban drainage and flood protection is presented in Figure 1.4.

Figure 1.4. Urban polder system

To develop an urban polder requires wise use of human and natural resources while, at the same

time, one needs to consider and limit the risk that cities pose on the quality of life for those who

live in, or are impacted by that development. The development and management of an urban

polder may host complex interactions between different demographic, social, policy, economic


8

and ecological processes. These processes often generate considerable opportunities, as well as

strong pressures for change, accompanied by environmental degradation. Based on the

framework of sustainable urban polder development as presented in Figure 1.5, it may be

observed that the government and private sector will play important and interrelated roles in

urban polder development and management (Figures 1.6, 1.7, 1.8).

Figure 1.5. Framework of sustainable urban polder development

In this Volume 1: General Aspects of the urban polder guidelines a general review will be

presented of the various relevant aspects. Attention will be paid to:

• definition of a polder, background and scope, as well as the purpose and objectives of the

guidelines;

• polder development in Indonesia;

• polder perspectives;

• planning;

• design aspects of urban polders;

• construction aspects of urban polders;

• operation, maintenance and management of urban polder water management and flood

protection systems.

This is the first volume of a set of four guidelines. The other three volumes give information on:

• Volume 2: Institutional Aspects;

• Volume 3: Technical Aspects;

• Volume 4: Case Study Banger Polder, Semarang.

1 Introduction

9

Figure 1.6. Urban drain Figure 1.7. Pumping station

Figure 1.8. Transportation infrastructure

1.1 Definition of a polder

A polder system is an engineering alternative that is appropriate and effective for flood control

and supports the development of rural and/or urban areas in lowland flood prone zones. For

successful development and management community involvement is needed. To ensure the

sustainability of management of the polder system, the involvement of the stakeholders or

communities who live inside the polder areas is required.

A polder system consists of dikes, drains, retention ponds, outfall structures or pumping stations

and other components, that create one integrated system. This system would have to be designed

in accordance with the location and the problems faced. Construction of a polder system can not

be done separately, but needs to be planned and implemented in an integrated way, with the

adjusted spatial plan and water management of the macro (river basin) system. Combination of

outfall structure or pumping capacity and retention in the drains and ponds would have to be


10

able to control the water level in a polder area and may have no negative impact on the drainage

system as a whole.

Polders can be found all over the world. Originally they were generally developed for

agricultural land use, but nowadays they can be developed for multiple land use, and especially

in densely populated countries for urban, or industrial land use. The need to create polders can

also gradually develop when the conditions in reclaimed lowlands deteriorate due to subsidence,

to a certain extent in combination with sea level rise.

Several definitions of polders exist. The most widely used ones are:

• ‘A polder is a tract of lowland reclaimed from the sea, or other body of water, by dikes,

etc. In the polder the runoff is controlled by sluicing or pumping and the water table is

independent of the water table in the adjacent areas’ (International Commission on

Irrigation and Drainage (ICID), 1996);

• ‘A polder is a reclaimed level area, with an originally high groundwater table, that has

been isolated from the surrounding hydrological regime and where the water levels

(surface and groundwater) can be controlled’ (Volker, 1982);

• ‘A polder is a level area, in its original state subject to high water levels (permanently or

seasonally, originating from either groundwater or surface water), but which through

impoldering is separated from its surrounding hydrological regime in such a way that a

certain level of independent control of its water table can be realized’ (Segeren, 1983).

In these guidelines the last definition will be used, as it leaves room for different configurations

and stages of polder development. This, despite the fact that this definition also makes it

possible to include areas, like rice fields, which obviously are not to be considered polders.

Using this definition, distinction can be made between polders in areas where waterlogging (or

even inundation) occurs either permanently (swamps, shallow sea and lake beds) or temporarily

(tidal lowlands, seasonally flooded river plains, low lying urban areas). This leads to a

distinction into three groups of polders, namely:

• impoldered low-lying lands;

• lands reclaimed from the sea;

• drained lakes.

Polder development and management requires a shared commitment. The role of the polder

community institution – which will be called Polder Board in these guidelines - is very

important in ensuring the sustainability of the urban polder area. Through the Polder Board, the

1 Introduction

11

community will be able to continue managing the activities related to sustainable polder

management, although the formal development project has been completed. When the Polder

Board sustains, it shows that the community has started to be independent. They have the

confidence, ability and commitment to manage the water management and flood protection

infrastructure of the polder which was built to overcome the problems of flooding and

inundation in the place where they live, conserve the local environment, may also improve the

economic situation, and to increase social life stability of the community. Therefore, it needs

serious attention of all parties who undertake the empowering programs for the Polder Board,

namely how to prepare a strategy that all parties give full support to the Polder Board.

The type of planning for an urban polder is entirely dependent on the way in which the polder

comes into being. If an urban polder is reclaimed from the sea or a lake, there is no local

population yet and no existing infrastructure to be considered. The possibilities for development

in the original state are generally limited, although the former users of the water (fisheries,

tourism sector) may have to be indemnified. But, if an urban polder is constructed in the

existing low-lying area, the planning will have to take into account the existing infrastructure

and the demands of the local population. Spatial planning alone is not enough for a successful

development of an urban polder; socio-economic planning is of equal importance, since only

this can guarantee that alternative solutions are considered to satisfy competing interests.

In an urban polder, the water level has to be maintained at a certain preferred level, not only

because of its land use but also because the stability and sustainability of construction works

depend on that water level. Therefore, urban polder water management is primarily concerned

with urban drains, structures and outlets. However, there is more to it. The water management

system has to be cleaned regularly; the drainage water must be drained by gravity where

possible through sluices at low outside water levels, or be pumped out from the polder when

drainage by gravity is not possible anymore. Maintaining of an agreed water level is also

essential for the natural landscape. Therefore urban polder water management requires a good

organization, with a thorough knowledge of what is an urban polder about.

Development of an urban polder cannot be carried out by the local population and stakeholders

alone. Effective guidance by supporting institutions is indispensable. It is necessary to help the

population in the polder in the proper operation, maintenance and management of the system

and in introduction of new techniques. However, the development of an urban polder cannot be

successful without concurrent development or adjustment of the social infrastructure. Thus, in


12

the first instance the institutional establishment or organization for the operation and

maintenance of the system will be needed.

1.2 Background and scope of the guidelines

In June 2001 a Memorandum of Understanding (MoU 2002 - 2005) was signed between the

Ministry of Settlement and Regional Infrastructure and the Ministry of Environment of the

Republic of Indonesia and the Ministry of Transport, Public Works and Water Management and

the Ministry of Housing, Spatial Planning and Environment of the Netherlands. This MoU was

renewed in 2006.

The MoU facilitated the Indonesian and Netherlands partners to seek solutions for the regular

flooding in several of the Indonesian water front cities. A seminar and workshop were organized

in November 2001 on the subject ‘Polder Systems in Waterfront Cities, a polder system as a

sustainable solution for flooding’. Indonesian participants in this seminar were represented by

the IRE, the Ministry of Settlement and Regional Infrastructure, the faculty of Social Affairs

and faculty of Civil Engineering of the UNPAR and the Municipality of Semarang. Two Water-

boards represented the Netherlands participants, i.e. Principle Water-board of Rijnland and

Water-board Groot Salland, Rijkswaterstaat, Road and Hydraulic Engineering Division (DWW)

of the Ministry of Transport, Public Works and Water Management, and the consulting firm

Witteveen+Bos. At the end of the seminar, conclusions, recommendations and a ‘resolution’

were presented. The Indonesian attendants of the seminar submitted the ideas, as laid down in

these documents, to the national authorities as well as to the authorities of Semarang city, which

approved them. Then the Semarang pilot polder idea was born.

Semarang municipality and the Ministry of Public Works, together with the other involved

parties in Indonesia, assessed the statements from the seminar. A Plan of Approach was

presented to the Municipality of Semarang. During this presentation the involvement of

Netherlands expertise with respect to institutional strengthening was requested. The need and

the interest for cooperation between the Indonesian and the Netherlands teams in order to

establish a Polder Board within the city of Semarang was stated explicitly. It was concluded that

the ideas as mentioned before would have to be elaborated and described in a project plan. The

project would consist of the following phases:

• Phase 1. Feasibility study;

• Phase 2. Foundation of the Polder Board;

1 Introduction

13

• Phase 3. Implementation of the Polder Board;

• Phase 4. Transfer of knowledge and capacity building;

• Phase 5. Construction of the infrastructure of the pilot polder (turning over of one of the

existing sub systems (approximately 500 ha) to a closed artificial drainage system, that is

called the pilot area).

Subject of the feasibility study was the ‘Institutional strengthening of water management in an

urban polder system as a sustainable solution for flooding problems’. The following parties

performed the feasibility study in 2003 - 2004:

• Agency for Research & Development of KimPrasWil;

• Municipal Government of Semarang City the Republic of Indonesia;

• Ministry of Transport, Public Works and water management of the Netherlands;

• Universities of Semarang and Bandung.

In the feasibility study it was investigated whether there would be sufficient social basis within

the city, the people and the involved politicians to proceed with the proposed approach: self-

financing local water management, based on people’s participation. The conclusion was drawn

that there was a great social basis and ambition among the people involved to proceed with the

establishment of the polder. Even more issues and aspects than originally formulated, were

analysed, studied and investigated. Interviews were held with stakeholders (shop owners,

building owners, industry, municipality, representatives form the inhabitants), meetings were

organised, open hearings, and even the imbedding of a new to be established Polder Board in

the existing organisations was presented. The Mayor of the city was enthusiastic and very

willing to proceed with the process to:

• establish a polder institution embedded in the existing local organisations;

• turn a one sub-drainage area into a so called closed water management system, to prove

that a ‘polder principle’ approach is a solution against flooding.

The Central Government of Indonesia (Public Works) was also very interested and considered

the pilot polder in Semarang as a demonstration model for other locations in Indonesia, like

Jakarta, Surabaya and other ‘sinking’ cities. Besides that the Ministry requested the preparation

of a guideline since the experience of the demonstration project could be spread over Indonesia

and be used for education purposes.

Following these initiatives two projects were awarded that would be interlinked. It concerned:


14

• Institutional setup of the Banger Pilot Polder Board;

• Technical aspects of the development of Banger Pilot Polder.

Related to these two projects guidelines on urban polder water management would have to be

prepared. It concerned the following four guidelines:

• Urban Polder Guidelines. Volume 1: General Aspects;

• Urban Polder Guidelines. Volume 2: Institutional Aspects;

• Urban Polder Guidelines. Volume 3: Technical Aspects;

• Urban Polder Guidelines. Volume 4: Case Study Banger Polder, Semarang

1.3 Purpose and objectives of the guidelines

The purposes of the four guidelines are:

• to be used as guidelines for supervisors, designers and also developers who are involved

in urban polder development projects and activities;

• to support in creating an environment, which is safe for living;

• to be used as guidelines for designing and implementing urban polder water management

systems which will concentrate on water quantity aspects.

The guidelines can be used for supporting designs, operation and maintenance of urban polder

water management and flood protection systems in order to achieve the following objectives

(Butler and Parkinson, 1997):

• maintenance of an effective public health barrier;

• avoidance of local or distant flooding;

• reliability in the long term and adaptability to future (as yet partly unknown)

requirements;

• community affordability;

• social acceptability.

The contents of the guidelines are summarised underneath.

Volume 1: General

The General Guidelines are aiming at providing information for planners, decision makers,

managers and non-experts to understand in general terms the proper way to reclaim and develop

coastal or lowland areas, concerning the scope of works and the global outline of the

1 Introduction

15

methodology. To assess the sustainability of urban polder development, the following indicators

will be presented:

• social progress which recognises the needs of the stakeholders;

• prudent use of natural resources;

• maintenance of stable levels of economic growth and employment.

Volume 2: Institutional aspects

The guidelines on institutional aspects are aiming at providing information for polder authorities

and government agencies that are dealing with, or responsible for legal aspects, organization,

operation, maintenance and management, social aspects and financing of urban polder systems

including water management and flood protection systems.

Volume 3: Technical aspects

The guidelines on technical aspects are aiming at providing information for engineers that are

dealing with, or responsible for investigation, survey, design, construction, operation and

maintenance works of urban water management and flood protection systems.

Volume 4: Case study on Banger pilot polder project

In Volume 4 a case study on the Banger polder area will be presented and discussed. The

information in this volume can be considered as an example of how to design, construct, operate

and maintain an urban polder. It covers legal, social, institutional, financial and technical

aspects, which are primarily based on the local conditions in Indonesia.

The Indonesian authorities could use these guidelines on urban polder development and

management in order to implement urban polder water management and flood protection

systems at those places in Indonesia where this would be required.


16

2 Polder development in Indonesia

2.1 Historical development

As far as it is known the Sisir Gunting Polder (3,000 ha) in North Sumatra is the oldest polder in

Indonesia, construction started in 1924. After 1975 the dikes and sluices gradually deteriorated

to such an extent that more than 1,000 ha became unused. This polder was followed in 1930

with the construction of the polder Alabio (6,000 ha) in South Kalimantan. At present this

polder is being upgraded. Two other polders that were primarily developed for agricultural land

use are the Setjanggang Polder (3,600 ha) on the North coast of Sumatra near Medan, Rawa

Sragi (7,400 ha) in Lampung Province, polders in the delta of the Kali Brantas in Eastern Java

(Group Polder Development, 1982).

2.2 Urban polders in Indonesia

Urban polder development in Indonesia started most probably around 1970 in Jakarta. Also in

Surabaya and Semarang urban polders have been constructed. Especially in Jakarta many small

polders were developed and will have to be developed in the near future (Figure 2.1).

Figure 2.1. Urban polder development in Jakarta


17

Basically two types of urban polders may be distinguished in Indonesia. The first type consists

of the polders that had to be constructed because the existing urban area became too low, mainly

due to subsidence. These areas general have the lay out that was gradually developed in the old

city. The other type consists of the polders that were reclaimed by private project developers.

These areas are generally well developed and have a rational lay out. The characteristics of

some of the urban polders will be described below.

Especially Jakarta and Semarang are waterfront cities, where flooding problems occur primarily

due to land subsidence and to a certain extent also due to the (continuing) rise of the sea level

(Figure 2.2). The data in Figure 2.2 show that especially as a consequence of subsidence more

or less daily flooding occurs and inundation of a few centimetres to decimetres on the streets is

common. This may cause severe disturbance to society and may disrupt not only economic

development of the region significantly, but it also may lead to retreat of companies from these

conurbations. This subsidence problem is acute; it needs utmost attention and solutions at the

short term. A brief review of the urban polders in Jakarta follows underneath.

-7,00

-6,00

-5,00

-4,00

-3,00

-2,00

-1,00

0,00

1,00

1990 2000 2010 2020 2030 2040 2050

year

m+

lev

el

in 1

99

0

Sealevel rise Subsidence 5 cm/year Subsidence 10 cm/year

Figure 2.2. Sea level rise (based on 60 cm/century, highest forecast Intergovernmental Pannel

on Climate Change (IPCC), 2007) and surface level (based on a supposed subsidence of

respectively 5 and 10 cm per year) compared to the reference level in 1990

Pluit Polder, Jakarta

The Pluit polder in Jakarta was developed around 1970. It is mainly used for housing. The Pluit

polder was developed by a project developer that constructed all the houses, road system, dikes,


18

public facilities, retention basins and a gravity outlet in combination with a pumping station

(Figure 2.3). The Pluit polder consists of the following components:

• Pumping stations. There are 11 pumps with a total capacity of 47.3 m3/s. The pumping

system can be grouped into 3 parts: the eastern pumping station consists of 1 pump with a

capacity of 3.7 m3/s and 3 pumps with a capacity of each pump of 3.2 m3/s. The central

pumping station consists of 4 pumps with a capacity of 4 m3/s each and the western

pumping station of 3 pumps with a capacity of 6 m3/s each. The retention basin of Pluit

Polder is presented in Figure 2.4;

• Gates. The gates consist of a weir in combination with siphons. Water will be drained

from the urban drainage canals to the Pluit retention basin;

• Urban drains. Capacities of the urban drains depend on the service area of each block.

Figure 2.3. Pluit Polder in Jakarta

Pantai Indah Kapuk polder, Jakarta

The Pantai Indah Kapuk polder was developed based on the polder system concept. This means

that the area has been provided with dikes to protect it against the seawater and runoff from

upstream. The dikes are also used as part of the road system of the polder. The development

started in the 1990’s. The polder has been completed with physical facilities that include a

drainage network, retention basin and a pumping system in order to maintain the polder water at

a certain preferred level. The layout of Pantai Indah Kapuk is presented in Figure 2.5.


19

Figure 2.4. Pluit Polder retention basin

Figure 2.5 Pantai Indah Kapuk, Jakarta


20

Sunter Polders, Jakarta

The Sunter polders consist of two polders, i.e. Sunter North and Sunter South polder, as

presented in Figures 2.6 and 2.7.

Figure 2.6. Sunter North Polder, Jakarta

Figure 2.7. Sunter South Polder, Jakarta


21

Kelapa Gading Polder, Jakarta

The lay out of the Kelapa Gading Polder is shown in Figure 2.8.

Figure 2.8. Kelapa Gading Polder, Jakarta

Polder Museum BNI, Jakarta

The proposed polder Museum BNI will be located in the old part of Jakarta. It is still in the

study phase. The Museum of BNI will be located between Kali Besar on the West and the

Ciliwung River on the East. During the rainy season these two rivers cause regular flooding. For

example, in 2002 the northern part of Jakarta was flooded, including the area of Museum BNI

with an inundation depth of 0.60 m. The objective of constructing the polder would be to


22

improve the urban drainage system and to protect the Museum BNI and its surrounding area

against flooding during the rainy season. As design criterion for the dike a chance of occurrence

of 1/25 per year will be applied. The location of the BNI polder is presented in Figure 2.9. The

polder will cover an area of 2 ha.

Figure 2.9. Proposed polder Museum BNI, Jakarta

3 Polder perspectives

23


An urban polder system consists of several components, which have to be integrated. The main

components are institutional, social, technical (design, construction, operation and maintenance)

and environmental. The development of urban polder in Indonesia needs to consider a balance

between water for livelihood and water as a resource as shown in Figure 3.1.

Economic

Efficiency

Equity Environmental

Sustainability

Management

Instruments

• Assessment

• Information

• Allocation

Instruments

Enabling

Environment

• Policies

• Legislation

Institutional

Framework

• Central - Local

• River Basin

• Public-Private

Balance ‘water for livelihood’ and ‘water as a resource’ in urban

polder development .

Figure 3.1. Economic and environmental considerations in urban polder development

The development of urban polders in Indonesia would have to take place in the framework of

the river basin system (Figure 3.2) and the planning framework of Indonesia as summarised in

Figure 3.3. In this figure the interactions at the different levels from National to local are shown

Figure 3.2. Urban polder development pattern


24

Figure 3.3. Relationship of spatial and water policies in Indonesia

3.1 Overall process cycle

The overall spatial planning cycle for the development of an urban polder is shown in Figure

3.4. In this figure the different levels of spatial planning and their interactions are shown.

National Spatial Plan

(RTRWN)

ProvincialSpatial Plan

(RTRWP)

DistrictSpatial Plan

(RTRW Kab.)

UrbanSpatial Plan

(RTRW Kota)

Detail Master Plan

(RDTR)

From Dissemination of Act of 26 year 2007on Spatial Planning by A. Hermanto Dardak

Directorate General Spatial Planning Indonesia

(Sosialisasi Undang-Undang No. 26 Tahun 2007)

Zoning Regulation

Figure 3.4. Spatial planning framework for urban polders


25

3.2. Socio-economic aspects

The socio-economic aspects of the two types of urban polders may be quite different. In the

urban polders that were developed due to the increase in flooding problems there was an

existing urban land use that has gradually developed with a variety of stakeholders that may

range from the poor urban population up to rich people, shops, offices and companies. The

polders that were developed by private project developers show a more uniform land use, with

the housing areas generally for the upper class of the population and the related facilities.

3.3. Policy, legal and Institutional aspects

There is not really a policy on urban polder development. There is certain specific legislation

that will be described in Volume 2 of these guidelines. In the first type of polders the

institutional aspects are generally not well developed and there is generally a lack of a clearly

identified Polder Board, with the assigned responsibilities and rights. The polders that were

developed by private project developers have generally a system of operation and maintenance

of the public facilities - including water management and flood protection - that is handled by

the project developer, or its successor in charge of exploitation. The inhabitants of the area pay

for these services to the project developer, or its successor.

3.4 Environmental impacts

The environmental impacts of the two types of urban polders may be quite different. The

environmental impacts of the first type of polders may concern the discharge of solid waste and

wastewater trough the outfalls - either discharge sluice or pumping station - to the receiving

water bodies. Other impacts that may be mentioned are the hampering of the discharge from

upstream areas, subsidence and increase in brackish or saline seepage. The polders that were

reclaimed by private project developers may have similar environmental impacts. However,

generally the collection of solid waste, and in certain cases the treatment of wastewater is better

organised and therefore the environmental impacts are not as significant.

3.5 Spatial planning

Spatial planning is ‘The integration of physical, social and ecological values into a sustainable


26

environment’ (Constandse, 1988). The development of areas determines the living conditions

for the stakeholders/inhabitants for many decades. Therefore spatial planning has to be

implemented in such a way, that for the new urban polders an environment will be created that

the settlers will rent or buy a house and shops, offices and industries will be started. This

especially applies to the polders that were reclaimed by private project developers, while they

want to obtain the best overall result of their investments.

For the polders that had to be constructed because the existing urban area became too low the

spatial planning generally plays a less important role, while generally the urban development

plans for these areas were of a general nature. In this case the crucial issue will be how to

integrate the development of the polder as a separate, but integrated unit in the urban spatial

planning framework (Figure 3.4).

3.6 Technical aspects

The technical project components have to be considered in their interactions and connectivity

with different disciplines, fields and stakeholders. The technical aspects play a role in the

identification of potentials and constraints, in the design phase, the construction phase and in the

operation and maintenance phase. In this Volume the major aspects with respect to the design

will be summarised. In Volume 3: Technical Aspects these aspects will be presented in much

more detail.

Construction and subsidence

Construction aspects are in general not very different compared to construction work outside

polder areas. However, there is a major aspect that will need all attention during the design and

construction phase. This concerns the aspect of subsidence after construction. Subsidence is of

importance for various reasons:

• structures and buildings in urban polder areas often have a pile foundation, which implies

that the level of the structure or building is more or less fixed. When after construction

subsidence occurs the surrounding land, as well as the soil under the structure or the

building will subside. Therefore all cables (electricity, telephone, television, etc.), pipes

(drinking water, wastewater, gas, etc.) need to be connected to the structure or building in

a flexible way, in order to be able to follow the subsidence without damage;

• subsidence may result in uneven settlement and crack formation in structures and


27

buildings;

• subsidence may result in the requirement of lower preferred water levels in the urban

canals, resulting in less discharge capacity in case of drainage by gravity through flap

gates, or tidal gates, gradually increasing requirement of drainage by pumping and finally

increase of the lift in pumping station;

• subsidence of dikes will result in the need to raise the dikes from time to time.

Operation and maintenance

The design of an urban polder water management and flood protection systems needs to take

into account the continuing maintenance requirements of the systems after they have been

constructed. The urban drainage system would have to provide for ease of maintenance and

include adequate access for maintenance equipment. Consequently, designers will need to

familiarise themselves with the capacity and capabilities of the authority responsible for

maintaining the urban polder water management and flood protection infrastructure – the Polder

Board - in order to provide facilities, which can be readily and economically maintained. The

purchase of special maintenance equipment requires considerable lead-time by the maintenance

authority for approvals and funding.

An urban polder water management and flood protection system would also have to be designed

such that maintenance activities can be performed without the risk of inadvertent damage to the

assets of the stakeholders in the polder. Stakeholders in this case include those responsible for

gas, electricity, telecommunications, water supply, solid waste management system and

sewerage services.


28

4 Planning

4.1 Identification of potentials and constraints

The identification of potentials and constraints in planning will be quite different for the two

types of urban polders. For the existing areas it will be of importance to identify potential

problems at an early stage and to prepare the required measures in such a way that they can be

timely implemented within the framework of the existing procedures of decision making and

budgeting. The practice learns that this implies generally a few years before the actual

implementation. For the new urban polder areas the planning will be generally based on the

estimation by the project developer how his organisation can obtain maximum profit from its

investments. The measures with respect to urban water management and flood protection would

have to fit in such overall assessments.

4.2 General planning framework

Background of the general planning framework is coming from the need of the society to have

physical space and public services as reaction on the economic growth or the need for protection

of the region from flooding and the development of the related coastal areas as presented in

Figure 4.1.

Figure 4.1. Background of the general planning framework

4 Planning

29

The fact that cities in Indonesia are rapidly growing implies that many people succeed in

surviving in them. This survival means being busy in earning a living and conquering a little

space. Whether the citizens grow old, are healthy or happy, and whether these cities will be able

to survive ecologically, is a different matter. In quite some cases, this will not be so, unless the

stakeholders combine their efforts for improvement.

To analyse the complicated issue of the actors in sustainable urban polder development, four

ingredients can be used (after Netherlands Development Assistance Research Council

(RAWOO), 2000):

• an organized community, concerned government agencies, credit provider(s), non-

governmental organisations (NGO);

• the concept of good governance with sustainable development as its central objective;

• the basic elements of sustainable and functional cities. According to them, cities ‘must be

livable - ensuring a decent quality of life and equitable opportunity for their residents. To

achieve this, they must be competitive, well governed and managed, and sustainable;

• a ‘city map’ with its surrounding world, with the important categories of actors. It is the

way how these actors: those present in the city but also the more remote ones in the

‘outside world’ interact locally, that defines whether there is or not an ‘enabling

environment’ working towards sustainable urban development promotion.

The conceptual framework of urban polder water management and flood protection systems can

be presented as below (after Ahlman, 2006). See Figure 4.2.

Figure 4.2 Conceptual framework of urban polder water management systems


30

4.3 Land and water development framework

The need for development of urban and industrial areas is caused by the rapid development of

cities all over the world (after Schultz, 1993). Due to this there is a great need for land and water

development, aiming at land reclamation, or at the improvement of living and production

conditions in the reclaimed lands and the development of urban and industrial areas with related

facilities.

The projects will have to be developed and implemented in such a way that on the one hand the

objectives are realised, and on the other hand the environrnenta1 impacts are at an acceptable

level. Projects may strongly differ in type and scale. Answers to the following crucial questions

determine the living conditions of the users for many decades:

• what will be the need for development;

• which level of service will be required;

• what will be the role of the government;

• what will be: the side effects of the development.

Through the history land and water development has gone through different stages. In a wet

country like the Netherlands, for example, first water management activities aimed at reclaiming

lowlands by simple small-scale drainage systems. Due to the resulting subsidence providing

safety against floods followed this. This was initially realised by making artificial mounds and

in a later stage by building dikes (Van de Ven, 2004). Then came the stage of agricultural water

management, which implied the discharge of excess water during winter. Later it also included

the provision of irrigation water for the higher areas. In the twentieth century, the Dutch ran into

a wide variety of water quality problems, which drew much attention in the seventieth and

eightieth. In the ninetieth, attention was drawn to a wider concept of water management, called

‘integrated water management’. In this concept, account is taken of all functions waters fulfil,

including those of nature and environment, so that these functions can be secured on the long

term. In the beginning of the twenty-first century the Dutch are still in this phase.

4.4 Spatial planning approaches

In spatial planning different planning levels may be distinguished, like national planning,

regional planning and local planning. In addition the following stages in planning may be

4 Planning

31

distinguished: proposal, institutional consultation, public consultation and decision.

Each planning level requires its detail, appropriate information and its set of procedures in

decision-making in relation to urban polders. These aspects will be briefly dealt with. Special

attention will be given to useful components of each planning level as well as to the interactions

between the planning levels.

Area and time scales

In each urban polder development project area and time scales may be distinguished. These

scales can be considered as the basic units in a project. For each level a different set of aspects is

of importance and different types of decisions will have to be taken during the development

process. The stages regard:

• area scale: house or building, quarter, local, regional, country, global;

• time scale: one season, one year, lifetime of elements, generation, century.

Area scales

When we go into some more detail regarding the area scales then at each level the items listed

below may be considered:

• at the level of a house, or a building of first importance is which plot size will be required

for the type of house that has to be built, in order to get a product that can be sold or

rented to a future user. Although the plot size is only one of the criteria to be considered,

it is a very important one while it determines the density of houses that can be realised for

example per ha, which will have a strong influence on the feasibility of an urban

development project;

• at the level of a quarter, the number of houses and buildings play a role in order to create

units with a logical ratio. For example a certain type of shop requires a certain number of

clients at a certain number of inhabitants you need a school, a doctor, or a hospital. These

aspects are generally approached at the level of a quarter;

• at local level it is first of all of importance, to determine at a very early stage, why the

area to be developed would attract people who want to settle there. Here aspects play a

role like availability of public transport, access roads, and economic activity;

• at the regional level one would have to consider especially the traffic that will result from

the development, and what facilities would have to be required regarding inter city traffic;


32

• at country scale it is the national settlement policy, which plays an important role;

• at a global scale, although there is certainly no planning at this level, one may observe

that there is a strong tendency towards urban and industrial development in coastal

lowland and delta areas. There are even forecasts that by 2025 more than 70% of world’s

population will live in such areas.

Time scales

When we go into some more detail regarding the time scales, then the following items may be

considered being of importance at each level:

• the smallest scale as far as a development project is considered, is created by ‘one

season’. This scale is important to determine: functions of systems components and

required operation and maintenance versus the capacity to get this implemented;

• if we look at the scale of one year, then the requirements of the systems during different

parts of the year are of importance. In this respect items like the functions that would

have to be fulfilled by the urban water management and/or flood protection systems

during the year are the relevant items. A clear distinction may generally be observed

between the requirements in the wet and the dry season;

• each element in a project like bank protection or a pumping station has a certain lifetime,

after which is has to be renovated or replaced;

• in each area generally a longer-term process is going-on which could be illustrated by

calling it the ‘generation scale’. This scale also implies that gradual improvements

generally have a better overall result compared to rapid large-scale improvements;

• the last step in the time scale concerns the ‘century scale’. Here the long term

perspectives will have to be considered regarding for example: population growth,

subsidence, rise of the mean sea level and environmental sustainability.

The spatial planning aspects as outlined before would have to be the basis of urban polder

master planning (Figure 4.3) and urban polder implementation planning (Figure 4.4).

4.5 Water resources aspects

Related to the water resources aspects three specific phenomena play a role in the development

of urban polders. They concern:

• the polder area is separated from its surrounding hydrological regime;

4 Planning

33

• the development of an urban polder may create obstruction to the discharge of upstream

areas;

• seepage in the polder and drawdown of groundwater tables may occur due to the

development of the urban polder.

Figure 4.3. Urban polder planning master planning

Figure 4.4. Urban polder implementation planning


34

Separation of the polder area from its surrounding hydrological regime

Due to the separation of the surrounding hydrological regime, the water management system of

the polder only needs to evacuate the excess rainfall and seepage water. So in principle a very

effective water management is possible, provided that during the design phase adequate data are

available on which the design can be based.

Obstruction to the discharge of upstream areas

The urban polders in Indonesia are often developed at the most downstream part of the various

river basins. By impoldering these areas obstructions may be created for the discharge of the

upstream areas. In such cases provisions have to be included in the designs to divert the

discharge of upstream areas around the newly created polder in such a way that at least the

original discharge capacity is being maintained.

Seepage and drawdown of groundwater tables

While the urban polder is the relatively deep part within the surrounding area, or even compared

to the sea, seepage will develop. This seepage may have significant influence on the design of

the water management system, because of its magnitude, the risk of salinity intrusion, but also

because of stability of banks of urban drainage canals. A side effect of seepage may be that the

groundwater tables in the area surrounding the polder may go down, resulting in subsidence in

these areas.

4.6 Geo-technical aspects

The geotechnical aspects especially play a role with respect to the construction of dikes and

flood protection provisions. Because of the often weak soils and the problem of subsidence they

may also to a certain extent cause foundation problems.

As far as dikes are concerned the various failure mechanisms are illustrated in Figure 4.5.

Especially care also needs to be taken with structures in dikes, like outlets and pumping stations.

Due to the differences in pressure, underflow and side underflow may easily occur.

4 Planning

35

Figure 4.5. Failure mechanisms of dikes

4.7 Environmental aspects

Environmental aspects of urban polders may concern especially:

• poor water quality, under both wet and dry weather conditions;

• solid waste disposal;

• erosion of and sedimentation in urban canals;

• weed growth in canals;

• discharge of contaminated water in the receiving water bodies.

A special environmental impact of urbanisation and urban polder development is the reduction

of ‘natural’ land with generally high environmental values and the transformation of it into

urban areas with generally a low environmental value. As a side effect of it with respect to flood

protection is has to be mentioned that this often also implies the removal of storage area and the

increase in peak discharges (Schultz, 2006).

4.8 Policy, social, economic aspects

For policy-making and planning of urban polder development integrated water resources

management (IWRM) aspects would have to be taken into account, which requires that:


36

• policies and priorities take water resources implications into account;

• there is cross-sectoral integration in policy development;

• stakeholders are given a voice in water management and flood protection planning and

management;

• water-related decisions made at local and river basin levels are in-line with the

achievements of broader national objectives;

• water management and flood protection planning and strategies are integrated into

broader social, economic and environmental goals.

An urban polder strategy plan would have to identify the urban water management and flood

protection related social and environmental characteristics that the community considers

desirable or valuable enough to be preserved or restored. The plan also needs to develop

appropriate management objectives and investigate strategies to satisfy these community values

in an economical and ecologically sustainable manner. Urban polder strategy planning is an

ideal mechanism to:

• identify urban polder problems within urban areas that may warrant further detailed

investigation and planning, such as flood mitigation works for major watercourses and

local flooding or pollution problems;

• provide a framework for the preparation of detailed urban polder master plans for new

development, redevelopment, or specific problem areas;

• enable a holistic approach to local area planning that is consistent and responsive to

community values and expectations.

4.9 Community involvement

Especially in the polders that had to be constructed because the existing urban area became too

low community involvement is for various reasons crucial for development and management,

non the least while generally at least the cost of operation and maintenance will have to be

charged in some way to the different groups of stakeholders, and generally also a certain amount

of the construction, upgrading or modernization cost. Therefore the community would have to

be fully informed, consulted and involved in plan preparation and decision making. The various

mechanisms will be described in Volume II of these guidelines.

4 Planning

37

4.10 Institutional and legal aspects

A legal framework is necessary on the one hand to regulate tasks and responsibilities of the

Urban Polder Board as well as of the stakeholders and the local, district, provincial and Central

government authorities. It would have to give the Urban Polder Board the basic instruments

with which they can carry out the tasks that are needed to maintain the polder. On the other

hand this framework is needed to assure the legislator - in this case the municipality, the

District, the Provincial, or the Central government authority - that it is in control of the tasks

that need to be implemented. The most important Indonesian laws that are applicable to urban

polders are: National Land Code, Town and Country Planning Act, Spatial Planning Law, Water

Resources Law (2007) and the Land Conservation Law (Undang undang Pengairan dan

Lingkungan masuk).

The Land Conservation Law prescribes that no person can clear such land or interfere with or

destroy trees and plants on such land. This is to prevent soil erosion and sedimentation.

Guidelines for the control of soil erosion and sedimentation have also been issued. Under the

Forest Enactment, State Authorities may also constitute any area as a reserved forest for the

purposes of protecting river basins. Upon such proclamation all activities within the area are

prohibited. Generally, the administration of land is undertaken through the National Land Code

and this law can also be used to control development. Detailed urban planning is sanctioned by

the State Authorities under the Town and Country Planning Act. Within local authority areas the

structure and local plans can play a critical role in controlling and determining appropriate

development and compatible land use patterns within the river basin context. The structure plan

is a policy statement whilst the local plan is a more detailed urban design plan. Drainage and

flood protection issues need to be part and parcel of the latter plan.

4.11 Procedures

Strategy planning

Urban polder strategy planning is undertaken fundamentally to establish urban water quantity

and quality management objectives for a polder. The information in this section has largely been

adapted from New South Wales, Department of Environment and Climate change (NSW EPA),

1996.


38

Planning period

Urban polder strategy plans need to be prepared to meet conditions up to some future point in

time and would have to be based on a reasonable time period for implementation. The following

factors would have to be considered in selecting an appropriate planning period:

• expected economic life of structural management measures recommended in the strategy

plan. The planning period would have to be of sufficient duration to assure essentially

that full benefit will be derived from the recommended facilities during their useful life;

• the period over which future development forecasts will be reasonably accurate. The

accuracy of forecasts is likely to decrease as the planning period increases. Inaccuracy of

long-term forecasts. Coupled with the small present values of benefits and costs far in the

future, tends to favour shorter planning periods.

Preparation of strategy plans

There is no rigid process for preparing urban polder strategy plans. The process to be adopted

for a particular area will depend on the physical, ecological, social, and administrative

characteristics of the area. Figure 4.6 shows the outline of a number of tasks that can be

undertaken when preparing urban polder strategy plans. The planning process would have to be

flexible and responsive to the characteristics of the area. The tasks outlined therefore serve as an

example rather than a prescriptive process.

The presented planning process is relatively detailed and may place a burden on available

resources. This detail is not intended to inhibit the development of strategy plans, but to provide

an idealised scenario if resources were not limited. However, where resources are limited (either

financial or staffing), interim or preliminary plans could be prepared. These plans could provide

a framework for urban polder management that could be improved over time. There can be

significant benefits associated with preparing and implementing interim or preliminary plans in

the short term rather than waiting until sufficient resources are available for a comprehensive

plan to be prepared. A more detailed description for each task is presented Volume III.

4 Planning

39

Figure 4.6 Urban polder strategy plan tasks (after New South Wales, Department of

Environment and Climate change (NSW EPA), 1996)


40

5 Design aspects of urban polders

5.1 Urban polders in the river basin context

Urban polder development will take place in a particular river basin. Therefore the design

process would have to be based on an integrated approach in a natural environment (air, water,

land, flora, fauna) based on the river basin as a geographical unit, with the objective of

balancing man’s need with the necessity of conserving resources to ensure their sustainability.

The development of an urban polder would have to be in line with the ultimate aim to achieve

the sustainable use of land and water for the benefit of the users in the river basin. Urban polder

water management systems needs to be planned and designed so as to generally conform to

natural drainage patterns and discharge to natural drainage paths within a river basin. These

natural drainage paths would have to be modified as necessary to contain and safely convey the

peak flows generated by urban development.

In order to minimise, prevent or mitigate potential problems of flooding, ensuring adequate flow

of water and prevention of deterioration of the water quality river basins would have to be

carefully managed, preserved and protected. The immediate land reserves surrounding rivers

and other water sources such as wetlands need to be similarly managed. Coordination and

management will be needed to cover the following aspects in order to develop a river basin in a

sustainable way:

• land and water;

• surface water and groundwater;

• the river basin and its adjacent coastal and marine environment;

• upstream and downstream interests.

5.2 Local parameters and conditions

The following design criteria are mandatory requirements for the planning and design of urban

polder water management and flood protection systems for existing urban areas as well as for

new urban polder development.

Public safety

Many of the requirements for the planning and design of urban polder water management and


41

flood protection systems either directly or indirectly consider the need to protect public safety.

Notwithstanding these requirements, urban polder water managers and designers would have to

consider the need or otherwise to implement additional measures to further protect public safety.

Examples of typical measures to improve public safety include:

• safety railings on crossings, headwalls or other locations where the public could fall into

drains or water bodies;

• limiting the depth of open drains;

• gentle side slopes on urban drains and on the sides of ponds, wetlands and lakes;

• maximum flow velocity criteria for urban drains;

• maximum velocity-depth criteria for flow on or across roads.

Land development

While allowance is made in the urban polder water management system for runoff from private

parcels, there may not be any provision to actually collect this runoff within private parcels or to

control the way in which it will reach the urban polder water management system. It is

important that subdivision layouts do not result in the concentration and discharge of runoff

from upstream parcels to adjacent downstream parcels in sufficient quantity to cause nuisance

conditions. Pedestrian pathways could be used to convey local surface runoff to solve such

problems.

In case of reclamation for new urban polders, natural vegetation would have to be retained

wherever possible to minimise erosion within the new urban polder. This will also reduce the

requirement for erosion and sediment controls during construction.

Land grading

Wherever practical, the natural slope of the land within the site would have to be retained as

much as possible to ensure development lots and roadways are freely draining. Grading of

development sites to a flat platform can result very flat grades in the urban polder water

management system. The site outlet will be temporarily or permanently below the water level of

the downstream conveyance system or receiving water. In the first case drainage by gravity may

be possible, while in the latter case drainage by pumping will be required.

Special design aspects in the development of water management and flood protection schemes


42

for urban polders in flat, flood prone areas are (Wandee and Schultz, 2003):

• vertical positioning of the urban area, compared to the surrounding rural area. A relative

small increase in level - say 0.50 m - will have as a consequence that initially inundation

will occur in the rural area and only in more extreme cases in the urban area as well;

• vertical positioning of the different elements within the urban area. A relative low location

of green areas and parks compared to roads and buildings will concentrate inundation

initially in these areas and only in more extreme cases problems may arise with the roads

and the houses.

Design standards

Urban polder water management and flood protection systems would have to be designed on the

basis that the cost/benefit of providing a certain level of protection varies with the type of

development. Urban polder water conveyance systems need to be planned, analysed, and

designed in accordance with the following in order to provide acceptable levels of safety for the

general public and flood protection for private and public property:

• hydrology and hydraulics;

• runoff conveyance.

Runoff must be discharged in a manner that will not cause adverse impacts on downstream

properties or urban polder water management systems. In general, runoff from development

areas within a river basin would have to be discharged at the existing natural drainage outlet or

outlets.

Within a river basin, various surface flow criteria may have to be applied to minimise both

flooding and major hazards from flooding of roadways, buildings, and other areas, which have

regular public access. The surface flow criteria comprise five basic limits:

• preferred water levels and acceptable exceedance of these levels

• an overland flow velocity and depth limit, which governs the stability of vehicles and the

ability of pedestrians to ‘walk out’ of flood flows;

• a flow width limit;

• a ponding depth limit;

• a design criteria limit, which is a probability/risk limit based on consideration of issues of

immunity/damage from flooding, safety, construction costs and community costs and

benefit.


43

The preferred water levels and acceptable exceedances may be summarised as follows:

• preferred normal conditions. These are the conditions one would like to maintain in the

polder area. They result in a preferred water level, or water levels and operation rules for

the pumping stations. The criteria are strongly linked to the soil type, or other land uses

like urban, industrial, recreation and nature conservation;

• design conditions. These are the conditions on which the design of the drains and

pumping stations is based. In general they are formulated as:

∗ exceedance of the preferred water levels;

∗ duration of the exceedance;

∗ the chance per year for which the prescribed exceedance occurs;

• extreme conditions. Although this is generally not a design criterion, control

computations can be made for extreme situations. In these situations bankfull storage is

generally accepted. When the results are unacceptable, the design criteria may be

modified.

Provisions for failure

Design of urban polder water management systems to pass or safely contain an extreme rainfall

of a given frequency implies that a surcharge will occur during a larger rainfall. All hydraulic

works sized by an extreme rainfall estimate are designed on a risk basis. None are ‘100% safe’

and there is always a finite probability that the structure will be surcharged either in a given year

or during its economic life. Therefore, it is important to ensure that the combined minor and

main system can cope with surcharge due to blockages and flows in excess of the design

capacity to minimise the likelihood of nuisance inundation or damage to private properties. In

establishing the layout of urban polder water management systems, it is important to ensure that

surcharge flows will not discharge onto private property during flows up to the main system

design.

5.3 Impoldering principles

Specifically for the development of flood prone areas is the approach to the physical

development related to flood protection. Basically distinction in three approaches can be made:

• put relevant infrastructure and valuable buildings and structures relatively high and accept

flooding of the less valuable parts in the flood prone area;


44

• protection with submersible dikes that protect the lands against regular floods, but are

overtopped during more extreme floods;

• high level of protection with dikes that only fail in extreme events.

The choice between these three basic alternatives is very crucial, while many aspects are

involved in the decision-making and the selected alternative strongly influences the living

conditions of the inhabitants for many generations. For urban areas generally the third approach

will be followed, while damage due to flooding and the disruption of the urban live is generally

so severe that only flooding under extreme conditions can be accepted.

5.4 Polder infrastructure

Polder water management systems generally consist of sub systems and a main system. In

addition there is the flood protection system. The sub system is intended to collect and convey

runoff from frequent storm events such that nuisance of internal (flash) flooding is minimised,

while the main system is intended to safely convey runoff as discharged by the minor drainage

system to receiving waters. The sub system/main system concept may be described as a ‘system

within a system’ as it comprises two distinct but interlinked drainage networks. The sub system

typically may consist of a network of kerbs, gutters, inlet structures, sewer pipes, open drains,

and detention/retention facilities whereas the main system typically consists of a network of

overland flow paths including roads, urban canals, natural channels and streams, culverts and

bridges, community retention/detention basins and ponds, pumping stations and flood

gates/tidal gates, which ultimately discharge into receiving waters. The flood protection system

generally consist of a ‘dike ring’ within it the required outlet and may be inlet structures for the

urban water management system.

Property drainage

If pipe drainage is provided within urban polder development, each parcel to be provided by a

pipe system needs to have an individual connection with the urban polder drainage from

buildings to the public urban polder main drainage system.

A public urban polder main drainage system would only have to be located within a parcel

where it is intended solely for the purpose of providing drainage for the parcel or adjacent

parcels. Such urban main drains would have to be located such that access can be readily


45

achieved and restrictions imposed on the use of the land due to the drains are minimised.

A drainage provision needs to be provided for urban polder main drainage systems located

within private parcels to provide access for maintenance. As drainage provisions can restrict

flexibility in locating buildings and other structures on a parcel, main drainage system

alignments, which minimise the need for such provisions, would have to be considered

wherever possible.

Rights of other authorities

Where an urban polder main drain is proposed to be located within close proximity to another

service, the designer would have to ensure that the requirements of the Polder Board responsible

for the urban drainage are met. Where there is significant advantage in placing an urban polder

main drain on an alignment reserved for another authority, it may be so placed provided that

both the authority responsible for maintenance of the urban polder drains and the other authority

concerned agree in writing to release the reservation.

Runoff quality control

Structural and non-structural controls to enhance the quality of surface runoff need to be

planned, analysed, and designed in accordance with:

• planning;


• structural runoff quality controls;

• non-structural runoff quality controls;

• runoff quality controls during construction;

Sediment retention: Surface water collected from disturbed areas would have to be routed

through a sediment pond or sediment trap prior to release from the area. Sediment retention

facilities would have to be installed prior to the grading or disturbance of any contributing area.

The requirements for water management engineers are intended to ensure that urban polder

water management and flood protection systems will enhance the appearance of an area while

ensuring that tree planting does not result in an increase in inundation or blockage of drainage

systems. Allowance would have to be made for the effects of landscaping in the hydraulic


46

calculations for urban drains. In order to minimise ongoing maintenance, the following aspects

need to be considered:

• no trees other than those with clean boles, strong crown structure, and no propensity for

root suckering may be planted in bank areas of urban drains;

• minimum spacing of trees would have to be 3 m;

• maintenance free ‘thicket’ zones used for hydraulic reasons need to have a minimum 3 m

clearance from lot boundaries to provide access for grass cutting;

• no vegetation other than grass may be planted within 3 m of a concrete invert in an

engineered waterway.

5.5 Feasibility aspects of urban polder development

The value of public and private property in urban areas is generally such that investments in

urban water management and flood protection systems are easily justified. An additional aspect

is that the value generally increases over time. This will pose in time additional requirements to

urban water management and flood protection systems as illustrated in Figure 5.1.

0

200

400

600

800

1000

1200

0 1:01 1:10 1/100 1/1,000 1/10,000 1/100,000 1/1,000,000

Design frequency

Rel

ativ

e co

sts Cost 1950 Damage 1950

Total 1950 Damage 2005

Total 2005

Figure 5.1. Relations between design frequency, cost of flood protection, related expectation of

damages and relative total cost. The cost line is only given for 1950, applicable for the situation

that no increase in the level of safety has been made since then. In theory the design frequency

would have to be taken that coincides with the lowest level of the total cost (Schultz, 2001)


47

5.6 Landscape and land use planning

Landscape and land use planning of urban polders would need to consider the following:

• improved integration of rivers, lakes, banks and their landscape systems in the urban

polder cycle and in sustainable ecosystems planning;

• strengthening of ecological and socially sustainable urban polder development strategies

for future city growth.

5.7 Design criteria

Flood protection schemes may have to protect both rural and urban areas in flood prone zones.

The design of such systems has to be approached fundamentally different compared to the

design of water management systems. When an urban drainage system can not remove the

excess water there may be inundation and damage to buildings and infrastructure. However,

when a flood protection provision fails there may be significant damage and casualties.

Therefore design standards for flood protection are generally substantially higher than design

standards for urban drainage systems. An essential difference between urban and rural areas is

that the value of buildings and property in urban areas per square metre is much higher than the

value of buildings, crops and provisions in rural areas. Also this difference has to be reflected in

the design criteria.

There are several methods to cope with the drainage water. The choice is governed by the

specific conditions with respect to topography, amount of water drained, and hydrologic regime:

• to collect excess water from the adjacent areas in the polder area and to remove it from

there. This solution may be the most economic one if the amount of water originating

from the adjacent areas is small compared with the amount that has to be removed from

the polder and especially when gravity drainage is possible (Figure 5.2);

Figure 5.2. Turn back dikes


48

To convey the water from the adjacent areas between dikes of the protected areas. The

two structures for internal drainage can eventually be combined to a single structure.

Under certain hydrologic conditions the catch canals for diverting the water from the

adjacent areas can be combined with irrigation canals. The combination may be feasible

in regions with distinct dry and wet seasons and where the amount of excess water from

the adjacent area is relatively small;

• to intercept the water running down from the adjacent areas by a catch canal (or

interceptor canal) before it reaches the protected area and to divert it to the river. The

canal will be at a high level thus making gravity flow to the river possible. A dike is

necessary to protect the low-lying embanked areas. The stability of this dike may be a

difficult matter (Figure 5.3);

Figure 5.3. Polder with catch canal

The catch canals act as drains in the rainy season and discharge by gravity into the river.

During the dry season they act as irrigation canals and water is supplied to them by

pumping from the river or by release from a reservoir. Catch canals can also be used to

collect the water removed by pumping from the polder. The catch canal is at a high level

and drains by gravity into the river. Its slope is smaller than that of the river (Figure 5.4).

Figure 5.4. Catch canal at a high level


49

Boundary conditions for design

Before boundary conditions for the design will be discussed, the domain of the polder would

have to be defined and the removal of excess water from upstream of the polder area would

have to be clarified. This will pose problems similar to the reclamation of waterlogged lands.

These problems result from the fact that when there is a need to remove excess water from the

area there is usually a flood in the river so that gravity drainage is impossible. In case of

drainage by pumping it is imperative to drain excess waters from lands with different elevations

separately so as to reduce the pumping costs. Instead of allowing the water from the high areas

(the ‘high water’) to gravitate to the low areas and to remove it from there by pumping, the

‘high water’ is kept at such an elevation that it can flow by gravity to the river. This is illustrated

in Figure 5.5.

P.S.: pumping station

A are high land river basins, B and C are in polder domain: B are terrace lands and C a

reclaimed backswamp lake.

Figure 5.5. Diversion of the river around the impoldered area and separation of the part of the

polder that still can be drained by gravity and the part that has drainage by pumping

The excess water from A is collected by a separate catch canal (α). This canal can have such a

high level that excess water can always be discharged to the river even when there is a flood. On

the other hand excess water from the lowest area can only be disposed off by pumping (PS)

even when the river level is low. Excess water from B is collected in a canal β, which is


50

separated, from area C. The level is such that water can gravitate to the river when the level is

not too high. When there is flood excess water can temporarily be stored in the area and/or in an

embanked retention reservoir and released by gravity when the river level is lower.

Depending on the critical river levels and the required canal levels a combination of a sluice for

gravity drainage and a pumping station for pump lift drainage can be applied together with a

retention basin to reduce the required pumping capacity.

5.8 Design approaches

Two design approaches may be followed: the traditional empirical design and optimisation. In

the latter approach, investments and operation and maintenance costs of the drainage system are

compared with the damage that can be expected in relation to the functioning of the system

(Schultz, 1982).

5.9 Impacts of subsidence and sea level rise

The most recent forecast for sea level rise concerns 0.19 - 0.58 m per 100 year

(Intergovernmental Pannel on Climate Change (IPCC), 2007) (Figure 2.2).

Subsidence in urban polders may occur after reclamation, or due to extraction of groundwater. It

may especially be a problem in humid tropical peat soils where it can occur at a rate of 10 - 15

cm per year. After a certain number of years this may imply that drainage by gravity will have

to be replaced by drainage by pumping.

For urban or industrial development in flood prone areas, the lands are often raised by landfill.

This may be realised to get a sufficiently high surface level, or to create better drainage and

bearing capacity conditions, especially during the building period. Due to the landfill an

additional subsidence and settlement process will be induced. Special provisions have to be

taken when houses are founded on a pile foundation, to prevent problems with house

connections of water, electricity and others.

In the planning stage of the development in a flood prone area, or of an urban drainage

improvement project, the assessment of the extent of subsidence is of vital importance, as

subsidence will influence the levels of watercourses and, in case of drainage by pumping the


51

lifting heights of pumps. Furthermore, in case of unequal subsidence the water management

system may be disarranged. Future preferred water levels can be obtained by subtracting the

predicted subsidence from the original ground levels.

As shown in Figure 2.2 the subsidence in the conditions of the urban polders of Indonesia is a

crucial problem, while the rate of subsidence is generally in the order of magnitude of 5 – 15 cm

per year. This subsidence is primarily caused by groundwater extraction in the deeper layers.

Due to this extraction the water pressure under the thick clay layers is lowered resulting in the

subsidence of the deeper layers and in time of the more shallow layers. This subsidence will

only stop when the extraction of the deep groundwater will stop.

5.10 New technologies

New technologies may refer to survey equipment, design methods, materials, construction

techniques and equipment, monitoring equipment, equipment for operation and maintenance,

different kinds of software, like: flood forecasting and early warning systems, hydrologic and

hydraulic models, GIS, remote sensing, etc.

Essentially all these new technologies have the objective to support and facilitate urban polder

development and management. In fact all that is needed is more or less available on the market.

The issue is, however, what will be the most applicable and affordable under the specific local

conditions.


52

6 Construction aspects of urban polders

6.1 Dikes, outlets and inlet structures

Dikes will have to be constructed as much as possible with locally available materials, provided

that the water retention function will be guaranteed. While in the urban areas space may be

limited often special constructions, like sheet piling, will have to be required. A very good

overview of structural measures to flood control is given by the publication Manual on planning

of structural approaches to flood management (Van Duivendijk, 2005).

Essential element in all dike construction work is the fact that development of leaks, or piping

will have to be prevented, especially during extreme conditions when the outside water level

May be substantially higher than the inside water level. Such leaks can especially develop at the

connection of structures in the dike and the dike body. Therefore such structures will have to be

provided with subsurface screens to prevent that underflow or side underflow will develop.

During the construction of the dike body itself care has to be taken that no sliding will occur due

to the development of overpressure during loading. This may imply that the dike body will have

to be installed in layers of such a thickness that no sliding will occur and that the next layer will

be installed when the overpressure has sufficiently disappeared from the low permeable layers.

In order to accelerate this process the application of horizontal drains, or vertical geo-drains

may be required.

Outlet and inlet structures for urban canals can be precast and field positioned to their proper

elevation. If the size of the structure is such that it cannot be transported, they can be built in

place. This might necessitate site dewatering during the construction process. Where it can be

planned, structures are installed before earthwork construction commences.

Construction of bridges, culverts, siphons, drop structures and regulation structures needs to be

undertaken in accordance with the drawings and specifications, and standards as applicable to

the concerned type of structure and work.

High water velocities through outlets would have to be avoided to prevent scouring and damage

to banks and the structure itself. This can be achieved by applying larger cross-sections for

outlets and urban canals and/or by lining the canal banks and protecting the outlet channel. On


53

the other hand, however, sedimentation in the urban canals needs to be prevented, if required,

by flushing them, for which relatively high velocities are required.

6.2 Urban drainage systems

Urban canals can be constructed by dredging equipment, by backhoes, by draglines, or by using

a combination of earth moving machinery. Where the soils will permit, earth moving scrapers

can be used for the upper part of construction until the canal under construction can no longer

accommodate the machine. At that point, a backhoe or dragline can be employed to excavate the

canal, or dredging equipment can be applied.

Survey distance and level control pegs may be installed at certain intervals along the urban

canal prior to commencement of construction. Where laser equipment is being used, machine

operators are provided with bed level and grade at the start of the urban canal and at subsequent

changes of direction and grade.

Construction of the urban normally commences with scrapers and backhoes at the downstream

end of the system. In waterlogged conditions a pilot canal may be installed first to dry the

landscape sufficiently to permit the shaping of the urban canal.

Bank forming and trimming is generally carried out with a grader. Reasonable compaction of

banks is generally achieved with the passage of machines.

Checking of the formation and finished construction levels is undertaken as the work proceeds.

Scope of Work

The work to be done under excavation for urban canals consists of the construction under all

conditions namely hard dry, wet and under water table conditions. The work to be done by the

Contractor will generally include clearing, stripping and removal of debris as required from

areas of excavations and dikes, excavating the required urban canals, transporting, placing, and

dressing the excavated materials in designated disposal areas or consolidated dikes care and

handling of water and all other work necessary to excavate the designated urban canals.

All areas within the right-of-way to be cleared, as shown on the design drawings or directed by


54

the engineer will have to be cleared of trees, brush, rubbish and other objectionable matter and

such materials will have to be removed from the site of the works or otherwise disposed of.

Fences, walls, buildings and other structures designated, will also have to be cleared from right-

of-way of the works and need to be suitably disposed of. The Contractor will be required to

keep clearing operations well in advance of other construction operations.

Excavations and dikes will have to be made to the lines and grades shown on the design

drawings. Spoil banks and waste areas will have to be levelled or sloped to drain and finished to

reasonably regular lines. Necessary precautions need to be taken to preserve the material below

and beyond the lines of excavation in the soundest possible condition.

Excavated materials will have to be disposed of in required dikes, backfill or in spoil banks, or

will have to be placed in approved waste areas or in other locations. Dikes, backfill, spoil banks

and waste areas need to be built in approximately horizontal layers carried across their entire

width to the required slopes. Construction may be accomplished by mechanical excavating and

hauling equipment, or by excavating or dredging machinery depositing the materials directly

from the excavation.

Where applicable, approved excavated materials can be used in consolidated dikes along the

canal. The approved materials would have to be placed in approximately horizontal layers. Prior

to and during placement operations, the material needs to have the proper moisture content for

consolidation. If the moisture content is less than that required for consolidation, it can be

supplemented by sprinkling and reworking the material during placement. If the moisture

content is greater than that required for consolidation, the material shall be dried by reworking,

mixing with dry materials or other approved means. If required, layers of the dike need to be

consolidated by routing the travel of the mechanical excavation, hauling and placing equipment

over the fill during construction of the consolidated dike.

Materials which will not stand on the slopes and may slide into excavated areas need to be

removed by the contractor in an approved manner, and the slopes need to be refinished. The

contractor may be directed to excavate potential slide areas beyond the limits of the original

excavation.

The contractor needs to protect the works from damage by rains, surface runoff, floods,

overflow of canals, overflow of rivers, failure of protective works or similar events which may


55

occur during the construction period. Any damage to the works resulting from such events will

have to be corrected by the contractor.

Rip rap can be installed for bank protection. Protection may be required where surface or side

inlets discharge into the urban canal, where the canal makes a sharp change in horizontal

alignment, or where insufficient space is available to make sloping banks.


56

7 Operation, maintenance and management of urban polder

water management and flood protection systems

The objective of maintenance is to secure a proper functioning of the urban polder water

management and flood protection systems and related facilities and equipment. Maintenance

can be distinguished in:

• routine maintenance;

• periodic maintenance;

• emergency maintenance.

Frequent and timely maintenance is of paramount importance for obtaining the benefits of the

systems. Especially in urban canals, or canal sections with low flow velocities regrowth of

weeds may be very fast, and can quickly reduce the already low flow velocities to practically

zero with detrimental consequences for water quality. Dikes have to be maintained in a good

condition in order to enable them to fulfil their function during a flood.

Routine maintenance concerns maintenance activities, which occur at least once a year. Besides

regular removal of weeds from canals and dikes, it includes minor repairs and servicing of

O&M equipment and facilities.

Routine maintenance activities can be planned and budgeted in advance on the basis of the

estimated labour, cost and required frequencies of the works. Removal of debris in front of

gates, and greasing, oiling and cleaning of structure components for water control structures in

the secondary canals are part of the regular duties of the O&M staff and gate operators.

Periodic maintenance, also called incidental or regular maintenance, consists of desilting and

reprofiling of canals and repair of dikes, structures, buildings, equipment, etc. These activities

need to be identified and quantified on the basis of yearly inspections and quantity surveys.

Although some periodic maintenance needs can be estimated from the supposed lifetime of

water control structures or facilities, the precise volume and location of the works and which

structures or equipment need to be replaced, will vary from year to year.

Emergency maintenance concerns repairs needed as a result of unforeseen calamities such as

collapse of dikes or water control structures, damage caused by flooding, etc. To prevent further

7 Operation, maintenance and management aspects of urban polders

57

damage, immediate action will generally be required and other ongoing maintenance activities

may have to be interrupted to make all manpower and equipment available for the emergency

maintenance. This maintenance is also needed in case of minor damage to structures and

surrounding earthworks, which impede the structure operation. For example the breakdown of

moving parts like winches and cables by which gates are opened and closed. Such damage may

severely affect the on-farm O&M and may result in crop damage. Urgent repair is then needed.

Emergency maintenance cannot be planned and budgeted in advance. Special funds will have to

be made available within the government budget. While budgets generally will have to be made

available at very short term, generally a provisional allocation will be required, dependent on

the short term need.

7.1 Operation of structures

Operators of outlets and inlets need to know the preferred water levels and, if applicable,

flushing requirements in the urban polders and how to operate the structures to maintain these

preferred water levels as good as possible. They also need to know how they will have to

operate the outlets or inlets during extreme conditions. Operators of pumping stations need to

know the instructions on pumps, motors, engines and control devices and need to follow the

best operating procedures.

Water control structures need to be cleared from weeds at regular (weekly) intervals.

Obstructing debris, hampering operation, is to be removed daily. The structures have to be

regularly inspected and any malfunction is to be repaired. It is of importance that repair is being

done at short notice. Moving parts need to be greased and hinges and groves need to be oiled at

regular intervals (every two months). Every four months old grease and oil need to be cleaned

using diesel.

Once per year, in the dry season, the concrete of the water control structure will have to be

cleaned from dirt and algae. The steel parts need to be cleaned and re-painted. Missing bolts,

nuts and padlocks need to be replaced. Small cracks in concrete walls and stone masonry of the

structure will have to be plastered with concrete mortar.

Maintenance and repairing of doors and gates in outlets can be realised by closing the outlet

temporarily with stoplogs, for which slots in the sidewalls are required in which the logs can


58

slide. These slots should be provided at both sides of the gate in case of varying inner and outer

water levels. In case of a tidal outlet with vertical doors a second set of doors might be

constructed, in order to ensure extra safety of the drained area against high outer waters.

Pumps depending upon water lubrication may not operate empty. Where pumps depend upon

riming, complete filling of water needs to be accomplished so pockets of air will not collect in

the casing around the shaft. Where prime movers are used, pump operation will have to be

regulated to provide the most efficient speed as determined from tests of characteristics curves.

Thorough inspection of the facility needs to be made periodically during operation, at least

monthly during periods of non operation, and just prior to the expected time of continuous or

peak usage. Occasional tests are desirable in order to detect poor operating efficiency.

Inspections would have to indicate the condition of the plant forebay and discharge bay areas,

and arrangements will have to be made for disposal of debris, drift and trash accumulations.

Inspections would also have to include test runs of pump and power equipment.

Bridges and buildings need to be cleaned and re-painted every year. The metal parts as bolts,

nuts and metal joints painted with an anti-corrosive paint. Missing bolts, nuts and joints will

have to be replaced. The offices and housing of O&M staff need to be tarred, painted and white-

washed.

7.2 Maintenance of urban polder water management and flood protection systems

The need for maintenance of urban polder water management systems differs fundamentally

from that of irrigation systems. Generally, maintenance of irrigation systems has to be executed

just before the start of the irrigation season and/or during this period. The irrigation water is

supplied in more or less known quantities, whereas it is generally obvious to the farmers or the

authority in charge that without maintenance the crops will suffer from an inadequate water

supply. The maintenance of urban polder water management systems is of a more preventive

nature. It has to be executed before a, to a certain extent unknown, wet period during which the

system have to fulfil its function. The amount of excess water to be stored and transported may

vary considerably, and the damage resulting from insufficient drainage may arise later than the

occurrence of the wet period (Schultz and De Vries, 1993). Maintenance can aim at removing

the cause of insufficient system performance or at preventing this from happening. In the first

case a proper monitoring is required, in the latter a schedule is needed, indicating the

maintenance activities and their planning. In case of urban polder water management systems

7 Operation, maintenance and management aspects of urban polders

59

the second option would have to be preferred. In most cases the aquatic vegetation is the

dominating factor of canal maintenance. An urban canal is by definition in a young phase in the

vegetation succession, and it has to stay in that phase to keep its hydraulic function. Often

aquatic vegetation is also needed as the roots of the plants offer a protection against erosion of

slopes. It would have to be kept in mind that it is hardly ever the case that an aquatic plant

species as such is unwanted; it is generally its quantity which causes trouble.

It seems straightforward that maintenance is considered the prime responsibility of the

stakeholders. However, if this is realistic depends very much on the local conditions. On the

other hand it is not realistic to expect that the government remains fully responsible for the

entire maintenance. Therefore, in order to safeguard a sustainable functioning of the urban

polder water management and flood protection systems, a framework would have to be

developed in such a way that after a certain initial period the stakeholders will be able to fund

the operation and maintenance of the entire systems themselves. This implies that before an

urban polder development project starts it would have to be clear to the stakeholders: what is to

be maintained and when, who is maintaining which part of the systems and how the financial

responsibility for the maintenance will be shared.

7.3 Laws, regulations and permits

Operation and maintenance of urban polder water management and flood protection systems

will have to take place within the regular Indonesian legislation. The general legislation like the

National Land Code, Town and Country Planning Act, Spatial Planning Law, Water Resources

Law and the Land Conservation Law seems to be adequate. However, a specific urban polder

regulation doesn’t exist and would have to be prepared and approved in the near future.

A specific aspect concerns the activities that may influence the sustainability of the urban polder

water management and flood protection systems. Special reference would have to be made to

the extraction of deep groundwater, resulting in subsidence rates in urban polder areas of 5 – 15

cm per year. These rates are so fast that the sustainability of the polder areas is at stake.

Therefore regulations that control such aspects are urgently needed.

7.4 Institutions in charge

With respect to the institutions in charge a principle scheme is shown in Figure 7.1. In this


60

figure a distinction has been made in the parties that are responsible and the parties that are

contributing. The Figure shows that only three parties are responsible. This implies that these

parties will have to reach agreement how the urban polder water management and flood

protection schemes will have to be developed, operated and maintained. Complication with

respect to this is the sharing of responsibility among the different government agencies. This

sharing of these responsibilities will have to be clarified and prescribed in the legislation during

the coming period.

RESPONSIBLE CONTRIBUTING

Consultants

Central Government Legislation, national Contractors, manufacturers

policy and strategy

Universities, schools

Polder authority/ Urban water management

Municipality/District/ and flood protection, Research institutes, NGO’s

Province/Balai receiving water bodies

Banks, donors

Stakeholders private sub systems

Int. organisations

Associations

Figure 7.1. Indicative schematisation of actors in urban polder water management and flood

protection systems

7.5 Stakeholder participation

In urban polder areas stakeholder participation will deal with funding of preferably at least the

operation and maintenance cost of the urban water management and flood protection schemes

and may be to a certain extent the funding of construction, upgrading of modernisation. In

addition they will be in charge of the discharge of excess water from their private plots.

The above implies that stakeholders need to have a say in the development of plans, as well as

in the organisation of operation and maintenance of the schemes. This will require regular

consultation with the stakeholders, but also representation of them in for example the board of

the Polder Board. Such aspects will be described in more detail in Volume II of these

guidelines.

References

61

References

Ahlman, S., 2006. Urban water management. Götenborg, Sweden.

Butler, D. and J.N. Parkinson, 1997. Towards sustainable urban drainage. Water Science and

Technology, vol. 35, no. 9.

Constandse, A.K., 1988. Planning and creation of an environment, IJsselmeerpolders

Development Authority, Lelystad, the Netherlands

Douben, N. and R.M.W. Ratnayake, 2006. Characteristic data on river floods and flooding; facts

and figures. In: Floods, from defence to management. In: Floods, from defence to

management. Proceedings of the 3rd

International Symposium on Flood Defence, 25 - 27

May 2005, Nijmegen, the Netherlands by Alphen, J. van, E. van Beek and M. Taal,

Taylor & Francis / Balkema Publishers, Leiden, the Netherlands

Duivendijk, J. van, 2005. Manual on planning of structural approaches to flood management.

International Commission on Irrigation and Drainage (ICID), New Delhi, India.

Forest Enactment

Group Polder Development, 1982. Compendium of polder projects. Delft University of

Technology, Delft, the Netherlands

Intergovernmental Pannel on Climate Change (IPCC), 2007. Climate Change 2007: Synthesis

Report, 12-17 November 2007, Valencia, Spain

International Commission on Irrigation and Drainage (ICID), 1996. Multi-lingual Technical

Dictionary, New Delhi, India.

Land Conservation Law

Munich-Re, 1997. Flooding and Insurance. Münicher Rückversicherungs-Gesellshaft. Munich,

Germany.

National Land Code

Netherlands Development Assistance Research Council (RAWOO), 2000

New South Wales, Department of Environment and Climate change (NSW EPA), 1996. A new

approach to environmental education in NSW — A NSW Government Green Paper,

Sydney, Australia.

Oudshoorn, H., B. Schultz, A. van Urk and P. Zijderveld, 1999. Sustainable development of

deltas. Proceedings International conference at the occasion of 200 year Directorate-

General for Public Works and Water Management, Amsterdam, The Netherlands, 23 - 27

November, 1998, Delft University Press, Delft, The Netherlands


62

Schultz, Bart, 1982. A model to determine optimal sizes for the drainage system in a polder, In:

Papers Polders of the World, International Institute for Land Reclamation and

Improvement, Wageningen, the Netherlands.

Schultz, Bart, 1993. Land and water development. Finding a balance between implementation,

management and sustainability, Inaugural address, IHE, Delft

Schultz, Bart, 2001. Irrigation, drainage and flood protection in a rapidly changing world.

Irrigation and Drainage, vol. 50, no. 4.

Schultz, Bart, 2006. Opportunities and threats for lowland development. Concepts for water

management, flood protection and multifunctional land-use. In: Proceedings of the 9th

Inter-Regional Conference on Environment-Water. EnviroWater 2006. Concepts for

Watermanagement and Multifunctional Land-Uses in Lowlands, Delft, the Netherlands,

17 - 19 May, 2006.

Schultz, Bart. Extreme weather conditions, drainage, flood management and land use. In:

Proceedings of the 10th International Drainage Workshop, Helsinki, Finland and Tallinn,

Estonia, 6 – 11 July 2008, Helsinki University of Technology, Helsinki, Finland.

Schultz, Bart and W.S. de Vries,1993. Some typical aspects of maintenance of drainage systems

in flat areas. Transactions of the 15th Congress on Irrigation and Drainage. International

Commission on Irrigation and Drainage (ICID). New Delhi, India.

Segeren, W.A., 1983. Introduction to the keynotes of the international symposium Polders of

the World. In: Final report of the international symposium Polders of the World.

International Institute for Land Reclamation and Improvement (ILRI), Wageningen, the

Netherlands

Spatial Planning Law

Town and Country Planning Act

UNDP Population Reference Bureau, 2007. 2007 world population data sheet, Washington DC,

USA.

Ven, G.P. van de (ed.), 2004. Man-made lowlands. History of water management and land

reclamation in the Netherlands. 4th edition, Utrecht, the Netherlands

Volker, A, 1982. Lessons from the history of impoldering in the world. In: Keynotes of the

International symposium Polders of the World, International Institute for Land

Reclamation and Improvement (ILRI), Wageningen, the Netherlands

Walesh, S.G., 1989. Urban Surface Water Management, John Wiley & Sons, London, United

Kingdom.

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Wandee, P. and B. Schultz, 2003. Some practical aspects of the new policy on water

management in the Netherlands polders. In: Proceedings of the 9th International Drainage

Workshop. Utrecht, the Netherlands, 10 – 13 September, 2003, Alterra, Wageningen, the

Netherlands.

Water Resources Law No.7, 2004.

ANNEX I. Glossary

65

ANNEX I. Glossary

Sources:

• WMO and UNESCO, International Glossary of Hydrology, 1992

• ISO 6107, Water quality -Vocabulary, Part 2, 1997

• ISO 5667-2, Water quality –Sampling- part 2: Guidance on sampling techniques, 1991

• ISO 5667-6, Water quality – Sampling – part 6: Guidance on sampling of rivers and

streams, 1990

• FAO (1985)

• Wikepedia, Internet encyclopaedia

Delta A delta is a landform that is created at the mouth of a river where that river

flows into an ocean, sea, estuary, lake, or reservoir or another river. Deltas are

formed from the deposition of the sediment carried by the river as the flow

leaves the mouth of the river.

Downstream Downstream means literally away from the source of a stream or river, along

the normal direction of the water flow.

Flood plain A flood plain, or floodplain, is flat or nearly flat land adjacent to a stream or

river that experiences occasional or periodic flooding. It includes the floodway,

which consists of the stream channel and adjacent areas that carry flood flows,

and the flood fringe, which are areas covered by the flood, but which do not

experience a strong current.

Monitoring continuous or frequent standardised measurement and observation of the

environment, often used for warning and control

Parameter property of water used to characterise it

River a natural body of water flowing continuously or intermittently along a well-

defined course into an ocean, sea, lake, inland depression, marsh or other

watercourse

Salinity ratio of mass of dissolved material in seawater to the mass of seawater

Stream water flowing continuously or intermittently along a well-defined course, as for

a river, but generally on a smaller scale

Upstream Upstream literally means "towards the source of a stream or river, or against the

normal direction of water flow.

Wastewater A combination of liquid and water-carried pollutants from homes, businesses,

industries, or farms; a mixture of water and dissolved or suspended solids

FINAL DRAFT


Volume 3: Technical Aspects

Jakarta, February 2009

Preface

i

Preface


Semarang Project (2007 - 2009). This was one of the projects under the Memorandum of

Understanding between the Indonesian Ministries of Public Works and of Environment and the

Netherlands Ministries of Transport, Public Works and Water Management, and of Spatial

Planning, Housing and Environment. The themes of the guidelines are: General Aspects,

Institutional Aspects, Technical Aspects, and Case Study Banger Polder Semarang. Support to

this project was given by the program Partners for Water and Rijkswaterstaat.


• Indonesia:




∗ Dr. Wanny Adidarma, MSc, Research Centre for Water Resources;

∗ Ir. Sri Hetty, MSc, Research Centre for Water Resources;

∗ Ir. Ratna Hidayat, Research Centre for Water Resources;

∗ Mr. Suhardjono, Municipal of Semarang Planning Board

∗ Prof. Dr. R.W. Triweko, MSc, Catholic Univ.of Parahyangan, Bandung.


∗ Prof. Dr. Bart Schultz, Rijkswaterstaat

∗ Dr. F.X. Suryadi MSc, UNESCO-IHE



Provincial and Municipal government staff.




Urban polder guidelines, Volume 3: Technical Aspects

ii

We hope that the guidelines may contribute to and improved development and management of


Contents

iii

Contents

Preface i

Contents iii

1 Introduction 1

2 Technical aspects of urban polders 3

2.1 General 3

2.2 Type of area 5

2.3 Physical planning 5

2.4 Technical aspects 6

3 Data collection and investigations for urban polder development 11

3.1 Required data 11

3.1.1 Meteorological data 11

3.1.2 Topographical data 13

3.1.3 Hydrological data 16

3.1.4 Soil properties, soil subsidence and geological data 18

3.1.5 Land use data 18

3.1.6 Socio-economic data 19

3.1.7 Environment data 20

3.2 Required investigations 21

3.2.1 Topography 21

3.2.2 Hydrological analysis 21

3.2.3 Soil properties, soil subsidence and geological investigations 22

3.2.4 Land use and land use development 32

3.2.5 Socio economy and trends 34

3.2.6 Environmental analyses 35

3.3 Data processing, storage and retrieval 36

4 Planning 37

4.1 General planning framework 37

4.2 Land and water development framework 46


iv

4.3 Spatial planning approaches 49

4.4 Topographical aspects 50

4.5 Landuse zoning system based on elevation classification 51

4.6 Water resources aspects 53

4.7 Geo-technical aspects 56

4.8 Environmental aspects should be combined with 4.9 57

4.9 Impact of urbanization 60

4.10 Urban master planning 61

4.11 Procedures 62

5 Design aspects of urban polders 65


5.2 Impoldering principles 71

5.3 Polder water management and flood protection systems 73

5.4 Erosion and sedimentation control in and around a polder 87

5.5 Flushing system in a polder 88

5.6 Landscape and land use planning 88

5.7 Boundary conditions for design 89

5.8 Design approaches and design standards 90

5.8.1 Design of embankments and dikes 91

5.8.2 Design of urban drainage 104

5.9 Environmental Impact assessment 106

5.10 Impacts of subsidence and sea level rise 108

5.11 New technologies 111

5.12 Wastewater treatment plant 118

5.13 Solid waste management 123

6 Construction aspects of urban polders 127

6.1 Dike, outlet and inlet structures 127

6.2 Urban water management systems 130

7 Management, operation and maintenance of urban polder systems 133

7.1 Management, operation and maintenance 133

7.1.1 Management 133

7.1.2 Operation 133

Contents

v

7.1.3 Maintenance 134

7.1.4 Operation of structures 141

7.1.5 Maintenance of urban polder water management and flood protection systems 142

7.1.6 Dredging water management systems 148

7.1.7 Planned maintenance and inspection 149

7.2 River basin management and maintenance of drainage systems 126

7..2.1 Plan for monitoring and demonstration 149

7.2.2 Planning of maintenance 149

7.2.3 Maintenance responsibilities 150

7.2.4 Maintenance needs assessment 150

7.2.5 Coordination with other agencies 151

7.2.6 Routine maintenance inspection 151

7.2.7 Environmental monitoring 152

7.2.8 Monitoring of maintenance implementation 153

7.3 Laws and regulations 154

7.4 Procedures and legalizing permission 155

7.5 Institutions 155

7.6 Stakeholder participation 156

References 159

ANNEXES

I Glossary 161

II Symbols 165

III Gumbell and IDF analysis 169

IV Unsteady flow model 175


vi

1 Introduction

1

1 Introduction

In most of the case, the existing urban area has often been considered densely populated.

Flooding may occur due to land subsidence of the coastal area and (continuing) rise of the sea

level. As a consequence of these phenomena in some urban areas in the coastal zone daily

flooding occurs and inundation of a few cm do dm on the street is common. See Figure 1.1.

Figure 1.1. Flooding in urban area

This causes severe disturbance to society and disrupts not only economic development of the

region significantly, but also leads to retreat of companies from these conurbations. These

problems are acute, need utmost attention and to be solved. A polder with its water management

system can be one of the solutions of these flooding problems.

An urban polder system consists of several components, which have to be integrated to each

other essentially. The main components are institutional, social, technical (design, operation and

maintenance) and environmental. In this project four volumes of guidelines will be prepared,

they are:

• Volume 1: General;

• Volume 2: Institutional aspects;

• Volume 3: Technical aspects;

• Volume 4: Case study: Banger urban polder in Semarang.

Training needs

Training and transfer of knowledge and skill in relation to survey, design, operation and


2

maintenance will be needed especially in line with stakeholder participation approach and the

depth of training required varies considerably. See Figure 1.2.

Figure 1.2. Training program as part of the participatory approach

2 Technical aspects of urban polders

3


2.1 General

Over the past three decades in Indonesia, general development and population growth have

placed more need for land for industrial development and human settlements. Some cities,

especially those in the coastal zone have inadequate land for industry and for houses. Increased

land development in the coastal zone has also created problems with environmental

management and the risk of flooding.

Indonesian cities are generally designed with open drainage systems, in which sewage and

storm water is transported. Maintenance of these systems is often far below the required level.

In addition, these systems get clogged with garbage such as plastic bags. Solid waste is in

general not well managed yet. As a result, rain- and sewage water are not taken away properly.

It is also clear that pumping regimes are not geared to the drainage systems. The problems of

one system are transposed to others.

In general, at river basin level is only developed to a limited extent. Deforestation contributes to

large-scale erosion and downstream sedimentation, in urban areas as well as rural areas. As a

result, riverbed elevations (up to 10 cm/y) and increased flood risks can be observed. Cities are

threatened by flooding by rivers and by storm water.

Due to the fast and often uncontrolled enlargement of the cities, water supply for industry and

the inhabitants is not growing. The best option would be the use of water from the rivers, but an

easier and nearer solution is uncontrolled extraction from groundwater. This leads to soil

subsidence, of in some areas over 10 cm/year). In coastal cities especially this land subsidence

in combination with high water spring tides often leads to flooding by the sea. Considerable

areas are already below sea level. This makes the poorer settlers in slums vulnerable. Soil

subsidence is a widespread problem that will continue for the coming decades, despite all kinds

of measures.

In some large coastal cities in Indonesia; flooding problems occur due to the settlement of the

coastal surface level and the (future) rise of the sea level. As a consequence, frequent flooding

occurs and inundations in the streets of a few centimetres to decimetres are common. The floods

cause severe disturbance to society, disrupting not only social life but also damaging health –


4

there are great health risks for the inhabitants of the affected urban areas. Economic

development is damaged significantly with companies retreating from the city. It affects the

functioning of infrastructure and often does damage to roads, sewers and warehouse buildings

with their contents. Central and local government has taken steps to address these problems,

however these have not been sufficient adequate and it was resolved by the government that co-

operation with the Netherlands would contribute to a proper solution.

These urgent problems need to be addressed by adequate flood protection measures. Polder

systems offer such a solution. Polder systems however ask for polder management, introducing

a new area of knowledge and skill. In several areas, the coastal and swampy areas show some

design and infrastructure planning weaknesses. In several of these areas frequent flooding

occurs, threatening any chance of a healthy urban environment and sustainable economic

development. In most of the cases, local governments, with the support of the central

government have carried out several measures to address the problems related to flooding.

The flooding as frequently occurring in coastal urban areas has a number of root causes. These

include:

• subsidence of the soil;

• increased open sea water levels;

• deforestation and related peak run-off characteristics;

• limited capacity and maintenance of the existing drainage infrastructure.

The lack of efficient and effective practices to deal with these problems creates difficulties for

local and national government in Indonesia. Counter measures may not be known, may be

costly or may not be effective. It was indicated by the Indonesian government that the

participation of the people is required to provide for more sustainable water management. This

may be a problem in some areas. Especially in the past, most of the regulations and financing is

guided by the central government in Jakarta. This has clear disadvantages: the match with

specific local problems cannot easily be made. Financial means are insufficient, both for

investment and especially for operation and maintenance. This problem is being exacerbated by

corruption. As a result, it seems the local population and stakeholders are passive. In the future,

with the decentralization approach, the local government will get more and more involvement in

the planning and the development of the related area.


5

2.2 Type of area

New development

New development is defined as the conversion of natural or rural areas into urban, commercial,

and/or industrial development. For new development proposals, the post-development peak flow

from the outlet point(s) of the site to the downstream public drainage system or receiving water

shall not exceed the pre-development flow. Pre-development peak flow shall be the estimated

flow from the site based on known or estimated flow basin conditions prior to development.

Development of the existing area

Development of an existing area is defined as the reconstruction of an existing urban,

commercial or industrial area and their urban polder water management and flood protection

systems. The degree of runoff control required will depend on the scale of the development and

the net change in impervious area. Flow control will be required for any development of

existing sites where:

• the density of the redevelopment, measured as the total equivalent impervious area of the

redevelopment, is greater than that of the existing development, and/or;

• the capacity of the existing urban polder water management and flood protection systems

does not meet the design storm criteria.

Special attention must be paid for the capacity of the existing drainage systems in comparison

with the proposed urban polder water management management and flood protection systems.

2.3 Physical planning

Aesthetics and ecological criteria

Aesthetics

The urban polder water management and flood protection systems shall be designed so that it

enhances the appearance of the area, and maximises its use by the community. Figure 2.1 shows

a schematic layout of an urban polder.


6

Landscaping

Landscaping is intended to ensure that an urban polder water management and flood protection

systems will enhance an area while not resulting in an increase in flooding. The urban polder

water management management and flood protection systems design shall take into account and

be part of the overall land development landscape design. The design should:

Figure 2.1. Schematic layout of an urban polder

• allow for landscaping or future changes in landscaping to enhance the visual appeal of the

system;

• enhance open space links through development areas;

• retain existing trees if possible and respect the functional use of the space;

• form part of and be sympathetic with the landscape character of the surrounding

neighbourhood.

2.4 Technical aspects

Design acceptance criteria

The following design acceptance criteria are mandatory requirements for the planning and

design of urban polder water management management and flood protection systems for


7

existing urban areas as well as new urban developments.

Public safety

Many of the requirements for the planning and design of urban polder water management and

flood protection systems presented in this guideline have either directly or indirectly considered

the need to protect public safety. Notwithstanding these requirements, urban polder water

managers and designers should consider the need or otherwise to implement additional

measures to further protect public safety. Examples of typical measures to improve public safety

include:

• safety railings on crossings, headwalls or other locations where the public could fall into

water bodies;

• limiting the depth of open drains;

• gentle side slopes on engineered waterways, basins and on the sides of embankments;

• maximum flow velocity criteria for engineered water management systems as well as

flow on or across roads.

Land development

Subdivision layouts: while allowance is made in the urban polder water management

management and flood protection systems for runoff from private parcels, there may not be any

provision to actually collect this runoff within private parcels or to control the way in which it

will reach the urban polder water management and flood protection systems. It is important that

subdivision layouts do not result in the concentration and discharge of runoff from upstream

parcels to adjacent downstream parcels in sufficient quantity to cause nuisance conditions.

Pedestrian pathways could be used to convey local surface runoff of such problems.

Land grading

Wherever practical, the natural slope of the land within the site should be retained to ensure

development lots and roadways are free draining. Grading development sites to a flat platform

can result in the urban polder water s management and flood protection systems having very flat

grades. The system may then be excessively deep at the site outlet and possibly below the tail

water level of the downstream conveyance system or receiving water. The existing topography

of some sites, such as in coastal areas, may naturally be very flat and consideration should be


8

given to regarding the site to introduce slope to promote free flow drainage.

Site clearing

Natural vegetation should be retained wherever possible to minimise erosion within an urban

polder. This will also reduce the requirement for erosion and sediment controls during

construction.

Design recurrence intervals

A system approach shall be adopted for the planning and design of urban polder water

management management and flood protection systems. The minor system is intended to collect

and convey runoff from frequent storm events such that nuisance flooding is minimised, while

the major system is intended to safely convey runoff not collected by the minor drainage system

to receiving waters. The major/minor concept may be described as a ‘system within a system’ as

it comprises two distinct but interlinked drainage networks.

Urban polder water management management and flood protection systems should be designed

on the basis that the cost/benefit of providing a certain standard of protection varies with the

type of development.

The minor system typically consists of a network of gutters, inlet structures, small open drains

and pipes, and on-site detention/retention facilities whereas the major system typically consists

of a network of overland flow paths including roads, drains, natural channels and streams,

engineered waterways, culverts, community retention/detention basins, pumping stations and

flood gate/tidal gate, which ultimately discharge into receiving waters.

For flood protection system, the design water level is a function of the economic value of the

hinterland (housing, people, environment etc.) and the accepted risk to human life.

To be able to determine the appropriate safety level the risk has to be known, requiring insight

in the damage per flood or damage event. A dike with a safety level T10,000 means that on

average once per 10,000 years the dike will overtop or break, or a probability of 0.01 % per

year. In relation to the possible damages, design recurrence interval for flood protection systems

should be much higher than for water management systems.


9

Runoff quantity control

Urban polder water management systems for the control of the quantity of surface runoff shall

be planned, analysed and designed in accordance with:

• planning;


• Rainfall-run-off control.

Flow control requirements are stipulated for the following categories of development:

• new development;

• development of existing sites.

Conveyance systems

Urban polder water conveyance systems shall be planned, analysed, and designed in accordance

with the following in order to provide acceptable levels of safety for the general public and

flood protection for private and public property:


• run-off conveyance.

Run-off must be discharged in a manner that will not cause adverse impacts on downstream area

properties or urban polder water systems. In general, run-off from development sites within a

polder must be discharged at the outlets.

Provisions for failure

All hydraulic works sized by a flood estimate are designed on a risk basis. None are ‘100% safe’

and there is always a finite probability that the structure will be surcharged either in a given year

or during its economic life. It is important to ensure that the combined minor and major system

can cope with surcharge due to blockages and flows in excess of the design capacity to

minimise the likelihood of nuisance flooding or damage to private properties. In establishing the

layout of urban polder water management and flood protection systems, it is essential to ensure

that surcharge flows will not discharge onto private property during flows up to the major

system design.


10

Urban water management and flood protection

In order to minimise ongoing maintenance, the following things should be considered:

• no trees other than those with clean boles and no propensity for root suckering may be

planted in over bank areas of engineered waterways;

• no tress on the dikes;

• minimum spacing of trees shall be 3 m;

• maintenance free ‘thicket’ zones used for hydraulic reasons shall have a minimum 3 m

clearance from lot boundaries to provide access for grass cutting;

• no vegetation other than grass shall be planted within 3 m of a concrete invert in an

engineered waterway.

The design of an urban polder water management and flood protection systems needs to take

into account the continuing maintenance requirements of the system after it has been

constructed. The water management and flood protection systems should provide for ease of

maintenance and include adequate access for maintenance equipment. Consequently, designers

will need to familiarise themselves with the capacity and capabilities of the authority

responsible for maintaining the urban polder water management and flood protection systems in

order to provide facilities, which can be readily and economically maintained.

An urban polder water management and flood protection systems must also be designed such

that maintenance activities can be performed without the risk of inadvertent damage to the

assets of the stakeholders in the polder. Stakeholders in this case include those responsible for

electricity, telecommunications, water supply, solid waste management system and sewerage

services.

4 Data collection and investigations for urban polder development

11

3 Data collection and investigations for urban polder

development

3.1 Required data

Urban polder water management and flood protection systems invariably deal with the natural

system and processes. The impact of engineering intervention of the natural system is not fully

known especially on how it affects the eco-system and eventually human lives. Continuous

research and development and human resources development program is required to gain better

understanding of these impacts and to provide direction for better performance of engineered

facilities especially for Indonesian application.

In the design phase, before doing the modelling work some data will be required in order to

indicate that there is a problem. Such observations constitute a data set in and usually indicate

the direction for subsequent data collection. At every stage of the preliminary analysis, one must

ask if measured data can solve the problem. If so, there is no need to model. If modelling is

required, there are three types of required data; model input data, calibration and verification

data, and verification data.

The roles of each institution should be well defined and coordinated which should cover the

collection of secondary data relevant to urban polder water management systems as follows:

• mapping - survey and mapping;

• population census - demographic;

• socio economic data - economic development planning;

• land use - regional and national development planning bureau.

3.1.1 Meteorological data

Rainfall

The length of rainfall period, which is preceded and followed by periods of no measurable

rainfall, is called rainfall duration or storm duration. The total depth or depth of rainfall is the

depth to which the rainwater would accumulate if it stayed where it fell on the ground. The

rainfall intensity refers to the time rate of rainfall. Generally, the rainfall depth is highest near


12

the storm centre, and it will decrease with increasing distance from the storm centre.

Probabilistic description of rainfall

Rainfall events are difficult to predict accurately by deterministic models. Their occurrence is

uncertain, and the rainfall depth and duration are highly variable in time and space. Rainfall

events are treated as random events and probabilistic methods are used to determine the

likelihood of their occurrence.

Frequency analysis

Frequency analysis is used to derive meaningful information from historical data. Frequency

analysis of rainfall aims to determine the return periods associated with different magnitudes of

the rainfall depth for a specified duration.

Intensity-duration return period curves

Design rainfall and return period

A hydrologist has to deal with natural phenomena, such as heavy rainfall and floods, whose

occurrence is essentially random. Since the cost of engineering structures tends to increase

rapidly with the rarity of the adopted design event, the choice of an appropriate design

frequency is ideally based upon an economic analysis in which the benefits of the works, in

terms of the damage costs avoided, are balanced against construction costs. These design

frequencies are generally expressed in terms of the 1-in-T year occurrence, which is defined as

X, whose probability of being equaled or exceeded in any one year is equal to (1/T).

Alternatively, the average time between occurrences of the event, X, is T years. Unfortunately,

this method of expressing the design standard can easily lead to misconceptions. For example,

the occurrence of the design event, X, in the current year does NOT mean that X will not occur

again for another T years. Care must be taken to distinguish between the probability of

exceedance (P), and the risk (R) of an event occurring within a design life for the system.

The connection between the two can easily be deduced from elementary concepts of probability.

For urban polder water management and flood protection systems any failure could result in

heavy losses of both lives and property, a design standard is often imposed for which the risk of


13

occurrence of the design storm is negligible. In these circumstances, the design flood is

generally based upon the probable maximum precipitation (PMP) of a design rainfall. The PMP

is defined as the depth of precipitation which, for a given area and duration, can be reached but

not exceeded under known meteorological conditions (Wiesner, 1970). In general, PMP is

estimated using one of two possible approaches (Wiesner, 1970; WMO, 1973):

• Meteorological methods;

• Statistical analysis of extreme rainfall depths.

3.1.2 Topographical data

The design of water management and flood protection systems of an urban polder requires

geological, topographic and soil maps. Generally the investigations require a sequence of

studies with increasing intensity. Therefore, two or three phases on the investigations can be

considered:

• reconnaissance level (pre feasibility study): the main objective is to identify the feasibility

of the proposed project, first of all on technical, but also on economic grounds, studies at

this level are mainly based on existing information but may also include some field

work/survey;

• semi-detailed level (feasibility study): alternative plans obtained from the reconnaissance

study are worked out to a preliminary plan so that the competent authorities can make a

decision; the data are the same as for the reconnaissance level, but are needed in more

detail;

• coordinates of existing stations in the area should be obtained from JANTOP (Jawatan

Topografi);

• at least one triangulation station will be chosen for use as the reference datum;

• detailed level (project designs): design of the selected project, including a list of

quantities and preparation of tender documents.

Topographical data requirements for water management and flood protection systems design are

as follows:

• topographic map with water management systems at scale 1:25,000 and 1:5,000;

• canal alignment map at scale 1:2,000 with contours at 0.5 m for flat areas;

• longitudinal profiles with horizontal scale 1:2,000 and vertical scale 1:200 or 1:100 for

smaller canals;

• cross-section with scale 1:200 or 1:100 for smaller canals and with interval 50 m.


14

The use of aerial photographs and satellite images is of great values in designing water

management systems. In the following part a new technology called Laser-altimetry will be

introduced.

Principles of Laser-altimetry

Laser-altimeters operate usually from an aircraft or a helicopter, although also orbiting satellites

are used (laser pulses can bridge long distances.) Airborne Laser-altimeter Systems (ALS) are

multisensor systems consisting of a reflector less laser range system and a positioning system. A

laser ranger determines the distances from the platform to arbitrary points on the earth's surface

by measuring the time interval between transmission of a train of pulses (up to 80,000 per

second) and the return of the signals. See Figure 3.1. A flying height of 1,000 m is typically

used during operational flights.

Figure 3.1, Principle of Laser-Altimetry (Courtesy: Survey Department Rijkswaterstaat,

Netherlands)

The positioning system determines the position and attitude of the laser ranger. This is

necessary for geo-referencing purposes, i.e. to determine the coordinates of the sensed points on

the terrain surface in a local or national system. During flight a (digital) video records the

terrain. The final accuracy to be achieved depends on many factors, including the properties of

the entire measuring system, flying height, terrain characteristics and applied processing

software.

Helicopters are better suited for high resolution coverage, because they can easily limit their

speed. Weather and sight conditions do only slightly affect flight surveys, making the technique

fairly well independent of season and daytime.


15

When water bodies are hit, parts of the pulses may penetrate water and reflect on the bottom of

the water body, enabling the measurement of water depths. Experiments in the Netherlands have

shown that laser-altimetry is able to map water levels of rivers. In urban areas, spurious height

values may occur when a pulse is specularly reflected on a ground point, e.g. on the paved road

surface.

Height Demands in Urban Areas

Since ALS provides high resolution height data with an accuracy level slightly above the

decimetre level, the technique is particularly suited for planning, monitoring and control

purposes.

ALS and Urban Polder Planning and Development

The need for easy evocation of the environment is as old as is the human capacity of

constructing buildings, bridges and roads. For example, integration of an architectural design

with its surrounding, represented by a 3-dimensional landscape model that includes existing

vegetation, facilitates highly the design process and gives engineers and planners an accurate

impression of how their design interacts with its surrounding as shown in Figure 3.2.

Figure 3.2, Part of a 3-dimensional City Model of Mannheim created by using Laser-altimetry

(Courtesy: Toposys Germany)

Urban polder planning and development requires increasingly 3-dimensional urban topography

models. When creating a 3-dimensional virtual world of existing or proposed reality, real data is

needed. This data should not only be 3-dimensional, but also very accurate and highly detailed.

In this case, ALS is providing highly automatically spatially highly detailed geo-data.

An example of ALS application is shown in Figure 3.3.


16

Figure 3.3 An example of ALS application

ALS and land subsidence

In principle, high resolution digital elevation model (DEM) are suited for detection of changes

of any heights and volumes. In particular, when time series are applied height and volume

changes can be traced. By regularly carrying out airborne laser-altimeter surveys, the level and

rate of subsidence can be estimated and modelled.

The only restriction for ALS applications seems to be unfamiliarity and unawareness among

users about its full potentials. Although the method is operationally applied, it still is not a

settled technique.

3.1.3 Hydrological data

Method of representing and predicting rainfall are therefore crucial in the design, analysis and

operation of urban water management and flood protection systems. The appropriate level of

detail in data collection depends on how the data will be used. Six broad categories can be

identified:

• Planning;

• Design;

• Construction;


17

• Operation;

• Maintenance;

• Monitoring and evaluation.

In Indonesia, rainfall data are collected by several departments and authorities including the

Meteorological and Geophysical Agency (BMG), Ministry of Public Works (PU) and Ministry

of Agriculture (Pertanian). The quality of the designs and analyses depends to a large degree, on

the quality of the rainfall data used. Therefore every effort should be made to search for and

obtain data from the data collection agencies.

River discharges

Long term as well as short term river discharges data can de collected from the Ministry of

Public Works in Indonesia, i.e. Research Centre for Water Resources Development in Bandung

or the related river basin authority (Balai Besar Sungai) which manages the related river (for

example Balai Besar Citarum who manages Citarum river). River discharges data can also be

measured by standard procedures of the Ministry of Public Works. See SNI 03-2415-1991 and

SNI 03-2819-1992

In case the urban polder outer water level will be influenced by the tides and waves, data on

tides, waves and littoral drift have to be collected and analysed as well.

Tides

These data should cover the mean sea level, highest high water spring, lowest low water spring,

mean high water neap and mean low water neap. Besides that information about the possible sea

level rise should also be considered in the design works.

Wind and run-up

Wind setup is a result of shear stress exerted by wind on the water surfaces, which causes a

gradient in the water surface.Wind data can be measured or collected from the nearest airport or

Meteorological and Geophysics Agency (Badan Meteorologi dan Geofisika, BMG) in Jakarta or

from ARGOSS (www.waveclimate.com). The data set should represent an area of at least 200

by 200 km, since waves are able to reach a steady sea state within this area. A larger area only

adds 5% to the significant wave height, using the formula of Brettschneider. The data sets

consist of data for wind direction and wind speed. Wind directions are analyzed first, second

histograms.


18

Wave and storm surge

Storm surges are caused by the local minima of atmospheric pressure. Wave data can be

measured or collected from the related institutions, foe example port authorities and

Meteorological and Geophysics Agency in Indonesia. Next to that, wave conditions can be

determined based on the related wind data. In this case the equations of Bretschneider can be

used.

Littoral drift

Littoral transport is the transport of non-cohesive sediments, i.e. mainly sand, along the

foreshore and the shoreface due to the action of the breaking waves and the longshore current.

The littoral transport is also called the longshore transport or the littoral transport. Based on

wind, waves, coastal sediment and bathymetry conditions, littoral drift can be analyzed.

3.1.4 Soil properties, soil subsidence and geological data

The main concern for the design of water management and flood protection systems is the

stability of embankments, dikes, side slope, erode ability of the canal systems and hydraulic

control structures.

The most important questions which a geo-technical investigation has to answer are:

• What kind of soils is found and at what depth; i.e. soft soils such as sand, clay or peat or

hard soils such as limestone and calcareous sandstone, or very hard soils such as quartzite

and basalt;

• What are the mechanical properties of the various soils with respect to their strength and

deformation characteristics;

• How pervious is the soil and does it contain water;

• Is the soil fissured or weathered;

• Will the soil degrade in (short) time.

The first step is to set up and design site investigation.

3.1.5 Land use data

Management and planning of urban space require spatially accurate and timely information on

land use and changing pattern. Monitoring provides the planners and decision-makers with

required information about the current state of development and the nature of changes that have


19

occurred. GIS and Remote Sensing become useful because it provides synoptic view and multi-

temporal Land uses/Land cover data that are often required.

To examine effects of different urban policies, residential, nature, commercial, and industrial

land uses associated with increasing population were spatially located and can be stored by

creating a digital database for further analysis. These data can be used for planning, design,

operational and maintenance purposes of a related urban polder.

3.1.6 Socio-economic data

Badan Pusat Statistik (BPS), the Central Statistics Agency in Indonesia, regularly revises and

published the national accounts data. These publications cover socio economic data in Indonesia

which includes the following aspects:

Government system

Since the beginning of 1999, Indonesia started a new era in the governing system, through the

adoption of a new law on Regional Government i.e. Act No. 22/1999 as Revised by Act No.

32/2004. This law based on decentralization concept therefore, local government has the

autonomy to manage their internal affair. However there are five issues which still under the

control of central government. These issues are foreign affairs, finance and monetary system,

legislation and law enforcement, religion as well as defense and security. As a consequences,

labor and industrial relations issues covered under the competency of local government.

However in dealing with labor and industrial issues, local government supposed to comply with

policies determined by central government such as articulated in national labor regulations.

Economic trends

There has been a relatively constant annual growth rate in the gross national product (GNP), of

almost 7.25%, between 1992 and 1995. The GNP per capita has increased from US $ 661 to $

978 during the same period but later on it decreased to US$710 in the year 2002 (WHO CORE

Indicators 2005). The percentage of poor, both total and rural, has shown marginal declines to

11.7% and 12.6% respectively. Oil and natural resources remain the predominant contributors to

growth. However, several other sectors, particularly agriculture, home industries and tourism,

have grown quite significantly. Poverty still remains a substantial problem. Regional inequities


20

in healthcare are important considerations, particularly maternal health, which is still a major

problem in rural areas.

According to Human Development Report 2006, the national Human Development Index (HDI)

was estimated at 0.711, ranking Indonesia 108 among 177 countries. However, it has improved

from the HDI value of 0.623 in 1990. Similarly, Indonesia’s Gender Development Index is

0.704, ranking it at 81 among 177 countries (UNDP, Human Development Report, 2006).

Applying the international criteria of $ 1 per day, the proportion of poor population in Indonesia

in 1990 was 20.6% and 17% in 2004. In 1998, the Indonesian Government adopted new

thresholds for the national poverty line that reflected a higher standard of living. Subsequently,

1996 poverty levels were adjusted to incorporate the 1998 criteria. During the economic crisis,

the proportion of poor population increased to 23.4% in 1999, and then declined to 18.2% in

2002 and 17% in 2004.

Demographic trends

According to final results of population census 2000, the population was 205.8 million (2000).

Population of Indonesia in 2006 was estimated to be 222 million (Biro Pusat Statistik, 2006).

The annual growth rate of population decreased sharply from 1.97 in 1980-90 to 1.34 during

2000- 2005; but it has slightly increased to 1.5 during 2000-03. The urban population in

Indonesia in 1990 was 31%, which increased to 42% in 2000 and 48% in 2005 (WHO, 2007). In

July 2006, the population under 15 years of age is 20%, population aged 15-59 years is 62.5%,

and population of 60 years and above is 7.5%. There is an increasing trend in the number of

older persons (over 60 years), which will demand more personalized healthcare services. The

Life Expectancy at birth for males has increased from 57.9 years in 1990 to 69 years in 2005.

Since 1960, the infant mortality rate (IMR) in Indonesia has decreased from 128 per 1,000 live

births in 1960, to 68 between 1986 and 1991, and to 32 per 1,000 live births in 2005

3.1.7 Environment data

Besides urban population, environment data should cover the following information in Table 3.1

and these data can be collected from several organizations in Indonesia, i.e. Ministry of

Environment (KLH), Central Statistics Agency (BPS), BAPPEDA and in other cases

universities.


21

Table 3.1 Environmental data

Internal freshwater resources per capita (cu. m)

Freshwater withdrawal

Total (% of internal resources)

Agriculture (% of total freshwater withdrawal)

Access to improved water source (% of total population)

Rural (% of rural population)

Urban (% of urban population)

Access to improved sanitation (% of total population)

Rural (% of rural population)

Urban (% of urban population)

Nationally protected areas (% of total land area)

3.2 Required investigations

3.2.1 Topography

Topographical mapping with contours is required for the design of urban polder water

management and flood protection systems. All data necessary to determine locations,

coordinates and levels will be obtained by direct measurement in the field or if available from

the previous project in the same area. The task includes the establishment of benchmarks with

appurtenant azimuth marks, traversing and levelling survey, ground survey, pot levelling,

computation of the results of the observations and mapping of these results.

The topographical data will be used as a primary data in designing the route of the water

management systems in the related area as well as zoning system for the new development

areas.

3.2.2 Hydrological analysis

An understanding of urban polder hydrology as one entity is necessary in order to design a

proper water management and flood protection systems in urban polders. Rainfall-runoff

analysis will be the most important hydrological analysis which has to be done in the design

phase. These practices are often referred to as urban polder water management and flood

protection systems. The purpose of design storms is to provide a design basis for water


22

management system and its hydraulic structures (After Hall, 1984).

The Natural Resource Conservation Service (NRCS) method can be used for both the estimation

of stormwater runoff peak rates and the generation of hydrographs for the routing of stormwater

flows. The simplified method can be used for drainage area up to 65 km2. The NRCS method

uses a combination of soil conditions and land uses (ground cover) to assign a runoff factor of

the related area. Part 630 of NRCS National Engineering Handbook provides detailed

information NRCS hydrology, and is the technical reference for WINTR-55, a computer

software.

3.2.3 Soil properties, soil subsidence and geological investigations

Field surveys and investigations are required for the planning and design of an urban polder

water management and flood protection systems. Most of the surveys and investigations and the

indicated levels of detail are for the detail design phase, and would generally also be undertaken

during the feasibility stage at a somewhat lower level of detail.

Especially for soft soils, investigation will include field tests such as permeability test, strength

test, loading test, as well as boring, sounding and sampling. Detail and method of soil

investigation depend on the type and scope of the facilities to be constructed. The level and

method of investigation for various steps of project implementation, i.e permeability study,

planning design, construction and maintenance will also be different.

Geological investigation

Related to the planning and design activities, description of soil and its geological conditions

around the potential locations for water management and flood protection systems components

(dikes, pumping stations, hydraulic control structures and canals) have to be made available and

the related field and laboratory investigations have to be done.

Information on the geological conditions in the polder area is used for many purposes in the

planning and design phase, e.g.:

• To determine the stability of the polder components;

• To determine possible settlements as well as land subsidence;

• Groundwater conditions and possible salinity intrusion in the groundwater;

• To formulate the design criteria for the polder components.

Geological investigation should also be done in case other construction project(s) will be done

in the surrounding (outside) area. Based on the geological investigation, possible impact of the


23

development (stability of the polder components and its performance) of the surrounding areas

can be avoided or minimized. Prediction of soft soil behavior usually calls for soil mechanics

calculations. These calculations generally call for a diagrammatic representation. The location

of various soil strata, water pressures and the relevant parameters need to be identified by soil

investigation. See also SNI 03-6802-2002 On Soil sampling and investigation procedures for

engineering purposes.

In order of representation, these are respectively:

• The use of archive material and maps;

• Determination of soil structure;

• The measurement of groundwater levels and piezometric pressure;

• Sampling;

• Parameter determination;

• Presentation of soil investigation data.

Before starting the site investigation, as much information as possible about the site and soil

concerned should be gathered. Not only data about the current site situation but also its past

history are useful. Experience obtained from projects of the same type with a comparable soil

structure can likewise be helpful. Such information can be extremely useful for devising the soil

investigation programme.

Regional geological, geotechnical, geohydrological and historical data can be obtained from

certain institutions such as Directorat Geologi dan Sumberdaya Mineral (Directorate of Geology

and Mine Resources) in Bandung, Bakosurtanal, Pusdata-PU (Data Centre PU) or other research

institutions; they often contain extremely valuable project-relevant information.

The site activities also should be done in order to get:

• Compilation of a preliminary geologic map of estimated geologic conditions over the entire

area of interest.

• Planning of field exploration activities and field and laboratory testing and their locations

that will meet design requirements.

• Conducting a briefing on geotechnical conditions for the planning and design process.


24

Soil Exploration

Determination of Soil Structure

The various soil strata can be differentiated based on classification and identification via sample

tests and based on soil exploration in situ and in the laboratory. Both classification and

identification tests are done on soil samples extracted by means of specific drilling techniques

on site. The same applies to laboratory tests for determining soil mechanics properties (strength,

stiffness, permeability and the like) Only by examining a sufficiently large number of samples

can a valid picture of the soil structure be derived.

Borings

Borings are expensive compared to Cone Penetration Test, (CPT), and are generally used for

soil classification and identification purposes or for the taking of samples. Borings are

somewhat less accurate for depths measurements than CPT’s sowing to the fact that there is no

continuous recording over the depth drilled.

Cone Penetration tests

In soil structure determination, the Standard (Electrical) Cone Penetration Test, (CPT)

especially Piezocone, involving measurement of adhesion or sleeve friction is particularly

important measurement. Differences in layers, for instance, between peat and clay having the

same cone resistance can be highlighted, thereby providing a distinctly more comprehensive

picture than obtained by measuring cone resistance alone. The measurement of pore water

pressure reflected by Piezocone has an important role also.

Laboratory Testing

The purpose of laboratory testing is to provide the basic data which to classify soils and to

quantitatively assess their engineering properties. Laboratory tests should be carefully

performed following the proper testing procedures for the soil involved and the information

desired. Laboratory tests of soils may be grouped into two general classes:

• Classification test: may be performed on either disturbed or undisturbed samples;

• Quantitative test: for hydraulic conductivity (permeability), compressibility and shear

strength. These tests are generally performed on undisturbed samples, except for materials


25

to be placed as controlled fill or materials that do not have an unstable soil structure. In

these cases, tests may be performed on specimens prepared in the laboratory.

Laboratory test should be selected to give the desired and necessary data as economically as

possible. Complicated and expensive test are justified only if the data will reduce costs or risk of

costly failure. In general, relatively few carefully conducted test on specimens selected to cover

the range of soil properties with the results correlated by classification or index test will give

good usable data. The primary test of importance to construction embankment on peat or

organic soils, in approximate order of increasing cost, are:

• visual examination;

• natural moisture content;

• chemical test;

• pH;

• conductivity;

• atterberg limit;

• grain size analysis (mechanical);

• laboratory vane shear;

• unconfined compression;

• moisture density or relatively density;

• permeability;

• loss on Ignition;

• direct shear;

• triaxial compression;

• consolidation.

All the investigations and tests have to follow and in line with the related standard in Indonesia

(SNI).

Soil Properties

Information on the soil properties will be used for many purposes in urban polder system

planning and design, e.g.:

• To diagnose the water management and flood protection problems;

• To suggest/evaluate possible solutions;

• To formulate design criteria.


26

The primary focus in building a structure on subsoil of low bearing capacity and high

compressibility is the control of stability and deformation. There are two important questions in

this connection: is the structure stable in all circumstances and is the deformation in the

structure allowable.

The second condition is known as shear failure occurs when shear stresses set up in the soil

mass exceed the maximum shear resistance that the soil can offer, i.e. its shear strength. This

condition must be regarded against in order to prevent disastrous failure.

The third is known as consolidation, which can take place over long periods – month, years,

decades, even centuries, after construction – especially in soils with low permeability. The

permeability and consolidation coefficients are used primarily for predicting how long the

consolidation process of a poorly permeable layer will take. In order to determine these

parameters, large scale tests will generally provide a more reliable result than tests performed on

a comparatively small soil sample. Estimates of the rate of settlement, and of the time within

which settlement will be virtually complete, are therefore important factors in design.

The parameters determined from laboratory test and in situ test are required for the basis of

analysis, so it has to be as representative as possible to the real soil conductions. Inaccurate

parameter can be very misleading in designs. Below are detail about required site test and

laboratory test and their parameters.

Parameter determined from site in shown in Table 3.2.

Table 3.2 Soil investigation parameters

Type Parameter

• Piston Sampler

• Field Vane Test

• Cone Penetration Test (CPT)

• Permeability

Undisturbed Sample

Cu, Cu.res

Qc, Fs

Kh, Ky

Parameter determined from laboratory is presented in Table 3.3.

Table 3.3 Soil parameters from laboratory investigation

Type of Test Parameter

• Cutting determination, weighing,

trimmed or cut sample

• Specific Gravity

• Atterberg Limits

γ, γdr, w

ps

wL, wP, IP


27

• Loss on Ignition

• Fibre Content

• Chemical

• UU Triaxial Test

• CU Triaxial Test

• Direct Shear

• Consolidation

Humus Content

Degree of humifications

Humus content, Chloride content, content

of other chemical components

Cu

Cu, c, c’.φ, φ’

c, φ

Co, Cv, k, Cω, Cr, mv, pg, Eoeo

Special requirements for peat parameters determination

Peat and organic soils are the ultimate soft soils in engineering terms. They are subject to

instability and massive primary and long term delayed consolidation settlements when subjected

to even moderate load increases. They are difficult to sample and test using normal soil

techniques. Below are special requirement for peat parameter determination.

Some of soil properties, which are of specific importance for the design of urban polder water

management and flood protection systems, are:

Texture

Soil texture refers to the size distribution of the constituent soil particles. The particle size

distribution curve provides the details needed in many formulae that relate particle size to

particular soil properties. The soil triangle as shown in Figure 3.4 used the basic United States

Department of Agriculture (USDA) classifications.

Figure 3.4. Selected base soils and gravels in texture triangle


28

Soils are not always uniformly graded. Some soils are missing certain ranges of particle size due

to their particular geological formation and these are known as gap graded soils. Gap graded

soils can pose problems when they are used as drain envelope material. The successful of a

granular material as a filtering material relies in part on how well the material is graded.

Soil bandwidth

From a practical point of view, it is desirable to have the soils in the region represented by a

band on the particle size distribution plot. From filed surveys there are often hundreds of soil

sample sieve analysis results available. It is not practical to display all these graphically and

hence a statistical methodology using quartiles is used to select representative bandwidths. An

example of the 25% and 75% quartiles are used as shown in Figure 3.5.

Figure 3.5. Representative soil particle size bandwidth

Liquid limit

The liquid limit (LL) is the water content where a soil changes from liquid to plastic behavior.

The original liquid limit test of Atterberg's involved mixing a pat of clay in a little round-

bottomed porcelain bowl of 10-12cm diameter. A groove was cut through the pat of clay with a

spatula, and the bowl was then struck many times against the palm of one hand.

Casagrande subsequently standardized the apparatus and the procedures to make the

measurement more repeatable. Soil is placed into the metal cup portion of the device and a

groove is made down its center with a standardized tool. The cup is repeatedly dropped 10mm

onto a hard rubber base until the groove is closed for 13 mm (½ inch). The moisture content at

which it takes 25 drops of the cup to cause the groove to close is defined as the liquid limit.

Another method for measuring the liquid limit is the Cone Penetrometer test. It is based on the

measurement of penetration into the soil of a standardized cone of specific mass. Despite the


29

universal prevalence of the Casagrande method, the cone penetrometer is considered to be a

more consistent alternative because it minimizes the possibility of human variations when

carrying out the test.

Plasticity

Soil consistency is an expression for the plasticity of the soil and as such its resistance to

mechanical deformation and disruption. The state of plasticity of a soil is mostly determined by

its clay and its moisture content and may be expressed by determining the Atterberg consistency

limits. For drainage, the most important of these limits is the Lower Plastic Limit (LPL). The

LPL may be determined by a simple hand kneading/rolling test.

Bulk density

Based on Figure 3.6, which shows the solid, water and air phase of the soil, the following soil

constants and parameters can be defined as follows:

Figure 3.6. Bulk density and soil moisture content

V soil = V solid + V pores;

Vpores= Vwater + Vair;

Porosity = Vpores/Vsoil

Where:

V= volume in cm3;

W= weight in gram;

ρ = density in gram/cm3;

BD= bulk density in gram/cm3;

θ = soil moisture content by volume or by weight in %

W dry soil = V solid * ρsolid (particle density = 2.65 g/cm3)

Wwater = Vwater * ρwater (density of water = 1.00 g/cm3)

BD = Wdry soil/Vsoil


30

θw = (Wwater/Wdry soil) * 100%, by weight

θv = (Vwater/Vsoil)*100%, by volume

θv = θw * BD

Plasticity index

The plastic limit is that moisture content of a soil at which it becomes too dry to be plastic, used

together with the liquid limit to determine the plasticity index which when plotted against the

liquid limit on the plasticity chart enables the classification of cohesive soils.

Palsticity Index = Liquid Limit – Plastic Limit

Natural water content

The natural water (or moisture) content, w (%), in the soil is defined as the ratio of the weight of

water to the weight of the solid particles.

Void ratio

The basic means of expressing the density of packing is to use the voids ratio (e):

e = Vv/Vs

where:

e= void ratio (-);

Vv= volume of the voids (m3);

Vs is the volume of the “solids” (soil particles) (m3).

Note that e can be greater than 1 (and it very often is for clay soils).

Groundwater table

Groundwater table provides valuable information on the subsurface drainage conditions in the

area. Groundwater table reflects the prevailing balance between the different groundwater

recharge/discharge components. As the balance changes, so does the groundwater table. When

the groundwater table is permanently or seasonally too close to the soil surface, control by

subsurface drainage systems may be required.

Soil subsidence

After reclamation through impoldering, the soil will ripen. This ripening process stands for all

physical, chemical and microbiological processes by which a freshly deposited mud is


31

transformed to a dry land soil. It essentially involves an irreversible loss of water. Freshly

deposited mud, rich in clay and organic matter, has water content of as much as 80% by volume.

This water content can be reduced by consolidation, evaporation from the surface, drainage

and/or extraction of groundwater.

The removal of water from the soil leads to a partial collapse of the initial, very open micro

structure, shrinkage and consequent fissuring of the soil, and an increase in the area of close

contact between individual particles and aggregates. Consequently soil ripening results in an

increase of the cohesive strength of a sediment. As a result, the sediments will shrink and settle,

leading to a subsidence of the surface.

For urban development in polders, the lands are often raised by landfill. This may be realised to

get a sufficiently high surface level, or to create better drainage and bearing capacity conditions,

especially during the building phase. Due to the landfill and additional subsidence and

settlement process will be induced.

In the planning stage of a polder, the assessment of the extent of subsidence is of vital

importance, as subsidence will influence the levels of watercourses and the lifting heights of

pumps.

Geological investigations

Related to the planning and design activities, description of soil and its geological conditions

around the potential locations for water management system components (dikes, pumping

stations, hydraulic control structures and canals) have to be made available and the related filed

and laboratory investigations have to be done.

Information on the geological conditions in the polder area is used for many purposes in the

planning and design phase, e.g.:

• To determine the stability of the polder water management and flood protection

components;

• To determine possible settlement as well as land subsidence;

• groundwater conditions and possible salinity intrusion in the groundwater;

• To formulate the design criteria for the polder water management and flood protection

components.

Geological investigation should also be done in case other construction project(s) will be done


32

in the surrounding (outside) area. Based on the geological investigation, possible impact of the

development (stability of the polder water management and flood protection components and its

performance) to the surrounding areas can be avoided or minimized.

3.2.4 Land use and land use development

Concern over land use change in Indonesia is relatively recent. Urbanization has impacted

significantly on spatial development in Indonesia, notably on urban land. For this reason an

urban land development policy which is able to respond to rapid urbanization is of extreme

importance to Indonesia.

During the economic boom of the 1980s and 1990s, many once-residential areas, especially

slum areas (‘kawasan kumuh’) in the city centre, were converted into hotels, luxury high-rise

apartments and shopping malls.

Developers who intend to acquire and assemble land for subdivision projects are required to

obtain land development permits (ijin lokasi) and land purchase permits. Archer (1993)

maintains that there are five basic functions of land permit systems in urban development:

• Guiding the location of the (formal) private land and building development projects;

• Coordinating the government and the formal private sector development activities;

• Facilitating land assembly for the development projects;

• Facilitating land assembly for large-scale development projects, including new town and

industrial estate projects;

• Attaching appropriate project development conditions to the permits for the land

acquisition for the proposed development projects.

In the past the land-development permit system in Indonesia was a top-down process which

essentially reserved land almost exclusively for the approved developers. The system granted

monopoly rights to the developers to purchase land from landowners at low prices. This system

neglected the rights of the landowners. Land acquisition is often a lengthy process, and can be

costly. Land acquisition for the purpose of public infrastructure development is administered

under the Presidential Decree (Keppres) 55/1993, which clearly states that land acquisition

should be done through direct deliberation (‘musyawarah’) and achievement of consensus

(‘mufakat’), and on a voluntary basis between the involved parties. Land transfers for the benefit

of the public interests, including road development, hospitals, schools, primary health care, etc.,

should entail the involvement of the land-owners and their associates, the legislative council

(DPRD) at a provincial, district, or municipal level, in both the utilization of land to serve public


33

interests and the valuation of the compensation offered. The decree also emphasizes that the

compensation of land transfers should be capable, at the very least, of improving the socio-

economic conditions of the respective land-owners. Recently, the Indonesian government has

reformed the land development permit (ijin lokasi). From 1999, developers were allowed only

to acquire land for industrial estates and housing projects that do not exceed 400 ha of land in

one province, and maximum of 4000 ha in the whole of Indonesia.

The National Land Agency (BPN) task is to manage land records, to process land titles and to

administer land development. Unfortunately, local government's capacity to manage and

implement the spatial plan (‘Rencana Umum Tata Ruang’), particularly in the monitoring and

control of land conversion, has also been technically inadequate.

‘Pajak Bumi dan Bangunan’ (PBB, Land and Building Taxes) is one of the prevailing property

taxes in Indonesia at present. According to Dorleans (1994) the revenues extracted from the

land and building tax (PBB) is insignificant in comparison to the profits extracted by private

developers. An obvious shortcoming of the current PBB system is that the tax valuation does

not take into account the various land-use categories.

Recently promulgated legislation in Indonesia for regional autonomy (Law 22/1999) recognizes

democracy, public participation, justice, plurality and increased autonomy for the local (district)

government to manage their own development affairs. This means that the local government and

communities will play a very important role in urban land development in their own

jurisdiction, without much intervention from central and provincial government. The role of

government in urban land-use development should move from the authority to the administrator,

and the private sector should play a larger role (Firman, 2002). Laws 22/1999 and 25/1999,

regarding fiscal decentralization in Indonesia, state clearly that the local government and local

communities through local representative councils or Dewan Perwakilan Rakyat Daerah

(DPRD), should have greater discretion in deciding what is best for the urban and regional

development in their own areas. At present, some city governments in Indonesia have initiated a

participatory urban development action plan, in which all stakeholders are involved as equal

partners in the decision-making process.

Indonesia's new legislation regarding regional autonomy stipulates that the central government

will deal only with fiscal and monetary affairs, international affairs, justice, religious affairs and

national economic planning and administration. District (Kabupaten) and city (Kota)

governments are authorized to implement programs in agriculture, education, health, public

works, environment and land use, cooperatives and labor. Accordingly, the land-use

development permits should now be granted by the mayor (Walikota) for municipalities (Kota)

and by a head of regency (Bupati) for Kabupaten. In 2001 the central government issued


34

Presidential Decree 10/2001 which prohibits local and provincial government to issue any

regulation pertaining to land-use development.

Land use regulation is a basic instrument for creating land values and shaping urban physical

growth (Menezes, 1988). Therefore, policy for the utilization of urban land resources should

contain the principles and control mechanisms of land use, including the land development

permit and the building permit. Land utilization in urban areas should be based on a spatial plan.

The problem with urban spatial plans (Rencana Umum Tata Ruang—RUTR) in Indonesia is

that they are intended and designed to control urban development in great detail. This obviously

cannot be fully implemented by the local government, due to the many constraints of the

resources available to implement the plan.

Urban spatial plans should be made accessible and available to the public, in order to motivate

them to actively participate in urban land development controls. The Local Development

Planning Board (‘Bappeda’) of the provincial administrative level (Province) and of the district

and municipal levels should be the institution that undertakes such coordination.

Land-owners need to be ‘share holders’ in the projects being carried out by developers on their

lands. This is the essence of a partnership between the private sector, the community and

government in urban land-use development. There is a need to establish a mechanism for land

transfers that can take ownership of the land from the owners.

3.2.5 Socio economy and trends

National Development encompasses the establishment of an advanced and just society.

Indonesia, specifically in terms of the socio-economic life, is committed to implement National

Development on the basis of the spirit of mutualism and brotherhood as the foundation for the

realization of social justice. This is stipulated in Indonesia’s constitution. Unfortunately,

National Development that should have benefited all parties, has become a process that has

created socio-economic and socio-cultural divergences. Data on socio economic as well as

socio-culture have to be collected and analysed carefully in order to minimize the negative

impact of the development on that aspects. The poor and weak have mostly become the

marginalized and then evicted, and in fact they have become alienated to those reaping the

benefits. A process of impoverishment is concurrent with city developments and renewals.

Urban polders can truly become places that are friendly, enjoyably and inspiring to their citizens


35

to live in peace and in the pursuit of happiness.

Urban development is not independent from development of rural areas. The National

Development Planning Bureau of the Republic of Indonesia or Badan Perencanaan

Pembangunan Nasional (BAPPEDA) strategically deploys an integral approach to development.

A balanced development between urban and rural areas is institutionally designed. There must

be an equivalent interdependence between the rural area and urban areas. The question that then

arises is: how can the urban areas empower the rural areas in the interest of harmonious life in

the cities, and vice-versa. The problem is how cities need to be designed so that the cities can

also function to revitalize themselves thereby concomitantly able to revitalize the rural areas in

an effective manner. There will be no places that are peaceful, comfortable and just if there is no

mutualism and brotherhood between the rich and the poor and between the urban areas and rural

areas.

3.2.6 Environmental analyses

Full environmental impact assessments (EIA or Analisa Mengenai Dampak Lingkungan

(AMDAL) in Indonesian) are required when developments exceed 10,000 ha. Although this

provides, in principle, a means to avoid environmentally unsuitable applications, the process has

proven susceptible to influence. The EIA has to be evaluated by the AMDAL commission of the

related ministry, and so it failed to provide a genuinely independent assessment.

For a project in ecologically sensitive areas, it may be obligatory that an environmental impact

analyses has to be conducted in which the possible environmental impacts are assessed on the

basis of a prescribed methodology and standards in Indonesia. An environmental analysis will

investigate how environmental damage can be avoided/mitigated and which measures could be

possible to help enhancing local/regional environmental values.

The notion ‘environmental effects’ considers the physical, chemical, biological and social

aspects that a project may have on the ecosystem. As such we can identify for any projects the

interrelationships between land, water and people. See Figure 3.7


36

Figure 3.7 Interrelationships among land, water and people

(after K. Pal and R. Rajappa, 1993)

3.3 Data processing, storage and retrieval

The main questions have to be answered of data processing, storage and retrieval are the

following:

• Which data are available in the system;

• How can the users retrieve and use the data and improve the data quality if needed.

For this purpose, information system (IS) will be needed and this system comprises the

infrastructure of physical and human resources to collect, process, store and disseminate data in

relation to the planning, design, operation and maintenance of the urban polder systems. In

creating the IS the advancements taking place in the field of electronics, computers and

communications is being exploited for data gathering, organizing data, establishing data

warehouse, and provide an information systems to the water resource management agencies,

polder authorities and other related agencies. IS will facilitate standardized documentation of

data through out Indonesia, quick and easy interpretation, provide gateway for advanced data

analysis through modeling for visualizing the system response to different situations as well as

disseminate information and knowledge to all the agencies and the actual water related users.

This IS will cover water and non-water data, technical as well as non-technical (social,

economic, ecology, environment) aspects of urban polder development.

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37

4 Planning

4.1 General planning framework

From a functional point of view, urban polder water management and flood protection systems

consist of planning, design, construction, operation, maintenance, monitoring and evaluation

functions, ideally carried out in the order indicated in Figure 4.1. These functions are shared

with or are common to most pubic services and facilities. Unfortunately, the planning function

receives too little attention in urban polder water management and flood protection systems as

well as in other public services and utilities.

Figure 4.1. Urban polder water management and flood protection phases

Urban polder water management and flood protection systems consist of various integrated

components, each of which is intended to perform one or more functions in controlling the

quantity of urban polder runoff. To a large extent, components of an urban polder water system

are visible or noticed only when they malfunction, or are alleged to malfunction. Another

somewhat unique characteristic of urban polder water management and flood protection systems

is that they function infrequently, that is, immediately after rainfall events.

The inhabitants generally take the urban polder water management and flood protection systems


38

for granted. Accordingly, inhabitants interest in and willingness to pay for planning, designing,

constructing, operating, maintenance, monitoring and evaluation of urban polder water

management and flood protection systems tend to literally rise and fall in relation to the

frequency of flooding or other related problems. This is particularly true for the planning

function, which generally seems to enjoy the least support from the general public and elected

officials. Urban polder water management and flood protection systems planning is normally

only undertaken in reaction to serious flooding, or other related problems. During and

immediately after a flood, the community is often willing to fund remedial efforts and planning

projects. However, months later, when the planning has been completed and costly

recommendations made, public interest wanes, little or nothing is done, and the cycle is

repeated.

Prevention of flooding using land zoning regulations, flow control storages, or flood protection

works is usually difficult to justify politically, before any floods have actually occurred. This

means that planning of flood free urban developments can be very difficult and that flood

problems are inevitable.

For general procedure of urban drainage planning, a standard from the Ministry of Public Works

is already available: SNI 02-2406-1991. In this standard, a summary is given about the

important factors which have to be considered in the urban drainage planning activities. These

factors cover technical, social as well as environmental aspects.

Need for planning

Urban polder water problems are complex involving economic, environmental, legal, financial,

administrative, and political facets. Urban polder water management and flood protection

planning is a method of addressing these complex problems in a co-ordinated and holistic

manner on a total urban polder basis.

There is an obvious need for urban polder water management and flood protection systems to be

planned and integrated into the urban form with other municipal services at the earliest possible

stage in the planning process for urban development. Urban polder water management and flood

protection system planning should not be done after all of the other decisions have already been

made as to the form and layout of a new urban area. It is this latter approach, which creates

urban polder water management and flood protection problems, which are costly to make the

4 Planning

39

correction. For established areas, particularly those undergoing land use change or urban

consolidation, there is a need to reconsider how urban polder water and flood are managed and

assess how these changes impact on both the built and natural environments. Unfortunately, the

importance of focusing on how urban polder water runoff and flood protection are to be

managed have not always been recognised in the past and how urban polder water and flood are

managed can impact on each land use in terms of water quality, flood risk, recreational

opportunities etc. An understanding of these inter-relationships will influence the form of new

development and determine what improvements need to be made within the established areas.

Planning principles

Urban polder water management and flood protection planning should be based on integrated

urban polder planning principles to ensure that all components of the plan are planned and co-

ordinated so as to achieve the desired result. Integrated urban polder planning is a philosophy

that balances social, economic, technical and environmental concerns to achieve sustainable

development.

Planning of urban polder water management and flood protection systems is a multi-faceted

exercise involving direct interaction between professionals having expertise in the following

fields:

• Aerial spatial planning;

• Hydrology and hydraulics;

• Public health and ecology;

• Cost and benefit.

Experience has shown that the following principles apply when planning and designing urban

polder water systems (after American Society of Civil Engineers (ASCE), 1992):

• Urban polder water management and flood protection systems should be a central part of

an overall urban polder management program involving all stakeholders, both the

community as well as government components. The ways in which proposed local urban

polder water systems fit existing regional systems must be quantified and discussed in an

urban polder water management and flood protection systems strategy plan;

• Urban polder water management and flood protection systems planning and design must

be compatible with river basin management plans and in particular, should be co-

ordinated with planning for land use, open space, and transportation. Erosion and


40

sediment control, flood control, site grading criteria, and regional water supply all closely

inter-relate with urban polder water management and flood protection systems;

• Urban polder water management and flood protection systems is a space allocation

problem and therefore an intrinsic part of the town planning process. All the components

of an urban polder water management system have the potential to both convey and store

runoff. If adequate provision is not made for the space demands of urban polder water

management and flood protection systems, runoff will overflow or encroach onto other

land uses, will result in damage or even disrupt the functioning of other urban

management and flood protection systems and services;

• Planning and design of urban polder water management and flood protection systems

generally should not be based on the premise that problems can be transferred from one

location to another. Providing conveyance-oriented solutions to solve urban polder water-

flooding problems usually only serves to transfer the problem to another location further

downstream. A storage-oriented approach by temporarily storing runoff in detention

and/or retention facilities can reduce the capacity required in downstream conveyance

systems, and thereby reduce the likelihood of flooding problems being transferred

downstream;

• An urban polder water management and flood protection systems strategy should be a

multi-purpose, multi-means effort. There are a number of competing demands placed

upon space and resources within an urban area. An urban polder water management and

flood protection systems strategy should therefore meet a number of objectives including

flood control, water quality enhancement, groundwater extraction and recharge, land

subsidence, control of erosion and sediment deposition;

• Planning and design of urban polder water management and flood protection systems

should consider the features and functions of natural drainage systems. Every urban

polder contains natural features that may contribute to the management of urban polder

water runoff under existing conditions;

• In new developments, urban polder water flow rates after development should

approximate pre-development conditions. Three inter-related concepts should be

considered:

- the pervious ness of a polder should be maintained to the greatest possible extent;

- the rate of runoff should be reduced. Preference should be given to urban polder

water management and flood protection systems, which use practices that maintain

vegetative and porous land cover;

- pollution control is best accomplished by implementing a series of measures, which

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41

can include source control, minimisation of directly connected impervious area,

community, and public facilities to control both runoff and pollution, this measure

includes the solid waste management.

• Urban polder water management and flood protection systems should be planned and

designed, beginning with the outlet or point of outflow from the polder. The downstream

conveyance system or receiving water should be evaluated to ensure that it has sufficient

capacity to accept design discharges without adverse backwater or downstream impacts

such as flooding, erosion and sediment deposition;

• urban polder water management and flood protection systems should not be put in place

if they cannot be maintained or will not receive regular maintenance. Failure to provide

proper maintenance reduces the hydraulic capacity of the system.

Planning approach

It is recommended that urban polder water management and flood protection systems planning

be undertaken in two distinct but complementary stages, namely:

• Urban polder water management and flood protection systems strategy planning;

• Urban polder water management and flood protection systems master planning.

These two stages of planning form part of a management approach to total polder management,

shown in Figure 4.2 that integrates polder wide, metropolitan/municipal, and local area planning

and management considerations. Urban polder management planning is undertaken to establish

objectives and practices for the management of water resources within an urban polder. Plan

development should concentrate on whole of polder issues, comprise a broad range of

objectives, and involve extensive community participation approaches.

A municipal plan prescribes the pattern of urban polder development, including:

• permissible land uses, location (zoning), and conditions of use;

• roads, public transport, cycle, and pedestrian corridors;

• major open space systems and landscape provision;

• recreation and facilities provision;

• ecological or natural amenity provision.


42

Figure 4.2. Planning approach (after NSW EPA, 1996a)

A municipal plan may also contain information which is relevant to urban polder water strategy

planning and urban polder water master planning, including:

• topographic details;

• geotechnical information including groundwater extraction and land subsidence;

• flooding, and other hazard areas;

• drainage and other service corridors, including existing water control infrastructure;

• descriptions of ecosystems requiring protection.

Preparation of strategy plans

There is no rigid process for preparing urban polder development strategy plans. The process to

be adopted for a particular area will depend on the physical, ecological, social, and

administrative characteristics of the area. Figure 4.3 shows the outlines a number of tasks that

can be undertaken when preparing urban polder strategy plans. The planning process would

have to be flexible and responsive to the characteristics of the area.

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Figure 4.3 Urban polder developmet strategy plan steps

These plans could provide a framework for urban polder management that could be improved

over time. More detail description for each step is presented below:

Step 1: Problem definition and establish a framework

The first step in the process of the preparation of strategy plans involves problem definition and

establishing the overall framework for the plan and the plan preparation process. This can

involve establishing:

• the purpose of the plan;

• responsibilities for urban polder management within the area;

• resource requirements for the preparation of the plan;

• the physical boundaries of the plan (e.g. area, metropolitan area);

• consultation processes with the community and other stakeholders.

Step 2: Planning objectives

In this step the objectives of the urban polder development have to be derived clearly.

Step 3: Data collection

Data collection must be done on the physical, social, and ecological characteristics of the area,


44

and its major urban water management and flood protection systems, such as rivers, streams,

lakes, ponds, etc. These data are useful for a number of purposes, including:

• describing the existing conditions within the area;

• identifying constraints and opportunities for improved structural and non-structural urban

water management and flood protection practices.

For an initial urban polder management plan, a preliminary assessment could be undertaken

using existing or readily available data. Any requirements for further information that arise

during the plan preparation process could be identified in the plan as an action to be

implemented.

Step 4: Development options

Using the available data collected in step 3, the existing conditions within the area can be

described. These conditions can include:

• topography, land use, and soils;

• hydrology (e.g. location, type, and severity of historic flooding, and low flow

characteristics);

• water quality and solid waste.

Development options are based on the assessment of existing conditions, which may provide

additional data for the plan, include:

• undertaking a preliminary assessment based on the existing or readily available

information. One of the actions specified in the plan could be to undertake further

detailed investigations. This information could also be supplemented by the use of

engineering or scientific judgement;

• site visits by experts in fields such as hydrology, hydraulics, water quality, ecology, and

geomorphology, who would use their knowledge of other urban polder systems to provide

a preliminary assessment of these characteristics in a short report.

A broad range of structural and non-structural management practices is available to address

identified urban polder management issues. Options incorporating different management

practices that could be applied to address global problems and area-specific problems need to be

identified.

It may be useful to obtain community input into the identification of development options. This

input includes:

• Social values such as public health and safety;

• Economic values in order to minimise property damage;

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• Water use where surface water or groundwater can be used to provide a water source for

domestic, stock, and industrial purposes;

• Property values where urban water management and flood protection systems can

enhance adjacent property values, particularly those adjacent to ponds, wetlands, lakes,

and natural channels.

Step 5: Analysis and evaluation of options

Analysis and evaluation of options should have to be based on the principles of ecologically

sustainable development which can be described as follows:

• Negative impacts of an urban polder on public health and safety needs to be minimised;

• Water quality in the area is to meet ambient water quality objectives;

• Flows within the area are to meet receiving water flow objectives;

• Degraded ecosystems needs to be restored where practical, including aquatic habitats and

riparian zones;

• Opportunities for the multiple use of the urban polder water management and flood

protection components are to be optimised, to the degree that they are compatible with

other management objectives;

• Negative impacts of new urban developments have to be minimised.

Compromises may need to be made between these objectives for practical and economic

reasons, to achieve balanced environmental outcomes, and to meet community expectations.

A preliminary evaluation of these options can be undertaken by assessing:

• Estimated capital cost (including any associated costs such as relocation of

infrastructure);

• Estimated operations and maintenance costs;

• Environmental impacts;

• Technical and administrative viability.

It is essential that the recommendations contained in the plan are realistic, making the goals of

the plan achievable, otherwise there is a risk of losing a degree of community support. Support

is likely to be maintained or improved if realistic achievable actions are recommended.

Step 6: Prepare development plan

The aim of the preparation of development plan is to summarise the management issues to

enable stakeholder review before investigating potential management options. This may result


46

in useful input from stakeholders on the importance of management issues, the values and

objectives used to derive the issues, and potentially highlight additional issues. The contents of

the report may include: an introduction, outlining the purpose of the report, description of the

area, description of existing area conditions, identified area values, urban polder management

objectives, and identified urban polder management issues.

It is generally effective to present these plans for public and the related stakeholders. Ample

time would have to be reserved to enable the stakeholders to prepare solid comments. Thereafter

it is advisable to show clearly how the comments have resulted in the modification of the draft

plans into the final development plan.

4.2 Land and water development framework

In analyzing the need for land and water development, for the urban and industrial areas, the

need is caused by the rapid development of such areas all over the world (Schultz, 1993). There

is a great need for land and water development, aiming at the improvement of living and

production conditions in the rural areas, land reclamation, and the development of urban and

industrial areas with related facilities. The projects will have to be developed and implemented

in such a way that on the one hand the objectives are realized, and on the other hand the

environmental impacts are at an acceptable level. The projects may strongly differ in type and

scale. Answers to the following crucial questions determine the living conditions of the users for

many decades:

• What will be the safety conditions living in a polder;

• What will be the need for development;

• Which level of service will be required;

• What will be the role of the government;

• What will be the side effects of the development?

Due to the rapid expansion of urban and industrial areas, the percentage of people living in

urban areas increased from 30% in 1950 to 43% in 1990 (United Nations, 2000). It is expected

that this development will continue to an estimated 61% in 2030. The major part of urbanization

is expected to take place in deltaic and coastal areas. This means that lands have to be prepared

for new urban and industrial areas. As the suitable locations have already been developed, this

will be increasingly difficult (Oudshoorn, et al., 1999).

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Safety conditions living in a polder

Safety conditions mean that the inhabitants who live in an urban polder should have ‘dry feet’

and healthy water’. Not only drainage and flood protection are important, but also stagnant

water which soon turns into a dirty and stinking pool in the water management system has to be

avoided.

Need for development

The future development of an urban polder area will be needed in line with the improvement of

the living quality in a polder. Any future development plan should apply a participation

approach where all the related stakeholders will be involved in the decision making processes.

Public hearing where musyawarah and mufakat (discussion and compromising) should be

considered in the development plan. Transparency in the management of the polder has to be

applied.

Required level of service

Investments in urban areas are generally justified by the need for areas for living, industry,

and/or commercial development. These projects are more complex than projects for rural areas,

as many more components have to be developed and integrated. Another essential difference is

that investments per square meter are much higher in urban areas than those needed in rural

areas. From a technical point of view the questions to be solved refer to the preparation of

building sites, foundation aspects, storage and removal of surplus rainwater, water supply for

the green areas, infrastructure, drinking water supply and sewerage, and required facilities.

In urban areas, investments in property are generally that high, that investment in the urban

water management system are easily justified. However, the level of service also concerns

various recreational facilities, like parks and sports fields, to make living in the urban area

attractive.

Role of the government

In most land and water development projects the government plays an important role, as they

initiate developments that fit in her development policy, and by preventing unwanted

developments. Concerning the technical aspects, they are in charge for land use, or development


48

plans, the required legal framework, standards concerning the functioning of systems, and in

many cases for the actual implementation. It will be clear that the different levels in the

government will play different roles.

Land acquisition and compensation

Basically, for land acquisition and compensation or replacement should be based on the

following principles (Kementrian Lingkungan Hidup (KLH), E1870):

• Private land must be substituted with another equally fertile land or another productive asset

of same value;

• Productive plant facilities should be compensated by market rate value of such plant

facilities as agreed by the owner.

Then consultation process for land/ asset acquisition should be done as follows:

• Setting up a Village Implementation Team and Village Administration and they shall

discuss owners whose assets are affected by the proposed projects in the village meeting

(musyawarh dan mufakat);

• Asset owners must receive explanation about their rights for compensation or other options;

• Agreement reached during the meeting shall be written and recorded as minutes of meeting;

• When owners demand compensation, the minutes should record people who receive

compensation and details of the compensated objects;

• The Minutes and receipts of compensation should be archived properly for future

inspection.

Complaints should be resolved at the village level first. If solution cannot be achieved then the

problem can be raised to higher level.

Side effects of development

Each development will result in side effects. In many cases these side effects caused a lot of

trouble (Volker, 1987). It is the responsibility of the organization in charge of the development,

to identify possible side effects and to prevent the negative ones as much as possible. This can

be realized by adapted designs, and by establishing a legal framework and control mechanism.

Some typical side effects are impact on the existing (geo) hydrological regime, damage to

existing natural values, soil and water. To prevent negative side effects as much as possible, an

environmental impact analysis and assessment has to be carried out and appropriate measures

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have to be taken based on that assessment.

4.3 Spatial planning approaches

Spatial planning and water management there are a close link between them. Province and

municipality (PemKot) are responsible for the spatial planning. The starting point is water has

an important role in the environment. For that reason a water map for spatial planning will be

needed in line with the development plan of an urban polder. Three main elements of an

integrated spatial planning of water resources systems in urban polder development are

presented in Figure 4.4.

Figure 4.4 Main elements in spatial planning in urban polder development

Each element composes of several activities as described below:

Planning and policy:

• Discussion with clients and stakeholders;

• Land evaluation and feasibility study;

• Conceptual Master Planning;

• Detail Master Planning and Detail Engineering design;

• Environmental impact assessment (AMDAL);

• Organization setting;

• Master planning and detail engineering design will be reviewed by consultant, BAPPEDA,

PU, private sector and communities (public hearing).


50

Implementation:

• Land acquisition and certification by municipality and BPN;

• Construction control by DPU and executed by consultants, private sector or communities;

• Environmental aspects and infrastructures management controlled by Environmental agency

(KLH, BPLHD), private sector or communities.

Controlling:

• Location permit (SIPPT) by Dinas Pertanahan dan Pemetaan, DTK, DPU, P2B, Dispenda;

• Site plan control permit by DTK;

• Infrastructure construction permit and control by DPU;

• Building construction permit and control by DTK, Dinas P2B or P2K.

Spatial land use planning has to be considered carefully in the planning phase and significantly

change in land use in the later stage may influence the operation pattern of the water

management system.

4.4 Topographical aspects

Good topographical maps, showing the lie of the land, are indispensable in urban polder

planning and design. For feasibility study, maps with a scale of 1:10,000 or 1: 25,000 showing

0.50 m interval contour lines will generally suffice for the planning of the water management

system.

For final planning and design, more detailed maps are required with map scales usually 1:5,000

to 1: 10,000 and with contour lines of 0.25 – 0.50 m.

Contour lines at 0.25 m are normally required for an urban polder area. Detailed topographic

maps are especially needed for the design of open water management system for polder areas.

Small differences in elevation are important and contour lines should be based on an adequate

number of points to provide a good picture of the micro-topography.

The topographic maps should also show the main elements of any existing water management

and flood protection systems and all relevant infrastructure features such as roads, power lines,

settlements, etc. To assess whether existing water management systems can be used,

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51

longitudinal profiles with a scale 1:5,000 or 1:10,000 with cross-sections at every 100 – 200 m

and scale 1:100 will, be needed as well. To assess outlet conditions it may be necessary to

extend the topographic mapping to well outside the polder area. For the design purposes,

topographical maps must have the interval of 0.10 m or less in relation to the surface relief of

the coastal areas.

Map preparation from aerial photography and state of the art remote sensing pictures are

generally sufficiently detailed for feasibility level study and planning.

Topographical data can be obtained from several institutions in Indonesia, among others are:

• Badan Koordinasi Survey dan Pemetaan (BAKOSURTANAL) with different scale

availability:

Scale

1:1,000,000

1: 500,000

1: 250,000

1: 100,000

1: 50,000

1: 25,000

1: 10,000

• Dinas Pertanahan dan Pemetaan Provinsi where the most used scales are: 1: 10,000 and 1:

5,000

In relation to land subsidence in the areas where groundwater extraction was done without a

proper control or monitoring, changes of topographical conditions should be considered

carefully. If possible a control work has to be done in order to make a correction to the existing

topographical data. All the topographical maps have to have the same reference level, i.e. Mean

Sea Level (MSL) or the Project Reference Level (PRL). For this purpose a stable and permanent

benchmarks have to be erected.

4.5 Land use zoning system based on elevation classification

Zoning principle has to be established for potential urban polder development and this zoning


52

has to be followed by the improvement of the urban polder water management and flood

protection systems performance.(to determine the boundaries, water management systems,

dikes, hydraulic control structures, pumping stations).

On the flood plains people are not allowed to utilize it. These flood plains (100 m from each

bank) must be free and can be used as temporary storages of flood water.

In the zoning system, different land use will be designed with different elevations. In case of

flood, first parks or wetland parks will be flooded and after that followed by roads. This zoning

system will act as structural runoff quality control system. An example of the zoning system is

presented in Figure 4.5.

An example of urban development without zoning system with different elevations is presented

in Figure 4.6. Inundation is everywhere as soon as run-off exceeds the capacity of the drainage

system.

Figure 4.6 Flood in the urban development area without zoning system

Figure 4.5 Zoning system in urban polder

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4.6 Water resources aspects

Water quantity

Urbanization impacts the rainfall-runoff process in a variety of ways. Infiltration is reduced due

to the addition of impervious surfaces, resulting in increasing quantities of run-off. An

understanding of urban hydrology is necessary in order to design a proper urban polder water

management and flood protection systems. Urban polder water management system will be

installed in order to control and to manage storm water run-off, therefore, a design run-off event

should be used.

The hydrologic cycle is the continuous, unsteady circulation of water from the atmosphere to

and under, the land surface and back to the atmosphere by various processes. The hydrologic

cycle is dynamic at a particular location may vary greatly with time. Temporal variations may

occur in the atmosphere, on the land surface, in surface waters, and in the groundwater of an

area. Figure 4.7 shows the global hydrologic cycle in schematic form. Figure 4.8 shows the

hydrological cycle for a river basin. The important processes are described below with emphasis

on factors that influence each process in the planning, design, and operation of urban polder

water management and flood protection systems (Walesh, 1989).

Figure 4.7. Schematic sketch of the global water cycle. Water storages and fluxes are indicated

by boxes and arrows (Oki and Kanae, 2006).


54

Figure 4.8. Hydrologic cycle for a river basin

Precipitation

Precipitation can occur primarily as rain. Annual amounts of precipitation are unpredictable and

variable ranging from approximately 2,000 mm to 4,000 mm for various locations in Indonesia.

In a sense, precipitation is the most important process in the hydrologic cycle because it is the

‘driving force’ providing water that must be accommodated in the urban environment.

Interception

Interception is the amount of precipitation that wets and adheres to aboveground objects

(primarily vegetation) until it is evaporated back into the atmosphere. The annual amount of

interception in a particular area is affected by factors such as the amount and type of

precipitation, the extent and type of vegetation, and winds. Interception is not likely to be an

important process in urban polder water management programs.

Depression storage

This process is defined as the amount of total precipitation detained in and evaporated from

depressions on the land surface. Depression storage is water that does not run off or infiltrate.

Surface type and slope, and the factors influencing evaporation affect depression storage.

Because of its small magnitude, depression storage is not likely to be important in urban polder

water investigations.

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Infiltration

Infiltration is defined as the passage of water through the air-soil interface. Infiltration rates are

affected by factors such as time since the rainfall event began, soil porosity and permeability,

antecedent soil moisture conditions, and presence of vegetation. Infiltration is a very important

process in urban polder water management systems and, therefore, essentially all hydrologic

methods explicitly account for infiltration. Urbanisation usually decreases infiltration with a

resulting increase in runoff volume and discharge.

Evaporation and transpiration

Evaporation is the process whereby water is transformed from the liquid or solid state into the

gaseous state. Transpiration is the mechanism whereby water moves up through vegetation and

is subsequently evaporated. Evapotranspiration rates are affected by factors such as temperature,

wind, vapour pressure, plant characteristics, and availability of soil moisture. Although

evaporation is of very little practical significance during precipitation events, evapotranspiration

is a very important factor in preparing hydrologic budgets for river basins, lakes, or reservoirs.

Surface runoff

Surface runoff, sometimes referred to as overland flow, is the process whereby water moves

from the ground surface to a waterway or water body. Surface runoff is affected by other

processes in the hydrologic cycle, such as precipitation and infiltration, plus factors such as

imperviousness and land slope. Surface runoff determines the quantity of urban polder water

that must be locally managed and affects the quantity of potential pollutants transported to

receiving waters.

Interflow

Interflow, sometimes referred to as subsurface flow, is the process whereby water moves

laterally beneath the land surface, but above the groundwater table. Interflow occurs until water

enters a waterway or water body; or is evapotranspired. Interflow is affected by the same factors

as those for surface runoff. Interflow is rarely explicitly analysed, it is usually considered part of

the surface runoff. Surface runoff, interflow, and precipitation falling directly on water bodies

are sometimes lumped together and called direct runoff.


56

Groundwater flow

Groundwater flow, sometimes referred to a base flow, is water moving laterally beneath the

water table toward and into a waterway or water body. Unlike most other processes in the

hydrologic cycle, groundwater flow is essentially a continuous process. It maintains flows in

natural and man-made conveyances and water impoundments. Urbanisation usually decreases

the amount of groundwater flow.

Stream flow

Due to the dependence of runoff on soil moisture and the extent of source areas, the runoff

characteristics from these non-urban river basins can be highly variable. The soil, topography,

and vegetation characteristics also influence the volume and rate of runoff. The presence of

vegetation influences evapotranspiration rates and groundwater characteristics, with runoff

volumes and rates generally being higher from a rural area than those from a forested area. As a

consequence of these factors, runoff characteristics from non-urban river basins can be highly

variable.

4.7 Geo-technical aspects

Most of the polder areas are found in regions with the following soil types: gleysols, fluvisols,

histosols or vertisols. The permanent or seasonal wetness of these soils greatly influences their

physical and chemical characteristics related commonly to their physiography. Under these

conditions several factors of negative influence on the reclamation process have to be taken into

consideration:

• Physical bearing capacity:

• Low-bearing capacity, causing settlement and instability of slopes forms serious

constraints for reclamation, construction of embankments, canals and roads, foundation of

structures and houses;

• Texture of soils: swelling-shrinking, root ability;

• Chemical properties: oxidation of peat, acid sulphate soils, salinity, soil toxicity;

• Conditions of seepage.

A special type of soil improvement for urban and industrial use, like local or integral landfill,

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may be required to create sufficient bearing capacity and drainage conditions. In most countries

where urban or industrial development takes place in polders it is still customary to raise those

lands above a certain level for safety reasons.

4.8 Environmental aspects

These aspects contain a brief summary of the broad physical, chemical, and ecological

processes, which occur in ‘natural’ (non-urban) aquatic systems. This information is presented

to enable development of an understanding of the impacts of urbanisation on these processes

and to help assess the appropriateness of urban polder water management practices. It should be

noted that these processes are often highly variable within and between river basins, and this

variability needs to be recognised when developing management strategies.

Two assessments are needed, i.e. environmental impact assessment (EIA) and strategy

environmental assessment (SEA).

Environmental impact assessment (EIA)

The impact of urban polder development may relate to different phase of the development i.e.

construction phase (pre construction, construction and post construction) and the related

activities which will influence the water quality in the urban polder water management systems

(black water, grey water, run off and solid waste).

Several sources of the pollutant from the new housing area can be treated, that is black water

with the septic tank, the solid waste with the 4R approach which are Reduce (individually

expenses), Reuse (reuse packing materials), Recycle (solid waste from the kitchens for

composting, metal for the agricultural equipments) and Recovery (processing to be the useful

material). Table 4.1 presents the possible environmental impacts from an urban polder

development.

Tabel 4.1. Possible environmental impacts of an urban polder development

Urban Polder

(housing area) Environmental impact evaluation

Existing area New

development

Pre construction phase


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Unrest and social jealousy of the community around

polder (outside)

V V

Open space is converted into urban polder retention

basin

V V

Construction phase

Social jealousy, if the local inhabitants were not

involved in the development

V V

Change in the ecosystem in the upstream and

downstream of the related urban polder

V V

Noise and air pollution to the environment V V

Post construction phase

Change in the land use pattern from open space into

aquatic (change in the water biota, kind of planktons and

the number of individuals benthos)

V V

Social change in the community's economics (polder was

also used for aquaculture as well as recreation)

V V

Other related activities

Black water pollution to the urban polder water

management system (from the houses that did not have

individual septic tank)

V *)

Grey water pollution (bathed waste water, washed and

kitchen) that was discharged directly to the urban polder

water management system

V V

Pollution from solid waste that entered the urban polder

water management system (because of the limited solid

waste transport facility and its management)

V **)

Pollution and the sedimentation from the run-off which

flow to the urban polder water management system (SS,

BOD, COD, coli form)

V ***)

Note:

*): New housing area: all black water is treated in the septic tank

**): New housing area: solid waste can be treated by using 4R approach (Reduce,Reuse,

Recycle and Recovery)

***) : New housing area: runoff does not contain polluted materials Strategy environmental assessment (SEA)

In Table 4.2 impact parameters and the possible environemntal management strategy are

presented.

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Tabel 4.2. Environmental management strategies for urban polder development

Source of the impact Benchmark to the

impact

Environmental management

strategy


Unrest and social jealousy of the community around polder (outside)

Relatively number of inhabitants around the polder understood the development plan of the related polder, also they were involved in the development activities in accordance with their capacity

Informed and socialized the urban polder development plan and if possible make use of the community's manpower around the related polder in accordance with their capacity

Open space is converted into urban polder retention basin

Air temperature before urban polder was built

Planting of trees in order to reduce the increase of air temperature in the future

Construction phase

Social jealousy, if the local inhabitants were not involved in the development

Local labours are involved in the development activities

Made use of local manpower in accordance with their capacity or the level of the expertise that was needed by the urban polder development activities

Change in the ecosystem in the upstream and downstream of the related urban polder

Function of the nature and the community's livelihood in the upstream and downstream of the related polder

To control the natural function of the upstream and downstream of the related polder

Noise and air pollution to the environment

The value and reduce in the quality of air and noise/the increase in dust quality and quantity

Controlled noise and the decline in the quality of air around the related polder


Change in the land use pattern from open space into aquatic (change in the water biota, kind of planktons and the number of individuals benthos)

The increase in the abundance and the diversity of the water biota in polder as the positive impact of the development

The prevention and the control so that water weeds will not grow too fast by doing: • to clean water management system

from water weeds; • to manage the domestic waste, so

that N,P will not flow to the urban polder water management system;

• seeding grass crap fish (functioned dual, that is as the controller to the weeds and has economic value)

Social change in the community's economics (polder was also used for aquaculture as well as recreation)

The social change in the community's economics around polder (no longer flood problem and the increase in the income from the aquaculture and recreation facility)

• to maintain the function of the polder in accordance with the plan (to manage the inflow to the polder)

• to run the operation and the maintenance of the polder and its infrastructure (pumping station, etc.)


Black water pollution to Black water that was not Individual treatment by using septic


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the urban polder water management system (from the houses that did not have individual septic tank)

treated in the individual septic tank

tank and its infiltration system (SNI 03-2398-2000)

Grey water pollution (bathed waste water, washed and kitchen) that was discharged directly to the urban polder water management system

Untreated grey water and discharged to the ditch

The treatment with eco-technology by using water decorative plants in order to reduce the source of the grey water pollutant

Pollution from solid waste that entered the urban polder water management system (because of the limited solid waste transport facility and its management)

The quantity of solid waste that was not carried or handled

4R approach for the housing area (Reduce, Reuse, Recycle and Recovery)

Pollution and sedimentation from the run-off to the urban polder water management system (SS, BOD,COD, coli form)

Rate of sediment (deposited in urban polder water management system) and the level of pollution

Sediment management and the source of the pollutant that entered urban polder water management system

4.9 Impact of urbanization

Runoff pattern will be affected by urban development. Runoff characteristics from undeveloped

areas are strongly dependent on soil characteristics, vegetation cover, and antecedent moisture

conditions. When a river basin is urbanised, large areas of natural vegetation are replaced by

development containing a high percentage of impervious surfaces such as roads, roofs, car

parks, and surface paving. These human alterations to land surfaces change the physical and

biological features that affect hydrologic processes.

The majority of the runoff from an urban area occurs from impervious areas, particularly for

frequent events. Impervious areas decrease the natural occurrence of rainfall infiltration and

depression storage, which increases runoff volumes. They also accelerate overland flow

velocities, which reduces flow travel times.

Runoff characteristics in urbanised areas are not strongly dependent on soil characteristics or

vegetation, and are consequently less variable than those under undeveloped conditions.

Urbanisation has a greater impact on frequent storm events than on rare events.

Figure 4.9 illustrates typical changes in river basin hydrology that can be expected as a result of

urbanisation. This figure shows that the post-development hydrograph differs from the pre-

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development hydrograph in three important ways:

• The total runoff volume is greater;

• The runoff occurs more rapidly;

• The peak discharge is greater.

Urbanisation and the resultant increase in population and activities associated with urban life

can dramatically change the quality of runoff within a river basin and its receiving waters. In an

urban polder, run-off should be discharged in a manner that flood hydrograph after the

development at least the same with the one before. Particularly in term of the peak and the

volume of the flood. In this case, low impact of the development approach should be followed.

Figure 4.9. Response of Stream flow to Urbanisation

If possible the original hydrograph should not be changed by establishing the development. The

low impact development approach attempts to match the pre-development conditions by

compensating for losses of rainfall abstraction through the following:

• Maintenance of infiltration potential, evapotranspiration and surface storage;

• Increase travel time to reduce rapid concentration of excess runoff.

4.10 Urban master planning

Urban planning covers a broad and interdisciplinary field such as urban design, statistics, land

use/planning law, urban economics, and planning practice. The master plan should go towards


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the goals in the planning of the related urban area.

As the world become increasingly urban in character, there is a growing interest in urban

planning. The main concerns of the planning profession are with the critical issues of urban and

regional growth and change, as well as environmental and social balance.

The traditional purposes of the urban Drainage Master Plan were to:

• Guide the related urban project program. (e.g., identify, select, cost, and prioritize water

management system construction projects);

• Establish a maintenance program for the water management and flood protection systems;

• Establish on-site conveyance system (design standards for level of peak flow conveyance).

Master plans seldom included requirements for development with regard to water management

system impacts (e.g. downstream flow and/or water quality impacts). Master plans were

sometimes utilized to assess potential future problems as well as to fix existing problems. Often

systems were evaluated under current conditions and future planned zoning to be able to assess

costs to current rate/tax payers or new developments. Because master plans were not usually

completed prior to some significant level of development, attributing these costs was important

to the development community as well as to the residents.

The new approach to urban polder water management system master plans is the integration of

the folowing aspects:

• Drainage and flood control;

• Water quality;

• Natural resources;

• Aesthetics of urban water management and flood protection systems.

This approach requires significantly more effort and should be thought of as one that will entail

adaptive management. That is, the master plan must include components that allow for changing

conditions as development occurs and the downstream systems react.

4.11 Procedures

Master plan controls urban development. The master plan has to be approved by the Provincial

planning authority (BAPPEDA) and the municipality and other national authorities as well

(BAPPENAS, Home Affairs, Public Works and Environment).

Urban planning is a continuous process of land use considerations, politics, administration, legal

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aspects and community involvement. More detail procedures refers to Volume 2, Chapter 2.1.1

on Poliicy, planning and preparation of urban polders.


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65


Design requires a great deal of information on the project, to be collected by means of field

investigation and secondary data collection from the related institutions. The design stage is a

chain of activities with many feedbacks; ones tries to repeatedly to assess the desired demand

and at the same time, insight increases into what is really necessary and how those needs can be

fulfilled. These data and information will in particular be used to:

• Diagnose the water management and flood protection problems;

• Search for ideas and possible solutions;

• Prepare design of water management and flood protection systems.


Hydrologic design concepts

Anyone involved in land and water development and the construction of houses, as well as

commercial, industrial, institutional buildings and the related infrastructure, must give

consideration to storm runoff. In addition to hydrologic considerations during the land

development stage, site development must consider drainage patterns after development.

Site development usually results in significant increases in impervious surfaces, which results in

increased surface runoff rates and volumes. At many sites where land development has resulted

in large amounts of imperviousness, on-site retention and detention basins can be used which

requires knowledge of routing of water through the hydraulic outlet structure, as well as

knowledge about surface runoff into the basin. The design must consider meteorological and

geomorphologic factors, and the economic value of the land, as well as human value

considerations such as aesthetic and public safety aspects of the design.

The main objective of hydrologic analysis and design is to estimate peak flow rates and/or flow

hydrographs for the design of urban polder water management and flood protection systems.

Differences between design floods and actual floods

Much confusion has resulted from lack of recognition of the fundamental differences between


66

these two types of flood estimation problems. Although the same mathematical procedures may

be involved in both cases, the implications and assumptions involved and the validity of

application, are quite different.

A design flood is a probabilistic or statistical estimate, being generally based on some form of

probability analysis of flood or rainfall data. A return period is attributed to the estimate. This

applies not only to normal routine design, but also to probable maximum flood estimates, where

the intention is to obtain a design value with an extremely low probability of exceedance. If a

design rainfall is used in the estimation of a flood, it is not intended to imply that if a rainfall of

that amount occurred at a given time, the estimated flood would result. Occurrence of the

rainfall when the polder was wet might result in a large flood of magnitude greater than the

design estimate, while occurrence of the rainfall when the polder was dry might result in

relatively little, or even no, runoff.

The approach to estimating an actual flood from a particular rainfall is quite different in concept

and is of a deterministic nature. All causes and effects require consideration. The actual

antecedent conditions prevailing at the time of occurrence of the rain are very important and

must be allowed for in estimation of the resulting flood.

Although the differences in these two types of problems are often not recognised, they have

three important practical consequences as follows:

• A particular procedure may be good or satisfactory for one case, but quite unsuitable for

the other. For example, the Rational Method using the probabilistic interpretation can be a

satisfactory approach for estimating design floods for small river basins, but it is not

satisfactory for estimating the flood resulting from a given historical rainfall;

• Concerns the manner in which values of parameters are derived from recorded data and

the manner in which designers regard these values and apply them. If actual floods are to

be estimated, values for use in the calculations should be derived from calibration on

individual observed events. If design floods are to be estimated, the values should be

derived from statistical analyses of data from many observed floods.;

• Concerns the manner in which parameters are viewed by designers and analysts. For

example, the common visualisation of the runoff coefficient as the fraction of rainfall that

runs off in a design flood is incorrect, and fundamentally misleading.


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Design for risk

Design of works to pass or safely contain a flood of a given frequency implies that a failure will

result with the occurrence of a larger flood. Failure in this sense does not necessarily mean that

the structure will be destroyed or even damaged, but that it fails to perform (for a limited period

of time) the service for which it was constructed. The occurrence of a flood larger than the

design event is referred to here as ‘surcharging’. All hydraulic works sized by a flood estimate

are designed on a risk basis and none are ‘100% safe’. See Figure 5.1.

Figure 5.1. Risk as the basis of design storm selection (diagrammatic)

For urban water management system, return period of 25 and 50 years should be considered.

The cost of designing protection against a very rare flood would be excessive, and it cannot be

justified on cost-benefit grounds. Therefore, extreme floods are not considered in the design of

urban polder water management systems.

Non-structural measures may also be used to mitigate the effects of floods larger than the design

event. They should be considered within the design process as possible alternative or

complementary components of the overall design. Examples are:

• Flood warning and forecasting systems coupled with evacuation strategies;

• Land-use regulation to restrict high-risk development or activities in areas subject to

damage from surcharged flows;

• Building controls, including the setting of minimum floor levels and/or platform levels

and land use zonation.


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Frequency analysis and return period

Every rainfall event is unique. Temporal and spatial distribution of rainfall varies seasonally as

well as within a storm event due to the prevailing climatic conditions at the time of the storm.

Just as every rainfall event is unique, the resulting runoff from a storm event is also unique. The

temporal and spatial distribution of the rainfall affects the temporal and spatial distribution of

runoff. Surface conditions such as the amount of vegetation, land use, type of soil, soil

condition, topography, and other factors affect runoff volume and distribution.

Hydrologic data are historical by nature. The variables relating to hydrologic data such as time

and space, rainfall variation, abstractions, surface conditions, and numerous others that affect

runoff are considered continuous-that is, quantitatively they can assume any real value.

Part of mathematics used to predict the likelihood of the occurrence of a random event is

probability. Statistics and probability concepts are frequently used in hydrologic analysis.

Design rainfall

An understanding of rainfall processes and the significance of the rainfall design data is a

necessary pre-requisite for preparing satisfactory drainage and runoff management designs.

Standard design criteria for Indonesia must be applied for defining the related return period.

Rainfall patterns in Indonesia

The frequency and intensity of rainfall in Indonesia is much higher than in most countries,

especially those with temperate climates. Drainage practices and methods, which have been

developed in other countries, may not always be suitable for application in Indonesia. The

design calculations for these methods have been adjusted in this guideline to suit Indonesian

conditions.

Design rainfall intensities

Although the design storm must reflect required levels of protection, the local climate and

conditions, it needs not be scientifically rigorous. It is more important to define the storm and

the range of applicability fairly precisely to ensure safe, economical and standardised design.


69

Two types of design storm are recognised:

• Synthetic;

• Actual (historic) storms.

Synthesis and generalisation of a large number of actual storms is used to derive the former. The

latter are events which have occurred in the past, and which may have well documented impacts

on the water management system. Rainfall intensity refers to the time rate of rainfall (mm/hr)

will vary over the duration of the events.

Design storm duration is an important parameter that defines the rainfall depth or intensity for a

given frequency, and therefore affects the resulting runoff peak and volume. Intense rainfalls of

short durations usually occur within longer-duration storms rather than as isolated events. It is

common practice (Packman and Kidd, 1980) to compute discharge for several design storms

with different durations, and then base the design on the ‘critical’ storm, which produces the

maximum discharge.

Rainfall Intensity-Duration-Frequency (IDF) relationships

The most common approach to establishing a design- storm volume involves use of a

relationship between rainfall intensity, duration, and the frequency or return period appropriate

for the related area. The three variables, frequency, intensity and duration, are all related to each

other. The data are normally presented as curves displaying two of the variables, such as

intensity and duration, for a range of frequencies. These data are then used as the input in most

storm water design processes.

In many cases, the hydrologist is able to use standard intensity-duration-frequency (IDF) curves

available for the location and does not have to perform this analysis by themselves. IDF curves

are graphical representations of the probability that certain average rainfall intensity will occur,

given duration; their derivation is discussed by MC Pherson (1978). These curves show

precipitation intensity on the ordinate, duration along the abscissa, and a series of curves

representing individual storm frequencies. They are mainly used in conjunction with the rational

method for determine peak run-off. An example of IDF curves are presented in Figure 5.2.

Care must be taken in the use of IDF curves. For example that they do not represent time

histories of actual precipitation events, but rather conditional probabilities of average rainfall

intensities. Also, the duration is not necessarily the duration of an actual storm but more


70

typically represents an interval within a longer storm. Users need to be aware of the limitations

of these IDF curves:

• The patterns should be reviewed using the additional data that is available in the last

period;

• The period of data from which the curves was derived was short, in some cases only 7

years. Few of the stations had more than 20 years of data. This means that there is a large

potential error in extrapolating to long return period such as 100 years;

• The limits of rainfall return period are between 2 years and 100 years.

More information about IDF analysis, see Annex 3.

Figure 5.2 Intensity-duration-frequency (IDF) of maximum rainfall curves for Jakarta based on

Talbot equation (Puslitbang Sumber Daya Air, 2007)

Present Indonesian practice

Research Centre for Water Resources (Puslitbang Sumber Daya Air) in Bandung has applied the

IDF method for urban drainage analysis in many places in Indonesia (Puslitbang Sumber Daya

Air, 2007). Several methods have been tested in Indonesia i.e. Talbot, Sherman and Ishiguro.

The results showed that Talbot method gives relatively smaller deviations in comparison with

other methods and this method is suggested to be used for urban drainage analysis in Indonesia.


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Data quality and acceptance

The daily rainfall record should be examined for quality, and in particular to identify any

instances of missing records. Occasional missing daily records may be acceptable, depending on

the purpose for which the data is used. For flood studies, particular care is required because it is

often found that the missing record is the actual record of most interest, i.e. a large storm or

flood event.

Historical storms

Historical storm data is used in calibration of models, as well as for the checking of past flood

occurrences. In an urban drainage situation, it is relatively rare to have good historical rainfall

data available close to the study area or river basin. Nevertheless, every effort should be made to

obtain such data. O’Loughlin has shown the importance of locating rainfall gauges close to or

preferably within the study area if accurate calibration is to be achieved. If detailed studies are

being undertaken and good calibration data is required, the density of rain gauges should be at

least 1 per km2.

5.2 Impoldering principles

In principle, a polder is an area that forms a hydrographical entity in which the water level can

be artificially controlled at a preferred water level, which deviates from the prevailing regional

open water level. The dikes from surrounding areas separate the hydrological regime. A polder

will be completed with canals, retention basins, control structures (weir, gates, etc.) and outlet

structures (gravity as well as pumping stations). In case water management system of the

polders is done by pumps, the pumps can be driven by steam or electric.

The methods used for draining polders with different altitudes are pumping at once from the

deepest part using gravity by collecting first the water on the deepest level or draining step by

step compartments separated by dikes and weirs saving potential energy. When the outer water

level is permanently above the desired inner water level, the latter can only be maintained by

pumping the excess water out of the polder. Three options are available for draining water in an

urban polder which is presented in Figure 5.3;

• One pumping station serves the whole polder area where a maximum energy and a large

pumping capacity will be needed;


72

• Pumping stations in series are used and drainage is done step by step;

• A belt canal is used where water first is pumped to the belt canal and from the belt canal

water is collected and pumped out from the system.

Figure 5.3 Polder drainage system by pumping

Polders may be divided into sections having different polder levels (see land use zoning). This

applies for example to a polder with an upper and lower part which would probably be better

served by maintaining a higher polder level in the upper part and a lower level in the lower part,

rather than one level for the entire polder. Different polder levels are also advisable where land

use conditions within differ significantly (zoning concept).

Where the surrounding polder drainage base is controlled by the sea or river, excess water may

be discharged from the polder by gravity drainage during period of low tide and during low

river flow periods when the outer water level falls below the inner water level.


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5.3 Polder infrastructure

Basic components

There are various systems in a polder, i.e. urban areas, public facilities, forests and nature

reserves. The various systems can be characterized by a number of main elements, which,

depending on their value and interrelation, determine the functioning of the system. Two

important functions of the urban polder system are:

• Flood protection to the polder as a result the inhabitants will feel safe to live in the polder;

• Polder water management (drainage, water retention and conservation).

The main elements of the water management system for the urban area are (after Schultz, 1982):

• Percentage of open water area (detention, retention and urban canals);

• The preferred water level in the urban polder area and outside water levels (in case of

gravity drainage system);

• The discharge capacity of gate or the pumping capacity;

• Dikes as flood protection measure.

A schematic layout of a polder is presented in Figure 5.4.

Figure 5.4. Schematic layout of a polder (Schultz, 1982)

It means that the water management systems in a polder mainly consist of an open water area

(canal network, retention and detention basins) and water control structures (dikes, pumps,

sliding gates, culverts).


74

The primary objective of the water management system is to keep the water level as appropriate

as possible in relation to the utilization of the polder. This implies that urban polderwater

management and flood protection systems have the following objectives:

• Drain excess rain or flood water;

• Protect the urban polder area from floods;

• Prevent flooding and salinity intrusion;

• Prevent severe drops of the groundwater table;

• Flush poor-quality water out of the systems;

• Control canal water-levels and provide water for domestic purposes (if any);

• Maintain sufficient water depth for water transportation (if any).

For these purposes the water control structures play a crucial role.

The water management and flood protection systems in urban polders must be taken into

account and given enough room to function more naturally. It also means that the urban plan

must adapt to the local water conditions and not the other way around. Most of urban polder

water management and flood protection systems will be artificial. The goal is to build a water

management and flood protection systems that approaches an ideal that is defined by functions

and qualities desirable in urban polders. These should not only be derived from the viewpoint of

its human inhabitants, but also from a viewpoint of sustainability and ecology.

Open water area

In an urban polder the primary function of water management system is drainage, i.e. the

temporary storage and eventual discharge of the water. A general procedure for determining

water management system is described as follows:

• Step 1. Determine design storm criteria for the system

• Step 2. Compute the inflow hydrographs for required design storm return period

• Step 3. Make a preliminary estimate of the required capacity of the water management

system. A preliminary estimation may be obtained based on steady computation and the

peak of inflow and outflow hydrographs, see Figure 5.5. This step includes all the water

management components, i.e. canals, detention, retention basins, gates, weir and pumping

stations;

• Step 4. To check the design capacity and its hydraulic performance. Based on the

preliminary estimated capacity of the system, a mathematical modeling simulation should

be carried out in order to evaluate the hydraulic performance of the system and if


75

necessary, the capacity of the system can be improved. For this evaluation proper

boundary conditions of the model have to be defined based on the design standard.

•

•

•

•

•

•

Figure 5.5 Inflow and outflow hydrograph

Detention and retention basins

They are most efficient means for urban polder water management. Such basins were designed

as flood control reservoirs.

Detention basins

A detention pond can be created by damming a channel or by excavating a pond into the

existing ground. Often, ponds are constructed by a combination of cut and fill. A detention basin

must have at least one service outlet. A detention pond is a low lying area that is designed to

temporarily hold a set amount of water while slowly draining to another location. In this case

the effect of fre board can also be considered as detention part. They are more or less around for

flood control when large amounts of rain could cause flash flooding if not drained with

properly. Normally it is a grassy field with a couple of concrete culverts running towards a

drainage canal.

It is preferable to have a site that is already topographically low, thus minimising the excavation

and earthwork needed to achieved the desired storage volume. Sites with favourable

topographic features are most likely to be found in undeveloped or newly developing areas.


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Retention basins

Retention basins are feasible best management practices for urban polder water management.

Retention basins retain a permanent pool during dry weather. During wet season, the incoming

run-off displaces the old urban polder water from the permanent pool from which significant

amounts of pollutants have been removed. The new run-off is retained until it is displaces by

subsequent storms. Retention basins lose water through the processes of evaporation and

infiltration. If the soil at the basin site is highly permeable, it may be necessary to seal the

bottom of the basin with a clay liner or an impervious geotextile.

An example of a retention basin in Tomang Barat in Jakarta is presented in Figure 5.6.

Figure 5.6. Tomang Barat retention basin

It should be recognised that retention and detention basins will form an integral part of the total

infrastructure for an urban polder. It is inevitable that people will have access to a basin,

especially if it is designed for multi-purpose usage incorporating active or passive recreation, or

sporting facilities. Accordingly, a basin must be designed with public safety in mind when the

facility is in operation and also during periods between storms when the facility is empty.


77

Pumping station

Several pumps are used for flood control. The Archimedean screw pump consists of an inclined

spindle fitted with a surrounding, spirally wound blade, which rotates within a fixed semi-

circular casing. Rotation speeds normally vary between 20 and 120 rpm. See Figure 5.7:

Figure 5.7. Archimedean screw pump

The much more widely used rotodynamic pumps consist of an impeller, which rotates within a

totally enclosing casing. An example is shown in Figure 5.8. The advantages and disadvantages

of these pumps are presented in Table 5.1 below.

Figure 5.8 Three types of rotodynamic pumps; propeller, mixed flow and

centrifugal (source: www.flygt.nl)


78

Table 5.1 Score table of pump station alternatives

Criterion screw pump propeller or axial centrifugal pump

investment costs -- ++ +/-

technical design lifetime (years) 20 10 10

efficiency (related to energy costs) + +/- +/-

durability ++ - +

accessibility and ease of maintenance + +/- +/-

simplicity of construction and E&M - ++ +/-

performance with heavy polluted water ++ +/- +

adaptability delivery head 1 - + +

1 Adaptability of screw pump possible by means of an adjustable upper casing screw

The discharge capacity is determined in relation with the retention capacity, because both form

a balance to withstand extreme rainfall events. The higher the pumping capacity, the smaller the

required retention area to reach the safety level or vice versa: A larger retention area requires

less pump capacity. The economic optimal combination is a pump capacity in combination with

a retention basin should be done.

An example of this relationship between retention capacity and pumping capacity is shown in

Figure 5.9.

Figure 5.9 Retention capacity versus pump capacity (Witteveen+Bos, 2007)

0

5

10

15

20

25

30

35

40

0 3 6 9 12 15 18

pump capacity

rete

nti

on

(h

a)


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Preferred water level in a polder

The water management systems have to convey and store the drainage water from the fields in

such a way that the water levels in the polder remains at acceptable levels. The design criteria

for water management system in a polder have generally been developed as follows:

Preferred normal conditions

These are the conditions one would like to maintain in the polder area. They result in a preferred

water level, or water levels and operation rules for the pumping stations. The criteria are

strongly linked to the soil type, land uses and its zoning system like urban, industrial, recreation

and nature conservation;

Design conditions

These are the conditions on which the design of the drains and pumping stations are based. In

general they are formulated as:

• exceedance of the preferred water levels;

• duration of the exceedance;

• return period for which the prescribed exceedance occurs and the return period should use

the Indonesian standard which is based on the Indonesian hydrological conditions.

Extreme conditions

Although this is generally not a design criterion, control computations can be made for extreme

conditions. In these situations bank full storage is generally accepted. When the results are

unacceptable, the design criteria may be modified.

Capacity of the water management system

A complete hydraulic transport system consists of ditches, main ditches and canals. If a

composite subsurface drainage system is installed, the collector drains replace the ditches.

Normally the distances between ditches and main ditches are based on its land use and economy

analysis, resulting in optimal plot sizes. The canals are located so that a minimum of earth

movement is required. The possible locations for sluices or pumping stations also determine the


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principal location of the canals. The discharge capacity of the hydraulic transport system is

normally such that a prescribed water level in the polder is not exceeded during a certain time at

a certain return period. This together with the accepted velocity in the different parts of the

system determines the cross-sections.

Canal system

A water management system receives drainage water from the field drainage systems. In a small

system, the field drainage system may be a uniform type. Next to convey the discharge from

urban drainage system it is also likely to receive natural drainage flow. The principal function of

the drainage system is to convey all the drainage water to the outlet point. The hydraulic

transport system of a polder can consist of collector drains, sub-main drains, main drains and/or

structures, like fixed or movable weirs, gates and/or pumping stations. From a water management

point of view, in principle the system has a double purpose, viz. water storage and the transport of

water to the pumping stations. It may also serve as water quality control indicator and the main

drains for recreational purposes. For the discharge, the following aspects of the hydraulic transport

system are especially of importance:

• Structure of the system;

• Polder water level;

• Percentage of open water.

Sluice

When an urban polder was design, dikes can protect them from being flooded. To enable the

drainage of excess water from the protected area, the dikes are provided with outlet structures.

One of these outlet structures is sluice. Figure 5.10 shows an example of sluices as an outlet.

Figure 5.10. Sluice


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Run-off management

There are a number of ways to deal with run-off in urban polders, such as combined sewer

systems, separated sewer systems, above ground and visible runoff systems, infiltration

facilities. A large number of different systems and methods has been introduced and

implemented over the years.

In most urban polders run-off from paved surfaces used to be led into the (combined) sewer

system, but starting in the previous century this has slowly been changing. There is a system

where clean storm water run-off does not belong in the wastewater sewer system. Working

towards a more natural runoff regime in urban areas all surfaces that are relatively clean should

be disconnected from the wastewater sewer system, instead of setting an arbitrary percentage as

a target.

The water that is prevented from entering the wastewater sewer system by disconnecting paved

areas will need to be accommodated in the urban polder water system. In the low-lying polders

there is far less storage available in the subsurface, due to the high groundwater table and lower

permeability of the subsoil. Infiltration will remain part of the solution, but other storage and

detention methods will need to be implemented.

There are a number of methods to retain storm water run-off on private properties e.g. rain

barrels and fixtures (sumur resapan). These methods depend on the will of the inhabitants to

participate and invest, so the effect on the water management of a whole neighbourhood will be

hard to predict. Disconnection of roofs and paved surfaces should become reasonably common

in new urban polders, but in these instances the water is not retained on the allotments, but

transported to infiltration facilities or open water in the area.

Compartment system in a polder

In case an urban polder covers a large area, a compartment system can be applied where a ring

dike separates each individual compartment. Compartmentalization can be done by constructing

embankments and these embankments subdivide a polder into different compartments, which

greatly controls the rate and sequence of the inundation. Because of the effect of these

embankments on the inundation, therefore, strategies to reduce the inundation damage of an

urban polder should focus at the design of the compartmentalization layout to minimize the

potential number of casualties and damage caused by the inundation. Each compartment has its

own outlet or gate/sluice or pump and its belt canal.


82

Compartmenting also has disadvantages however. Small compartments fill rapidly, adversely

affecting the safety inside. Even if a soil body, over which a road or rail line runs, does not have

the status of flood defence, it does have the effect of compartmenting. The consideration of pros

and cons is needed in that case too. Either the situation will remain unchanged or measures will

be introduced to create openings in the (unintended) compartmenting dike.

Storm surge, wave and run up

Storm surges are caused by the local minima of atmospheric pressure. A storm surge analysis

has to be carried out.

Determination of wind set-up

Wind set-up should be determined by using extreme wind speeds derived from the wind data

set. An example of cumulative density and probability exceedance curves for wind speed are

shown in Figure 5.11.

First the extreme wind speeds are defined for different return periods and then the area of

interest for the wind set-up is determined. Finally the wind set-up is calculated for different

return periods.

Figure 5.11 Comparison for probability of exceedance of wind speed (Witteveen+Bos, 2007)

An example of the extreme wind speeds derived from the ARGOSS data set are presented in

Figure 5.12 This extremes are for omni-directional wind speeds. The fitted curve (red) is

situated below the observed wind speeds, this can be caused by the data that is not shown in the

figure (more to the left). An extra line (dashed) is drawn through the observed wind speeds and


83

this line is also taken into account for the determination of the wind set-up. This dashed line is

used as an upper limit.

Figure 5.12. Extreme wind analysis for Semarang (Witteveen+Bos)

Wind set-up only occurs when water is trapped, so the area has to be:

• Enclosed;

• Relatively shallow so the return flow is limited.

An example in Figure 5.13 two options are drawn for a shallow water enclosed bay.

Figure 5.13 Possible enclosed bays with fetch length (Google Earth Pro)

The calculation of the wind set-up the continuous line is used as border for the area of interest;

at the line the water is deeper. A longer fetch results in a higher wave and higher wind set-up.

The following equations can be used for the determination of the wind set-up:

end of shallow water enclosed bay

entire fetch length


84

Fi

gh

Uci

ww

w

a

ww

w

=

=

η

ρ

ρ2

where:

cw: air-water friction coefficient, between 0.0008 to 0.003 (-);

F: Fetch length (m);

g: gravity acceleration (m/s2);

h: water depth (m);

iw: wind induced gradient (-);

U: wind speed (at 10 m height) (m/s);

ηw: maximum set-up (m);

ρa: mass density of air (kg/m3);

ρw: mass density of water (kg/m3).

It is recommended to verify the wind set-up calculations with measurements of stations near the

project area, because that may improve the reliability of the results. As a conservative approach

the cw is chosen 0.003.

Wave height and wave set up

The wave height at deep water is estimated with the equations of Bretschneider:

=

75.0

2

42.0

275.0

22

53.0tanh

0125.0

tanh53.0tanh283.0

w

w

ww

s

U

gh

U

gF

U

gh

U

gH

Where:

g: gravitational acceleration (m/s2);

Hs: significant wave height (m);

Uw: wind speed (m/s);

h: water depth (m);

F: fetch length (m).

Input is wind speeds varying from 15 to 22 m/s (with return periods of 1 to 1,000 years and

water depth varying from 30 to 50 m. The minimum and maximum wave periods are

respectively 5 and 8 seconds. The deep water wave period is transformed to the near shore wave


85

length by taking into account refraction and diffraction of the waves.

Wave set-up

Wave set-up is the result of depth induced wave breaking. Wave set-up occurs in the breaker

zone. See Figure 5.14. It has its maximum at the shoreline and is zero at the first breaker line.

This first breaker line is the location were the largest waves (e.g. during design conditions) will

break due to the limited depth. Structures located somewhere between the first breaker line and

the shoreline should take into consideration wave setup in the design conditions.

Figure 5.14 Wave set up

Wave run up

Wave run up is the phenomenon that waves, which reach a structure, will move upward the

slope of the structure until all kinetic energy is transmitted to the structure. The magnitude of

wave run up depends on the slope angle of the structure, the presence of a berm and the

roughness of the slope. The wave set-up can be calculated by using the following equation

(Battjes, 1983).

where:

γbr: breaker parameter (-);

tan: slope steepness (-);

T: wave period (s);

L: wave length on deep water (m);

2

max

2

tan

3.0

gT

H

L

Hs

s

H

ss

br

bbr

π

αγ

γη

==

=

=


86

S: wave steepness (-);

Hb: wave height at the breaker line for regular waves (m);

ηmax: wave set-up (m).

Wave set up reduction measure

A measure to reduce wave set up might be adjusting the slope steepness. When a slope

steepness of 1:4 or 1:5 is applied in stead of 1:3, a reduction of respectively 25% and 40% will

be achieved.

Wave run-up

The wave run-up can be calculated with the equation stated below.

The explanation of some symbols is shown in Figure 5.15.

where:

Hs: spectral significant wave height (m);

A: safety margin coefficient (-);

γb, γf, : correction factor berm, roughness, oblique wave attack (-);

BB: berm length (m);

Lberm: corrected berm length (m);

kB: coefficient for berm width (-);

hB: distance between SWL and berm level (m);

х: berm level factor (-);

kh: coefficient for berm level (-);

ξm-1,0: breaker parameter (-);

0,10%2 −= mfbmu AHR ξγγγ

β

βγβ

0022.01−=

( )

−=

=

−

−=

−−=

x

hk

L

B

BLH

LHk

kk

Bh

berm

B

Bbermm

bermmB

hBb

π

γ

cos5.05.0

)/(2

/21

11

0

0


87

Ru2%: wave run-up (m).

Figure 5.15 Explanation of symbols

In the calculations, the following dike profiles should be assessed:

Basic profile: side slope, top layer conditions (smooth or rough);

Rup up reducing measures: berm: for example 5 m and roughness coefficient: for example 0.55

for rock armour layer.

5.4 Erosion and sedimentation control in and around a polder

Transport of sediment in water management systems influence to a great extent the

sustainability of a water management system. Unintentional or unwanted erosion or deposition

of sediment in canals will not only increase the maintenance costs, but also leads to an unfair

and inadequate flow capacity of the system and the related head works. The control of sediment

transport capacity in a water management system greatly depends on the flow conditions. If

flow velocity is too high, it may cause erosion and if it is too low, it may cause sedimentation.

Special attention should be paid in case of an urban polder bordered by coastlines. A stable

coastline should be considered, littoral drift and onshore-offshore sediment transport should be

checked and if necessary coastal protection works have to be provided.

( )

−=

=

−

−=

−−=

x

hk

L

B

BLH

LHk

kk

Bh

berm

B

Bbermm

bermmB

hBb

π

γ

cos5.05.0

)/(2

/21

11

0

0

reference level at

middle of berm

SWL

Hs

Hs

Lberm

BB

hB

Ru2%


88

5.5 Flushing system in a polder

Flushing will be needed in order to maintain the quality of the canal water in polder areas. For

this purpose, the flow velocity in the canal has to have a certain limit in order to be able to flush

the water and remove the deposited sediments from the water management system.

5.6 Landscape and land use planning

Landscaping

All the water management components facilities should be tastefully incorporated into the urban

setting in which they reside. This is not a hydrologic consideration, but is a consideration, which

will be used by the public to judge these facilities. Aesthetics of the finished facility is therefore

extremely important. Wherever possible, designs should incorporate naturally shaped basins

with landscaped banks, footpaths, and selective planting of vegetation enriching the area and

provide a focal point for surrounding development. Sympathetic landscaping and the resulting

improvement in local visual amenity will also encourage the public to accept retention and

detention basins as an element of the urban environment and not as a target for vandalism.

Trees and shrubs should not be planted on basin embankments as they may increase the danger

of bank failure by ‘piping’ along the line of the roots.

Establish land ownership

In anticipation of screening of land for potential detention and retention sites, land ownership

should be determined for large or otherwise significant parcels of land. Large tracts of

undeveloped publicly owned land are most desirable, followed by undeveloped privately held

land. Fully or partially developed public or private parcels of land in need of redevelopment

may also offer opportunities for siting a detention facility.

The ownership of large parcels of land in the polder area, particularly potential detention or

retention sites, should be determined as early as possible in the planning process. Careful

identification of current ownership and intended use, in combination with an assessment of

recreational and other needs of a community can lay the groundwork for successful negotiation

for purchase and development or redevelopment of property for flood control in combination

with other uses.


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5.7 Boundary conditions for design

In relation to the outside conditions, it is important whether the sea, a river, lake, or canal

borders the polder. Although differences occur within each of these groups, some general

characteristics are important, such as the behaviour of floods, the possibilities of forecasting.

The sea causes one of the most dangerous flooding. This generally has the disadvantage that

only short-term forecasting of some hours can be made and that the wave action can be very

destructive. This, and the reduced wave action, may result in a decision for a lower level of

security for polders along rivers that for polders along the sea.

If polders bordering lakes or canals are flooded, then the flood is normally caused by a

catastrophe and not by a hydrological extreme. In most cases the water body causing the flood

as well as the areas that can be influenced will be small.

The conditions and management of the water outsides the polder can be of importance in the

design of the dike around the polder and the discharge structure. Regular fluctuations are

especially of importance in the design of discharge sluices and the determination of the lifting

device in the pumping station.

Design should be based on the following technical programming and its relationship with other

aspects as shown in the following Figure 5.16:

Figure 5.16 Boundary conditions of a polder

Run-off conditions from the outside areas which will affect the polder boundary should also be

considered and checked. Collector drains along the polder dikes should be considered in many

cases. This run-off can be directly from the surrounding areas or upper rivers.


90

5.8 Design approaches and design standards

The main goal of urban polder development is to provide a living environment for people. To

provide a living environment where inhabitants like to live and where they enjoy safe and

healthy conditions.

Flood control and flood protection in a polder

Flood protection around polders means the construction of dikes, which may cause side effects.

Side effects of a hydraulic nature occur when, before embanking, the river overtops the banks.

Elimination of the overland flow results in a rise of the flood levels. The effect is mostly

pronounces in the case of flash flood with rapid rises.

Each urban polder will be unique and will have its own specific problems and opportunities the

goals and requirements differ from case to case. Three main guiding principles for designing

urban polders are:

• A natural groundwater regime should be pursued, with minimal permanent draw downs to

reduce subsidence;

• Local detention and retention of storm water runoff in combination with pumping and

outlet capacity should be maximised;

• Effort should be made to improve local water quality.

The surface flow criteria comprise three basic limits:

• Preferred water levels and acceptable exceedance of these levels

• A ponding depth limit;

• A design criteria limit, which is a probability/risk limit based on consideration of issues

of immunity/damage from flooding, safety, construction costs and community costs and

benefit.

The preferred water levels and acceptable exceedances may be summarised as follows:

• Preferred normal conditions. These are the conditions one would like to maintain in the

polder area. They result in a preferred water level, or water levels and operation rules for

the pumping stations. The criteria are strongly linked to the soil type, or other land uses

like housing, industrial, recreation and nature conservation;

• Design conditions. These are the conditions on which the design of the drains and


91

pumping stations is based. In general they are formulated as:

- Exceedance of the preferred water levels;

- Duration of the exceedance;

- The chance per year for which the prescribed exceedance occurs.

• Extreme conditions. Although this is generally not a design criterion, control computations

can be made for extreme situations. In these situations bankfull storage is generally

accepted. When the results are unacceptable, the design criteria may be modified.

All hydraulic works sized by an extreme rainfall estimate are designed on a risk basis. None are

‘100% safe’ and there is always a finite probability that the structure will be surcharged either in

a given year or during its economic life. In establishing the layout of urban polder water

management systems, it is important to ensure that surcharge flows will not discharge onto

private property during flows up to the main system design.

Two design approaches may be followed:

• Empirical design: Empirical design is normally based on the conditions that were occurred

in the past from which general data have been deduced;

• Optimization: In the optimisation approach the investments and maintenance costs of the

water management system are compared with the economical output and damage that can

be expected in relation to the functioning of the system.

Zoning approach in an urban polder

The surface level morphology will be used to design different land use with different elevations.

In this surface level morphology, open water (canals, retentions and detentions), street levels,

park levels, paved areas and floor level of housing have to be designed completed with its area

(ha). This surface level morphology will be used in the floodwater management analysis.

Based on these elevations, it will be clear which area/land uses will be first inundated in case of

flood. Of course the flood level of houses will locate at the highest elevations and as the result

they will be the last to be inundated.

5.8.1 Design of embankments and dikes

High water levels that will influence an urban polder can be caused by:


92

• Storms that drive up water levels at sea and on lakes;

• Precipitation that increases the discharge of the rivers.

On the river the rise in the water level is greater and most notably longer than at sea. Besides

high water levels, waves form the most visible threat to flood defences. Waves increase the

pressure or are the source of extra impact on defence structures, both on the outside and the

inside in the case of wave overtopping. The difference in character observed of water levels

along the coast and along the rivers is reinforced by the wave loads. High water levels along the

coast are caused by storms and are therefore always accompanied by high waves, while high

river discharge values are independent as shown in Figure 5.17.

Figure 5.17 Link between waves and water level at sea and river

The protection against flooding by flood defences is never absolute. Upper limits of natural

phenomena like wind and rain are not known. Instead it must be assumed a certain exceedance

probability of these phenomena. Under extreme conditions flood defences can collapse and the

land behind will be flooded.

Under less extreme conditions the behaviour of the flood defence cannot always be predicted, so

there is always a (small) probability of collapse.


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The consequences of a flood can be far-reaching: loss of human life, goods and means of

production and damage to landscape, nature and cultural heritage. The approach is addressed

below, along with the choices that have to be made and the developments involved.

In the case of water defence the risk is the probability of flooding combined with the

corresponding consequences. This can be expressed as the probability (so many times a year)

multiplied by a certain consequence (a measure of the loss of money and/or human life). The

measure for the risk is the average loss of money or human life per year. The definition of a

certain accepted risk indicates that the greater the consequences the smaller the probability must

be. It is not possible to totally preclude risk, because the probability 0 is impossible, given the

lack of an upper limit to natural phenomena. The choice, and so also acceptance of a risk level is

accordingly all about pros and cons. In practice emotions also play a role in the ultimate choice.

For an urban polder with a flood protection, society must reserve finances, a sort of insurance

premium, for the evacuation of people and the repair of damage. The higher, stronger and more

reliable the flood protection, the smaller the probability of collapse and damage. And so the

smaller the risk and the insurance premium.

On the other hand, the improvement of flood protections also demands sometimes great social

sacrifices. This is all about the expense for the construction and maintenance of flood

protections, and the loss of landscape and nature that can be the consequence of the construction

or improvement of flood protections.

The requirements set for the degree of safety of the areas behind it must therefore be based on a

consideration between the social sacrifices and the benefits of flood protections. The risk

approach is an aid here, by which both certain occurrences (investments) and uncertain

occurrences (probability of dike collapse and the consequences) can be assessed. If the

investments and the sacrifices are both expressed in financial terms then an econometric

calculation can be made, to determine the optimal safety level. Any loss of human life makes

this approach a discussible one to say the least. In the consideration both objective and

subjective elements play a role.

The consequences of a flood are not the same for every urban polder area. They especially

depend on the nature of the threat and the characteristics of the dike ring area. The

consequences of a flood by river water is for example, different to those by sea water: fresh


94

versus saltwater, warning for evacuation in the long term versus warning for evacuation in the

short term, et cetera. A small polder will fill more rapidly than a large one, and people will have

less time to evacuate. In a deeper polder there will be more damage than in a shallow one. In a

dike ring area where many people live and work and where there is a great deal of industry, the

damage will be greater than in a sparsely populated area. The consequences depend on the

degree to which the population in an urban polder area is prepared for evacuation and the

effectiveness of that preparation. As the consequences of a flood increase the probability of a

flood must decrease. This basic principle determines the requirements set for the flood

protections.

Because the sacrifices and the benefits are not the same for every urban polder area, the

outcome of the consideration, and so the desired degree of safety, from one urban polder to

another vary.

The protection against flooding will always demand attention. There are various reasons for

asking attention:

• Firstly, the natural phenomena involved have a dynamic character (rise in the water level,

sedimentation in the rivers, and subsidence of the land) and flood protections are worn by

time;

• Secondly, the components in the sacrifices-benefits consideration change, like the

sacrifices of construction and maintenance of the flood protection and the consequences

of any dike collapse;

• Thirdly, the evaluation of sacrifices can change under the influence of changed social

insights, not least due to the occurrence of flooding. Adaptations to flood protections do

not occur continuously, but periodically. Due to the time dependent factors mentioned

the safety level typically decreases as long as man fails to intervene as time goes by. This

should be taken into account when setting requirements for flood protections.

Distinction within an urban polder area

The sacrifices and benefits of improving flood protections differ not only between two dike ring

areas, and within the system of flood protections round one dike ring area. The sacrifices will

differ in an urban area and a rural area. The benefits of improving flood defences are formed by

the reduction in (the probability of) the harmful consequences of flooding. The consequences of

collapse of parts of the encircling dike can vary due to variation in the height of the site, but also


95

the spread of population, buildings and industry over the related urban polder area. Differences

in the consequences may also be caused by the nature of the threats (sea or river for example)

and the type of flood protection (flooding/inundation due to a dike collapse is quicker and more

violent than at a culvert with a limited opening that has not been closed).

Safety level of the polder and calculation of risk and damage

Floods are caused by a number of events. For the design of an urban polder there are two

principal mechanisms that are relevant with regard to flooding:

• High water level outside the polder (high water at sea or river);

• High water level within the polder area due to heavy rainfall.

Because of these threats a polder can be designed with flood protection (dikes), which provide a

certain safety level against floods. The pumping station or gate and possible a retention basin

provides a certain safety level against inundation. However, the level of safety of the hinterland

is related to the exceeding frequency of the high water level.

The design water level is a function of the economic value of the hinterland. As an example, in

the Netherlands the flood defence of these polders must be able to withstand extreme hydraulic

conditions that may occur between once per 1,250 and 10,000 year. This standard is the result of

comprehensive cost benefit and safety analysis. The safety levels for inundation, caused by

excessive rainfall are highly determined by the functions in the polder and ranges from once per

5 year for agriculture to once per 100 year (urban and industrial areas).

It is important to realise that protection against flooding is never absolute. Upper limits of

natural phenomena are not known so a certain exceeding probability is assumed. Risk can be

expressed as:

Risk = probability multiplied by the corresponding damage

To be able to determine the appropriate safety level the risk has to be known, requiring insight

in the damage event. A dike with a safety level T10,000 means that on average once per 10,000

years the dike will overtop or break, or a probability of 0.01% per year.

Three types of damage as a result by flooding can be spit up in:


96

• Direct damage and; direct damage concern the damage to objects, capital goods,

buildings, and can be summarised as damage:

- To buildings and infrastructure;

- To means of production, machinery’s;

- To assets;

- To lost goods, raw materials, including lost yields;

- Caused by outfall of production, outfall of trains, etc.

� Indirect damage; the primary forms of indirect economic damage can be summarised as

damage in the form of:

- Halted production processes to companies with a logistic relation to the inundated

area;

- Time loss for any traffic in or out of the area.

� Intangible damage, which is damage in the form of:

- Impact on health;

- Impact on social structure.

Calculation of damage and damage functions

This is based on a Dutch research on damage-caused by floods. Even though the situation in

The Netherlands may differ in many ways from that in Indonesia, the damage functions can be

applied for the Indonesian conditions, since they only describe the damage as percentage of the

total value. It is advisable to do research on the damage factors in Indonesia as function of the

inundation depth.

The damage can be calculated with the following formula:

∑=

=

n

i

iii SnS1

α

Where:

S= damage;

αi = damage factor category i;

ni= number of units category ;

Si= maximum damage per unit in category i.

The damage factor αi is of great importance. This factor is mostly determined by the depth of


97

inundation. The inundation depth will be discussed in the next part. The damage is dependent on

the number of units and the maximum damage of units. The maximum damage is considered to

be equal to the value of units. The number of units times the maximum damage of units is equal

to the value for groups of assets.

In flood prone area, measures should be taken to prevent damage during floods as much as

possible. Therefore in flood prone area of a urban polder, the damage is reduced with 25%.

If there is no data available of the indirect and intangible damage, the following parameters can

be used:

• Indirect damage: 10% of direct damage;

• Intangible cost: 5% of direct damage.

Inundation depth

In respect to the inundation depth there is a major difference in inundation depth between a

flood caused by rainfall or flood caused by high water level tides. A flood caused by rainfall is

limited to volume, while flood caused by sea is determined by its level, see Figure 5.18.

Figure 5.18. Inundation depth (Witteveen+Bos, 2008)

Safety level inundation caused by heavy rainfall

The allocation of retention basin is of primary importance in the safety against inundation. It is

Rainfall limited by

Inundation depth limited by volume

Inundation depth determined by

Sea

Mean Sea Level

High water level

Polder


98

impossible to guarantee safety from inundation by merely providing large pumping capacity, a

minimum amount of retention will be a first requirement.

Obviously also the other aspects of the water management system are of relevance, like the

channel capacity and the pumping capacity. The optimum pump capacity (in relation with the

retention capacity) has to be determined. The safety level and the retention capacity form a

balance. A higher safety level requires more retention, a lower safety level a lower retention

capacity.

Damage in a urban polder as a result of rainfall

The safety level of an urban polder determines the frequency of inundation and the severity of

the inundation. A polder with a low safety level will have a small retention basin. When there is

heavy rainfall, the retention basin will overflow and inundation will occur. A polder with a high

safety level will have a large retention basin, which would be able to store extreme rainfall

events. The inundation depth determines the damage factor. Based on the damage factor,

affected area and the value of all assets in the affected area the damage can be determined.

Based on the frequency of occurrence of extreme rainfall events, the total damage in the related

return period and the average damage per year can be calculated.

Table 5.2 and Figure 5.19 show an example of the investment cost, the damage in 20 years (for

example) and the total of investment cost and damage. It can be seen that the minimum cost

(total) is at a safety level of T10 year.

Table 5.2. Investment cost and damage (in million USD)

Safety level polder

Additional

investment cost Damage in 20 years Total

T2 0.5 12.1 12.6

T5 2.2 4.3 6.5

T10 3.7 1.6 5.3

T25 5.6 0.4 6.0

T50 7.0 0.0 7.0

T100 8.6 0.0 8.6


99

0

2

4

6

8

10

12

14

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

Safety level polder (T)

Co

st

(millio

n U

S$

)

Investment cost Damage total

Figure 5.19 Additional investment cost and damage

Benefit/Cost ratio

Based on estimation of the yearly damage in the current situation, the potential for damage

reduction in a urban polder can be calculated. The difference between the damage of the polder

and the current situation is the damage reduction or benefit. If this ratio is >1, the benefit (or

damage reduction) is higher than the investment cost. Then the realisation of the polder is

feasible. If the ratio is <1, the investment cost are higher than the benefits, the polder is

economically not feasible.

Note: Even a polder with a B/C-ratio <1 can be feasible because of the social impact. In The

Netherlands even a B/C ratio of 0.2 is considered to be feasible because of the social impact.

Safety level flood caused by high water level outside the polder

The safety level of the dikes and the construction cost form a balance as well. A higher safety

level requires a higher dike, a lower safety level a lower dike. In respect of flood protection, the

danger to human lives has to be added in the assessment of safety level.


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Safety levels and design water level

Table 5.3 shows an example of the design water level the dike has to withstand for several

safety levels of the dike. It can be seen that the difference between the design crest level for a

dike with a safety level of T1 and T10,000 is only 0.25 m.

Table 5.3 Safety levels and design water levels

Safety level of dike

Design sea level (m+MSL)

T1 0.90

T10 0.95

T100 1.05

T1,000 1.10

T10,000 1.15

Damage to assets

An urban polder with a low safety level will have a lower dike which will overtop more

frequently than a higher dike. The sea can be considered as a water body of unlimited volume.

Overtopping of the dike by the sea will result in inundation of the entire polder up to sea level

(this does not concern overtopping by waves, but a sea level above dike level). Based on the

frequency, the depth of inundation and corresponding damage factor and the inundated area, the

damage can be determined.

This is the damage to assets, buildings and infrastructure. The total damage in 10,000 years can

be translated to an annual average and to a total damage in 20 years. Table 5.4 and Figure 5.20

show an example of the investment cost, the damage in 20 years and the total of damage and

investment cost. It can be seen that a safety level of 10,000 years is the optimum: the total cost

are the lowest.

Table 5.4 Investment cost and damage (in 1000 USD)

Safety level polder

Additional

investment cost Damage in 20 years Total

1 0 1,244,830 1,244,830

10 60 128,480 128,540


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0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

0 1 2 3 4 5 6

safety level

co

st

an

d d

am

ag

e (

1000 U

S$)

Investment cost Damage

100 180 13,200 13,380

1,000 240 1,320 1,560

10,000 300 140 440

Figure 5.20 Investment cost and damage

Risk to human life

With inundation depth of higher than 1m there is a considerable threat to human life. The

probability a person will die depends on the warning time, time of breaching of the dike and

time of filling of the polder and inundation depth.

Related design standards and Code of Practises issued by the Ministry of Public Works (SNI)

should be applied in designing water management system in urban polder systems in Indonesia.

The design life time is the period in which the dikes fulfil its function: withstanding extreme

conditions at sea with a design return period based on the Indonesian Standard (SNI) should be

considered. Schematic dike is given in Figure 5.21.

Figure 5.21 Schmeatic dike embankments

clay fill

design water level inside outside

crest width


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Failure mechanisms

In the assessment of the safety of dikes and dams the following failure mechanisms are

important. See Figure 5.22.

• Inundation of the dike ring area through a combination of high water level and wave

overtopping without the collapse of the defence structure (A);

• Erosion of the inner slope by the force of the flowing water and by a combination of high

water level and wave overtopping (B);

• Instability (sliding) of the inner slope, due to either infiltration of the overflowing water in a

combination of high water level and wave overtopping , or water pressure against the

defence and increased water pressure in the subsoil (C);

• Shearing of a soil body, also by water pressure against the defence and increased water

pressure in the subsoil (D);

• sliding of the outer slope in the case of a rapid fall in the outside water level after high water

(E);

• Instability of the inner (or outer) slope by exiting seepage water through the soil body

(micro-instability) analogous to failure mechanism C, but at lower water levels (F);

• Piping as a consequence of seepage flow through the subsoil so that erosion starts behind

the dike and soil is borne along (sand boils) (G);

• Erosion of the outer slope or the toe and foreshore by current or wave movement (H, I);

• Large-scale distortions of the soil body (J);

• Mechanical threats like shipping (L).

Figure 5.22 Failure mechanism of a dike


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Maximum pond depth

The maximum pond depth within the basins should not exceed 2.5m under normal operating

conditions for the maximum design flow for which the primary outlets have been designed, i.e.

the maximum design storm with a certain return period flow that does not cause the emergency

spillway to operate under normal design conditions.

Top widths

Typical embankment top widths are shown in Table 5.3.

Table 5.3. Recommended top width for earthen embankments (USDA, 1982)

Height of embankment (m) Top width (m)

Under 3 2.4

3 to 4.5 3.0

4.5 to 6 3.6

6 to 7.5 4.2

Side slopes

For ease of maintenance, the side slopes of a grassed earthen embankment and basin storage

area should not be steeper than 4(H):1(V). However, to increase public safety and facilitate ease

of mowing and general maintenance, side slopes of 6(H):1(V) (or flatter) are recommended.

Freeboard

The elevation of the top of the settled embankment shall be a minimum of 0.3m above the water

surface in the basin when the emergency spillway is operating at maximum design flow.

Fill material

All fill material in earthen embankments should be free from brush and other organic material

subject to decomposition. Fill material should be compacted to at least 95% of the maximum

density obtained from compaction tests performed by the Modified Proctor method of ASTM


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D698. To allow for settlement of the embankment, the design height should be increased by

10% where hauling equipment is used and 5% where compaction equipment is used.

5.8.2 Design of urban drainage

• detention and retention basin

A stage-storage relationship defines the relationship between the depth of water and storage

volume in the storage facility. The volume of storage can be calculated by using simple

geometric formulas expressed as a function of storage depth. This relationship between

storage volume and depth defines the stage-storage curve. An example of a simple stage-

storage curve is illustrated in Figure 5.23.

Figure 5.23 Typical stage-storage curve

Stage-discharge relationship

A stage-discharge curve defines the relationship between the storage water depth and the

discharge or outflow from a storage facility. A single composite stage-discharge curve

should be developed from all primary and secondary outlets. Figure 5.24 illustrates the

construction of a stage-discharge curve for an outlet control device.


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Figure 5.24. Composite stage-discharge relationship

• Weirs can be sharp-crested, broad-crested, V-notch or proportional weirs.

• Trash racks, the susceptibility of inlets to clogging by debris and trash needs to be

considered when estimating their hydraulic capacities. Trash racks must be large enough

such that partial plugging will not adversely restrict flows reaching the control outlet.

• Mechanical devices. On large basins, such as flood storage reservoirs and flood storage in

urban lakes, electrically or mechanically controlled devices are often used to regulate the

basin outflow.

• Vertical gate. A vertical sluice gate can be used as an effective control. Two types of

vertical gate are normally used, namely: the sliding gate, and the ‘fixed-roller gate’.

• Erosion protection

Two parts should be checked, i.e. primary outlet and downstream waterway.

- Primary outlets

The only measures required are generally the protection of the bed and banks from

erosion for a few metres downstream by stone pitching or other means. Where the

head exceeds 1 m, a structure for dissipating energy should be provided in order to

prevent erosion.

- Downstream waterway

Stone pitching or riprap should protect the channel bed and banks immediately

downstream of stilling basins. Where the outfall from the basin is piped, this should

be provided for a distance of at least four times the diameter of the pipe.


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5.9 Environmental Impact Assessment (EIA)

Environmental issues constitute an inseparable and interwoven component in todays overall

water resources project planning and management. To account for it is a challenge; best left to

the dedicated engineer and scientist, who are conscious of the social role of their profession.

The urban polder water management engineer must understand what the environmental

movement is all about. The term ‘environment’ has been used in these guidelines according to

the definition of Brackley (1988) as:

The conditions, circumstances and influences under which an organisation or system exists. It

may be affected or described by physical, chemical and biological features, both natural and

man-made. The environment is commonly used to refer to circumstances in which man lives.

In the planning process, an environmental impact assessment (EIA) or Analisa Dampak

Lingkungan (AMDAL) has to be carried out in order to eliminate or minimize the

environmental impact of the urban polder development. The objectives of EIA are to ensure

that:

• Environmental, technical and social concerns are integrated into the design of development

projects based on a sustainable spatial planning, water management and its infrastructure;

• Civil society is aware of related environmental/ social impacts and can take part;

• Costs of appropriate mitigation measures are incorporated into projects feasibility studies.

The procedure and steps for enforcement and EIA:

• Legislative and administrative approaches are used to introduce EIA into the development

planning process:

• Legislation creates a mandate to apply EIA as an environmental management tool;

• Administrative procedures establish who does what, when and how;

• Environmental standards contained in technical guidelines (air, water, soil,

biodiversity).

� Enforcement implies:

� Administrative procedures are followed;

� Environmental standards are achieved.

If environmental assessment is a statutory requirement, local expertise will be needed to carry

out the work that this will impose. Local expertise, for both the public and private sectors, must

be developed through adequately funded training and technology transfer programmes. Training


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should focus on the skills needed for an intersectional decision making process at the crucial

points in the project cycle. It should not aim to make pseudo EIA specialists out of other

technical specialists. See also Chapter 4.8 on Environmental aspects.

Policy framework

Government policies in areas such as water, land distribution and food production, especially if

supported by legislation, are likely to be highly significant for land and water development

projects. An EIA should outline the policy environment relevant to the study in question.

Results are also likely to be most easily understood if they are interpreted in the light of

prevailing policies. Increasingly, at many national levels, new environmental policies are being

introduced. Such policies are often supported by legislation. Legal and policy issues have far-

reaching consequences for the environment and are included here to illustrate the complex

nature of environmental issues.

Social context

A project or programme and its environmental impacts exist within a social framework. The

context in which an EIA is carried out will be unique and stereotype solutions to environmental

assessments are therefore not possible. Cultural practices, institutional structures and legal

arrangements, which form the basis of social structure, vary one region to another.

It is a fundamental requirement to understand the social structure of the area under polder

management, as it will have a direct impact on the project and the EIA. Recommendations for

new legal controls or limits may also form part of the EIA output; for example, stipulating a

particular flow regime in order to maintain a wetland.

If land acquisition, economic rehabilitation (providing an alternative source of income) or

resettlement of displaced people is factors in any proposed development, special care will be

needed in carrying out the EIA. In this case, Land Acquisition and Resettlement Action Plan

(LARAP) prior to the design has to be carried out. These issues are socially and politically

sensitive and legally complex and must be identified early, during screening.

Poor people often find themselves in a vicious circle. They are forced by their poverty to exploit

natural resources in an unsustainable manner and suffer from increasing poverty because of


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environmental degradation. High population growth is linked to poverty and further contributes

to the dynamics of the vicious circle as ever-increasing demands are made on finite natural

resources. Therefore, the needs of the poor, their influence on the project and the project’s

impact on vulnerable groups all require particular attention in an EIA. As indicated before,

sustainable development cannot be sustainable if it keeps the poor in their vicious circle of non-

sustainability.

5.10 Impacts of subsidence and sea level rise

Land subsidence and sea level rise are two major problems which have to be considered in the

development of urban polders.

Land subsidence

Land subsidence in a soft clay area should be considered carefully in the design of an urban

polder. In a number of cases, problems have occurred that can be attributed to design and

construction techniques that have not sufficiently taken into account the local water,

groundwater and subsoil conditions (Opperman, 2006). It is important that these conditions are

taken into account during the complete lifetime of the project, from initial design and planning,

to building site preparation and construction, and finally during the further maintenance of the

system. An example of a subsidence effect is show in the following Figure 5.25:

The biggest problem in urban areas that are located on soft sub soils is subsidence due to over

withdrawal of groundwater. It is often also the underlying cause of other problems. Salinity

intrusion in groundwater system will also increase as groundwater depletion impact. Soft sub

soils such as clay and peat will subside when a load is applied or when the groundwater table is

lowered.

Consolidation due to loading and subsidence due to the drawdown of the groundwater table are

slow processes that can continue for a very long time. In peat the problem of lowered

groundwater tables is worse as this type of soil will oxidise when exposed to air. This

oxidization process is irreversible. Subsidence can also occur unrelated to human involvement.

The geologic history, for example, can have a residual effect on surface level movements. Clay

covered by subsequent sediment layers will consolidate under the accumulated load.


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Figure 5.25. Subsidence exposing foundation piles of a bunker in the Dutch countryside

More and more large cities and urban areas have encountered significant economic impact from

land subsidence caused by pumping of ground water from unconsolidated sediment. The areas,

most of which are coastal, include Jakarta and Semarang. Flooding related to decreased ground

elevation is the principal adverse effect of the subsidence. Lesser effects include regional tilting,

well-casing failures, ´rising´ buildings, and ground failure or rupture. Subsidence of most of these

urban areas began before the phenomenon was discovered and understood. Thus, the subsidence

problems were unanticipated. Methods to arrest subsidence typically have included control of

ground water pumping and development of surface water to offset the reductions of ground water

pumping. Ground water recharge should also be considered.

The monitoring of the vulnerable area due to the tidal inundation under the scenario of extended

land subsidence plays an important role in long-term urban coastal zone development and

management.

Sea level rise

One of the most significant potential impacts of climate change is sea level rise that may cause

inundation of coastal areas, shoreline erosion, increase of salinity intrusion in the groundwater

system, destruction of important ecosystems such as wetlands and mangroves and influence the


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drainage capacity of the coastal areas. As global temperatures increase, sea level rise already

underway is expected to accelerate due to a thermal expansion of upper layers of the ocean and

melting of glaciers.

In the last few decades, coastal urban drainage systems that prevent roads and residences from

being flooded have improved to the point where, in most areas, flooding from rainfall rarely

amounts to more than a minor inconvenience. These improvements have occurred in part because

developers, highway engineers, and flood insurance officials have decided that the benefits from

less flooding outweigh the costs, and in part because those who design drainage systems have

become better able to determine the size necessary for the desired level of flood prevention. The

design of an urban coastal drainage system depends on the amount of runoff expected during a

major storm and the elevation of the area being drained. Although the amount of rainfall and the

severity of the worst storm vary from year to year, it has been reasonable to assume that

historical weather records provide a reliable guide to future precipitation and runoff over the

design life of the project. With few exceptions, one could assume that the elevation of an area

will not change. Provided that the system has been maintained properly, it could be assumed to

maintain its ability to remove water at the design flow rate.

Accelerated sea-level rise is regarded as one of the most costly and most certain consequences of

global warming. If sea-level rise increases at rates projected by the United Nation’s

Intergovernmental Panel on Climate Change (2001) during the next century, many of the world’s

low-lying coastal zones and river deltas could be inundated. Several of the world’s most heavily

populated coastal cities are particularly vulnerable to inundation due to human interactions with

urban development processes.

High water tables in coastal areas also limit natural drainage. With water tables just below the

land surface, a rainstorm can rapidly saturate the soil (raise the water table to the surface). The

saturated soil increases runoff by decreasing the ability of water to percolate into the ground.

Areas that are currently below sea level require forced drainage. Most of the areas, which are

well below sea level, are completely encircled by levees.

The following adaptation strategies would aid in reducing, but not eliminate:

• Upgrade and strengthen levees and drainage systems;

• Design and maintain flood protection on the basis of historical and projected rates of local

subsidence, rainfall, and sea-level rise;

• Minimize drain-and-fill activities and other human developments that enhance


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subsidence;

• Protect and restore coastal defences;

• Develop flood-potential maps that integrate local elevations, subsidence rates, and

drainage capabilities (for use in the design of ordinances, greenbelts, and other flood-

damage reduction measures).

Because of the low elevations of the areas, gravity drainage is not always possible. As sea level

rises, some areas that currently have gravity drainage may have to shift to forced drainage.

Gates and flap gates may provide a cost-effective interim solution for such areas. During low

tide, the gates could be open to permit gravity drainage, while during high tides they could be

closed.

Areas that currently use forced drainage will also require modifications. Larger pumps may be

necessary to work against the higher tail water and to handle the larger capacity resulting from

decreased natural drainage and percolation, and possibly increased runoff. While new systems

may require larger pumps, existing systems are more likely to use additional pumps. In addition

to increasing pump capacity, it will often be necessary to increase the capacity of the system

that delivers the storm water to the pumping station.

As the drainage capacities of water management system, and pumping facilities decrease with

sea level rise, one alternative design would be to include more detention or retention facilities in

the drainage basin, preferably located near the headwaters of the polder area.

5.11 New technologies

In the new technologies include the computer software as well as hardware and especially

related to the design, construction, operation and maintenance works will be discussed.

Computer simulation models of urban polder water management systems represent the most

effective and viable means for evaluating system response to various design and management

strategies.

Computer software

Much new computational software has been developed worldwide based on the intensive


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research effort in urban hydrology, hydraulics and geographical information system. However,

it should be borne in mind that proper use of such a new method or tool requires a good

knowledge of the detailed operations which the method or tool can perform. The engineer

should have knowledge of the hydrological and hydraulic processes simulated by the tool he/she

is planning to use.

In hydrology and hydraulics, computer simulation has been significantly enhanced by the use of

graphic displays to aid in data entry and editing, for instance to follow graphically changes in

the hydraulic gradient as the simulation progresses. The rapid improvements in both software

and computer hardware mean that, in the future, the possibilities will be limited only by the

imagination and skill of the user.

Geographic Information Systems (GIS)

GIS enable the user to incorporate a wide range of information about the physical system into a

computer database. This can include not only information about the ground surface, but details

of the urban infrastructure.

Rapid developments are occurring in the GIS field in order to integrate all the elements

described above into a complete mapping and hydrology/hydraulics analysis and design

package that can:

• Provide area physical feature mapping;

• Compute hydrologic model input parameters;

• Model the rainfall/runoff process to determine design flows;

• Provide the capability for on-screen design of the system, including conveyance

structures;

• Optimise the final design;

• Map or draw the system as designed, including plan and all structural components.

These developments can eliminate many of the repetitive calculations in water management

system design. Opportunities for linkage to GIS systems are an important factor in the selection

of computer models. It should be noted that the requirements for checking and verification of

designs so developed would still be necessary.


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Mathematical modelling of urban polder water management systems

Urban water management system models represent an essential tool for planning, design,

operation, maintenance and management of urban polder water management assets. Special

attention must be given to the selection of an adequate model to reflect the problem at hand,

development of data collection, knowledge of best modelling practices and correct interpretation

of results to address planning, design, operation and maintenance needs.

Some mathematical models which can be used in urban polder planning, design, operation and

maintenance are:

• DUFLOW, SOBEK (one dimensional hydrodynamic model);

• MICROFEM (groundwater model);

• SWAT (soil and water assessment in relation to landuse change).

Those individuals involved in the related modelling work should also have a sound

understanding of the operational performance requirements of urban polder water management

systems, hydraulics, urban hydrology, field survey and procedures, capabilities and limitations

of modelling software.

Modelling procedures

According to the requirements of the software used, the designer will first assemble and

carefully check all the following required data:

• Design rainfall;

• Topographical conditions and drainage geometry;

• Hydraulic roughness;

• Runoff coefficients;

• Rainfall abstraction parameters.

In many cases, some of the desired data will not be available and the designer will have to make

assumptions and/or use default values given in the user’s manual of the chosen software. If

these default values seem unsuitable for the design conditions, the designer should test the

model sensitivity to these values, using their probable range.

The first review and analysis of the required and available data is very important and should not

be attempted without a detailed user’s manual. After the preliminary analysis, and according to


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the design objectives, water management network complexity, available data, computer

facilities, the designer should be able to select an appropriate modelling procedure and software

to suit the desired purpose.

Application of computer modelling

Computer modelling became an integral part of urban polder water management system,

planning and design. In this guideline, the discussion will be limited to model for the simulation

of hydrologic and hydraulic processes in urban polder water management systems.

Advantages and disadvantages of computer modelling

A very important factor is that almost all computer models can fully account for storage in all

stages of the hydrologic/ hydraulic routing. Modelling is not a good substitute for data

collection. Although modelling is generally cheaper than data collection, the uncertainties

involved, mandate the collection of data for model calibration and verification.

The purposes of the modelling works can be:

• To support and evaluate design of water management system (flow capacity and its

hydraulic performances);

• To support and study operation strategies of water management systems by checking their

hydraulic performance under a particular strategy;

• To support and study any maintenance program of water management system.

Objectives of modelling of urban polder water management systems

If a problem does require modelling, the corresponding modelling objectives should be clearly

defined. Models may be used for objectives such as the following:

• To characterise the capacity of water management systems based on urban runoff and its

spatial flow distributions;

• To perform frequency analysis on hydrologic, e.g. to determine return periods of any

storm or flood;

• To provide input to economic analyses.


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Basic input data

All models require the user to enter some form of input data. For quantity simulation, these data

include:

• Polder areas;

• Imperviousness;

• Topographical conditions and slopes;

• Roughness, channel, shapes, sizes;

• Characteristics of hydraulic structures or controls such as weirs, orifices and pumps;

depth-area-volume-outflow relationships for storage units;

• Information on downstream hydraulic controls, such as river stages or tidal elevations.

A critical factor in successful hydraulic modelling of existing water management systems is an

accurate and proper survey to determine invert elevations and channel conditions.

Initial and boundary conditions

The calculation starts with a prescribed set of initial conditions and must incorporate, was it

progresses through time, the appropriate boundary conditions. In the interests of efficiency, it is

desirable that the prescribed initial conditions should be as realistic as possible. In most cases,

dry bed should be avoided, otherwise a slot approach should be done. In general, the effects of

the initial conditions will decay as the calculation progresses; Zoppou and O’Neill (1981) have

drawn attention to certain cases in which errors in the initial conditions may not decay.

The boundary conditions, which may include a specification of discharge as a function of time

(for example, a flood hydrograph), a specification of stage as a function of discharge (a rating

curve) and a specification of stage as a function of time (for example, a tide curve).

Calibration and verification

The process of calibration of the model involves the adjustment of the model to cause it to

reproduce, with an acceptable degree of precision, known prototype behaviour. Verification

holds the parameters constant and tests the calibration on an independent data set. Calibration is

used to estimate the value of flow parameters, and verification is used to test the validity of the

estimation. Adjustment (usually on a trial-and-error basis) of the following features may be

undertaken:


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• Details of the computation scheme itself;

• Time step ∆t;

• Definition in the model of the channel geometry;

• Values of the roughness parameter for various parts of the channel network;

• Boundary conditions.

Failure to reproduce prototype behaviour may be due to errors in channel geometry in the

numerical model. Such errors may arise either from actual errors in survey information or from

erroneous entry of data into the model.

Accuracy

Consideration of the accuracy of the scheme involves assessment of the ‘correctness’ of the

results yielded by the scheme – that is, of the extent to which the calculated parameter values

are in agreement with the ‘true’ physical values. The accuracy of a computation scheme will

depend upon the extent to which higher-order terms are included in the finite-difference

expressions derived from the basic differential equations. The accuracy of the results derived

from a given model can also be improved by decreasing ∆x and ∆t.

Sensitivity analysis

If calibration and verification of the model can not be done, e.g. design a new urban polder

water management system then the user should perform a sensitivity analysis (with hypothetical

data if necessary). Varying key parameters by known percentages and inspecting the change in

output. In this way, it will be easier to know which parameters should be changed during the

calibration process.

Uncertainty analysis

Uncertainty analysis is rapidly becoming accepted practice. It involves varying the model input

parameters and examining the effect on the output.

Uncertainty analysis can be used to compute expected output variability as a function of ill-

defined input parameters. This technique can serve as a means of quantifying the model’s

acceptability. Uncertainty analysis can also be useful in evaluating the relationship between

field data sampling and modelling. Hypothetical sampling scenarios can be tested to understand


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the expected uncertainty in model output. Uncertainly analysis can also be used to quantify

model acceptability (expansion of goodness-of-fit testing).

Production runs

Following the calibration and verification processes, the model is ready for engineering

application. At the design level, the detailed analysis of an existing system, proposed system, or

system improvements will be investigated. Examples include analysis of alternative surface

drainage patterns and location of detention or retention storage facilities. Design models must be

capable of realistic simulation of hydrologic and hydraulic phenomena.

Another important division of models is into deterministic and stochastic types. Deterministic

models attempt to reproduce physical, chemical and even biological processes (to the extent that

such processes can be understood scientifically) to produce outputs, while stochastic models

represent the outcomes of processes by statistical analysis.

In practice many models use a mixture of the two techniques. Processes that are too complex or

poorly understood to be modelled deterministically, may be represented by statistical

characteristics; while many statistical models also employ simple process-type mechanisms.

Data availability is another important consideration. For instance, complex flow routing cannot

be performed in a drainage system without extensive, which may lead the engineer to a simpler

technique that is not so data intensive.

For ‘operational’ models there are three most important criteria to be checked:

• Model must have documentation. This must include a technical reference, a user’s manual

that describes input data requirements, outputs to be expected, and computer requirements.

Documentation is the characteristic that most often distinguishes a model that can be

accessed and used by others from the other computerised procedures described in the

literature;

• Model must have support. Normally this is provided on commercial terms by the original

software developer. Support means that the user can obtain answers, by telephone, written

correspondence or email, to problems that arise during model implementation and use;

• Software should have been widely used by other than just the software developer.

Regardless of its technical virtues, a procedure described in a single journal article or

report with no experience or ‘review’ by the engineering community is a poor candidate

for use by a third party.


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Hydrologic models

Most hydrologic models attempt to simulate the Rainfall-runoff process. This ensures that the

effects of rainfall, the single most important hydrologic variable, are properly taken into

account.

Hydraulic models

All hydraulic models are deterministic and cover free surface flows as well as pipe flows. The

basic hydraulic and hydrodynamic equations are well known and described in Annex 4.

Different hydraulic models take various approaches to solving these equations within the

bounds of user friendliness, reasonable computing requirements, and stability. Unlike the

situation with hydrologic models, the basic hydraulic principles are common throughout the

world.

Many flow phenomena of great importance to the engineer are unsteady in character, and cannot

be reduced to steady flow by changing the viewpoint of the observer. In unsteady flow,

velocities and water depths change in time at any fixed spatial position in an open channel. In

nature, open channel flow is almost always unsteady, although for simplification it often is

analysed in a quasi-steady state. In these cases, numerical models should be applied.

Land use change and rainfall-run-off models

A model on soil and water assessment in relation to landuse change can be used in order to

analyse and to evaluate the effect of land use change to the run-off pattern in an urban polder.

5.12 Wastewater treatment plant

It is important to clarify two terms, sewerage and sewage or wastewater, because they are often

used incorrectly:

• sewerage is a system of pipes used to collect and carry sewage, which is the wastewater

discharged from domestic premises;

• sewage/wastewater on the other hand consists of human wastes, paper, and vegetable

matter.


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This type of waste is organic as it consists of compounds of carbon and can be broken down by

micro-organisms into simpler compounds, which are stable and not liable to cause a nuisance.

Communal wastewater would normally comprise of 99.9% water and 0.1% solids.

Besides communal wastewater sewage there is industrial wastewater and many industrial wastes

are also organic in composition and can be treated by micro-organisms in the same way as

domestic sewage. This type of treatment is called biological treatment and the strength of the

sewage is measured in terms of BOD (biochemical oxygen demand), which is a measure of the

amount of oxygen used by the micro-organisms in breaking down the wastewater into stable

compounds. In a community, the sewerage collection system will collect the wastewater from

communal, commercial, and industrial premises and will carry it to the point for treatment prior

to its final disposal or reclamation for reuse.

Levels of Wastewater Treatment Plant

Conventional wastewater treatment, typically, consists of a combination of physical, chemical,

and biological processes and operations to remove solids, organic matter and, sometimes,

nutrients from wastewater. General terms used to describe different degrees of treatment, in

order increasing of treatment level, are preliminary, primary, secondary, tertiary and advanced

level. See Figure 5.26 below:

In rural and per-urban environments, wastewater can be treated in alternative, low-cost

treatment systems such as septic tank. In this case, the treatment of wastewater should be

referred to Standard on Operational Techniques of individual Septic Tank (SNI 03-2398-2000).

The objective of preliminary treatment is the removal of coarse solids and other large

materials often found in raw wastewater. Removal of these materials is necessary to

enhance the operation and maintenance of subsequent treatment units. Preliminary

treatment operations typically include coarse screening, grit removal and, in some cases,

comminution of large objects. In grit chambers, the velocity of the water through the

chamber is maintained sufficiently high, or air is used, so as to prevent the settling of

most organic solids.


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Figure 5.26 Levels of wastewater treatment plant Preliminary treatment level

Primary treatment level

The objective of primary treatment is the removal of settleable organic and inorganic solids by

sedimentation, and the removal of materials that will float by skimming. Approximately 25 -

50% of the influent biochemical oxygen demand (BOD5), 50 - 70% of the total suspended

solids (TSS), and 65% of the oil and grease are typically removed during primary treatment

(Pescod, 1992). Some organic nitrogen, organic phosphorus, and heavy metals associated with

solids are also removed during primary sedimentation, but colloidal and dissolved constituents

are not affected. The effluent from primary sedimentation units is referred to as primary

effluent.

Primary sedimentation tanks or clarifiers may be round or rectangular basins, typically 3 - 5 m

deep, with hydraulic retention time between 2 and 3 hours. Settled solids (primary sludge) are

normally removed from the bottom of tanks by sludge rakes that scrape the sludge to a central

well from which it is pumped to sludge processing units. Scum is swept across the tank surface

by water jets or mechanical means from which it is also pumped to sludge processing units.

In large sewage treatment plants, primary sludge is most commonly processed biologically by

anaerobic digestion. In the digestion process, anaerobic and facultative bacteria metabolize the

organic material in sludge, thereby reducing the volume requiring ultimate disposal, making the


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sludge stable and improving its dewatering characteristics. Digestion is carried out in covered

tanks (anaerobic digesters), typically 7 - 14 m deep. The residence time in a digester may vary

from a minimum about 10 days for high rate digesters (well mixed and heated) to 60 days or

more in standard rate digesters. Gas containing about 60 - 65% methane is produced during

digestion and can be recovered as a energy source. In small treatment plants, sludge is processed

in a variety of ways including aerobic digestion, storage in sludge lagoon, direct application to

sludge drying beds, in process storage as in stabilization ponds, and land application.

Secondary treatment level

The objective of secondary treatment is the further treatment of the effluent from primary

treatment to remove the residual organics and suspended solids. In most cases, secondary

treatment follows primary treatment and involves the removal of biodegradable dissolved and

colloidal organic matter using aerobic biological treatment processes. Aerobic biological

treatment is performed in the presence of oxygen by aerobic microorganisms (principally

bacteria) that metabolize the organic matter in the wastewater, thereby producing more

microorganisms and inorganic end-products (principally CO2, NH3 and H2O). Several aerobic

biological processes are used for secondary treatment differing primarily in the manner in which

oxygen is supplied to the microorganisms and in the rate at which organisms metabolize the

organic matter.

High rate biological processes are characterized by relatively small reactor volumes and high

concentrations of microorganisms compared with low rate processes. Consequently, the growth

rate of new organisms is much greater in high-rate systems because of the well controlled

environment. The microorganisms must be separated from the treated wastewater by

sedimentation to produce clarified secondary effluent. The sedimentation tanks used in

secondary treatment, often referred to as secondary clarifiers, operate in the same basic manner

as the primary clarifiers described previously. The biological solids removed during secondary

sedimentation, called secondary or biological sludge, are normally combined with primary

sludge for sludge processing.

Common high-rate processes include the activated sludge processes, trickling filters or

biological filters, and rotating biological contactors (RBC). A combination of two of these

processes in series (e.g. trickling filter followed by activated sludge)is sometimes used to treat

municipal wastewater containing a high concentration of organic material from industrial

sources.


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Tertiary and/or advanced treatment level

Tertiary and/or advanced wastewater treatment is defined as the additional treatment needed to

remove suspended solids and dissolved substances remaining after conventional secondary

treatment (Metcalf and Eddy, 1991). For example, individual treatment processes are necessary

to remove nitrogen, phosphorus, additional suspended solids, refractory organics, heavy metals,

and dissolved solids. Because advanced treatment usually follows high-rate secondary

treatment, it is sometimes referred to as tertiary treatment. However, advanced treatment

processes are sometimes combined with primary or secondary treatment (e.g. chemical addition

to primary clarifiers or aeration basins to remove phosphorus) or used in place of secondary

treatment. The principal tertiary treatment processes for wastewater reclamation are: filtration,

nitrification-denitrification, phosphorus removal, coagulation-sedimentation, carbon adsorption,

and others). An example of wastewater treatment plant is presented in Figure 5.27.

Figure 5.27 Wastewater treatment plant

Sludge Treatment

The sludge from extended aeration plants is rendered stable by the treatment process and can be

dewatered by mechanical techniques (such as chamber filters, belt filters or centrifuges from 1%

solids to 15 or 20% solids. The sludge can then be mixed with domestic refuse and turned into

compost or disposed as landfill.


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The sludge from primary settling tanks and conventional activated sludge processes is unstable

and needs further treatment by digestion (either aerobic or anaerobic). But usually anaerobic

digestion is used because in addition to stabilization, methane gas generated can be converted to

either heat energy or electric energy.

The final disposal of sewage sludge can be by a number ways such as:

• Co-disposal with domestic refuse on a landfill site;

• Disposal in the sea;

• Incineration.

Sludge must undergo biological, chemical or heat treatment, long-term storage or any other

appropriate process. The objective of this treatment is to kill off disease causing organisms.

These restrictions are difficult to meet in the case of small plants and the amount of sludge used

in agriculture has declined in favour of co-disposal with domestic refuse in landfill sites Waste

Water Treatment Plant Process Selection

One of the most challenging aspects of a wastewater treatment system design is the analysis and

selection of the treatment process and technologies capable of meeting the requirements. The

methodology of technology and process selection does generally include several evaluation

steps that vary depending upon the complexity of the project, the wastewater influent conditions

and the desired treatment levels required.

Total Suspended Solids

High contents of TSS are a measure for the removal of contaminants as well as viruses that tend

to adsorb to solids. TSS also forms an indicator for the removal of heavy metals, as most heavy

metals adsorb to solids.

5.13 Solid waste management

The overall goal of urban solid waste management is to collect, treat and dispose of solid wastes

generated by all urban population groups in an environmentally and socially satisfactory manner

using the most economical means available. Local governments or polder authorities are usually

authorized to have responsibility for providing solid waste management services, and most local

government laws give them exclusive ownership over waste once it has been placed outside a

home or establishment for collection. As urban centers grow economically, business activity and


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consumption patterns drive up solid waste quantities. Solid waste accumulations and official

solid waste dumping facilities raise public concerns because of potential smoke from open

burning, odors, insects, rodents, gaseous emissions and water pollution that might result. To

successfully develop new and improved solid waste disposal facilities requires strong

commitment to public/stakeholders consultation and consensus building. To a lesser extent,

transfer and treatment facilities also trigger public concerns, often about truck traffic, and

require public/stakeholders consultation as part of development plan. There are numerous

opportunities for community-based solid waste primary collection, recycling and composting

systems through involvement of neighborhood and non-government organizations working

closely with inhabitants. Successful cost-recovery for solid waste improvements relies on

public/stakeholders consultations that enable local government, municipality or polder authority

to understand the public’s service preferences and willingness to pay.

It is expected that solid waste can be managed and recycled. System sharing task responsibility

between community and government work will be needed. Community: separate the type of

solid waste into 3 types of garbage: organic, recycle (plastic, metal, bottle, glass, paper) and

materials which can be burned. An example of this system can be found in Kelapa Gading urban

polder system in Jakarta.

Specific objectives of solid waste management include:

• Environmental protection. To protect the health and aesthetic conditions of the living

environment by removing waste in a sanitary fashion;

• Convenience. To provide a desired level of service (e.g., in terms of frequency and point of

collection);

• Continuity. To provide for stability of this vital service. A contingency plan shall be

available for periods when there is an interruption of collection service;

• Resource recovery and waste minimization. To reclaim and conserve natural resources;

• Safety. To store and collect the waste in as safe a manner as possible;

• Efficiency. To achieve all these objectives with the highest productivity and least cost.

Collected solid waste is typically hauled from the point of collection to a disposal site in the

collection vehicle. Collection of solid waste should be referred to the Urban Solid Waste

Operational and Management standard in Indonesia, SNI 19-2454-2002 (Tata cara Teknik

Operasional Pengelolaan Sampah Perkotaan). The domestic garbage can be collected in a

garbage bin at each house. Then, the assigned personnel pick the garbage up to bring it to the

nearest temporary garbage collector. Solid waste may be collected and managed by either


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municipality or polder authority. There may also be a combination of approaches, depending on

conditions at a specific installation. The solid waste will be loaded into the trucks and brought to

the final solid waste dumping area.

The inhabitants and all other stake holders should pay for the garbage collection at their houses.

The inhabitants have to be motivated and be aware of the problems of s and are willing to pay

for garbage collection. About operational techniques for solid waste management in Indonesia

refers to SNI 19-2454-2002.


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The failure of the water management and flood protection systems to function properly can

often be traced back to construction and maintenance issues. By utilizing appropriate

construction practices and conducting systematic and proper maintenance, the system should

function properly.

6.1 Dike, outlet and inlet structures

Dike slope stability

Dikes will have to be constructed as much as possible with locally available materials, provided

that the water retention function will be guaranteed. While in the urban areas space may be

limited often special constructions, like sheet piling, will have to be required. A very good

overview of structural measures to flood control is given by the publication Manual on planning

of structural approaches to flood management (Van Duivendijk, 2005).

Essential element in all dike construction work is the fact that development of leaks, or piping

will have to be prevented, especially during extreme conditions when the outside water level

may be substantially higher than the inside water level. Such leaks can especially develop at the

connection of structures in the dike and the dike body. Therefore such structures will have to be

provided with subsurface screens to prevent that underflow or side underflow will develop.

During the construction of the dike body itself care has to be taken that no sliding will occur due

to the development of overpressure during loading. This may imply that the dike body will have

to be installed in layers of such a thickness that no sliding will occur and that the next layer will

be installed when the overpressure has sufficiently disappeared from the low permeable layers.

In order to accelerate this process the application of horizontal drains, or vertical geo-drains

may be required.

The method of construction

The method chosen for building a dike has an important effect on maintenance at a later stage.

Maintenance is affected by it directly, for example:

• Clay for dike heightening must be built in layers and compacted layer by layer, for instance

with bulldozers or vibration rolls. If this does not happen layer by layer or if compacting is


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not carried out in a mechanical way, but only using the tracks or bucket of the hydraulic

excavator, this always causes settlement later on. The consequence of this is that a dike crest

will appear to be lowered after a lapse of time and revetments will settle and lose their

mutual connection. If a dike or bank revetment is constructed during a wet period there is a

big chance that the underlying layers of clay settle, because it is impossible to compact clay

sufficiently in wet periods;

• If an under water slope has not been completely covered with rip-rap over the whole

breadth, a transition has to be formed between the rip rap and the area covered with other

materials. From experience it is known that such joints are often the cause of damage;

• Materials delivered to the site have to be compared with the specifications as described in

the bill of quantities. Otherwise it can cause maintenance later on, for instance because fine

materials can move internally but also wash out through a surface layer.

Effects on groundwater

The forced inflow of storm water into the ground will affect the groundwater levels and water

quality in the regions where it occurs. The impact on groundwater needs to be considered and

accounted for in the design of buildings. As an example, buildings with basements may not be

feasible if the groundwater levels are raised above basement floor elevations. This problem may

be solved by the installation of under drains.

Outlet and inlet structures

Outlet and inlet structures for urban canals can be precast and field positioned to their proper

elevation. If the size of the structure is such that it cannot be transported, they can be built on

site. This might necessitate site dewatering during the construction process. Where it can be

planned, structures are installed before earthwork construction commences.

Construction of bridges, culverts, siphons, drop structures, pumping stations and regulation

structures needs to be undertaken in accordance with the drawings and specifications, and

standards as applicable to the concerned type of structure and work.

High water velocities through outlets would have to be avoided to prevent scouring and damage

to banks and the structure itself. This can be achieved by applying larger cross-sections for

outlets and urban canals and/or by lining the canal banks and protecting the outlet channel. On


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the other hand, however, sedimentation in the urban canals needs to be prevented, if required,

by flushing them, for which relatively high velocities are required.

Culvert, gate inlets/outlets

They shall be adequate to avoid hazardous flooding and failures of road or embankment

structures. The required level of protection to prevent road flooding shall be consistent with the

design requirements. At many locations, either a bridge or a culvert fulfills both the structural

and hydraulic requirements for the stream crossing. Choose the appropriate structure based on

the following criteria:

• Construction and maintenance costs;

• Risk of failure and risk of property damage;

• Traffic safety;

• Environmental and aesthetic considerations;

• Construction expedience.

The selection of material for a culvert depends on several factors that can vary considerably

according to location. Consider the following variables:

• Structure strength, considering fill height, loading condition, and foundation condition;

• Hydraulic efficiency, considering Manning’s roughness, cross section area, and shape;

• Installation, local construction practices, availability of pipe embedment material, and joint

tightness requirements;

• Durability, considering water and soil environment (pH and resistively), corrosion (metallic

coating selection), and abrasion;

• Cost in relation to the availability of materials.

The most economical hydraulic structure has the lowest total annual cost over the design life of

the urban polder water management system.

Pumping station

Pump sizes are usually selected to provide multiple pumps rather than a single pump of

appropriate size. Smaller pumps are usually cheaper, and with multiple pumps, the loss of one

will not shut down the entire pump station.

Every pumping station should have an on-site standby electrical generator regardless of the


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presence of redundant utility power. Standby generators are usually powered by diesel or

gasoline.

Control circuitry includes the flood level at which the pump station will be activated, sequence

of operation, activation of the standby generator when necessary, deactivation when the flood

event has passed, and operation of any night security lighting. Controls may also include

communication with a central office on the station’s status regarding water levels, pump

readiness, utility electrical power, standby generator fuel level, security, or other central office

concerns.

The pumping station structure should meet requirements for public safety, local extreme

weather conditions, site security, and maintenance operation. Consider also aesthetics and the

possible need for future expansion.

6.2 Urban water management systems

In this part, general construction criteria for different urban water management components will

be discussed. During construction the tender documents and specifications will provide

generally instruction on quality control during construction period as well as the materials used.

Quality control of materials can be achieved by using certified suppliers or materials that have

been certified by specific organization in Indonesia.

Urban canals can be constructed by dredging equipment, by backhoes, by draglines. or by using

a combination of earth moving machinery. Where the soils will permit, earth moving scrapers

can be used for the upper part of construction until the canal under construction can no longer

accommodate the machine. At that point, a backhoe or dragline can be employed to excavate the

canal, or dredging equipment can be applied.

Survey distance and level control pegs may be installed at certain intervals along the urban

canal prior to commencement of construction. Where laser equipment is being used, machine

operators are provided with bed level and grade at the start of the urban canal and at subsequent

changes of direction and grade.

Construction of the urban water management systems normally commences with scrapers and


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backhoes at the downstream end of the system. In waterlogged conditions a pilot canal may be

installed first to dry the landscape sufficiently to permit the shaping of the urban canal.

Bank forming and trimming is generally carried out with a grader. Reasonable compaction of

banks is generally achieved with the passage of machines. Checking of the formation and

finished construction levels is undertaken as the work proceeds.

Scope of Work

The work to be done under excavation for urban polder canals consists of the construction under

all conditions namely hard dry, wet and under water table conditions. The work to be done by

the contractor will generally include clearing, stripping and removal of debris as required from

areas of excavations and embankments, excavating the required urban canals, transporting,

placing, and dressing the excavated materials in designated disposal areas or consolidated

embankments. Care and handling of water and all other work necessary to excavate the

designed urban canals.

All areas within the right-of-way to be cleared, as shown on the design drawings or directed by

the engineer will have to be cleared of trees, brush, rubbish and other objectionable matter and

such materials will have to be removed from the site of the works.

Excavations, embankments and dikes construction will have to be made to the lines and grades

shown on the design drawings. Spoil banks and waste areas will have to be leveled or sloped to

drain and finished to reasonably regular lines. Excavated materials will have to be disposed of in

required embankments, backfill or in spoil banks, or will have to be placed in approved waste

areas or in other locations. Embankments, dikes, backfill, spoil banks and waste areas need to be

built in approximately horizontal layers carried across their entire width to the required slopes.

Construction may be accomplished by mechanical excavating and hauling equipment, or by

excavating or dredging machinery depositing the materials directly from the excavation.

Where applicable approved, excavated materials can be placed in consolidated embankments

along the canal. Prior to and during placement operations, the material needs to have the proper

moisture content for consolidation. If the moisture content is less than that required for

consolidation, it can be supplemented by sprinkling and reworking the material during

placement. If the moisture content is greater than that required for consolidation, the material

shall be dried by reworking, mixing with dry materials or other approved means. If required,


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layers of the embankment need to be consolidated by routing the travel of the mechanical

excavation, hauling and placing equipment over the fill during construction of the consolidated

embankment. and dikes. Materials which will not stand on the slopes and may slide into

excavated areas need to be removed by the contractor in an approved manner, and the slopes

need to be refinished.

The contractor needs to protect the works from damage by rains, surface runoff, floods,

overflow of canals, overflow of rivers, failure of protective works or similar events which may

occur during the construction period. Any damage to the works resulting from such events will

have to be corrected by the contractor.

Rip rap can be installed for bank protection. Protection may be required where surface or side

inlets discharge into the urban canal, where the canal makes a sharp change in horizontal

alignment, or where insufficient space is available to make sloping banks.

Water management system should be constructed during the dry season when the ground is able

to support the heavy machines. Urban polder water management systems shall be provided to

the shape and location as shown on the approved engineering plans. Lining will conform to the

profile of the drain and is to be provided as soon as possible after forming the drain.

The connection of the urban polder water management system to a macro water management

system outside the polder must be designed and constructed in an integrated way by considering

all new development and redevelopment in the related area. New development and

redevelopment shall be required to participate in the design and construction of the macro water

management system that serves the development of the area.

7 Management, operation and maintenance of urban polder systems

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7 Management, operation and maintenance of urban polder

systems

An urban polder water management and flood protection systems in common will prove

effectively functioning only if it is designed correctly, constructed properly, and maintained

properly and regularly. This not only requires a firm grasp of hydrological, hydraulic, and

structural design principles, but also a sound understanding of operational and maintenance

requirements.

7.1 Management, Operation and Maintenance

Management, operation and maintenance are three separate things, but they are closely related.

7.1.1 Management

Management is the care that, in general, public works require being able to answer the purpose

for which they were constructed. For urban polder in Indonesia these works are, in the task of

the polder board. This task should be carried out as a joint effort between policy-makers and

engineers. In order to adequately carry out the task of caring for water management and flood

protection systems, dikes and banks the polder board must have legal powers to enforce

sanctions.

7.1.2 Operation

When there is water control structures in an urban polder water management system these have

to be operated according to the purpose and objectives of the urban polder water management

system, unless there is a general agreement among those concerned that another operation rule

will have to be followed.

It is recommended that the normal operation rules will be followed and that only the rules for

extreme wet conditions will be followed when this is at least agreed by the polder board,

municipality and provincial Public Works.


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7.1.3 Maintenance

In general the polder board itself is responsible for maintenance and carries this out by itself. If

necessary with the support of contractors. It’s not always necessary that the duty of carrying out

maintenance is connected to the task of management. Maintenance measurements have the

purpose of improving the condition of the water management and flood protection systems.

Therefore the manager has three options:

• To repair to the original condition;

• To repair to a reduced condition than the original (mostly temporary repair);

• To repair to a better condition than the original.

Weighing up the costs plays an important role in the choice of repair. It may be more efficient to

execute combined maintenance measurements. Maintenance should be executed on the basis of

inspection reports or after damage has occurred. Preferably maintenance should be carried out

before the storm surge season, because during this period there is a much smaller chance for

extreme load circumstances so that failure of the dike will be much reduced.

If the polder board does not have its own maintenance service at its disposal, maintenance cab

be carried out by contractors. A disadvantage of executing maintenance by contractors often

means that quality is more or less under pressure. Therefore supervision of the work is always

necessary. An execution of maintenance carried out by using own employees, generally

guarantees a better quality.

Whether maintenance is carried out by the polder board itself or by contractors, the possibility

of carrying out maintenance in a practical way should always be aimed for, so therefore:

• It should be possible to carry this out quickly and easily, preferably using mechanical

equipment;

• It should be accessible or created with easy accessibility for maintenance equipment;

• It should be financially attractive.

The conditions should already be created at the moment of the design of the system. This is

possible if design and choice of applied materials are in accordance with each other. The

maintenance of water management and flood protection systems is dependent on the conditions

actually found. On the basis of this condition preventive or corrective maintenance can be

executed.


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Finances

The urban polder board finance their work entirely from the service fee which they levy on

those concerned: the inhabitants, the owners and users of land and property (all stakeholders) in

the area covered by the polder board. Therefore the polder board is made up of representatives

of these groups of stakeholders because they have an interest in the work of the polder authority.

Flood control works always have to compete for resources with the demands from other types of

public service. To underline the fact that a good maintenance of sea and river dikes for example

is a general issue, the central government as well as provincial government contribute towards

the cost of maintenance. The reason is that flooding nearly always affects the surrounding and

not simply the area covered by the polder board. So the consequences of flooding are also

perceptible.

Maintenance can be defined as: the upkeep of previously invested (sometimes considerable)

capital or in other words: keeping works permanently in a good working condition. To keep a

dike for example in good working condition, it is clear that carrying out maintenance is

necessary. Maintenance however depends on, and is influenced by:

• Design;

• Choice of applied materials;

• Manner of execution.

Design and choice of applied materials

A choice for a less durable design in general means lower cost of construction, but often implies

higher maintenance costs. This in contrast to a design of which the cost of maintenance is lower,

but the cost of construction is higher because of a more durable design. World wide social

acceptation is beginning to play a more important role. In particular the influence on the

environment has become an issue. Indirectly these factors can influence the maintenance as

well.

Previous history

Knowledge of the design, choice of applied materials and the construction of dikes and banks is

of great importance for maintaining these works. It is important to be aware of the previous


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history. With this knowledge adequate measures can be taken when calamities to the water-

management and flood protection systems occur. If there are no data files available, it can be

collected by means of:

• Field investigation;

• Measurement made only once such as: level survey, air photos, drilling, sounding and so

on.

Permanent data that needs to be measured only once are:

• Situation, structure and geometry of foreshore;

• Structure subsoil of the dike by soil investigations;

• Structure and geometry dike body (types of soil and cross section);

• Revetments and objects such as sluices, pumping stations, roads, fences and so on;

• Hydraulic limiting conditions (water levels, wave heights and wave direction).

Variable fixed data which can change over a period of time, for example crest height, the height

just before the toe of the dike, changes in the geometry of the dike, the position of the gates and

ground surface have to be updated regularly. Both the fixed and the variable data have to be

arranged and updated systematically. At the same time they ought to be accessible, preferably

by a technical management register. An inspection system with maintenance program in fact can

be mapped out with the help of the data from such a technical management register. In this

register variable data can be updated after each inspection and after carrying out every measure

of maintenance. The fixed data of new or improvement works have to be added to the register

only once.

Management register

The data that has to be saved in the register can be conveniently arranged by description of the

following three categories:

• Basic data for more or less uniform sections of a dike;

• Detailed data for the determination of quality(standard)values as a reference when

damage occurs;

• Elements that occur out from other uses of dike or bank.

Setting up a management register for the first time, the checklist mentioned below can be used .

The most important parts are mentioned for the three categories. In all events, these parts have

to be described if they are presented on the dike or bank.


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Checklist management register

• Basic data on behalf of sections of the dike and bank

- Outline maps;

- General and administrative data which cover starting-points of design, loads and also

other use of dike or bank;

- Characteristic geo-technical longitudinal section;

- Characteristic cross section of dike and foreshore;

- Secondary dikes (if any);

- Data details for determination of quality (standard) values

- Structure of dike and bank;

- Coastal structure (foreshore);

- Revetments and transition constructions.

• Elements arising out of other uses of the dike or bank

- Roads, cables and service pipes;

- Buildings and pumping stations;

- Road signs;

- Vegetation;

- Culverts and barrages;

- Sheet piling, quay walls and groynes.

Inspection system

In order to carry out an inspection system correctly, the dike should be divided in sections with

lengths as large as possible. The sections should be selected in such a way that they are

relatively uniform with respect to:

• Cross section;

• Subsoil, revetment and loading conditions;

• Use of dike or bank for which such features as: road function, buildings, industry,

recreation, landing stages and so on.

The inspection system should provide information on:

• What (the kind of damage pattern characteristics);

• Where (location and depth);

• When (how often);


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• How (which measuring method) and by whom data should be collected, saved, and

evaluated.

With these data a manager is able to determine the actual condition of the water retaining

structure and to diagnose changes in strength of the dike. After that, if necessary, reduction of

strength can be corrected by maintenance or improvement.

However it is difficult to give a detailed description of an inspection system because it depends

very much on the actual situation. Some remarks will be given as a guideline in the following.

An inspection system is mainly determined by:

• Accuracy of inspection method;

• Frequency of inspections;

• Which difference between initial quality levels (standard) and the action limit, where

maintenance or other measurements are necessary, is acceptable.

Accuracy

Inspection can vary from rough, mostly visual observation, to carrying out special

measurements with, if necessary, special measuring equipment to detect hidden damage.

Carrying out inspections in a quick and cheap way, should always be the aim. Rough inspection

is normally quick and cheap and will often be carried out first for that reason. For dike elements,

where failure has a direct influence on the flood protection, the following phased of inspection

system shall be chosen:

• Rough visual inspection: observation of peculiarities and subsidence of top layers;

• Detailed inspection: periodical measurements, for example cracks in asphalt concrete

layers or bearings along the toe of the dike;

• Special inspection: for example to detect cavities under revetments of asphalt and

concrete layers.

Frequency

Inspections should be performed once or twice a year at fixed points in time. Incidental

inspections should be performed after every hard storm and extreme high water and will

generally start with a rough visual inspection of the total dike length. Inspections also depend on

the age of the dike that have to be inspected and the results of the preceding inspections.


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Measuring the condition of dike elements is often difficult and expensive, that is why these

works are mostly only visually inspected. Behaviour models of these construction elements are

actually not known. Nevertheless more information, based on the grounds of inspection reports,

is possible with regard to:

• Increased knowledge of ageing processes;

• Decision to change over to a more detailed inspection;

• Decision to arrange maintenance;

• Determination of a following inspection.

Periodical measurements are very important to manage and maintain water-retaining

constructions. Measurements give the manager insight into the actual condition of the dike. But

measurements also mean: finding out something for example how the dike is built up. If such

measurements are not carried out there will be a lack of data.

When carrying out measurements, it is of course always necessary to see if the delivered effort

conforms to the intended profit. Practical experience and insight of the manager of the

constructions remains essential for timely maintenance diagnoses.

When choosing an inspection system it is important that the observations can be related to

failure limits (see next table). On the basis of which decisions can be made for taking measures,

like executing maintenance or more detailed inspection.

An example of condition parameters, damage patterns and described failure limits are presented

in the following Table 7.1:

Table 7.1 Condition parameter, damage pattern, failure limits and ultimate failure

Condition

parameter

Damage pattern Failure limits

Ultimate failure

mechanism

slope of foreshore steepened slope along

the toe

no steeper than 1:3 Geotechnical stability

crest height change of crest

height

design height without

calculated

measurements for

settlements

erosion of crest and

inner slope

quality toe

protection

decreasing height of

rip rap covering

max. reduction of

height 0.30 m

erosion


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quality of stake row visual deterioration no rotting erosion of outer slope

strength of stone

revetment

one or several blocks

lifted out or settled

no stones lifted out

and close connections

erosion of outer slope

washed in joints of

concrete columns

washed out joint

materials

more than 1/3 of

stone height is

washed out

erosion of outer slope

quality of grass

revetment

visual lacking of

grass

covering degree

reasonable

erosion

Table 7.2 Damage pattern, inspection and repair measures

Damage pattern Inspection Repair measure

steepened slope bathymetrical survey foreshore

one month before

and after storm season

sand supplement or bottom

protection of foreshore

change of crest height geodetically survey once per

1 to 5 year depending on

last inspection results

heightening of the dike

decreasing height of rip

rap

covering

visual observation of height

reduction

supply of toplayer stones

visual deterioration stake

rows

visual observation of stake

rows, if needed pull a test

pile

replacement of rotten stake

rows

one or several blocks lifted

out or settled

visual observation one

month before and after

storm season and after

every storm surge

replacement of lifted out or

settled blocks

washed out joint materials visual observation one

month before storm surge

refill the joints with proper

material

visual lacking of grass visual observation of grass

revetment during growing

season

adapt grazing, combat

vermin, sow grass seed


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Apart from the damage patterns mentioned before unpredicted damage patterns may also occur.

To detect this last type of damage in time, a rough visual inspection of the total dike length

should be executed two months before the storm season. Every two years after completion of a

dike the cross section geometry of the dike should be surveyed to detect unexpected

deformations of the construction.

7.1.4 Operation of structures

Operation of structures in an urban polder water management system should be based on the

operation rule. The operation rule should be derived by the polder board in coordination with

the municipality and local Public Works authority based on the hydrological condition in one

hand and preferred water level in the polder. Two operation rules can be distinguished, i.e.:

• Normal condition ;

• Extremely wet condition.

Operation rules should be set up in a simple way, and understandable. Any misinterpretation of

the operation rule has to be avoided. If possible the operation rules should not change every day

and if possible may be per week. Only in the extreme conditions, a special operation rules have

to be applied.

Operation will as much as possible have to be determined by the operation rules as outlined in

the design. The planning will include:

• Seasonal plan (wet or dry weather conditions;

• O&M plan;

• Plan for monitoring and demonstration

Gates and pumping stations

Gate and pumping station operators need to keep daily records of the actual gate or pumping

operation. This information needs to be evaluated by the O&M staff in relation to water quality

and quantity in the service area of the gate or pump. This will give an indication of the

effectiveness of the gate or pumping operation, and will support decisions on operation targets if

modifications from the original targets are needed.

Gates

Gate operation is related to the water body which is served by the gate, i.e canal system or


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retention and detention basins. Gates should be operated based on the required water level in the

polder.

Pumps

For actual operation, the pumping facilities should be controlled under imperfect information.

The time during which the pump operates may vary from only a few days annually to more

extended periods of continuous operation. An operation and maintenance manual will be needed

for the pumps and put schematics on one page for the operator’s use.

7.1.5 Maintenance of urban polder systems

The objective of maintenance is to secure a proper functioning of the water management and

flood protection systems and related facilities and equipment. Maintenance can be distinguished

in:

• Routine maintenance;

• Periodic maintenance;

• Emergency maintenance.

Frequent and timely maintenance is of importance for obtaining the benefits of the systems.

Especially in canals, or canal sections with low flow velocities re-growth of weeds may be very

fast, and can quickly reduce the already low flow velocities to practically zero with

consequences for drainage and flushing of the system.

Routine maintenance


regular removal of weeds from canals and embankments, it includes minor repairs and servicing

of O&M equipment and facilities. An overview of the routine maintenance activities is

summarized in Table 7.3.

Table 7.3 Overview of routine maintenance activities

Activity Location Interval *)

(months)

Frequency

(times/year)

Responsible

Clearing debris in front Urban drainage Daily 365 Polder board


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of gates or pumping

stations.

canals

Grass cutting on canal

slopes and

embankments.

Flood protection

embankment

Urban drainage

canals

12

6/12

1

1/2

Polder board

Canal cleaning (aquatic

weeds)

Urban drainage

canals

6/12

1/2

Polder board

Minor repairs and

reshaping of

embankments

Flood protection

embankment

Urban drainage

canals

12

12

1

1

Polder board

Water control

structures:

* greasing

* oiling

* cleaning

* tarring and

painting

All water control

structures

6

6

6

12

2

2

2

1

Polder board

Tarring and painting of

bridges, jetties and

buildings

Various 12 1 Polder board

Minor repairs and

maintenance of

facilities and equipment

• office

• houses

• equipme

nt

12 1 Polder board

Main rivers cleaning Dredging and

flood protection

embankment

12 1 Provincial Public

Works

*) Indicative figures, dependent on specific system conditions

Due to large variations of soil and hydrological conditions in urban polder area, the re-growth


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rate of vegetation on embankments and in the canals may differ widely. Through experience and

monitoring over the years the frequencies of routine maintenance activities may have to be

adjusted to the local conditions.

Routine maintenance activities can be planned and budgeted in advance on the basis of the

estimated labour, cost and required frequencies of the works. Removal of debris in front of gates

or pumping stations, and greasing, oiling and cleaning of structure components for water control

structures in the secondary canals are part of the regular duties of the O&M staff and gate

operators.

Grass cutting

The embankments of the drainage canals require routine maintenance at various intervals.

During each round of maintenance the following activities need to be carried out:

• Slashing or cutting of grasses and weeds on the canal bank, starting from the water line

until the outer foot of the embankment;

• The weeds need to be cut near the base of the stem (0.05 to 0.10 m+surface), using a

sickle, cutlass, slasher, scythe or mechanically. The roots and rhizomes must not be

removed as they provide valuable protection against erosion;

• The weed debris must be collected and disposed off outside the embankment where it

may be burned when safe.

The labour output criterion for grass cutting is estimated at 225 - 450 m2/labour-day depending

on the height and density of the weeds and grasses.

Canal cleaning

During each round of maintenance the following activities need to be carried out:

• Cutting loose and removing floating and submerged plants and algae from the canal bed

and canal side slopes; the weeds must be cut as low as possible near the base of the stem

using a sickle, cutlass, scythe or mechanically;

• The weed debris must be removed from the canal bed by hand or using a rake, and be

deposited and burned behind the embankment;

• Weed clearance in the secondary and tertiary canals can best start at the downstream end,

and proceed in upstream direction. Preferably the maintenance of the canal beds should

be carried out synchronous with the maintenance of the banks;

• Obstructions for the water flow like tree trunks, fishing nets, or temporary checks would

have to be removed to ensure the free flow of water.


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The labour output criterion for canal cleaning is estimated at 165 m2/labour-day.

Minor repair and shaping of embankments

Erosion gullies caused by rainfall, cracks caused by drying out and shrinking of the soil and

potholes made by traffic in embankments will have to be repaired timely because this type of

damage tends to expand rapidly. The dikes and embankments need to be inspected at regular

intervals and each year the following repair activities will have to be carried out:

• Erosion gullies, soil cracks and potholes in the dike have to be cleared of weeds, mud,

debris and other material;

• The holes have to be filled-up and compacted; the top of the soil fill need to be shaped

convex, so that runoff of rainfall is ensured;

• Holes in the embankment, made by rats, crabs or other animals, need to be closed.

Labour output for this type of activity is estimated at 500 m2/labour-day.

Maintenance of structures and buildings

Water control structures need to be cleared from weeds at weekly intervals. Obstructing debris,

hampering operation, is to be removed daily. The structures have to be regularly inspected and

any malfunction is to be reported. It is of importance that repair is being done at short notice.

Moving parts need to be greased every two months. Hinges and groves oiled every two months,

every four months old grease and oil need to be cleaned using diesel.

Once per year, in the dry season, the concrete of the water control structure will have to be

cleaned from dirt and algae. The steel parts need to be cleaned and re-painted. Missing bolts,

nuts and padlocks need to be replaced. Small cracks in concrete walls and stone masonry of the

structure will have to be plastered with concrete mortar.



have to be replaced. The offices and housing of O&M staff need to be tarred, painted and white-

washed.

Major damages to structures and buildings will have to be reported and repaired under the

periodic maintenance program. In case of emergencies immediate repair will have to follow.


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Periodic maintenance

Periodic maintenance, also called incidental or regular maintenance, consists of re-profiling of

canals and repair of embankments, structures, buildings, equipment, etc. These activities need to

be identified and quantified on the basis of yearly inspections and quantity surveys. Although

some periodic maintenance needs can be estimated from the supposed lifetime of water control

structures or facilities, the precise volume and location of the works and which structures or

equipment need to be replaced, will vary from year to year.

Actual siltation may vary largely from place to place, as well as from time to time: the rate of

sedimentation is often highest immediately after construction or modernisation when no

protective vegetation cover has developed yet on the embankments.

Desilting

Desilting of the urban drainage system is required when the depth of the canal becomes too

shallow for drainage and flood protection is impeded. The exact timing for desilting is

determined by yearly measurements of a number of cross-sections at fixed locations.

Primary urban polder drainage canals are too deep for manual re-excavation, and hydraulic

excavators or dredgers have to be used. If the canal is too wide for a long-arm excavator the use

of a pontoon is required including a second excavator for positioning the pontoon. The use of

smaller cutter dredgers in the larger canals has proved to be a feasible alternative in combination

with hydraulic excavators for the shaping of the canal sides and embankments. Special attention

should be given to avoid too deep excavation by the dredger near the sides of the canal since

this may result in severe sliding of the embankments. Based on experience in various projects,

the effective productivity per excavator is estimated at 30 m3/hour, or 150 m3/day. For a

dredger this is about 1500-2000 m3/day.

Secondary urban polder drainage canals can be desilted with machines or by manual labour. The

canals must be cleared of weeds first. For manual excavation, the traditional tools are hoes

(cangkul) and baskets. Productivity of manual excavation is generally between 1 to 2

m3/labour-day, due to the muddy conditions in which the works have to be executed. Efforts

have been made to increase productivity by developing more appropriate tools for manual

excavation, like dredging scoops and specially designed hoes and forks. These are operated


147

from the canal bank, thus avoiding the bother of working in muddy conditions and climbing the

slippery side slope.

When the routine maintenance in tertiary urban drainage canals is properly done, then periodic

maintenance will generally not be required. When routine maintenance will have to be done it

will be generally done manually by the polder board.

Emergency maintenance


collapse of embankment, dikes or water control structures, damage caused by flooding, etc. To

prevent further damage, immediate action will generally be required and other ongoing

maintenance activities may have to be interrupted to make all manpower and equipment

available for the emergency maintenance. This maintenance is also needed in case of minor

damage to structures and surrounding earthworks, which impede the structure operation. For

example the breakdown of moving parts like winches and cables by which gates are opened and

closed. Or sudden collapse of embankments causing flood damage or problems with the pumps,

need to be reported immediately and should not wait for the regular reporting. Urgent repair is

then needed.


be made available within the polder authority budget. While budgets generally will have to be

made available at very short term, generally a provisional allocation will be required, dependent

on the short term need.

Supervision of contract maintenance work

When the work cannot be done by the polder board, it will have to be awarded to professional

contractors, based on contracts of a sufficiently large size. It is recommended to involve to the

extent required O&M field staff in the supervision of activities carried out in their working

areas. Before the start of the works, the contractor will have to submit for approval a detailed

planning and activity schedule, indicating work methods and sequence of activities. The plan

will have to be made in such a way that interference with the water management function of the

drainage canals and water control structures is minimized. After approval by the stakeholders,

the work plans of the contractor should be explained to the supervisory and the O&M staff of


148

the Polder Board. The contractor is not permitted to interfere with the operation of the water

control structures.

The criteria for an acceptable quality of the works have to be specified in the tender documents.

These criteria should be the reference for acceptance of contractors work. During

implementation of the works, the contractor should permanently have a representative available

at the system. They will always have to inform the supervisors in advance about the location of

work implementation.

Effect of design on maintenance costs

Maintenance costs can be kept to a minimum by the careful design of the polder, outlet

structures, and any adjoining amenity area. The judicious planting of shrubs and trees can be

used to guide the public along preferred routes. Grass-cutting costs can be kept to a minimum

(in areas used for formal recreation or where grass is used for scour protection) by keeping the

slopes of embankments and other areas flat enough for machine mowing. Equipment can

operate on slopes of up to 4(H):1(V) but slopes of 6(H):1(V) or flatter are preferred.

7.1.6 Dredging water management systems

In general, dredging is the removal of earth from the bottom of a stream, river, retention basins,

canal or other water body for the purposes of drainage and flushing. In this particular cases,

dredging water management systems mean to improve or to maintain the design profiles of the

water management systems which have been changed due to sedimentation processes. A

significant portion of all dredge materials are deposited either in the water or immediately

adjacent to it, often resulting in problems of water quality. Proper disposal of dredge spoils has

to be considered carefully.

Dredging water management systems shall only be permitted for the following purposes and

only when other alternative are impractical:

• To improve water quality or aquatic habitat;

• To maintain drainage , flushing and improve navigability and water flow;

• To mitigate conditions which could endanger public safety;

• To create or improve public recreational opportunities.


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7.1.7 Planned maintenance and inspection

It is essential that all the polder components are subject to regular inspection and maintenance.

In some circumstances, failure to carry out routine maintenance could result in blockage of the

primary outlets and premature filling of the basin under normal flow conditions, leaving no

storage available for flood control. It is essential that the responsibility for future maintenance

under the polder board should be clearly established. The frequency and requirements for

routine inspection will depend on the type and size of the polder, the local circumstances. The

frequency of inspections and maintenance visits may vary widely and should be reviewed

continually in the light of any problems experienced on site and any long-term changes in

maintenance requirements. A maintenance programme should be drawn up, staff allocated, and

the duties and responsibilities confirmed in writing.

7.2 River basin management and maintenance of water management systems

River basin management will be carried out by the related Balai Sungai.under the Ministry of

Public Works. This activity included the maintenance of the main river systems.

7.2.1 Plan for monitoring and demonstration

Monitoring serves to evaluate the effectiveness of the O&M, to identify any changes or

fluctuations in the natural (soils, rivers, water quality) and man-made (canals, embankments,

structures) conditions, and to collect data for future planning purposes. Aspects to be monitored

include:

• Land use;

• Rainfall;

• River and canal water levels;

• Groundwater depth;

• Actual gate- or pumping operation;

• Maintenance condition of other hydraulic infrastructure.

Each year, before the annual budget preparation, a plan should be made what to monitor, where,

and how often. Besides the data collection program, the monitoring plan should specify the

equipment, materials and budget required, the staff responsible for data collection, and how and


150

by who the data are going to be processed and used.

7.2.2 Planning of maintenance

Planning of maintenance concerns:

• Assessment of maintenance needs for preparation of cost estimates and budget requests;

• Planning of implementation of the works after the budgets been allocated.

To prevent large fluctuations in the required maintenance budget it will be of importance that

the annual costs for the maintenance needs remain more or less the same. The priority ranking

of maintenance works can help to define the final implementation plan. Certain works with low

priority may have to be postponed in favour of newly identified and more urgent activities.

Most routine maintenance works are likely to be carried out by labourers directly employed by

the Polder Board.

7.2.3 Maintenance responsibilities

Responsibilities for the maintenance works of water management and flood protection systems

in the polder will be under the Polder Board. For the main rivers will be under the related Balai

Sungai of the Ministry of Public Works.

7.2.4 Maintenance needs assessment

Maintenance needs have to be assessed prior to the preparation of the annual budgets. Realistic

budgets should be based on actual needs, Need Based Budgets (NBB) approach for pengairan

can also be used for urban polder systems. Based on the general frequencies and needs as shown

in Tables 7.2 and 7.3 the assessment of actual maintenance needs requires the following:

• Updated system inventories, in terms of:

• Length and cross section of canals and embankments;

• Number, type and design dimensions of structures and buildings;

• Number and type of O&M equipment.

These data, together with required frequencies of the work, will form the basis for the routine

maintenance needs;

• Survey of maintenance conditions to determine the periodic maintenance requirements.


151

The surveys include:

• Condition of canals, embankments and structures;

• Amount of sedimentation in canals;

• Condition of facilities and equipment.

Each year cross sections of canals where heavy siltation occurs need to be surveyed to

determine the quantities. Re-excavation or desilting is justified only when the water

management function of the canal is impeded.

The periodic maintenance needs should be assigned a priority ranking:

• High priority: items which, if not carried out, will seriously risk to make proper use of

the infrastructure or equipment impossible;

• Medium priority: items which, if not carried out, will restrict the use of the

infrastructure or equipment optimum use, without making it entirely impossible;

• Low priority: items which could be delayed for another year without serious

consequences.

7.2.5 Coordination with other agencies

Close coordination with the other related agencies is required, in particular with the local

government and municipality staff (Camat, Kepala Desa, Kota Madya, DPU). It is

recommended to have a meeting with all the concerned parties at relevant moments in the year.

Topics to be discussed will depend on the time of the year and besides planning and

implementation of O&M (gate- and pumping station operation, flooding, drought) should also

include maintenance aspects.

7.2.6 Routine maintenance inspection

During their day-to-day work the field staff can observe regularly the condition of primary and

secondary canals, embankments and water control structures. This forms the basis for regular

(preferably monthly) inspection reports on maintenance needs and maintenance implementation.

These reports would preferably have to be entered into the Maintenance Record Book or BCP

(Buku Catatan Pemeliharaan).

In the Record Book a priority ranking may be added, for example: 1 = urgent (proper

functioning of the infrastructure is jeopardized, urgent action is required); 2 = important but not


152

urgent; 3 = less important.

Items which can be repaired by the field staff themselves are not entered in the Record Book.

7.2.7 Environmental monitoring

Monitopring of environmental aspects should also cover different phases of the development,

i.e. pre construction phase, construction phase, post construction phase and the related other

activities which are presented in Table 7.4.

Tabel 7.4. Environmental monitoring of urban polder

Source of impact Environmental monitoring


Unrest and social jealousy of the community

around polder (outside)

Socialisation of the urban polder development

plan periodically during pre construction stage

and the utilisation of manpower from the

community around the polder

Open space is converted into urban polder

retention basin

Trees planting in the polder

Construction phase

Social jealousy, if the local inhabitants were not

involved in the development

Utilisation of the local manpower in the

construction stage

Change in the ecosystem in the upstream and

downstream of the related urban polder

Control of dust and noise to the upstream and

downstream community during the construction

stage

Noise and air pollution to the environment Control the time for construction activities

(noisy dredging equipment) and control of the

construction materials transportation by using a

cover in order to reduce air pollution


Change in the land use pattern from open space

into aquatic (change in the water biota, kind of

planktons and the number of individuals

• Management was done in the urban polder water

management system;

• Management was done periodic four times


153

benthos) per one year or was adapted to the schedule

that will be established later.

Social change in the community's economics

(polder was also used for aquaculture as well as

recreation)

• Management of the urban polder

environment was carried out periodically


Black water pollution to the urban polder water

management system (from the houses that did

not have individual septic tank)

Monitoring of black water that was discharged to

the urban polder water management system

should be done monthly

Grey water pollution (bathed waste water,

washed and kitchen) that was discharged

directly to the urban polder water management

system

Monitoring of grey water that was discharged to

the urban polder water management system

should be done monthly

Pollution from solid waste that entered the urban

polder water management system (because of

the limited solid waste transport facility and its

management)

Monitoring of solid waste that was entered to the

urban polder water management system should

be done monthly

Pollution and the sedimentation from the run-off

which flow to the urban polder water

management system (SS, BOD, COD, coli

form)

Monitoring of sediment and water quality (SS,

BOD, COD, coliform excrement) in the urban

polder water management system should be done

every rainy season

7.2.8 Monitoring of maintenance implementation

Maintenance works can be executed by Polder Authority, contractors or by labourers recruited

directly by the O&M organization. Regular information on progress and quality of maintenance

works is needed to enforce the correct and timely execution of the works. The information also

provides the basis for payments to Polder Authority (in case they do maintenance work for

secondary or primary canals), or to contractors. Monitoring consists of data collection,

processing the data into meaningful information, and reporting the results. Based on the

monitoring and evaluation results, allowing them to evaluate the effectiveness of the O&M and

draw conclusions useful for future O&M planning in the unit.

Performance evaluation


154

Monitoring results will give insight in the functioning of the systems at the different levels.

They will have to be used to identify the best improvement options for a specific system. It is

advisable to annually evaluate the monitoring results and to determine options for improvement.

In this way systems performance will gradually improve.

7.3 Laws and regulations

Laws and regulations which have to be considered in setting up polder authority, operation and

maintenance of urban polder water management systems in Indonesia are as follows:

• Regulation of the Ministry of Public Works No. 63/PRT/1993 River development and its

space boundary conditions.

• Law No. 23 year 1997 management of the environment

Stating that:

- every one has the same right in participating in the management of the environment;

- every one is compulsory to maintain the function of the environment and to protect and

to overcome the damage on the environment;

- stated that society has a equal chance to participate on the environmental management

where environment is a public goods.

• Law No. 22 year 1999 local government

Stated that:

- with the implementation of the decentralization, provincial, kabupaten, city area level

which should manage the need of the local inhabitants based on the society aspiration;

- the right of the local government covers all aspects excluded political foreign affairs,

military defence, juridical, monetary and fiscal, religion;

- the local government covers public works, health, education, agriculture,

communication, industry and trading, investment, environment, land use, cooperation

and man power;

- the tasks of local government and local board of representatives and financed by local

budgeting;

- to develop the city, the local government has to apply the community participation in

order to utilize the stakeholders involvement.


155

Other related laws are:

• Law (Undang undang) No 32 year 2004 Local Government

• Law No 11 year 1974 about water resources.

• Home Affairs Ministry Decree No 12 year 2003 Tasks and responsibility of the irrigation

management service in provincial and district/city level.

• Law (Undang undang) No7 year 2004 Water Resources in Indonesia

• Law (Undang undang ) No 33 year 2004 Financial balance between Central and Local

Government

• Law (Undang undang) No 26 year 2007 Spatial Planning

7.4 Procedures and legalizing permission

The procedure should start with the spatial planning which will cover local and regional level.

The involvement of the government (municipality, province and central level) is presented in

Figure 7.1.

Figure 7.1 Legalization procedure

7.5 Institutions

Polder board is a board who has the following tasks and it is supposed to be sustainable and


156

presented in Figure 7.2:

• Institutional and cost recovery issues of the urban polder system as these require a

professional organization;

• Operation and maintenance of the water management system;

• Flood Control and solid waste management.

Figure 7.2 Sustainable urban polder management system

7.6 Stakeholder participation

It is important that lines of communication and contacts as part of the stakeholder participation

activities can be established during the planning period and maintained thereafter, so that any

problems regarding the operation, maintenance, or use of the detention basin can be brought to

the notice of operational staff quickly and prompt action taken. It is also very important that the

person or team responsible for the design liases closely with and seeks the advice of the staff

that will be responsible for its future operation and maintenance. This should cover questions of

safety, access for personnel and plant, and methods of dealing with blockages and the possible

failure of equipment or power supplies. Inquiries should be made about any problems

experienced with previous installations and the design amended where necessary to devise

improvements. On completion, the works must be handed over formally after ensuring that

operational staff is fully conversant with the installation, have been trained in the operation of

special equipment, and are aware of all maintenance requirements.

Proper cost

recovery system

Strong and good

organization

Good law and

regulations

Integrated water

management appr.

Sustainable Urban Polder Management


157

A Community based flood control program diagram is presented in Figure 7.3.

Figure 7.3. Community based flood control program


158

References

159

References

Albertson, M.L., L.S. Tucker and D.C. Taylor (editors). Treatise on Urban Water Systems,

Colorado State University, USA, 1971

ASCE/EWRI.Standard Guidelines for the Design, Installation, Maintenance and Operation of

Urban Stormwater Systems, USA, 2006

Batjjes, J.A. Short waves. Lecture Notes. IHE. The Netherlands. 1983.

Department of the Army, the Navy and the Air Force. Solid waste management. USA, 1990

Department of Public Works. Guidelines on Spatial Planning Control in Urban Areas. Jakarta,

2006

Butler, D and J.W. Davies. Urban Drainage. Spon Press. London, UK, 2004.

Duivendijk van. Manual on planning of structural approaches to flood management (ICID, New

Delhi, India, 2005

Huis in ‘t Veld, J.C (Ed). The closure of tidal basins. Closing of estuaries, tidal inlets and dike

breaches. Delft University Press. 1984.

James, W., K.N. Irvine, E.A. Mc Bean, R.E. Pitt and S.J. Wright (eds). Contemporary modeling

of urban water systems. Monograph 15. CHI, Guelph, Ontario, Canada, 2006.

Luijendijk, J., E. Schultz and W.A. Segeren. Polders. Development in Hydraulic Engineering.

Elsevier.

Mays, L.W. Urban storm water management tools. McGraw-Hill, London, 2004.

Oki T. and S. Kanae, 2006, Global Hydrological Cycles and World Water Resources, Science,

vol. 313, 1068-1072.

Osman Akan A. and R.J. Houghtalen. Urban hydrology. hydraulics, and urban polder water

quality. Engineering applications and computer modelling. John Wiley & Sons, Inc. New

Jersey, USA. 2003

Shanks, R.L. (chief ed). Pumping station design. Butterworths, UK, 1989

Smedema, L.K., W.F. Vlotman, D.W. Rycroft. Modern land drainage. Planning, design and

management of agricultural drainage systems. A.A. Balkema Publishers, London, UK,

1988

Shaw E.M. Engineering hydrology techniques in practice. Ellis Horwood Limited, Chichester,

UK, 1989

Teatini, P. and G. Gambolati. The impact of climate change, sea storm events and land

subsidence in the Adriatic. The impacts of climate change on the Mediterranean area

conference: Regional scenarios and vulnerability assessment, Venice, December 1999


160

Witteveen+Bos, UNESCO-IHE. Projectvoorstel, Development pilot polder Semarang and

guidelines polder development. The Netherlands, 2007

Witteveen+Bos, UNESCO-IHE. Conceptual design report, Development pilot polder Semarang

and guidelines polder development. The Netherlands, 2008

MASMA Urban Storm Water Management, Laman Web Rasmi Jabatan Pengairan & Saliran

Malaysia, http://www.water.gov.my

UNESCO, Guidelines on Non-structural measures in urban flood management. IHP-V

Technical Documents in Hydrology No. 50, Paris, 2001

Van Aalst, W. (edt.) The closure of tidal basins, closing of estuaries, tidal inlets and dike

breaches, Delft University Press, The Netherlands, 1984.

Van Dijk, M.P. Managing cities in developing countries, the th83eory and practice of urban

management. Edward Elgar, UK, 2006.

Annex 1. Glossary

161

ANNEX I. Glossary

Abbreviation Explanation Commentary

BAKOSURTAN

AL

Badan koordinasi Survey dan

Pemetaan

National agency for survey and

mapping

Bappeda Badan Perencanaan Dearah regional planning agency

BAPPENAS Badan Perencanaan Pembangunan

Nasional

National development planning

agency

BCP Buku Catatan Pemeliharaan Maintenance record book

BoD Basis of Design

BOD Biochemical Oxygen Demand mass concentration of dissolved

oxygen consumed under specified

conditions by the biological

oxidation of organic and/or

inorganic matter in water

BPN Badan Pertanahan Nasional National land agency

BPS Badan Pusat Statistics Central Bureau of Statistics

Calibration experimental determination of the

relationship between the quantity

to be measured and the indication

of the instrument, device or

process which measures it

Coliform

organism

microorganisms found in the

intestinal tract of humans and

animals

COD Chemical oxygen demand

CPT Cone penetration test


162


Data collection process of collection, storage and

processing of data up to data

dissemination, with emphasis on

the type of data, the storage and

transfer facilities and procedures

and the QA/QC routines of the

processed data

DEM Digital elevation map

DPRD Dewan Perwakilan Rakyat Daerah Local representative councils

DPU Dinas Pekerjaan Umum regional Public Works

DGCK Directorate General Cipta Karya Director General of public works

DTK Dinas Tata Kota City planning Service, Ministry of

Public Works

GIS Geographical Information System

GNP Gross national product

HDI Human developmentindex

IMR Infant mortality rate

KLH Kementrian Lingkungan Hidup Ministry of Environmental

LARAP Land Acquisition and Resettlement

Action Plan

Monitoring: continuous or frequent

standardized measurement and

observation of the environment,

often used for warning and control

MSL Mean sea level

NPV Net Present Value

NRCS Natural Resources Conservation

Service

O&M operations and maintenance

Parameter property of water used to

characterise it

Pathogens micro organisms that can cause

disease in other organisms or in

humans, animals, and plants

Annex 1. Glossary

163


PB Polder Board

PBB Pajak Bumi dan Bangunan Land and Building taxes

pH absolute value of the decimal

logarithm of the hydrogen -ion

concentration (activity). Used as

an indicator of acidity (pH<7) or

alkalinity (pH>7)

PMP probable maximum precipitation

PoR Program of requirements

PRL Proyek Reference Level

PSDA Pengelolaan Sumber Daerah Air Regional department of water

resources management

PU Departmen Pekerjaan Umum Indonesian Ministry of Public

Works

PusAir Puslitbang Air water section of research and

development centre

PfW Partners for Water

RUTR Rencana Umum Tata Ruang General spatial land use planning

SNI Standard Nasional Indonesia Indonesian national standard

Stream water flowing continuously or

intermittently along a well-defined

course, as for a river, but generally

on a smaller scale

ToR terms of reference

TSS Total suspended soild

V&W Ministry of Public Works,

Transportation and Water

Management

Dutch Ministery van Verkeer en

Waterstaat

UDPKS Urban Drainage Plan Kali Semarang

VROM Ministry of Housing, Spatial

Planning and the Environment

Dutch Ministery van

Volkshuisvesting, Ruimtelijke

Ordening en Milieubeheer,


164


Wastewater a combination of liquid and water-

carried pollutants from homes,

businesses, industries, or farms; a

mixture of water and dissolved or

suspended solids

Water quality

standards

specific levels of water quality

which, if reached, are expected to

render a body of water suitable for

its designated use

W+B Witteveen+Bos

ANNEX II. Symbols

165

ANNEX II: Symbols


166

Symbols

A = cross sectional area (m2)

B = bed width (m)

BB = berm length (m)

BD = bulk density (gram/cm3 or kg/m3)

cu = undrained shear strength

C = discharge coefficient for a circular pipe = 0.90 (-)

C = runoff coefficient (-)

c = hydraulic resistance of the confined layer (day)

cv = Coefficient of consolidation (m2/s)

cp, cs, = consolidation constants (-)

cp’, cs’, = consolidation constants (-)

cw: = air-water friction coefficient, between 0.0008 to 0.003 (-)

d1 = layer thickness before subsidence (cm)

e = void ratio (-)

Eo = open water evaporation (mm/time step)

Ep = potential evapotranspiration (mm/time step)

Eps = potential evapotranspiration from the root zone (mm/time step)

F = fetch length (m)

Fs = shape factor (of armour stone) (-)

g = gravity acceleration (m/s2)

Gc = pumping capacity (m3/s)

h = water depth (m)

hB = distance between SWL and berm level (m)

Hb = wave height at the breaker line for regular waves (m)

Hd = height of the surrounding dike (m+surface)

Hs = significant wave height (m)

Hs = spectral significant wave height (m)

Ip = Plasticity index of soil (-)

iw = wind induced gradient (-)

Iw = water depth related to preferred polder water level (m)

kB = coefficient for berm width (-)

kh = coefficient for berm level (-)

kh = hydraulic permeability (m/day)

Symbols ______________________________________________________________________________________________________________________

167

ky = hydraulic permeability (m/day)stage index (-)

k = soil hydraulic conductivity (mm/time step)

Kobv = cost of main drains (€/m)

L = wave length on deep water (m)

Lberm = corrected berm length (m)

mv = coefficient of volume change

n = porosity (%)

Ow = open water area (ha)

Owm = area of open water at instant t (m2)

P = precipitation (mm/time step)

Qc = cone resistance

Ru2% = wave run-up (m)

r = annual interest rate (%)

S = annual subsidence (m)

S = wave steepness (-)

S = damage

SP = depth of the water level (m-surface)

tan = slope steepness (-)

T = return period (year)

T = time (day)

T = wave period (s)

tdk = side slope of the surrounding dike embankment (-)

Tgb = horizontal component of the side slope above the water level (-)

Tgo = horizontal component of the side slope below the water level (-)

U = wind speed (at 10 m height) (m/s)

Uw = wind speed (m/s)

V = volume in (cm3)

Vv = volume of the voids (m3)

w = initial water content (-)

wl = liquid limit

wp = plastic limit

W= weight (gram);

x = event

х = berm level factor (-)

y = depth of water in the drain (m)


168

∆t = time step (hours)

€ = Euro currency

αi = damage factor category i

γ = unit weight or weight density

γbr = breaker parameter (-)

γb, γf, = correction factor berm, roughness, oblique wave attack (-)

ξm-1,0 = breaker parameter (-)

Φ = angle of repose

ε = initial porosity (-)

θ = soil moisture content by volume or by weight (%)

θ = moisture (%)

ρ = density (gram/cm3 or kg/m3);

ρa = mass density of air (kg/m3)

ρsolid = particle density (2.65 g/cm3)

ρw = mass density of water (1.00 g/cm3 or 1000 kg/m

3)

ρd = bulk density of a dry clod at -1,500 kPa (pF = 4.18) moisture potential (kg/m3)

ρm = bulk density of a moist clod at -33 kPa (pF = 2.53) moisture potential (kg/m3)

ηmax = maximum set-up (m)

ANNEX III. IDF analysis

169

Annex 3: Gumbell and IDF analysis


170

Return period and Gumbel- Distribution functions

Return period

The Gumbel-analysis is based on yearly maxima. Of every year the maximum rainfall intensity

for certain periods (1 minute up to several days) is taken. All maxima are ranked from low to

high. The return period of all 100 rainfall-maxima is calculated by the following formula

(Benard’s approximation):

4.0

3.01

1

+

−−

=

N

RT

In which:

T=return period of the rainfall event (years);

R= number of ranking;

N=number of maxima.

Fitting of the Gumbel distribution

An extreme value distribution, which is successful in hydrological applications, is the Gumbel

distribution. The standard (cumulative) Gumbel distribution function follows,

))/)(exp(exp()( βα−−−= xxG

whereα and β represent location and scale parameters that are found so that the Gumbel

distribution function fits the given data. This data set =x {X1, X2, X3, …, Xn} of extreme

values are supposed to be independent. )()( XXPxG i <= represents the probability that an

extreme value takes on a value less than a given value X .

The function βα /)( −= xy is called the ‘reduced variate’, such that

))/11ln(ln()))(ln(ln( TxGy −−−=−−= . In here, T is the ‘return period’, which is a

statistical measurement denoting the average recurrence interval over an extended period of

time.


171

In order to fit the data to a particular Gumbel distribution, the two shape parameters α and β

need to be estimated, which can be done by several methods. Linear regression had been used to

estimate these parameters.

Subsequently, the observed extreme values {X1, X2, …, Xn} can be plotted alongside the y-axes

in a graph. In case the reduced variate y and T are put on the horizontal, the Gumbel distribution

becomes a straight line.

Some examples of Gumber distribution curves are given in the following figures.

Gumbel distribution functions


172


173

Bell’s equation is valid for 5 minutes till 120 minutes rainfall duration.

))(ln(10

60 ectbTaRRdT

t −+=

Where:

T

tR : design rainfall t minutes duration with T year return period;

10

60R : design rainfall 60 minutes duration with 10 years return period;

a, b, c, d and e : Bell’s coefficients and they are 0.21, 0.52, 0.54, 0.25 and 0.5 consecutively.

Based on short duration rainfall data from 14 automatic rainfall stations which are spreaded over

Indonesia, the Bill’s equation was re-modifiedin order to get the best approach to the rainfall

characteristics in Indonesia.

In order to apply the Bell equation, one condition should be fulfilled that the availability of the

maximum daily rainfall from the nearest rainfall station should cover at least 20 years data.

Based on these data, averaged annual maximum daily rainfall 1440R and design rainfall with 10

years return period 10

1440R can be determined.

The following Table III.1 shows two different coefficients for 1440R less than 90 mm and

greather than 90 mm.

Table III.1 Modified Bell’s cooefficients

Group a b c d e

1 0.16 0.68 0.52 0.25 0.50

2 0.10 0.47 0.43 0.35 0.49

To determine 10

60R , a simple linear interpolation can be used:

1440

4141.0

1440

10

1440

10

60 )(7113.0 RRRR =

IDF curve is divided into three parts, one part is using the Modified Bell equation (see above) ,

second part for 125-360 minutes rainfall duration and the third one is using the duration of 361-

1440 minutes. These last two equations can be described as followed:


174

For 121-360 minutes rainfall duration:

)1440/()120()( 08.11.1

1201440120 ttRRRRTTTT

t −−−+=

And for 361-1435 minutes rainfall duration:

)1440/()120)(( 3601440360 ttRRRRTTTT

t −−−+=

ANNEX IV. Unsteady flow model

175

ANNEX 4: Unsteady flow model


176

Theoretical background

Unsteady flow in open channels by nature is non-uniform as well as unsteady because of the

free surface. Mathematically, this means that the two flow parameters (i.e. flow velocity and

water depth or discharge and water depth) are functions of both distance along the channel and

time for one-dimensional applications. Problem formulation requires two partial differential

equations representing the continuity and momentum principles in the two unknown dependent

parameters. Unsteady flow can be classified into gradually varied unsteady flow and rapidly

varied unsteady flow. In the first case, the change in depth is gradual; consequently the effect of

streamline curvature is not significant.

Basic equations

Although the governing equations of continuity and momentum (St. Venant equation) can be

derived in a number of ways, in this notes, a control volume of small but finite length , ∆x, that

is reduced to zero length in the limit to obtain the final differential equation. The derivations

make the following assumptions (Yevjevich 1975; Chaudhry 1993):

• the shallow water approximations apply so that vertical accelerations are neglectable,

resulting in a vertical pressure distribution that is hydrostatic; and the depth, y, is small in

comparison with the wave length so that the wave celerity c= √(gy);

• the channel bottom slope is small, so that cos2θin the hydrostatic pressure force formulation

is approximately unity, and since sin θ ≈ tan θ = S0, the channel bed slope, where is the

angle of the channel bed relative to the horizontal plane;

• the channel bed is stable, so that the bed elevations do not change in time.

The flow can be represented as one dimensional with:

• a horizontal water surface across any cross-section such that transverse velocities are

negligible;

• an average boundary shear stress that can be applied to the whole cross-section;

• the frictional bed resistance is the same in unsteady flow as in steady flow, so that the

Manning or Chezy equations can be applied to evaluate the mean boundary shear stress.

Additional simplifying assumptions made subsequently may be true in only certain instances.

The momentum flux correction factor, β, for example, will not be assumed to be unity at first

because it can be significant in river overbank flows.


177

Continuity equation

For the continuity equation, it will be derived from a control volume of height equal to the

depth, y, and length, ∆x. The basic statement of volume conservation through the control

volume is:

Net Volume Out = - Change in Storage in the time interval ∆t.

This can be expressed as:

∂Q/∂x ∆x ∆t - qL ∆x ∆t = - ∆x ∂A/∂t ∆t

Where:

qL : lateral flow rate per unit length of channel (m3/s/m);

A : cross-sectional area of flow (m2);

Figure1. Control volume for derivation of continuity equation

Dividing by ∆x ∆t and taking both the control volume length and the time interval to zero, the

continuity equation becomes:

∂A/∂t + ∂Q/∂x = ql

By substituting dA = Bdy where B = channel top width at the free surface, then the continuity

equation:


178

B∂y/∂t + ∂Q/∂x = ql

Momentum equation

The momentum equation is derived from the forces which are acting on the control volume.

Pressure, gravity, and shear forces are considered, and these forces must balance the time rate of

change of momentum inside the control volume and the net momentum flux out of the control

volume. In the x flow direction, the momentum equation can be written as:

Figure 2. Control volume for derivation of momentum equation

Fpx + Fgx -Fsx = ∂/∂t [∫A ρvxdA] ∆x + ∂/∂x [∫A ρv2xdA] ∆x - ρ ql ∆x vlcos Φ=0

Where:

Fpx = pressure force component in the x direction;

Fgx = gravity force component in x direction;

Fsx = shear force component in the x direction;

ql = lateral flow per unit of length in the flow direction;

vl = velocity of lateral inflow inclined at angle Φ to the x direction.

Expression can be developed for each of the force terms. By assuming a hydrostatic pressure

distribution, the pressure force, Fpx = Fp1 – Fp2, and is given by:


179

Fpx = - ∂/∂x ( γhc A) ∆x = - γA ∂y/∂x ∆x

Where:

hc = vertical distance below the free surface to the centroid of the flow cross-sectional area;

A = cross-sectional area on which the force acts;

A hc = ∫y(x)0 [y(x) – η] b(η ) d η , which represents the first moment of the area about the free

surface;

b = local width of the cross-section at height η from the bottom of the channel.

The gravity force component in the x direction is given by:

Fgx = γ A ∆x S0

Where:

S0 = bed slope = tan θ, which has been used to approximate sin θ for small values of slope.

Finally, the boundary shear force in the x direction can be expressed as:

Fsx = τ0 P ∆x

Where:

τ0 = mean boundary shear stress;

P = boundary wetted perimeter.

On the momentum flux side of the momentum equation, the next convective flux of momentum

out of the control volume can be written as:

∂/∂x [∫A ρv2xdA] ∆x = ∂/∂x [βρv2

A] ∆x

Where:

β = momentum flux correction factor;

v = mean cross-sectional velocity.

The time rate of change of momentum inside the control volume for an incompressible fluid

becomes:


180

∂/∂t [∫A ρvxdA] ∆x = ∂/∂x [βρv2 A] ∆x

∂Q/∂t + ∂/∂x (β Q2/A) + ∂/∂x (ghc A) = gA (S0 – Sf) + qlVl cos Φ

Or in another form in case of the lateral flow is zero :

∂Q/∂t + ∂ β Q v/∂x + gA ∂h/∂x + g |Q|Q/(C2AR) =0

Where:

β = coriolis coefficient (-)

A = cross-sectional area (m2)

B = storage width (m)

C = Chezy resistance coefficient (m0.5/s)

h = water level (m)

R = hydraulic radius = A/P (m)

P = wetted perimeter (m)

1-D Hydrodynamic Models

Among the best-known and widely used 1-dimensional open channel hydrodynamic models are

SOBEK, MIKE-11, DUFLOW and EXTRAN. Hydrodynamic models are recommended for

situations where storage behaviour and other time-dependent effects such as varying tailwater,

are being considered. Steady-state models can give misleading results in such situations.

Solution Methods

At the present time, finite-difference methods form the basis of the most commonly used

procedures for the solution of the equations: the partial differential equations are replaced by the

corresponding finite-difference expressions, and values of flow parameters (stage and flow

velocity) are derived at discrete locations within the channel and at discrete values of time. The

calculation starts from a set of initial conditions specified (for each member of a set of discrete

values of x) at an initial value of time, and solutions (for stage and velocity) are obtained at

discrete values of x at successive values of time – that is, solutions are obtained at discrete

points on an x-t grid, on which the grid spacings are denoted by ∆x (the incremental distance

along the channel) and ∆t (the time increment). It is not necessary that ∆x and ∆t have constant

values over the entire x-t grid, although a constant value is usually specified for the time


181

increment ∆t.

Finite difference methods can be classified as

• explicit methods;

• implicit methods.

In an explicit method, the determination of the flow parameters at a given value of x (position)

and t (time) is carried out without reference to the parameter values at other values of x at the

same value of t – that is, the advancement of the solution through a time step is carried out at

one grid point at a time. An implicit method, on the other hand, involves the setting-up and

solution of a set of simultaneous equations involving the unknown parameter values at all values

of x (together with the boundary conditions) at a given value of time. Some methods incorporate

features of both classes, and hybrid implicit-explicit methods exist.

Numerical Stability

In practice, stability requirements impose upper limits on the spacing (∆x) of values of x and on

the time increment ∆t used in the calculation. The conditions for stability in computation

schemes of the explicit type are generally defined by the relation known as the Courant

Criterion:

∆x/∆t >= v + (gd)0.5

Where:

V: the flow velocity (m/s);

d: flow depth (m);

g: gravitational acceleration (9.8 m/s2).

This relation has the effect of fixing maximum value of the time step ∆t for a given grid spacing

∆x and specified flow conditions. Computation schemes of the implicit type are inherently more

stable than explicit schemes, as a result of the interaction amongst the simultaneous equations

which are solved at each time step in an implicit scheme.

Model calibration

Model calibration consists of adjusting model parameters (e.g. imperviousness, roughness) until

the predicted output agrees with measured observations. The calibration process should be

performed simultaneously for all available storms in order to procedure a robust calibration. In

this instance, the single set calibration parameters will result in less-than-perfect fits for any


182

single storm but better for all storms together and presumably better for further predictions.

During the calibration process, care must be taken to make sure that the physical parameters are

not adjusted outside their reasonable range to achieve a ‘calibration’.

Verification

Verification of the model involves further confirmation, after the process of calibration has been

completed, of the model’s ability to reproduce known prototype behaviour. The prototype data

used in verification of the model should obviously be independent of the data used as the basis

for calibration of the model.

Final DRAFT


Volume 4: Case Study Banger Polder, Semarang

Jakarta, February 2009

Preface

i

Preface


Semarang Project (2007 - 2008). This was one of the projects under the Memorandum of

Understanding between the Indonesian Ministries of Public Works and of Environment and the

Netherlands Ministries of Transport, Public Works and Water Management, and of Spatial

Planning, Housing and Environment. The themes of the guidelines are: general aspects,

institutional aspects, technical aspects, case study Banger Polder Semarang. Support to this

project was given by the program Partners for Water and Rijkswaterstaat.


• Indonesia:




∗ Ir. Moh. Farchan, MSc;

∗ Mr. Suhardjono, Municipal of Semarang Planning Board.


∗ Prof. Dr. Bart Schultz, Rijkswaterstaat

∗ Dr. F.X. Suryadi MSc, UNESCO-IHE



Provincial and Municipal government staff.

Urban polder guidelines, Volume 4:Case Study Banger Polder, Semarang

ii




We hope that the guidelines may contribute to and improved development and management of


Contents

iii

Contents

Preface i

Contents iii

1 Introduction 1

2 The Banger Pilot Polder in Semarang 3

2.1 Historical development of the polder system of Semarang 4

2.2 Selection of Banger Pilot Polder 5

2.3 Land use in the Banger Pilot Polder 6

2.4 Water management and flood protection system of Semarang in the river basin

context 7

2.5 Socio-economic aspects of the Banger Pilot Polder 8

2.6 Policy, legal and institutional aspects of the Banger Pilot Polder 9

2.7 Environmental impacts of developments in the Banger Pilot Polder 9

3 Interaction land use, water management and flood protection in the Banger Pilot Polder11

3.1 Identification of potentials and constraints 11

3.2 Planning framework for the Banger Pilot Polder 11

3.3 Land and water development framework of the Banger Pilot Polder 13

3.4 Spatial planning approach 15

3.5 Water resources aspects of the Banger Pilot Polder 16

3.6 Topographical conditions of the area 26

3.7 Geo-technical aspects of and subsidence in the Banger Pilot Polder 27

3.8 Environmental aspects of the Banger Pilot Polder 33

3.9 Policy, social, economic aspects of the Banger Pilot Polder 36

3.10 Institutional and legal aspects of the Banger Pilot Polder 36

4 Organisation structure for the Banger Pilot Polder 39

4.1 Realisation phase 39

4.1.1 Initiation to establish a Polder Authority 39

4.1.2 Establishment of the Polder Authority 39


iv

4.2 Management phase 39

4.2.1 Organisation of water management and flood protection for the Banger Pilot

Polder 39

4.2.2 Tasks and responsibilities of the Banger Polder Authority 41

4.2.3 Stimulation of stakeholder involvement 42

4.2.4 Organization and working mechanisms 42

4.2.5 Human resources development within the Banger Polder Authority 43

5 Social aspects and human resources development 45


5.1.1 Communication with stakeholders in the Banger Pilot Polder 45

5.1.2 Stakeholder commitment and participation in the Banger Pilot Polder 45


5.2.1 Governance 45

5.2.2 Communication with stakeholders in the Banger Pilot Polder 45

5.2.3 Stakeholder participation in the Banger Pilot Polder 46

5.2.4 Human resources development 50

5.2.5 Social impact assessment 50

6 Financial aspects 63


6.1.1 Cost for construction, operation and maintenance of the water management and

flood protection system for the Banger Pilot Polder 63

6.1.2 Feasibility aspects of Banger Pilot Polder 64


6.2.1 Budget planning and allocation for the Banger Pilot Polder 67

6.2.2 Identification of stakeholders in the Banger Pilot Polder 68

6.2.3 Taxation system and tariff setting for the Banger Pilot Polder 69

7 Legal aspects 71



8 Design aspects of water management and flood protection for the Banger Pilot Polder 73


Contents

v

8.2 Impoldering principles applicable to the Banger Pilot Polder 74

8.3 Polder infrastructure for the Banger Pilot Polder 98

8.4 Landscape and land use planning in the Banger Pilot Polder 113

8.5 Boundary conditions for the design of water management and flood protection for the

Banger Pilot Polder 114

8.6 Design approaches and design standards applicable to the Banger Pilot Polder 123

8.7 Impacts of subsidence and sea level rise on water management and flood protection

for the Banger Pilot Polder 128

8.8 Mitigation measure 128

9 Construction aspects of water management and flood protection for the Banger Pilot

Polder 129

9.1 Dike, outlet and inlet structures 129

9.2 Water management system for the Banger Pilot Polder 134

10 Management, operation and maintenance of the water management and flood protection

system for the Banger Pilot Polder 137

10.1 Operation of the structures 137

10.2 Maintenance of the water management and flood protection system for the Banger

Pilot Polder 138

10.3 Institutions and their responsibilities for operation and maintenance of the water

management and flood protection system for the Banger Pilot Polder 142

10.4 Stakeholder participation in operation and maintenance of the water management

and flood protection system for the Banger Pilot Polder 144

References 145

ANNEXES

I Glossary 147

2 The Banger Pilot Polder in Semarang

1

1 Introduction

An urban polder system consists of several components, which have to be integrated to each

other essentially. The main components are institutional, social, technical (design, operation and

maintenance) and environmental. In this case four volumes of guidelines will be presented, they

are:

• Volume 1: General;

• Volume 2: Institutional aspects;

• Volume 3: Technical aspects;

• Volume 4: Case study: Banger urban polder in Semarang.

Based on Volume 1, 2, 3 and Technical study of Banger polder in Semarang which has been

carried out by Witteveen+Bos this volume was prepared and this volume will discuss about the

case study in Semarang (Banger polder).


2


3


Vision of the Banger Pilot Polder:

• stakeholders active participation;

• on urban flood mitigation.

Mission:

• to increase active participation of the people in order to improve effectivity and

efficiency of the sustainable development of the area;

• to improve the local institutions capability as a basis of stakeholder participation

approach;

• to improve managerial and technical capacity in order to optimise the involvement of the

stakeholders in the development.

The area of the Banger Pilot Polder is presented in Figure 2.1.

Figure 2.1. Area of Banger Pilot Polder


4

All data needs to be collected for the Banger polder area as shown in Figure 2.1, plus an

additional 20 meters outside the boundary of the polder.

2.1 Historical development of the polder system of Semarang

Semarang is presented as a waterfront city, where flooding problems occur due to land

subsidence of the coastal area and (continuing) rise of the sea level. As a consequence of these

phenomena daily flooding occurs and inundation of a few cm do dm on the street is common.

This causes severe disturbance to society and disrupts not only economic development of the

region significantly, but also leads to retreat of companies from these conurbations. These

problems are acute and need utmost attention and to be solved. A schematic figure of an urban

polder is presented in Figure 2.2.

Figure 2.2. Schematic layout of an urban polder

The idea to set up an urban polder system in Semarang as a pilot project is the result of the

cooperation between Indonesian and the Dutch with the following objectives:

• high level exchange of knowledge;

• technology and methodology adaptation from the Netherlands by providing stimulant

activities;

• implementation of Integrated Water Management and Flood Control Model on urban

context.


5

For that purposes, a pilot polder is selected which is Banger area in Semarang.

2.2 Selection of Banger Pilot Polder

The selected Banger Pilot Polder is derived from the major drainage channel/river that traverses

the area: the Banger river. The area is located in the North-Eastern part of Semarang. The pilot

area encloses the Kecamatan Timur (Sub-district East), which is densely populated with

approximately 84,000 inhabitants. The area of the Banger Polder comprises an area of 527 ha.

The area of the Banger Pilot Polder is subdivided into the following administrative units:

Kecamatan (Sub-District), Kelurahan (Sub-sub-District), Rukun Warga (RW), Rukun Tangga

(RT). This subdivision is presented in the currently existing administrative hierarchy in Figure

2.4. A Kecamatan is subdivided into several Kelurahan of which Kecamatan Semarang Timur

has 10. A Kelurahan is the lowest official administrative unit with an official head called Lurah.

Each Kelurahan is subdivided into Rukun Warga or RWs and Rukun Tetangga or group of

several neighbourhoods or RTs. In the Banger Pilot Polder area there are a total of 77 RWs and

568 RTs. A RT is a cohesive group of households, forming one neighbourhood. These

households have a somewhat close relationship which each other. The RT heads fall under the

Lurah, but have no official title. An RW is a group of several RTs together, but is generally of

less importance in the administrative structure. The total number of households in Kecamatan

Semarang Timur, thus in the Banger Pilot Polder area is approximately 17,000. The total

number of RWs and RTs per Kelurahan in Kecamatan Semarang Timur is presented in Table

2.1.

Figure 2.4. Administrative structure of the Banger Pilot Polder area


6

At the outer north side of Kecamatan Semarang Timur, Kelurahan Tanjung Mas, belonging to

the Sub-District Semarang Utara is located. Officially, this Kelurahan is not included in the

Banger Pilot Polder, but depending on technical design options and community interests, parts

of Tanjung Mas could be incorporated.

Table 2.1. Kelurahan, RW and RT subdivision in Kecamatan Semarang Timur (Bappeda, 2005)

No Kelurahan Number of RW Number of RT

1

2

3

4

5

6

7

8

9

10

Kemijen

Rejomulyo

Mlatiharjo

Mlatibaru

Bugangan

Kebon Agung

Sarirejo

Rejosari

Karangturi

Karangtempel

11

7

6

9

7

4

8

15

5

5

77

44

42

64

67

27

50

130

27

40

Moreover, harbour area Tanjung Mas is an important stakeholder, due to its location on the

seacoast border of the polder, which is of high relevance to the possible locations of the polder

dike within Tanjung Mas’ administrative area. Kelurahan Tanjung Mas has been involved from

the start within the Institutional Component of this cooperation project.

2.3 Land use in the Banger Pilot Polder

The official land use map that has been collected is the land use map for year 1993. At south

Banger area, the land use is dominated by settlement. There is only a small area for trading and

service industry, and for industry. While at the north Banger area, the land use is divided by

facility (railway), water pond and empty field. There is no official settlement use in this area.

The updated condition of the land use in the polder area can be seen on the aerial photos.

Settlers have occupied some of the area of railway facility as well. It is because of the increase

of population in Semarang.


7

2.4 Water management and flood protection system of Semarang in the river basin context

Integrated Water Resources Management means that a process which promotes the coordinated

development and management of water, land and related resources, in order to maximise the

resultant economic and social welfare in an equitable manner without compromising the

sustainability of vital ecosystems. In this case Banger polder development within its river basin

should be considered as coordinated management of resources in natural environment (air,

water, land, flora and fauna) based on river basin as a geographical unit, with the objective of

balancing man’s need with necessity of conserving resources to ensure their sustainability. The

development of Banger polder should be in line with the ultimate aim of water resource

management in order to achieve the sustainable use of land and water for the benefit of all users

in the river basin.

Any water resources development project in Indonesia should be based on the Law (Undang

Undang) No. 7 year 2004 about Water Resources. In this law, responsibility and tasks in relation

to utilization, control, coordination and water conservation are described.

More coordination and managements will be needed to cover the following aspects in order to

develop the JRATUNSELUNA river basin in a sustainable way where Banger polder area is

under this river basin area:

• land and water;

• surface water and groundwater;

• the river basin and its adjacent coastal and marine environment;

• upstream and downstream interests.

For policy-making and planning of Banger polder development an integrated approach should

be followed which requires that:

• policies and priorities take water resources implications into account;

• there is cross-sectoral integration in policy development;

• stakeholders are given a voice in water planning and management, with particular

attention to securing the participation of women and the poor;

• water-related decisions made at local and river basin levels are in-line with the

achievements of broader national objectives, and;

• water planning and strategies are integrated into broader social, economic and

environmental goals.


8

2.5 Socio-economic aspects of the Banger Pilot Polder

The Banger polder will protect 84,000 inhabitants, 527 ha and some important stakeholders like

the railway company and the Pertamina Oil Company. Next to that some important enterprises

can be mentioned which domicile in the Polder Area. They shall receive the benefit where their

business shall run properly and do not disturbed by rob (high tide). Related party in this

category, as follows:

Private-owned enterprises

Business activity in form of store and business centre located in polder area that experiences

inundation. Manufacture industry, in particular, inland water users, they mark as party who

bears responsibility for subsidence (penurunan muka tanah) caused by excessive inland water

using habit.

State-Owned Enterprises (BUMN)

PT. Pelindo Indonesia, area office of Tanjung Mas Port

Inundation due to the high tides (Rob) occurs in vicinity of Tanjung Mas Port, in particular in

Jalan Ronggowarsito and Jalan Mpu Tantular where it greatly blockades the flow of goods trade

outside and inside port. Annually, the estimated 6-10 cm of subsidence will make rob (high tide)

become more and more severe. Obviously, it shall disturb port activity, which serves as the

main port and of economic importance for Semarang and other areas in Central Java Province.

Container loading process is likely to be hindered for 2 days and even more. Therefore, do the

goods flow, for instance, export goods (furniture), which come from Jepara, Kudus and Demak

leading to port, must go through a longer road. This is an unproductive and time-consuming

route; the vehicle must go round through toll highway and pass into North artery road in

Western Semarang to avoid rob (high tide). It can be a great benefit to PT Pelindo Indonesia,

Area Office of Tanjung Mas Port in case of rob (high tide) if inundation and flood can be

settled.

PT. Kereta Api Indonesia (PT KAI)

The inundated railway always disturb train schedule and bring loss to passengers and

corporation. Efforts to increase the elevation of railways surely take great cost. Presently, the

4,900 m railways located in Central Drainage, which connect Tawang station with Tanjung Mas


9

Port, have been in constant problem; regularly inundated. Thus, railways are not optimal in use

and it simply concludes that its economic period will last shorter with higher damage potency.

There shall be great benefit to PT. KAI, if flood and rob (high tide) can be settled. PT. KAI has

some valuable assets, which now cannot be explored optimally because they locate in rob (high

tide) areas. Some of them: a number of land (129 ha land in Central Drainage Area), warehouse

and much other various facilities.

PLN, PT. Telkom and PDAM

These BUMN’s have many duct cable that go through various city drainage canal whose

elevation and water surface is much shorter, so it likely disturbs the drainage stream. This is the

result of great mass of wastes and dump hook onto and amassed inside. The similar thing also

happen on PDAM`s water pipes.

2.6 Policy, legal and institutional aspects of the Banger Pilot Polder

To identify all the regulations, laws and related legal aspects which exist in Semarang area in

relation to the setting up and development of a waterfront city or a polder. Next to that the

potential institutions related to the urban polder development in Semarang area have been

studied. Coordination with municipality of Semarang and BAPPEDA is a very important factor

in relation to the spatial planning of Semarang area and the development of Banger urban

polder.

2.7 Environmental impacts of developments in the Banger Pilot Polder

By closing the river mouth, salinity intrusion will be blocked and no brackish water will be in

the Banjir Canal. This impact will influence the ecology of the area..

Ground surface conditions and land subsidence estimation zonation is shown in Figure 2,5 and

potentially inundated areas based on the existing conditions are presented in Table 2.2.


10

Figure2.5 Surface level and land subsidence

Table 2.2. Potentially inundated area

MSL High water spring Design water level

year ha % ha % Ha %

2006 57 11 304 58 357 68

2018 323 61 405 77 444 84

2028 429 81 447 85 489 93

9 cm/year

7 cm/year

5 cm/year

3 Interaction land use, water management and flood protection in the Banger Pilot Polder

11

3 Interaction land use, water management and flood

protection in the Banger Pilot Polder

3.1 Identification of potentials and constraints

Potential

• To develop and reclaim the coastal area of Semarang more in the sea direction. This

development should be done in an integrated way which will accommodate not only urban

development but also port and environmental conditions (flood, coastal

erosion/sedimentation and mangrove ecology);

• To improve the health conditions of the people due to better sanitation system;

• To protect and improve the environment (management of solid waste, cleaning of river

water).

Constraints

• Lack of experience and knowledge on integrated coastal zone management and

development;

• Lack of financial support which will be needed for the development;

• Lack of integrated river basin management and polder management which can play an

important role in order to supply fresh water to the area in relation to the land subsidence

control in the area.

Based on these potentials and constraints it is clear that the Banger pilot polder can be used as a

case study where they can show and teach the local communities how to manage water and

flood by applying and operating a polder system.

3.2 Planning framework for the Banger Pilot Polder

Indonesian cities are generally designed with open drainage systems, in which sewage and

storm water is transported. Maintenance of these systems is often below the required level. In

addition, these systems get clogged with garbage such as plastic things. As a result, rain- and

sewerage water is not drained properly. Besides storage areas (retention basins) are not

sufficiently available, it is also clear that pumping regimes are not geared to the drainage


12

systems. Next to hat, planning in the river basin level is only developed to a limited extent. De-

forestation contributes to large-scale erosion and sedimentation in the river basin system, in

urban areas as well as rural areas. The fast and often uncontrolled enlargement and development

of the cities, water supply for industry as well as for drinking water is not improved as well. In

order to fulfil the demand, the best option would be the use of water from the rivers but water

quality treatment processes have to be provided and it is costly. An easier solution is extraction

of groundwater and this leads to serious soil subsidence and in long term will cause increase of

salinity intrusion in the groundwater system and flood problems.

To overcome these problems, an integrated approach and community participation of all the

related stakeholders should be followed in deriving the planning framework for the Banger pilot

Polder in Semarang.

Land use, spatial planning and land ownership

Mapping data of the land use, spatial planning and the land ownership in the polder area have

been collected from the following sources:

• Regional Planning Board (Bappeda) of Semarang;

• Public Works office (PU) of Semarang;

• Previous study undertaken by Research and Development for Water Resources Centre

(Pusair), Ministry of Public Works;

• Aerial photos (Google Earth);

• Regional Spatial Planning (Rencana Tata Ruang Wilayah (RTRW) Kota Semarang Tahun

2000 -2010, Pemkot Semarang 2004);

• Detail Spatial Planning Semarang City (Rencana Datail Tata Ruang Kota Semarang

Bagian Wilayah Kota (BWK) I (Kec. Semarang Tengah, Kec Semarang Timur, Kec.

Semarang Selatan) Tahun 2000 - 2010, Pemkot Semarang 2004).

Land use which can be specified in:

• housing;

• small businesses;

• industries;

• infrastructure (roads/railways);

• parks/green areas;

• playing and sporting fields;


13

• fishing ponds;

• water (canals).

This land use map is presented in Figure 3.1.

Figure 3.1. Land use map of 1993 with the Banger drainage system

Spatial planning

• existing spatial planning for the polder area of Semarang City (BAPPEDA);

• plans for road reconstructions;

• empty buildings in de polder area;

• landownership;

• ownership of the land within the polder.

3.3 Land and water development framework of the Banger Pilot Polder

In general, land and water development projects have to fit into the development policy of a

country or a region. Land and water development projects may strongly differ in type and scale.


14

This refers to the reclamation and development of new areas, as well as to the improvement of

existing areas. Various development approaches can be followed. Distinction can be made in:

• large scale rapid development;

• small scale gradual development.

Another distinction in approach exists between:

• directly based to the final stage;

• step wise development.

For the different approaches it has to be taken into account that a project will have to follow

various stages, and should include the socio-economic and environmental consequences of the

proposed development.

Banger Pilot Polder can be categorized as a small scale gradual development and also directly

based on the final stage approach.

For the improvement of the Banger Pilot Polder area, the following aspects play a role:

• role of the central government and role of the local government;

• determination of improvement options;

• consultation and communication with the stakeholders;

• establishment of a polder authority and cost recovery;

• land ownership.

In the improvement of the Banger existing areas the government generally plays a guiding role

during the whole process. In the case generally different levels of government will have to co-

operate, with their different responsibilities. In the improvement of existing areas various

options or combinations of these options generally arise, like:

• water management system, roads system, or water transport system;

• re-land use planning;

• institutional setting in relation to the management of the polder;

• operation and maintenance plans.

In Banger Pilot Polder there are no established institutions (Polder Authority) yet as elsewhere

in the country. In order to promote attractiveness of the Banger Pilot Polder and to prevent any

stagnation in management of the area it will be quite important to install as soon as possible the

required Polder Authority in the polder.


15

3.4 Spatial planning approach

The Master plan 2000-2010 will be used where the following land use and functions are

envisaged:

• kelurahan Kemijen and Rejomulyo. The function of this area is trading supported by

particular facilities, residential area and industry. Development towards grocery trading and

warehouses;

• kelurahan Mlatibaru and Mlatiharjo. Dominant function of this area is housing, supported by

trading area and home industry area;

• kelurahan Kebonagung and Bugangan. Dominant land use is trading and services,

residential area and industrial area;

• kelurahan Sarirejo an Rejosari. Land use in this area is trading, services and residential area

supported by home industry. Development towards into non-grocery trading and home

industry;

• kelurahan Karangturi and Karang Tempel. Land use is trading and service with residential

area; development directed to non grocery trading.

The Master Plan is presented in Figure 3.2.

Figure 3.2. Master plan kecamatan TimurBanger area


16

Land ownership

At the south Banger area, most area is private such as private persons and companies. In the

middle of the polder there is an area owned by Pertamina (state owned oil company) for their oil

distribution depot. At the north Banger area, most of the area is owned by PT KAI (state owned

railway company) and PT KAI owned land and is occupied by settlers. See Figure 3.3.

Figure 3.3. Land ownership in Banger area

3.5 Water resources aspects of the Banger Pilot Polder

Several electronic files, which content the existing drainage systems, have been collected from

the local Public Works (Dinas PU) of Semarang. Dinas PU office of Semarang has made of the

existing drainage system in the whole Semarang city including Banger area. This drainage

system has been prepared in the GIS format (ARC view). An AutoCad file has also been

prepared for the drainage system. The drainage system defines the drainage channel consisting

of primary, secondary and tertiary level, and the flow directions. However, this map does not

contain the bottom levels of each channel and the hydraulic structures such as gates, pumps and

culverts. Additional survey needs to be undertaken for further design works. The map of the

existing drainage system in Banger is presented in Figure 3.4.


17

Hydrological boundaries

The southern boundary is Jl. Brigjen. Katamso, instead of Jl. Sompok, because:

• the area (between Jl. Sompok and Jl. Brigjen Katamso) is mainly discharging to Banjir

canal Timur and not to Kali Banger;

• the area south of Jl. Brigjen. Katamso belongs to another sub-district. From an

organisational point of view it is easier not to include this area in the polder;

• this area (between Jl. Sompok and Jl. Brigjen Katamso) is only part of a village

(keluharan) and not including a whole village. From a social point of view, it is better not

to put the boundary within a village.

Although the boundary of the polder is Jl. Brigjen. Katamso, there still can be some leakage

from the southern area through culverts under the road. For this reason, the assumption is made

that 75% of the southern area is discharging to the Kali Banger. The basin area is 0.75*40 ha =

30 ha.

Data collection on the Existing drainage system covers the following:

• primary and secondary channels (grid of 50 m):

∗ dimensions/cross-sections of the channels (width at surface level, talud, bottom

level);

∗ flow direction;

• culverts:

∗ dimensions;

∗ bottom level;

∗ length;

∗ condition (new, middle, need to be repaired);

• gates:

∗ crest level;

∗ possible gate height and gate width;


∗ operation (hours opened, hours closed per day (mean);

• pumps:

∗ type of pump and its capacity;

∗ downstream level (mean) as well as up stream level (mean);


18


∗ operation (hours in use per day);

• bridges:

∗ dimensions of pillars (if any);

∗ height of plate of the bridge.

Figure 3.4. Existing drainage systems in Banger area

Meteorological data:

• existing research on rainfall data;

• data of rainfall per hour for the last 100 years (if possible) in Semarang;

• data of daily evaporation for the last 25 years;

• wind data.

Hydrological data:

• water system of surrounding area: flow directions of channels of surrounding area;

• sea levels:

∗ tides (average and high) and mean sea level;

∗ storm surges, wind (direction, frequency of occurrence, wind force) and wave

conditions.


19

Tidal characteristics

Tidal characteristics are presented in Table 3.1 (Tide Tables (Daftar Pasang Surut, 2006,Dinas

Hidroseanografi) which shows the maximum and minimum water level during spring as well as

neap tides.

Table 3.1. Tidal characteristics

Tidal condition Abbreviation Level (m+MSL)

Lowest low water spring

Mean low water spring

Lowest low water neap

Mean sea level

Highest high water neap

Mean high water spring

Highest high water spring

LLWS

MLWS

LLWN

MSL

HHWN

MHWS

HHWS

-0.50

-0.37

-0.10

0.00

+0.10

+0.38

+0.50

Sea level rise

Due to global warming the sea level may rise. The Intergovernmental Panel on Climatic Change

(IPCC) projects a rise in global sea level of 0.19 m to 0.58 m by the year 2100. The generally

accepted prediction is a sea level rise of 0.20 m in 50 years, or an increase of 4 mm/year.

Storm surges

A storm surge analysis has been carried out. The data for sea level pressures is determined from

NCDC. The data is measured at a weather station on land and consists of daily mean pressure

taken over a period of six years, from 1994 until 1999 and presented in Figure 3.5. This figure

shows the measured sea level pressure at Semarang. The minimum and maximum pressure is

respectively 1,005 mBar and 1,017 mBar. The difference between the minimum and maximum

measured mean sea level pressure is 12 mBar. As a conservative approach the maximum

difference is taken 20 mBar. This difference in sea level pressure is equal to a difference in

water level is 0.20 m.


20

Figure 3.5. Sea level pressure at weather station Semarang (NCDC)

Wind setup

A wind set up analysis has been carried out. Due to different wind speeds the wind setup varies

per chance of occurrence. In this stage the wind setup is rounded up in steps of 0.05 m

representing the recommended values (upper limit values).

Table 3.2. Wind setup for different chance of occurrences

Wind speed

(m/s)

Wind setup

(m)

Chance of

occurrence

(per year) ARGOSS more

extreme

trend

ARGOSS more

extreme

trend

recommended

1/1 13.6 15 0.15 0.19 0.20

1/10 15.3 17 0.19 0.24 0.25

1/100 16.8 20 0.23 0.33 0.35

1/1,000 18.1 22 0.27 0.40 0.40

Internal discharge

The households produce wastewater within the borders of the polder. The source of this water is

groundwater (extracted at great depth) or drinking water, originated outside the polder. An

indication of this additional discharge is:


21

• number of inhabitants within the area: 84,000;

• water use per person: 185 l/day;

• total water use: 15,500 m3

/day, spread throughout the project area.

• Waste water from small and medium industries: 2.600 m3

/day

• Total waste water production is 18,100 m3

/day (= 0.2 m3

/s)

Land area

Table 3.3 shows the different kind land areas in the polder.

Table 3.3. Land use in ha

Housing Water Other Total

Kemijen 42 9 45 96

Rejomulyo 38 0 2 40

Mlatiharjo 46 2 7 55

Mlatibaru 35 2 3 40

Bugangan 34 2 10 46

Kebon Agung 34 0 3 37

Sarirejo 40 0 6 46

Rejosari 55 3 10 68

Karangturi 35 0 1 36

Karang Tempel 56 2 5 63

Total 415 20 92 527

Based on the following assumptions, a distinction can be made between different run-off areas:

• housing: 90% paved, 10% unpaved;

• water: 100% open water;

• others: 60% paved, 40% unpaved.

In Kemijen, a large part of the area is unpaved in the current situation. In future, this area will be

developed to container terminals and other transport facilities. For this area also the assumption

is made that 60% will paved and 40% is paved. Table 3.4 presents the different run-off areas.


22

Table 3.4. Paved, unpaved and open water areas in ha

Paved Unpaved Open water Total

Kemijen 64 23 9 96

Rejomulyo 35 5 0 40


Mlatibaru 33 5 2 40

Bugangan 37 7 2 46


Sarirejo 40 6 0 46

Rejosari 56 10 3 68



Total project area 428 79 20 527

Wind set up

The wind setup for the pilot polder Semarang is based on ARGOSS data and the storm surge on

data from NCDC. Table 3.5 shows the recommended values for wind setup and storm surge for

different chances of occurrence. Wind setup only occurs when water is trapped, so the area has

to be:

• enclosed;

• relatively shallow so the return flow is limited.

In Figure 3.6 two options are drawn for a shallow water enclosed bay. In this case the

calculation of the wind setup the continuous line is used as border for the domain; at the line the

water is deeper, but the fetch is longer (33 km), resulting in a higher wind setup.

Table 3.5. Wind setup based on ARGOSS data

Recommended Chance of occurrence

(per year) Wind setup

(m)

Storm surge

(m)

1/1 0.20 0.20

1/10 0.25 0.20

1/100 0.35 0.20


23

1/1,000 0.40 0.20

Figure 3.6. Possible enclosed bays with fetch length (Google Earth Pro)

Meteorological data

Rainfall

Table 3.6 presents the rainfall for several duration times and chance of occurrences. These

rainfall figures is calculated with a Gumbel-distribution function (maxima per year), based on

the rainfall data of 1959-1966, 1976, 1978-2006 of Semarang Automatic Rainfall Gauging

Station (96835). In Volume 3: Technical Aspects, the principle of Gumbel-distribution function

and the Gumbel-distribution functions for the different duration times are also presented.

The Gumbel analysis is compared with the previous study, carried out by PU, see Table 3.7. It is

very clear that the previous study and the present study (Gumbel) analyses give similar results.

Table 3.6. Rainfall (mm)

MIN. Hours T2 T5 T10 T25 T50

10 24 29 34 41 46

15 32 39 47 58 65

30 50 63 69 76 82

60

1 71 88 94 102 108


24

2 87 106 129 158 180

3 92 112 138 170 193

6 103 135 159 191 214

12 114 168 192 222 245

24 116 180 207 241 266

Table 3.7. Differences Gumbel distribution and previous study (mm/day) for 24 hours

Chance of occurrence (per year) Previous study Present study: Gumbel

1/2 120 116

1/5 175 180

1/25 225 241

Table 3.8 presents the statistical analysis of the rainfall for Semarang data based on the rainfall

data of 1977 - 2007.

Table 3.8 Average, maximum and minimum monthly rainfall for Semarang (1977 – 2007)

Rainfall

Semarang

1977 - 2007 Maximum daily

rainfall (mm)

average monthly

rainfall (mm)

mimum monthly

rainfall (mm)

wet season December 253 306 106

Januari 276 399 145

Februari 252 329 82

March 192 241 72

transition April 117 197 38

May 141 156 26

dry season June 88 97 0

July 93 61 0

August 77 58 0

September 130 90 0

October 110 152 0

transition November 150 231 102

Yearly

average

2317


25

Evaporation

Table 3.9 presents the monthly average evaporation. The evaporation is average of the monthly

evaporation of 1987-2006, based on the Semarang Station data (96835). In Table 3.9 monthly

precipitation is also completed with the monthly water balance conditions (surplus or shortage).

Table 3.9. Monthly evaporation

Month Evaporation

(mm/day)

January 3.60

February 3.75

March 3.98

April 4.17

May 4.17

June 4.18

July 4.88

August 5.45

September 5.95

October 5.57

November 4.52

December 3.82

Climate change

The Intergovernmental Panel on Climate Change (IPCC) has been established by WMO and

UNEP to assess scientific, technical and socio- economic information relevant for the

understanding of climate change, its potential impacts and options for adaptation and mitigation.

Temperature

The temperature in Indonesia will increase, although the amount of warming is projected to be

less than the global average, because of the proximity to the sea. Table 3.10 shows the predicted

warming in Indonesia.

Table 3.10. Temperature change in Indonesia (°C, A=Annual, W=Winter, S=Summer)


26

2020 2050 2080 Topic

A W S A W S A W S

Warming 1.05 1.12 1.01 2.15 2.28 2.01 3.03 3.23 2.82

3.6 Topographical conditions of the area

Data collection

Topographical data have been collected from several sources as follows:

• digital data of surface level with a grid of 50 m for the polder, measured within the last 3

years, with a good landmark (no subsidence of the landmark);

• digital data of surface level with a grid of 150 m outside the polder: Boundaries of the

polder area:

∗ east side: Banjir canal Timur;

∗ north side: 300 m;

∗ west side: Jalan Empu Tantular, Jalan Merak, Kali Baru, Jalan Ki Mangunsarkoro,

Jalan Erlangga Timur;

∗ south side, Jalan Sriwijaya;

∗ several electronic files have been collected from the Public Works of Semarang

(DPU, 2006). The existing map of surface level (digital terrain model) in Semarang

was prepared in 2000 by Indra Karya as the Consultant for the Semarang Drainage

master plan. This model is defined by spot height points and contour lines. In the

pilot polder area, the surface spot height points are quite densely located.

The maps of surface level in the pilot polder area can be seen in Figure 3.7. The northern part of

the area (North of Jl. Citarum) is partly below MSL level. The surface level is between –0.8

m+MSL and +0.6 m+MSL. In the middle part (between Jl. Kartini and J. Citarum), the surface

level is above MSL: MSL 0 up to +1.6 m+MSL. The south (south of Jl. Kartini) is relatively

high, 1.6 up to +6.1 m+MSL.

The obtained data could not be correct anymore due to two reasons:

• land subsidence;

• settlement of the landmark, used for the survey.

To check if the surface level data are correct, an additional survey has to be carried out


27

Figure 3.7. Topographical conditions of the area

3.7 Geo-technical aspects of and subsidence in the Banger Pilot Polder

The northern part of Semarang City consists of natural low land, which widens from west to

east. The width is 4 km in the west, 7 km in the central part and 12 km in the east. The land

consists of alluvial deposits from breaches and rivers. This soil consists of clay, sand, silt and

gravel. The Banger polder is part of this alluvial area. The mid-central part of Semarang City

(south of the Banger polder) consist of the Damar Formation. This formation consists of

sedimentary rock, volcanic rock, lava flow rock, intrusion rock and also pyroclastic rock.

Geohydrological and geotechnical data

• soil type of surface and deeper laying layers;

• groundwater table of aquifers and phreatic groundwater (data of last 5 years);

• current groundwater extraction in Semarang;


28

• geotechnical data needed for construction of dikes.

Table 3.11 Geotechnical conditions and soil types

Soil profile, stratification of the subsoil and soil parameters are presented in Table 3.12

Table 3.12. Soil profile

Depth (m)

from to

Description

0

25

> 75

25

75

soft marine clay; the Standard Penetration Test (SPT) blow counts vary

between 3 to 10 blows/m.

medium stiff to stiff clay; the SPT blow count more ore less increases with

depth from about 30 blows/ft to 80 blows/m

hard sandy silt/siltstone layer

Geohydrology of Banger Polder

The geohydrology of the Banger Polder is presented in Figure 3.8. The top layer consists of

alluvial deposits of clay, sand and silt. The thickness of this layer is 65 m. The groundwater

level ranges from 2 m-surface level at the northern area to 4 m, south of the project area. Below

this layer, two aquifers are present:

• delta Garang Deposits Aquifer. This is the upper aquifer, consisting of volcanic breccia,

at a depth of 65 m-surface level. The thickness is 10 m. The transmissibility of the aquifer

is 20 – 1000 m2/day. This aquifer used to be artesian, but due to groundwater extraction,

the hydraulic head is lowered to below sea level and still is lowering. The hydraulic head

Depth

(m)

from to

Name Liquid

limit

(%)

Plastic

limit

(%)

Plasticity

index

(%)

Natural water

content

(%)

Void

ratio

0

25

>75

25

75

Very soft clay

Very stiff silty

clay

Very hard

sandy silt

80 -120

80 – 110

-

30 – 40

30 – 40

-

40 – 90

40 – 80

-

40 – 80

30 – 50

-

1 - 2

1 - 1.5

-


29

has lowered from 5 m-surface level in 1980 to 17 to 25 m-surface level;

• coast quaternary deposits Aquifer. This is the second, lower aquifer, with a depth of 85 m

below surface level. The thickness is 10 m. The transmissibility of the aquifer is 100 –

500 m2/day. The hydraulic head is 13 to 25m-surface level.

Groundwater extraction

The groundwater extraction is started in 1842 in Fort Wilhelm I (now known as Pelabuhan

Tanjung Mas). In the year 2000 the total registered deep wells are 1029 units with the total

volume of 39 million m3/year (Siswanto and Susilo, 2000). The increasing in the number of

wells is 14% per year, but in the increase in volume is almost 34% per year. Groundwater

discharges by deep wells in Semarang area are presented in Table 3.13.

The location of the wells is presented in Figure 3.9. The groundwater extraction may cause up

coning of enclosed seawater at greater depth.

Figure 3.8. Geohydrology of the Banger Polder


30

Figure 3.9. Location of wells

Table 3.13. Groundwater discharge by deep well

Groundwater extraction Year Number of

wells M3/day/well M

3/day M

3/year

1900 16 73.1 1,170 427,050

1910 18 72.8 1,310 478,150

1920 18 77.8 1,400 511,000

1932 28 57.5 1,610 587,650

1982 127 295.0 37,460 13,672,900

1985 150 293.8 44,064 16,083,360

1990 260 236.8 61,570 22,473,050

1995 316 234.6 74,130 27,057,450

1996 659 122.3 80,594 29,416,810

1997 745 129.9 96,798 35,331,270

1998 776 127.6 98,998 36,134,270

1999 1060 103.3 109,531 39,978,815

2000 1029 104.3 107,369 39,189,685

Groundwater extraction is located in industrial, office and housing area. The upper layer is for

raw water for PDAM (water supply) and is used for private drinking water. The second, deeper

layer is used for extraction of industries. Because the groundwater extraction is more than the

recharge, the hydraulic head of the aquifers is lowering.


31

Groundwater conservation

Siswanto and Susilo (2000) divide Semarang conservation based on following criteria:

• total extracting groundwater volume;

• maximum groundwater lowering (Depth and rate of lowering);

• maximum groundwater quality degradation;

• negative impact to the environment.

Based on above criteria, Semarang divided into 6 conservation zones (Figure 3.10):

• zone 1: critical zone, the zone located in the shore side covered by alluvium deposits and

divide by piezometric contour with elevation 20 m-surface level. The land subsidence

also happens in this area rapidly. Groundwater level in this area 22 – 30 m and the depth

of the aquifer is 30 – 150 m. The extraction from the aquifer is limited to 100 m3/day. The

Banger Polder lies in this critical zone;

• zone 2: dangerous zone, the zone located near shore area covered by alluvium suspension

and divide by piezometric contour with elevation 10 to 20 m-surface level. This zone is a

buffer area for the critical zone. The depth of the aquifer in this area is 30 – 90 m-surface

level and extraction of groundwater from the aquifer is limited to 60 m3/day;

• zone 3: safe zone 1, the zone located near shore area that covered by alluvium suspension

and the valley that covered by volcanic rocks from Damar formation, with piezometric

contour less than 10 m-surface level. Groundwater extraction for industrial use is still

permitted with condition that the extraction is in the aquifer deeper than 30 m with

maximum discharge of 150 m3/day;

• zone 4: safe zone 2, the zone is located in hilly area consisting of old volcanic rocks from

Damar formation with breccias suspension from mount Ungaran. The groundwater level

ranges from 15 to 51 m-surface level. The productive aquifer has a depth of more than 60

m. Groundwater extraction for industrial uses is still allowed, if extracted of aquifer

deeper than 60 m and with a maximum discharge of 200 m3/day;

• zone 5: safe zone 3 (V), the zone located in the valley of mount Ungaran covered by old

volcanic rocks and young volcanic rocks which created by mount Ungaran which is

Andesit and Bassalt lava, breccias and cold magma. The confined groundwater level is 1

to 27 m-surface level. The aquifer depth is 20 – 80 m-surface level. The zone is

functioning as recharge area;

• zone 6: safe zone 4 (VI), the zone located in the centre and southeast Semarang, placed in

hilly area, covered by tertiary sediment rocks, clay rocks, Napal, sandstones,


32

conglomerates, breccias and limestones. Saline water is found in some wells in this area.

Figure 3.10. Zones groundwater conservation

Land subsidence

It is well known that the land subsidence is occurred at northern part of Semarang City. Some

studies have been carried out in the past. Many investigations into the groundwater systems

have been carried out with different objectives but excessive groundwater abstraction has been

identified as the primary cause of the land subsidence. Data collection covers the following:

• existing research on land subsidence;

• surface levels of the last 50 years (if existing);

• groundwater extraction of the last 50 years.

This guideline describes and compares the results of some studies and reports the predictions for

the land subsidence for the future. Data and maps have been collected from the following

sources:

• benchmark measurement by JICA, 1997 and benchmark measurement by SUDMP, 2000;

• Semarang Urban drainage Master plan Project, Volume 2, by PT. Indah Karya, 2000;

• pengkajian Banjir dan system drainase dan efek penurunan air tanah kota Semarang, by

PU, 2001;

• pengukuran elevasi bollard-B dan bollard-T pada kawasan PT.Sriboga Raturaya

pelabuhan Tanjung Emas dengan TTG-449 Srondol Semarang’, by Politeknik Negeri

Semarang, 2005;


33

• monitoring Land Subsidence in Semarang, Indonesia, by Muh. Aris Marfai – Lorenz

King, Journal of Environmental Geology, Springer Berlin / Heidelberg.

The rate of land subsidence ranges from 5 cm/year in the south to 9 cm/year in the northern

area. The land subsidence is mainly caused by the groundwater extraction.

As a summary, the prediction of subsidence rate at Banger area is presented in Figure 3.11

(Witteveen+Bos, 2007).

Figure 3.11. Prediction of land subsidence rate in Banger area

Land subsidence due to lowering of groundwater will continue if over capacity extraction of

groundwater keeps continue. It has to be a control and limitation of groundwater extraction for

industrial or residential purposes, which required full attention from the government.

3.8 Environmental aspects of the Banger Pilot Polder

Data collection of environmental aspects covers the existing sanitation facilities and garbage

system.

• sanitation:


34

∗ location and type of sanitation systems (e.g. septic tank);

∗ number of users per sanitation system;

∗ maintenance and age of the sanitation system;

∗ satisfaction of the users.

• occurrence of water related diseases, its sources and water quality (nutrients, heavy

metals)

Solid waste

The domestic solid waste is collected in a garbage bin at each house holding. Then, the assigned

personnel pick the solid waste up and bring it to the nearest temporary solid waste collector. At

this point, solid waste will be loaded into the trucks and brought to the final dumping place at

Jatibarang at Mijen district. The volume of solid waste is estimated at 175 m3/day.

This project indicates that the inhabitants are aware of the solid waste problems (health and

environment) and are willing to contribute or to pay for solid waste collection system.

Seawater intrusion

Seawater intrusion is caused by over-exploitation of aquifers. Freshwater that contaminated with

5% seawater can no longer be used for common purposes such as drinking water, agriculture

and farming. Figure 3.12 where interface fresh water and saline groundwater, without

groundwater extraction is shown.

Figure 3.12. Up coning saline groundwater without groundwater extraction

Up coning saline groundwater, due to groundwater extraction is presented in Figure 3.13.


35

Figure 3.13. Up coning saline groundwater with groundwater extraction

Ecology

To improve water quality and for aesthetic (social) reasons, it is possible to realise a more

ecological river, with a green zone along the river with (water) plants and trees, or perhaps a

park or recreational area. This green zone also can act as retention (zonation system). During the

public hearings, several residents indicated to want a more green river. A risk of a more green,

ecological profile of the river is that this green area might be used for settlement in future or as

garbage location, so this is a point of attention.

Fishponds

The fishing and selling of the Bandeng-fish is an important source of income of the fishermen.

The habitat of the Bandeng fish is brackish water. In the polder concept, the water will change

from brackish to fresh water. This will decrease the population of the Bandeng fish or even can

make this species disappear. In the conceptual design an assessment will be made between:

• change to fishing and selling of fresh water fish;

• inlet of seawater in the ponds.

To prevent algae over growth, the water management system must have a flushing capacity and

has to be implemented.


36

3.9 Policy, social, economic aspects of the Banger Pilot Polder

Data on social and economy cover the following:

• socio-demographic data (income, profession, housing situation, transport means, social

habits and behaviour, etc);

• per area/district/neighbourhood: list of relevant stakeholders, main local leaders, local

representatives, etc.

• social cohesion within the polder and willingness to pay;

• existing social problems related to flooding;

• inhabitants:

∗ mean income per household per community;

∗ value of assets;

∗ ability to pay per community.

• industries:

∗ profit;

∗ number of employees;

∗ value of assets and ability to pay.

• small business:

∗ profit;

∗ number of employees;

∗ value of assets and ability to pay.

• water: importance for income (e.g. fishing ponds, vegetable gardens).

3.10 Institutional and legal aspects of the Banger Pilot Polder

The main legislation is the Major Decree of Semarang No. 050.05/A.0257/2007. In this decree it

stated clearly all the legislations, which were used as the basis of this decree. This decree stated

clearly the setting up of the Execution Team of Banger Polder in Semarang, which composes of

Steering Committee and Project Implementation Unit (PIU). The composition of the PIU and

their institutions are presented in Table 3.14

Table 3.14. Composition of the executing team and PIU for Banger polder

Name Position in the incoming institution Position in the team


37

H. Sukawi Sutarip,

SH, SE

Major of Semarang Chairman of the steering

committee

Drs. Soemarmo HS,

MSi

Secretary of Semarang city Secreatry of the steering

committee

Drs. Hadi Purwono Head of BAPPEDA Semarang Member of Steering Committee

H. Achmad

Kadarisman, ST,

MM

Head of DPU Semarang Member of Steering Committee

(O&M, DED)

Drs. Suseno, MM Head of DPKD Semarang Member of Steering Committee

(Financial)

Nurjanah, SH Head of Law Division,

Municipality Secretariat of

Semarang

Member of Steering Committee

(Organization & Legislation)

Farchan, ST. MM Head of PPIII Division, BAPPEDA

Semarang

Chairman of PIU team

Ir. Suhardjono,

M.Eng

Head of Sub-division

KIMPRASWIL, BAPPEDA

Semarang

Secretary of PIU

Nik Sutiyani, ST,

MT

Head of sub-division Mining and

Energy, BAPPEDA Semarang

Member of PIU team (O&M)

Kumbino, ST Head of Drainage Section, DPU

Semarang

Member of PIU team (O&M)

Heni Arustiati, SE,

MM

Staff DPKD, City of Semarang Member of PIU team (Financial)

Sutanto, SH Staff of Legislation Section,

Municipality Secretariat of

Semarang

Member of PIU team

(Organization and Legislation)

Firdaus Setyawan Kecamatan Semarang East Member of PIU team

(Organization)

Drs. Bambang

Purnomo, Aht

Kecamatan Semarang North Member of PIU team

(Organization)

Ir. Fauzi, MT Head of Sub Service on Water

Resources, DPU Semarang

Member of PIU team (DED

Technical setting)

Nurkholis, ST, MT Head of Sub Service on Areal Member of PIU team (DED


38

Development, BAPPEDA

Semarang

Technical setting)

Ir. Sugeng Yusianto,

MT

Staff of BAPPEDA Semarang Member of PIU team (DED

Technical setting)

Hardono, ST Staff DPU Semarang Member of PIU team (DED

Technical setting)

Dwi Supriyadi, ST Staff DPU Semarang Member of PIU team (DED

Technical setting)

The tasks of the steering committee and PIU are as presented in Table 3.15.

Table 3.15. Task of the steering committee and PIU

Team Task

Steering

Committee

• to set up policy for planning and execution of the Banger Polder System;

• to guide the execution of the PIU team;

• to facilitate the cooperation between PIU and the related parties;

• to supervise and control of the PIU works.

PIU • to prepare the institutional setting of the Banger Polder Authority in

Semarang in cooperation with the Banger society and inhabitants together

with HHSK;

• to prepare detail engineering design of Banger Polder System in

cooperation with Banger polder society and inhabitants and also with

Witteveen+Bos consultant;

• to consult, coordinate and socialize all the activities related to the Banger

Polder System with the related parties;

• to prepare report of the execution of the Banger Polder System and the

related activities and report it to the Major of Semarang

Next to that, Law (Undang undang) No.7 year 2004 about Water Resources has to be

considered and used as the foundation for the development of water resources in

Indonesia.

4 Organisation structure for the Banger Pilot Polder

39


4.1 Realisation phase

4.1.1 Initiation to establish a polder authority

To initiate the management of a pilot polder of Banger (PPB) a temporary board has been set up

which consist of persons from different background.

PPB has regular meeting with the municipality of Semarang, BAPPEDA and public hearings

with other related parties in the development of Banger polder.

4.1.2 Establishment of the Polder Authority

The establishment of the polder authority is still under discussion. A close coordination and

cooperation with Semarang municipality has to be maintained. The polder authority should not

have the same level with the municipality.

4.2 Management phase

4.2.1 Organisation of water management and flood protection for the Banger Pilot Polder

The objective of the polder organization is to operate and maintain the entire Banger polder

infrastructure, so that the function of water management system can be properly operated and

appropriately maintained. This will cover the following:

• Operation and maintenance of water management system;

• Institutional/Administrative, Financing and Funding Affairs Management for polder

activity, as generally required and in act and capacity as professional organization.

• Flood Controlling and solid waste management.

For that purpose, two different organizations will be needed:

• Polder Board:

• Polder Authority.


40

Temporary Polder Authority

Currently, within the scope of work of the Institutional Component a temporary Polder

Authority (PA) has been established and is active under the community founded organizations;

Sub-System North and Sub-System South, consisting of several Kelurahan as presented in Table

4.1. At present Sub-System North is most active, as daily flooding due to tidal influence as well

as flooding during periods of rain seriously affects their area. Overall, Sub-System South is only

affected during extreme rainfall and/or long periods of rain.

Table 4.1. Kelurahan membership in North and South Sub-Systems of the PA

Sub-system north Sub-system south

Kemijen

Rejomulyo

Tanjung Mas

Mlatiharjo

Mlatibaru

Bugangan

Kebon Agung

Sarirejo

Rejosari

Karangturi

Karang Tempel

Inhabitants

The number of households, inhabitants and the population density per village (kelurahan) in

Kecamatan Semarang Timur are presented in Table 4.2. For reference, the data for Kelurahan

Tanjung Mas in Kecamatan Semarang Utara is also included.

Table 4.2. Number of inhabitants of Kecamatan Semarang Timur (Bappeda, 2005)

Kelurahan Total number

of

households

Total number

of

inhabitants

Total area

surface

(km2)

Population

density

(people/km2)

Kemijen

Rejomulyo

Mlatiharjo Mlatibaru

Bugangan Kebon Agung

3,382

1,003

1,548

2,087

13,362

4,357

6,061

9,447

0.96

0.40

0.55

0.40

13,919

10,893

11,020

23,618


41

Sarirejo

Rejosari Karangturi

Karangtempel

2,342

1,224

2,603

4,659

904

1,408

9,354

4,821

10,228

17,758

3,642

4,633

0.46

0.37

0.46

0.68

0.36

0.63

20,335

13,030

22,235

26,115

10,117

7,354

Total 21,160 83,663 5.27 15,875

Kecamatan Semarang Utara

Kelurahan

Tanjung Mas

RW (16) and RT (125)

6,178 29,343 3,33 8,812

4.2.2 Tasks and responsibilities of the Banger Polder Authority

As discussed in the previous part, two different organizations will be involved, i.e. Polder Board

and Polder Authority.

Polder Board

• to define general policy;

• supervision all the related activities in the polder;

• to select the chairman and executing staffs the Polder Authority;

• to define and to legalize all the regulations related to the Polder Authority.

Polder Authority

• to do the flood defence and protection: protection against flooding from the sea, rivers

and surrounding areas (dike management);

• to do water quantity management: managing the amount of water and ensuring that it is

kept at the right level, which includes drainage, flushing and irrigation (if any)(Water

level regulation (operating pumps on/off, dredging));

• to do water quality management by starting to set up solid waste management (in

cooperation with Municipality) and cleaning of the water management systems from its

wastes (and also sanitation should be mentioned as next step to be taken)


42

4.2.3 Stimulation of stakeholder involvement

Stimulation programme in the Pilot Polder Banger in the mean time is in relation to the solid

waste management processing and recycling in the polder area. All the required machens have

been purchased and coordination with the municipality of Semarang has still to be done in order

to find a proper location for the stimulation activities.

4.2.4 Organization and working mechanisms

The organization of the Polder Authority structure should have a link with the Municipality of

Semarang as well as Provincial and Central Government, which is presented in Figure 4.1.

Figure 4.1. Administration structure of Polder Authority

The organization of the Polder Authority is presented in Figure 4.2, which can be divided into

two different parts, i.e. Polder Board and Polder Authority.

Besides delivering attention on election system as to put member in organization, capacity

building, skilled people, aptness and human resources competence is absolute requirement. It is

anticipated by the presence of improved human resources selection system, it can lead

organization into betterment and progress.


43

Figure 4.2. Polder Authority organization

4.2.5 Human resources development within the Banger Polder Authority

Capacity analysis of polder management organization can be done in 3 approaches, i.e.:

• classic;

• financial competence;

• performance.

Further, to measure Polder Authority performance and capacity, it can be done through checklist

study. When one organization meets 7 variables, there will be KSM obviously, for instance,

KSM of Class A, Behaviour and C.

Regularly, forum aimed at community-care for flood will be held whose membership consists of

entrepreneur, civil servant, university, Research Centre for Water resources Development (for

water related problems) and various dependable related parties as to offer suitable input for

development of polder management organization into improvement.

To improve and maintain the technical and non-technical skills of the Polder Authority

conducting training programmes for the staff will be needed.


44

5 Social aspects and human resources development

45



5.1.1 Communication with stakeholders in the Banger Pilot Polder

Communication with stakeholders will be done by public hearing as well as regular meeting

with the polder authority and all the related parties. The communication is hardly needed

especially related to the operation and maintenance of the Pilot Polder Banger.

5.1.2 Stakeholder commitment and participation in the Banger Pilot Polder

The commitment and participation of the stakeholders are reflected by participating in the fee

system which is related to the operation and maintenance of the urban polder system and also

actively participating in the public hearing as well as regular meeting with the polder authority.


5.2.1 Governance

The Polder Board should recognize the importance of good corporate governance as

implanting the good governance system increases the services and ensures sustained

development of the polder while enhancing confidence in the authority among its

stakeholders. The Polder Board always adheres to good corporate governance principles as

well as strictly complying with laws and regulations related to the operation and

maintenance of the related polder. The Polder Board should create and maintain awareness

of good corporate governance practice and business ethics related to management and staff

of polder authority at all level.

5.2.2 Communication with stakeholders in the Banger Pilot Polder

The people in the Banger area have been introduced to the polder system, through previous

programs and/or projects. Some have never head of it, others have heard it been mentioned and

know it can help against flooding and yet others know all about it. A pond near the railway


46

station in Semarang City is called ‘Polder Tawang’, most probably derived from an old Dutch

name. Although all people know about this pond and always refer to it when speaking about

‘polders’, it unfortunately creates a misunderstanding and misinterpretation of the ‘polder

concept’, which is now by a lot of people considered as a ‘pond’ instead of a lower lying area

protected from flooding by a system of dikes, outlets and retention basins. However, people do

mention dikes and higher outlet capacity such as pumps and gates as technical solutions to the

flooding problems as described in detail in the Proposal

Action Plan book of the North Sub-System. It is evident that more awareness needs to be

created on this topic, particularly to be sure that all the people will understand and know the

changes living in a polder entail as well as knowing the benefits of a polder in the context of

floods and knowing the contribution related to operation and maintenance needed to keep a well

operating polder system running.

5.2.3 Stakeholder participation in the Banger Pilot Polder

The 84,000 inhabitants of district (kecamatan) Semarang Timur and the 6,000 inhabitants of

Village (Kelurahan) Tanjung Mas are important stakeholders for the realization and operation

and maintenance of the Banger Pilot Polder. Representing the inhabitants, the official local

leaders, local representatives, community leaders and the leaders and members of the North and

South-Sub System of the temporary Polder Authority play a major role as actors that could have

an either positive or negative effect on the implementation of the pilot polder project in the

Banger area.

Next to the people who are living in the polder, other important stakeholders are:

• Local Government: Municipality of Semarang (DPU and Bappeda);

• Bina Marga (Highway);

• PT. Kereta Api Indonesia PJKA (Railway company);

• PT. Pertamina (Oil Company);

• Hospital Panti Wilasa;

• Small to middle businesses and Shops.

In the Banger area, it is evident that the inhabitants and communities have to cope with floods

on a daily basis, especially in the northern area (Kelurahan Kemijen and Rejomulyo). The high

tide periods are a daily nuisance to the people living in the northern part of the Banger area.


47

Water levels increase up to knee level, which turns out to be a common phenomenon in the lives

of the inhabitants. The ground floor of the houses is often built on a higher level, if it can be

afforded and if not, daily water intrusion is something the people just have to cope with.

To the people, it seems that daily flooding is not really considered as a problem. The people see

it as part of life and do not seem to realize that due to both technical and institutional changes in

water management as well as changes in individual and community conduct, they could live

without these daily floods. On the other hand, extreme floods, which do not occur on a daily

basis, cause much more damage and are considered as an actual problem by the people. The

North Sub-system is fairly active to try to contribute reducing such severe damage due to such

extreme floods in the future. In the southern area, problems caused by flooding are less alarming

as the area is situated at a higher level and tidal influence is minimal. In general, the inhabitants

have a higher living standard and most houses are built at higher levels.

Public hearings

In public hearings, inhabitants were asked to write down the main problems in their

neighbourhood. Most inhabitants are aware that floods are causes by the high tide of the sea or

by heavy rainfall. They are also aware that the water gates of the secondary and tertiary

channels do not work due to the high water level in the Kali Banger as well as that the situation

is worsened by sedimentation and large amounts of garbage in the channels and ditches.

Another problem mentioned by the people is the continuous construction of (illegal) semi-

permanent and wooden/bamboo houses near and on the riverbed of Kali Banger. Figure 5.1

shows the public hearing session, which has been carried out during the project phase.

Figure 5.1. Public hearing


48

Awareness and behaviour concerning garbage

In general, the people have some level of awareness regarding garbage and garbage collection.

However, it seems that people are not as much bothered with it, as long as it does not affect

their direct living area, such as inside their homes. Garbage around their house, or even next to

their house in the small ditches, around the public toilets or on the community paths, does not

seem to cause a problem.

In the past, an attempt has been done to set up a garbage management system. Garbage was

collected from each household and brought to a temporary garbage location by the community.

The inhabitants paid for the garbage collection at their houses (Rp 2,000.- or € 0.20 per

household per month). Unfortunately, the local Government did not collect the garbage at the

temporary garbage location and the project failed. However, such a project does indicate that

part of the inhabitants seem to be aware of the essentiality of a good garbage collection system

and are willing to adapt their behaviour accordingly and are also willing to contribute some part

of their income to support community and Government garbage collection programs.

During public hearings, residents mentioned that the garbage and sediment in the channels and

ditches also cause or worsen the effects of floods. They also indicated (by asking what they can

do themselves to decrease the damage caused by flooding) that they could clean the channels

and ditches to improve the water system. Garbages, which are accumulated near the pumping

station, should also be avoided (see Figure 5.2)

Figure 5.2. Garbage around pumping station


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Sanitation and health conditions

In the northern part of the Banger area, the majority of the people have a low income. Habitants

make use of public toilets and toilets without septic tank at or above the Kali Banger. Using a

toilet just above the river should be avoided in the future as shown in Figure 5.3. During

flooding, it often happens that septic tanks cannot work properly anymore and overflow due to

bad or no maintenance. In the north, especially in Kelurahan Kemijen, people suffer from skin

diseases, due to the (daily) flooding and the bad quality water, caused by garbage and direct

discharge of wastewater from households and toilets into the Kali Banger. Diarrhea is also a

common illness people suffer from in that area. There is hardly any statistical information on the

number of people suffering from skin diseases or Diarrhea or any other water related diseases,

as people are not used to reporting such diseases at the local community clinics. Most people

have grown used to having such health problems and have learnt how to live with them.

Figure 5.3. Toilet above Kali Banger

People in the southern part of the Banger area have middle to high income. Most households

have septic tanks, although it is not clear how often these are maintained and what the quality of

the wastewater is when discharged into the Kali Banger. Mostly, people have good quality

houses, which are built on a higher level, so flooding is only a problem in times of extreme high

rainfall. Most inhabitants only suffer the inconvenient circumstances during high water, but

have no direct health and sanitation problems worsened by flooding.


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5.2.4 Human resources development

The levels of education of the inhabitants vary in the project area. Most inhabitants graduate

from elementary school, junior high school and senior high school. Only around 8% of the

inhabitants graduate from higher education level academies or colleges. This is shown in Table

5.1.

Table 5.1. Level of education in Kecamatan Semarang Timur (Bappeda, 2005)

Type of school Total number of inhabitants

No education

Not graduated from Elementary school

Not yet graduated from Elementary school

Graduated from Elementary school

Graduated from Junior High School

Graduated from Senior High School

Graduated from Academy

Graduated from College

4,178

4,314

13,939

14,767

12,351

11,372

2,863

2,958

Total

66,742

(from total inhabitants: 83,663)

5.2.5 Social impact assessment

The social impacts that have been identified by the primary and secondary stakeholders.

There are direct as well as indirect impacts.

• Positive impacts

Direct impacts

Five positive direct impacts have been identified for the Banger Polder project. A summary

of the direct positive impacts and the main affected stakeholders is given in Table 5.2.

- Population and Banger Area free from flood and inundation

The main positive impact of the Banger Polder project is that the population and the

Banger area will be free from flood.


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The current (daily) flood and inundation is disrupting life, since houses are inundated

regularly, renovation of houses and reparation of assets is required, floor levels of

houses has to be heightened and diseases are spread through the water.

- Increased involvement of Local Government

The Banger Polder project will increase the involvement of local government as they

are the main project owner and are also institutionally involved through their

representation in the Polder Board (PB). The local government is represented by the

Municipality of Semarang (Bappeda and DPU).

- Increased community involvement

The Banger Polder project will increase the community involvement through their

representation and active involvement in the PB. All Kelurahan in the Banger Area are

represented in the PB.

- Increase of public awareness

Public awareness will increase, especially concerning awareness on flood and

inundation and how to overcome them. Most of the public awareness will be conducted

through the PB.

- Increase of awareness local government

Awareness of the local government related to flood and inundation management will

increase because the establishment of the PB will provide sufficient information about

flood and inunda-tion management to the local government through their

representatives.

Table 5.2. List of positive direct impacts of the development of Banger Polder

Direct impact Main affected stakeholder

Population and area free from flood and inundation

North Banger inhabitants

Municipality of Semarang

State owned companies

Private companies

Hotels and restaurants

Hospitals and polyclinics

South Banger inhabitants

Increased involvement of Local Government Municipality of Semarang

PB

Increased community involvement North Banger inhabitants


52


PB

Increase of public awareness



Increased awareness of Local Government Municipality of Semarang

• Positive indirect impacts

Seven positive indirect impacts have been identified for the Banger Polder project. A

summary of the indirect positive impacts and the main affected stakeholders is given in

Table 5.3.

- Increase of land and asset value

Land free from flood and inundation will have more value than areas suffering from

daily floods and inundation.

- Improved health conditions

The health condition of inhabitants will improve because flood and inundation no

longer occur in the Banger Area. Flood and inundation contribute to the spreading of

water borne diseases, such as diarrhea and skin diseases. Furthermore the living

conditions in the houses will become less humid and healthier, since the groundwater

level will be controlled at a lower level.

- Improved quality and sustainability of housing

Quality and sustainability of housing will increase as no more or limited flood (return

period 10,000 years) and inundation (return period 10 years) will take place. Floods

reduce the quality and sustainability and also affect the lifetime of infrastructure

including housing, due to rotting of wood, deterioration of paint and damage to

foundations. Maintenance and rehabilitation of housing will be less and the lifetime

of housing can be achieved according to its design.

- Increased quality and durability of roads

The quality and durability of roads will increase as no or limited floods will take

place. Flood damages the road and reduces their durability. The bad condition of the

roads increases the costs of transportation. Furthermore, the maintenance and

rehabilitation of roads will be less and lifetime of roads can be achieved according to

their design.


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- Reduced expenditures and increase of income

Household expenditure will decrease and incomes will increase, since there will be

no more expenses for:

� damaged assets (furniture, vehicles, audio installations, etc);

� damage to housing;

� costs for protection of houses (heightening floor level);

� damage to roads;

� less losses of income due to diseases (days not working);

� medicine and healthcare.

- Increased local employment and business opportunities

Local employment and business opportunities will increase due to decrease in flood

and inundation. As the Banger Area will not be flooded frequently anymore,

economic activities can keep on running without interruptions. Relocation of shops

or markets will no longer be required.

Because of the economic benefit of the Banger polder project (see chapter 7), the

demands of the inhabitants will increase (ie. additional restaurants and retail shops,

etc.). This condition creates new opportunities for the inhabitants, that have a

significant positive effect on their economy and employment.

- Water quality improvement in the Kali Banger

It is expected the water quality of the Kali Banger will decrease, although a flushing

system will be implemented.

The improvement of the water quality in the Kali Banger can only be achieved

through improvement of sanitation and solid waste management in the polder area

improved sanitation can avoid discharge of untreated wastewater into Kali Banger.

This impact is one of the critical impacts of the Banger Polder project.

Table 5.3. List of positive indirect impacts of the Banger Polder project

Indirect impact Main affected stakeholder

1. Increase of land and asset value North Banger inhabitants


Private companies

2. Improved health conditions North Banger inhabitants

Hospitals and polyclinic


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3. Improved quality and sustainability of housing

4.


5. Increased quality and durability of roads North Banger inhabitants

South Banger inhabitant

Government

Private companies


Reduced expenditure North Banger inhabitants


Private companies

Increased local employment and business opportunities North Banger inhabitants


Private companies

Water quality improvement in Kali Banger North Banger inhabitants


Private companies

Positive cumulative impacts

One positive cumulative impact has been identified for the Banger Polder Project: Increased

social equity between North and South Banger Area

The social equity is represented visually by the housing conditions. Since the quality of housing

will increase, the social equity between the North and South Banger area will also increase. The

(poorer) North Banger inhabitants will be able to increase the housing conditions, because their

expenditures on flood related damage decreases and income increases. On the long run, the

northern area will look more comparable in terms of housing quality to the southern area.

Adverse impacts and mitigation measures

• Adverse direct impacts

Eight adverse direct impacts have been identified for the Banger Polder project. A summary

of the direct adverse impacts and the main affected stakeholders is given in Table 5.4.

- New local regulations

Adverse impact


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New local regulations will be issued, especially in relation with the establishment of the

PB. These regulations will be applied only in the polder area. Since the regulation

applies locally, overlapping with other existing regulations can occur. For example in

solid waste management, new regulations implemented by the PB can overlap the

existing ones, which could cause inhabitants to pay a double fee for garbage collection.

Mitigation measure

Close co-ordination between the PB and the Municipality of Semarang can mitigate the

adverse impact. Furthermore informing the inhabitants can convince the inhabitants and

other stakeholders of the new regulations.

- Need for improved sanitation, water supply and garbage management

Adverse impact

A polder as a closed system requires improved sanitation and garbage management.

Poor sanitation and lack of garbage management will increase the contamination of

water (especially in the Kali Banger). Improvement in the wastewater system is

required to avoid heavy contamination of the Kali Banger.

Garbage is thrown into the Kali Banger because of a poor garbage management system

and habit. In the closed water system, garbage will not be transported to the sea

anymore. Therefore improvement of garbage management is required.

Mitigation measure

To avoid increase in the level of contamination of the Kali Banger, it is crucial for the

PB and the Municipality of Semarang to prioritise improvements in sanitation and

garbage management facilities.

Socialisation by the PB and the Municipality of Semarang is needed to explain and

create awareness to be able to improve garbage management and sanitation.

- Changes in flora and fauna

Adverse impact

Changes in flora and fauna will occur, especially in the aquatic environment. The

change from brackish to sweet water due to the closed polder system could change the


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aquatic habitat. The change in fish species might influence the people’s fishing and

eating habits.

Mitigation measure

If this has a major negative impact on the inhabitant’s income and business habits,

specific training on the new fish species should be arranged through the Municipality

and the PB.

- Disturbance in accessibility during construction period

Adverse impact

Implementation of the polder system requires construction of dikes and a pumping

station. The construction activities will increase traffic in the Banger Area due to

mobilisation and demobilisation of construction materials and equipment’s. Disturbance

in accessibility to inhabitants’ houses and working places is a direct adverse impact of

the Banger Polder during the construction period. This impact only occurs during the

construction period, assuming that after construction all potential accessibility is

recovered and all threats to public safety have been removed properly.

Mitigation measure

Good management and arrangements for the traffic and temporary storage of

construction materials and equipment’s will reduce disturbance in accessibility. Proper

alternative access options to houses, shops and buildings will have to be provided. Both

the Municipality of Semarang (especially DPU) and the PB will have to provide for

this.

- Reduced public safety during construction period

Adverse impact

Construction of dikes and a pumping station will increase traffic in the Banger Area

which will increase potential risk of traffic accidents. This impact only occurs during

construction period.

Mitigation measure


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Appropriate traffic arrangements inside the project area (including a clear Standard

Operating Procedure (SOP) for the truck drivers) during the construction period will

have to be implemented by the contractor (under supervision of DPU) to reduce

potential risk of traffic accidents.

- Potential risk of public safety due to living below sea level

Adverse impact

The sea level is higher than the surface level inside the polder. After 20 years, the

surface level is between 1.50 m-MSL and 2.00 m.-MSL A flood can cause an

inundation depth of 2.50 to 3.00 m. A safety level of a flood once per 10,000 years has

been chosen the during design process to avoid floods from sea. However, extreme

events the sea level might rise above the dikes.

Furthermore due to lack of maintenance of the dikes, the safety level can lower.

Mitigation measure

First of all, proper maintenance is required to maintain the safety level as determined

for the dikes (10,000 years return period). Maintenance will be carried out by the PB.

Secondly an evacuation plan shall be prepared. The evacuation plan should include a

warning system and evacuation plan and a test.

- Compulsory payment for operation and maintenance

Adverse impact

The polder system will need to be maintained, which will mostly be the responsibility

of the PB with support from the Municipality (mostly DPU). The cost of operation and

maintenance of the polder should be paid regularly by the inhabitants. This fee will

have to be paid to the PB. This has an impact on inhabitants, as they will have an extra

monthly cost to take into account.

Mitigation measure

Continued socialisation is required by the PB, since the polder system will not sustain

without O&M. Because floods and inundation’s will not occur, inhabitants will become

more reluctant to pay. Furthermore, the ability to pay will increase, because the

expenditures on floods decrease.


58

Subsidies could be applied for poor households to reduce their fees for O&M.

Households with higher revenue could pay higher O&M cost. Subsidies could also be

applied according to the type of building categories. Commercial buildings could pay

higher O&M fees compared to regular residences. These kind of payment procedures

will have to be developed timely before implementation of the fees by both the PB and

the Municipality of Semarang.

- Compulsory resettlement

Adverse impact

The construction of dikes, retention basin and the pumping station requires space and

land. These polder-elements are planned to be located in housing or commercial areas

which would then need to be relocated. Inhabitants could oppose to resettlement if

insufficient information is provided.

Mitigation measure

Regular socialisation and communication with the inhabitants should take place,

especially by the Municipality of Semarang and the PB.

The resettlement compensation scheme should be based on the people’s need.

Compensation can be implemented through cash payment or relocation to other areas.

This is the Municipality’s responsibility.

Table 5.4. List of adverse direct impacts and mitigation measures

Direct impact Main affected stakeholder Mitigation measure

New local regulation North Banger inhabitants


PB


Coordination between PB and

the Municipality

Socialisation

Need of improved sanitation,

garbage management and water

supply



improvement sanitation and

garbage management

socialisation

Changes in flora and fauna North Banger inhabitants training on new species


59

Disturbance of accessibility

during construction period



Private companies

management of traffic and

storage of materials and

equipment

Reduced public safety during

construction period



Private companies

Appropriate traffic

management

Potential risk of public safety

due to living below sea level



Private companies


Maintenance warning system

evacuation plan

Compulsory payment for

operation and maintenance



PB

- socialisation

- subsidies poor households

- contribution based on

assets/housing

Compulsory resettlement North Banger inhabitants Compensation socialisation

Adverse indirect impacts

Three adverse indirect impacts have been identified for the Banger Polder project. A

summary of the indirect adverse impacts and the main affected stakeholders is given in

Table 5.5.

- Change in land use patterns/habits

Adverse impact

The change in land use patterns/habits is related to the change from regularly inundated

area to dry area. The dry land can be used to develop new residential areas or

commercial areas (shops and market). When these areas were inundated they could only

be used as fish ponds. Change in land use patterns/habits needs to be controlled by the

Municipality of Semarang. Uncontrolled new residential areas will create new slum

areas in the polder.


60

Mitigation measure

Local spatial planning inside the polder area needs to be developed by the Municipality

of Semarang together with the PB to control development of housing areas or other new

infrastructure. Local spatial planning is also closely related to the protection of flood

plain and retention basin areas needed in the polder.

- Potential conflict between inhabitants (in polder and outside)

Adverse impact

Potential conflicts could occur between inhabitants in the polder area and inhabitant

outside the polder area. The inhabitants outside the polder who are not protected against

flood and inundation can be jealous.

Mitigation measure

The Municipality of Semarang should prepare comprehensive action plans for currently

excluded areas concerning flood protection programs, based on experiences from the

Banger Pilot Polder. These plans should be properly and timely communicated to and

discussed with the inhabitants outside the polder area. Socialisation of the successes of

the Banger Polder should take place to explain that these can be replicated to other areas

in Semarang that suffer from the same problems.

- Increase in population size

Adverse impact

The Banger Polder project can cause an increase in the number of population, since the

Banger Polder will provide better living conditions, which will attract people to move

there and stay.

Mitigation measure

The increase of population can be limited by the control of the spatial plan and the

control on illegal settlements.

Table 5.5. List of adverse indirect impacts and mitigation measures

Indirect impact Main affected stakeholder Mitigation measure

Change in land use

patterns/habits



control by spatial plan


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Potential conflict between

inhabitants



flood protection measures

area outside polder

Increase in population size North Banger inhabitants


Private companies

control by spatial plan

control on illegal

settlements

Adverse cumulative impacts

One adverse cumulative impact has been identified for the Banger Polder Project.

- Lack of resources

Adverse impact

Increase in the population size and economic level due to implementation of the polder

system will increase the demand for resources. An excessive increase in this demand

could create a lack of resources in the polder area.

Mitigation measure

The PB and Municipality of Semarang should issue regulations about use of resources.

For example, compulsory connection to water supply network for commercial activities

(shops and markets).


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6 Financial aspects

63

6 Financial aspects


6.1.1 Cost for construction, operation and maintenance of the water management and flood

protection system for the Banger Pilot Polder

Investment and construction costs

Investment and construction costs for development of pilot polder project in Semarang will

become the basis for determination of the needs of development fund for polder system in

Semarang outside the operational and maintenance cost. Investment and construction costs will

include direct cost and indirect cost. Direct cost is cost related directly with the physical supply

of polder system or in other word as construction cost, which shall cover the design cost,

construction material cost, pumping cost, worker/labour cost and miscellaneous. This cost also

included the rehabilitation cost, which will bring properly back the function of the water

management system. The indirect costs include permits cost, land-clearing cost, reclamation

cost and miscellaneous.

Construction cost dikes:

• include surveys, design, supervision;

• contingencies.

Construction cost pumping station and hydraulic structures and this part includes surveys,

design, supervision.

Operational and maintenance cost

Operation activity of a physical system is an activity for the usage of system in accordance with

its allocation; meanwhile maintenance activity is an activity having intention to avoid the

occurrence of deterioration of physical system such as polder system. The failure of

maintenance activity as the supporting function for operation activity within polder system not

only inflicted on the needs of reparation or replacement cost for one of system component

which might consume quite big amount of cost, but on being intruded of the company’s social

and economic activities which in its turn will impact on degradation upon quality of living


64

environment. As a public system, support and cooperation (participation) by the community and

government in seeking for the needs of some funds in order that system will keep being

operated shall be an absolute and un able to be avoided maters. The fund collecting from the

beneficiaries will be placed into two groups of main cost; they are operational cost and

maintenance cost.

Operational cost will cover the following:

• pump fuel and pump grease cost;

• labour cost;

• equipment and working facility cost;

• administration of Polder Authority cost and overhead cost.

Maintenance cost will cover the following:

• spare part and supporting material cost;

• construction repair material cost;

• service cost;

• labour wages cost;

• maintenance administration cost and overhead cost.

Land acquisition and resettlement

These activities include:

• for retention basin;

• for dikes.

Yearly maintenance cost

This part includes the following:

• maintenance dikes and hydraulic structures

• energy (electricity cost) pumping station

• heightening of dikes that are initially constructed for 10 years are not included, assuming

that Extension I and II will be developed

6.1.2 Feasibility aspects of Banger Pilot Polder

6 Financial aspects

65

Cost components

Land price in area (Banger, Extension I and Extension ii/Port)

The land prices in the project area are varies depend on the position and location. In the north

part, of the area near the banger river, land price ranging from Rp 300,000 – Rp 400,000. While

on the project boundary in Jl. Ronggowarsito and Jl. Katamso ranging Rp 2,000,000 – Rp

4,000,000 based on the NJOP (Nilai Jual Objek Pajak). Based on an average value of Rp

4,000,000 (conservative approach), the total value of the project area (527 ha) is Rp 2,10 billion

(€ 170 million).

Assets in project location can be considered as valuable buildings and infrastructures that have

economic value to the activities, environment and inhabitants in the project area and Semarang

city. Economic Infrastructure in Kecamatan Semarang Timur in 2005 consisted of middle up

Scale industry (7), small industry (147), home industry (379), hotel (3), canteen (256), trading

(535), transportation (157), services (698), others (139). Besides the following companies are

important assets:

• infrastructure (railroads, roads);

• PT. Pertamina (Oil Company);

• hospital Panti Wilasa;

• PT. Indonesia Power (Tanjung Mas);

• Pelindo (Harbour), Tanjung Mas;

• DPLAD (Army);

• public schools.

Economic growth

The rate of capital income in Semarang 1993 – 1998 is increased by 17% per year. The growth

in industrial, trading and transportation sectors increases 12% per year.

Damage components

In this part, several damages components will be discussed. The total damage in relation to a

flood consists of:

• direct damage;

• indirect damage;


66

• intangible damage;

• depressed land values (and loss of land) in flooded areas.

The damage is calculated for a period of 20 years.

Direct damage

The damage caused by floods to infrastructure, buildings, assets, livestock. The depth and

frequency of floods are considered in measuring the direct damage.

Indirect damage

The indirect damage are considered as disruption to normal activities to the business and daily

routine, upheaval in living conditions and also additional costs in Rob and flood fighting (rising

the ground floor, rising the roads, built small dikes, etc) the cost of the indirect damage is

difficult to measure but usually assumed as fixed percentage of direct damage. The CIDA,

Flood Control Manual, Ministry of Public Works to calculate it as a percentage of the direct

costs have suggested it:

• residential 15%;

• agriculture 10%;

• commercial 37%;

• industrial 45%;

• public buildings 34%;

• highway 25%;

• railways 23%.

Intangible damage

The intangible damage of floods in the project area can be describe as death, illness, depression

also degradation in environment quality. The damage can reduce the quality of labour, land and

capital, also subsequently lowering the households’ income. The loss of this intangible damage

as per CIDA flood control manual is 5% of the GDP. World Bank suggested that value of the

intangible loss is 20 - 80% of the income of the affected people in the area.

Depressed land values (and loss of land) in flooded areas

6 Financial aspects

67

The land in the area affected by floods is valued lower than the area free from floods.

Economic feasibility analysis and conclusions

• project Economic analysis (EIRR);

• sensitivity analysis;

• risk analysis.


6.2.1 Budget planning and allocation for the Banger Pilot Polder

Budget planning for each year has to be prepared based on the operation and maintenance

requirement for the Banger polder. Next to the contribution from all stakeholders to the Polder

Authority, if it is needed, a subsidy from the local or provincial or central government can be

proposed.

One of the important aspects for the sustainability of the Banger polder system shall be a proper

funding system. This funding as much as possible shall involve stakeholders as the party

receiving benefits through the existence of the polder.

Sustainability has been determined by the capacity to compete for scarce financial capital

available in the income or savings account of the government (World Bank, 1990).

Within the community-based development, self-reliance concept shall become one of the

matters, which must be developed. Self-reliance means that the community shall be more

dependable on their community resources rather than depend on the supporting resources from

outside/foreign parties. The mentioned self-reliance is particularly within financial or funding

matters. The approach of self-reliance within community development being afforded by

centering on interest of how to identify and develop all the available resources under such

community and trying to maximize this local resources for the importance of community. The

positive impact by the appearing of this self-reliance is that the community becomes more

autonomous, freer to determine matters of their interests, improve their self-confidence and

pride as well as self-esteem within the community. The funding system that might support the

sustainability for development and maintenance of a polder shall be the funding system under


68

characteristics of participative, fair and support autonomous. A participative funding system

means a funding system being designed based on agreement of all the stakeholders within

polder target area and capable to reflect their active participation under such funding.

In order to create such funding system as being described above, then the effort to recognize the

local profile and target community shall be the beginning phase that is important to be

performed. Because of that must be laid out a profile description concerning the polder area,

which contains information of physical infrastructure as well as community condition existing

within the polder target area. In detail such area profile will contain for information regarding:

• all stakeholders component within the polder target area in order to describe a

participative funding system;

• numbers of physical infrastructures existing within the polder target area in including its

ownership identities;

• conditions of financial capability from each stakeholder within the polder target area.

6.2.2 Identification of stakeholders in the Banger Pilot Polder

In essence, stakeholders in Banger polder compose of inhabitants, institutions and enterprises

resided in Banger polder area.

Inhabitants

Inhabitants who live in and outside-inundated areas constitute those who shall receive benefit.

They shall receive the benefit directly from the Banger polder system.

Enterprises

They shall receive the benefit where their business shall run properly and without any damage

due to floods. Related parties in this category are:

• Private-Owned Enterprise

Business activity in form of store and business centre located in polder area that

experiences inundation. Manufacture industry, in particular, inland water users, they mark

as party who bears responsibility for subsidence (penurunan muka tanah) caused by

excessive inland water using habit.

• State-Owned Enterprise (BUMN)

6 Financial aspects

69

In this category they are:

∗ PT. Pelindo Indonesia, Area Office of Tanjung Mas Port

∗ PT. Kereta Api Indonesia (PT KAI)

∗ PLN, PT. Telkom and PDAM

6.2.3 Taxation system for the Banger Pilot Polder

In order to maintain the sustainability of the Banger polder system, a management system has to

be developed where it will cover both the institutional and financial aspects.

Within the institutional aspect, must be explicitly formulated which institution will be

responsible toward the operational, maintenance and development of polder system. While from

the financial aspect, there should be a certainty concerning sources of fund to finance operation,

maintenance and development activities upon such polder system.

The development of the Banger polder system in a developing area (Semarang) will face

complexity having relation with the current prevailing regulations, local values, as well as

aspiration of the community. In line with democracy era, the community participation must be

included and considered in the process of decision-making.

Taxation can be based on a participative, equity and independent approach (partisipatif, adil dan

mandiri) which is considered to be sustainable.

This approach can create a mechanism of defining tariff based on the capacity and possible

contribution of each stakeholder to the water management problems in urban polder system.

Funding strategies must be considered for its implementation possibilities. The concept of full

cost recovery must be applied. The beneficiaries must participate in bearing the funding in

accordance with their buying capability. The cost analysis and beneficiary classification must be

carried out, in order to design the tariff structure from taxes and retributions. The government’s

subsidy if being required in case of very large budget will be needed e.g. dredging of Kali

Banger and possible ought to be explicitly formulated of its sources, targets, and purposes of its

supplying. The sustainability within this case shall be the key issue in implementation of a

Banger polder system.


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7 Legal aspects

71

7 Legal aspects


From the legislation point of view, the problems related to floods and high tide water level

inundation are not managed in an optimal way yet (Table 7.1). One of the reasons is the

participation and involvement of the stakeholders in the system is still neglected.

Table 7.1. Legislation

Legislation Topic

Undang undang No. 16 year 1950 Setting up of large cities within West Java,

Central Java, East Java and Yogyakarta

province

Undang undang No. 23 year 1997 Environmental management

Undang undang No.7 year 2004 Water Resources in Indonesia

Undang undang No. 32 year 2004 Local Government

Undang undang No. 33 year 2004 Financial balance between Central and Local

Government

Undang undang No. 26 year 2007 Spatial planning

Regulation of the Ministry of Public Works

No. 63/PRT/1993

River development and its space boundary

conditions

Regulation of Semarang city No. 5 year 2004 Spatial planning of Semarang city year 2000-

2010

Regulation of Semarang city No. 6 year 2004 Detail spatial planning of Semarang city part I,

year 2000-2010

Regulation of Semarang city No. 8 year 2004 Detail spatial planning of Semarang, city part

III, year 2000-2010


Settlement of disputes

Any dispute between two or more water user institutions for example between Polder Authority


72

and any other user arising from the operation of the polder system will be referred to the Justice.

But, before going to the Justice, Musyawarah dan Mufakat (discussion and compromising) have

to be done. During the management phase, Law (Undang undang) No.7 year 2004 about

Water Resources has to be considered and used as the foundation for the management

and development of water resources in Banger polder.

8 Design aspects of water management and flood protection for the Banger Pilot Polder

73

8 Design aspects of water management and flood protection

for the Banger Pilot Polder


The Banger polder area is located in the Semarang Timur sub-district (Kecamatan) and in a part

of the Semarang Selatan sub-district. The area north of Jalan Brigjen. Katamso belongs to

Semarang Timur sub-district, and the area south of Jalan Brigjen. Katamso belongs to Semarang

Selatan sub-district, see Figure 8.1. The Semarang Timur sub-district consists of ten (10)

kampungs (kelurahan): − Kemijen; − Rejomulyo; − Mlatibaru; − Mlatiharjo; − Kebon Agung;−

Bugangan; − Sarirejo; − Rejosari; − Karangturi; −Karang Tempel.

Figure 8.1. Sub-districts (Kecamatan)

It can be seen that the borders of the kampungs are within the preliminary boundaries of the

polder, except kampung Peterongan at the south. The boundary of the polder divides the

kampung.


74

Two principal mechanisms for Banger polder are relevant with regard to flooding the following

safety levels are determined:

• high water level outside the polder (in this case governed by high water at sea and Banjir

Kanal Timur), safety level 1/10,000 years;

• high water level within the polder area due to heavy rainfall, safety level 1/10 years.

The polder has a natural gradient from high to low, which follows the direction South (the

mountains) to North (the sea). The location of the pumping station should therefore be

preferably chosen in the North of the polder. To minimize construction costs, the pumping

station has to be located as close as possible to suitable receiving water. The polder does not

directly border to the sea, so either the Kali Banger (outside the polder) or the Banjir Kanal

Timur can function as receiving body. The discharge capacity of the Kali Banger is estimated to

be limited, since bund walls of fishponds block its flow. The Banjir Kanal Timur is therefore a

better option. This determines the location of the pumping station to be in the Northeast corner.

8.2 Impoldering principles applicable to the Banger Pilot Polder

The design of the polder in this case has two principal mechanisms that are relevant with regard

to flooding:

• high water level outside the polder (in this case governed by high water at sea);

• high water level within the polder area due to heavy rainfall.

High water level outside the polder

Historically the safety definitions of a flood defence were formulated by the ‘highest known

water level’. The flood defence was designed at that level plus a certain margin. The level of

safety of the polder is related to the exceedance frequency of a defined high water level. The

required safety is elated to the economic value of the polder (housing, people, environment etc.)

and the accepted risk to human life. This is especially relevant for low-lying areas in the

Netherlands, which can be as low as -7 m+MSL. In the Netherlands where the polder concept

has been applied for centuries, the flood defence of these polders must be able to withstand

extreme hydraulic conditions that may occur once per 10,000 year in the urban part of the

Netherlands and 4,000 year in the more rural areas. This standard is the result of comprehensive

cost benefit and safety analysis. Figure 8.2 shows the design water level for different several


75

safety levels. The design of Banger water level for T10,000 is estimated based on the design

water levels of 1 year return period till 1,000 years return period. The Banger polder will mainly

protect residential and commercial functions. Floods will cause a lot of damage to these

functions and the effect is progressively worse as the polder subsidise lower and lower below

sea water level. After a period of 15 years the polder will be so low that there will be a risk to

human lives. In Figure 8.2 it can be seen that the safety level has a minor impact on the design

water level; the difference between a crest height for 1:1,000 or 1:10,000 does not differ less

than a decimetre. This decimetre is insignificant in light of the large overheight that needs to be

included to compensate land subsidence. Therefore, a design chance of occurrence of the dike of

10,000 years is chosen.

Figure 8.2. Safety level

High water level inside the polder

Within the protective dike ring of a polder the potential damage of a flood caused by the rainfall

is limited to the damage of rainfall within the polder area. In general this is not associated with a

danger to human lives, and therefore a lower safety level is allowed. In the Netherlands

inundation of urban areas, caused by extreme rainfall, may occur once per 100 year. For the

Banger polder a design chance of occurrence of inundation of 25 years was proposed in Phase 1.

A period of 100 year would be recommended from a technical point of view, but given the

extreme rainfall this would result in a very large retention basin, and this is not considered

economically or socially feasible.

There are three types of polders possible in this area:

• gravity driven polder;

• belt canal system;


76

• separated system.

For discharge capacity and water quality reasons a minimum water depth of 50 cm is

recommended. From environmental point of view, this water depth also prevents mosquitoes to

lay their eggs.

Gravity driven polder (Minimum construction costs, maximum energy requirements)

In this type of polder, water in the Banger area flows north by gravity to the lowest point in the

polder. From the lowest point, the water is discharged by pump. A sketch is presented in Figure

8.3.

Figure 8.3. Gravity driven system in Banger Polder

Water table

MSL-2.00 m

Water table

MSL-0.50 m

Water table

MSL+0.50 m

weir

dam

pumping station

flow direction


77

It can be seen that the water flows (by gravity) from a level of +1.5 m+MSL to a level of 0.7 m-

MSL. From this lowest point, water is discharged to the sea. This is also shown in Figure 8.4.

Because the water level (0.7 m-MSL) in the lowest polder section is lower than low tide (0.4 m-

MSL), water cannot be discharged by gravity and water has to be discharged by pump.

Figure 8.4 Gravity system

Construction requirements

This polder system can be easily adapted in the existing drainage system, which is also a gravity

driven system. This system requires the following main structures:

• 2 weirs and width of crest: 5 m;

• 1 pumping station (capacity approximately 6 m3/s, with one spare pump).

Construction costs are approximately € 1.3 million, without VAT (annex I).

Energy requirements

Because all water is collected in the lowest point of the polder, the surplus of water of all polder

sections has to be discharged by pump, with a relatively high hydraulic head difference. The

yearly discharge is 15.8 million m3 (rainfall minus evaporation and waste water). The hydraulic

head is 3.25 m on average in the first 10 years and 4.15 m from the 10th till the 20th year. With

a pump efficiency of 50%, the average power consumption is 280,000 kWh per year in the first

ten years and 360,000 kWh per year between the 10th and 20th year. With a price of 0.01

€/kWh, the energy costs are 2800 €/year and 3600 €/year respectively.

The calculation is reported in Table 8.1 and 8.2.


78

Table 8.1. Energy consumption gravity driven system

Discharge unit

rainfall 2,330 mm/year

evaporation open water and unpaved 1,200 mm/year

evaporation paved 270 mm/year

paved area 396 ha

area unpaved and open water 164 ha

average evaporation (distribution paved / unpaved) 542 mm/year

seepage/infiltration -365 mm/year

netto rainfall and seepage 1,423 mm/year

waste water 18,140 m3/day

waste water 1,182 mm/year

area polder system 560 ha

discharge volume (area*(netto rainfall + waste water) 1.46E+07 m3/year

pomp capacity 6 m3/s

hours in use (full capacity) 675.37 uur

hydraulic head

design water level upstream (a) 1.1 m MSL

downstream (b) -2.0 m MSL

average land subsidence first 10 years (c ) 0.45 m

required extra hydraulic head (d) 0.5 m

average hydraulic head 0-10 years (a-b+c+d) 4.05 m

average land subsidence 10-20 years (d) 1.35 m

average hydraulic head 10-20 years (a-b+d) 4.95 m

efficiency

efficiency 0.6 [-]

power ((g*Hydraulic Head*Q)/efficiency)

power first ten years 3.97E+02 kW


79

power 10-20 years 4.86E+02 kW

power Consumption (Power*hours in use)

power consumption first ten years 2.68E+05 kWh

power consumption 10-20 years 3.28E+05 kWh

price kWh (USD) 0.07 USD/kWh

energy Costs

energy consumption first ten years 18,783 USD/year

energy consumption 10-20 years 22,957 USD/year


The Banger polder system requires a relatively low operation and maintenance level. The main

system has only 2 weirs and one pumping station.

Belt canal system (high construction costs, minimum energy requirements)

Belt canals are channels collecting water from adjacent polders and water table areas. The water

table in the belt canal can be higher than water table in the adjacent polders. In the Netherlands,

these polder-belt canal systems are developed to be able to discharge the water of the belt canal

to the sea by gravity (through a tidal gate). However, water has to be discharged by pump from

the polders to the belt canal, but with a lower hydraulic head. Figure 8.5 and Figure 8.6 present

the concept of a polder-belt canal system. In the Banger Polder, the river Banger can act as a

belt canal. Figure 8.7 shows that in the south part, the water flows by gravity to the Kali Banger

and flows in north direction. In the middle and north part of the polder, the Banger acts as a belt

canal. The level of the belt canal (Kali Banger) is higher than the water level of the surrounding

areas. Therefore, water is discharged by pump from the adjacent areas to the Kali Banger. Water

is discharged to the sea or Banjir canal Timur by a tidal gate. Figure 2.6 shows the belt canal in

the Banger Polder.


80

Table 8.2. Energy consumption Belt canal system

Discharge unit

rainfall 2,330 mm/year



paved area 396 ha

area unpaved and open water 164 ha


seepage / infiltration -365 mm/year




area polder section 1 370 ha




hydraulic head polder section 1

design water level upstream (a) 0.2 m+MSL

downstream (b) 2.0 m-MSL

average land subsidence first 10 years (c ) 0.45


average hydraulic head0-10 years (a-b+c+d) 3.15 m



efficiency 0.6 [-]

power Consumption (Power*hours in use) polder section 1




discharge volume (area*(netto rainfall + waste water) 3.E+06 m3/year


81








average hydraulic head0-10 years (a-b+c) 1.45 m



efficiency

efficiency 0.6 [-]




total power Consumption (polder section 1 and 2)



price kW (USD) 0.07 USD/kWh

total Energy costs



Figure 8.5. Polder-belt canal system

Q3

gravity

Belt canal

sea

polder section I

water level:

MSL-2.00 m

polder section II

water level:

MSL-0.50 m

polder section III

water level:

MSL+0.50 m

H2 H1

Q1 + Q2 + Q3

tidal gate

South North


82

Figure 8.6. Schematic polder-belt canal system


This belt canal system requires a change of the existing drainage system. This system requires

the following main structures:

Figure 8.7. Polder-belt canal in Banger polder

pumping station

weir

tidal gate

flow direction

belt canal Kali Banger

dike Kali Banger

Water table:

MSL-2.00 m

Water table:

MSL-0.50 m

Water table:

MSL+0.50 m


83

• embankments along the Kali Banger, to withstand the higher water level now and in the

future and the total length of embankments is approximately 7,000 m;

• 4 pumping stations (total capacity approximately 5 m3/s).In every polder section at each

side of the Kali Banger a pumping station is required;

• parallel channels along the Kali Banger to collect the rainwater and discharge it to one of

the pumpings stations. Required length of the parallel channels, around 7,000 m;

• 1 weirs and 5m width of crest;

• 1 tidal gate.

Construction costs are approximately € 3.7 million, without VAT, see Table 8.3.

Energy requirements

The Kali Banger can discharge by gravity. However polder section 1 and 2 have to discharge by

pump to the Kali Banger. The area of polder section 1 and 2 is 370 ha (67 %). The hydraulic

head of polder section 1 is 3.15 m on average in the first 10 years and 4.05 m from the 10th till

the 20th year. The hy-draulic head of polder section 2 is 1.45 m on average in the first 10 years

and 1.95 m from the 10th till the 20th year. The average power consumption of both polder

sections is 160,000 kWh per year in the first ten years and 200,000 kWh per year between the

10th and 20th year. The energy costs are 11,000 USD/year and 14,000 USD/year respectively.

The calculation is reported in Table 8.4.


This polder system is requires higher operation and maintenance level than the gravity driven

system. The main system has 1 weir, 4 pumping station, a tidal gate and additional dikes.

Especially the tidal gate is a vulnerable structure. It is located in the dike and therefore needs

regular inspection and maintenance.

Separated canal system (high construction costs, minimum energy requirements)

In this type of polder 3 individual polder sections discharge separately to the Banjir Kanal

Timur. Figure 8.8 shows the concept of the separated polder system. This system is meant to

make use of the potential energy height of the higher polder sections II and III. By separating


84

the polder section, the energy height of the polder sections can be used without using a belt

canal system through the Banger polder.

Unfortunately the water level in the Banjir Kanal Timur is also increasing in southern direction.

The gradient of the river varies between MSL at polder section I and 3.00+MSL m at polder

section III. The in-side and outside water level for the three polder section is:

• polder section I: inside water level 2.00 m-MSL, outside water level (Banjir Kanal Timur)

between 0.50-MSL m and 0.50 m+MSL: Gravity discharge is not possible;

• polder section II: inside water level 0.50 m-MSL, outside water level (Banjir Kanal Timur)

is 2.00 m+MSL: Gravity discharge is not possible;

• polder section III: inside water level MSL+0.50 m, outside water level (Banjir Kanal Timur)

is 2.50 m+MSL to 3.00 m+MSL: Gravity discharge is not possible.

Figure 8.8 Separated system in Banger polder

Polder section I:

Water table MSL-2.00 m

Polder section II:

Water table MSL-0.50 m

Polder section III:

Water table

MSL+0.50 m

dam

flow direction

pumping station


85

All 3 polder sections require pumping stations to discharge the water, the reduction on energy

costs is limited. Furthermore, all polder sections require retention basins to buffer the water

temporarily. In polder sections II and III there is not much land available.


This separated canal system requires a change of the existing drainage system. This system

requires the following main structures:

• 3 pumping station (total capacity approximately 6 m3/s, + spare pumps). In every polder

section a pumping station is required;

• 2 channels between the Kali Banger and Banjir Kanal Timur, total length 1,000 m;

• 2 dams in the water system.

Construction costs are approximately USD 4.2 million, excluding VAT.

Energy requirements

The 3 polder sections have to discharge by pumps. The hydraulic head in the first 10 years of

polder section 1, 2 and 3 is 4.05, 3.25 and 2.75 m respectively. From the 10th till the 20th year

this is 4.95, 3.75 and 3.25 m. With a pump efficiency of 60%, the average power consumption

of both polder sections is 250,000 kWh per year in the first ten years and 300,000 kWh per year

between the 10th and 20th year. The energy costs are 17,000 USD/year and 21,000 USD/year

respectively. See Table 8.3.

Table 8.3 Energy consumption Separated system

Discharge Unit

Rainfall 2,330 mm/year



paved area 396 Ha

area unpaved and open water 164 Ha


seepage / infiltration -365 mm/year





86

area polder section 1 370 Ha



hours in use (full capacity) 669.34 Uur



downstream (b) 2 m-MSL

average land subsidence first 10 years (c ) 0.45


average hydraulic head0-10 years (a-b+c+d) 4.05 m



Efficiency 0.6 [-]









design water level upstream (a) 2 m+MSL








87

Efficiency

Efficiency 0.6 [-]









design water level upstream (a) 2.5 m MSL

downstream (b) 0.5 m MSL






Efficiency 0.6 [-]




total power Consumption (polder section 1,2 and 3)



price kW (USD) 0.07 USD/kWh

total Energy costs




This polder system is requires higher operation and maintenance level than the gravity driven


88

system. The main system has 3 pumping stations and 2 channels between the Kali Banger and

Banjir Kanal Timur.

Analysis on construction and energy cost

The gravity driven polder system is relatively cheap in both construction and operation and

maintenance (O&M), but relatively expensive in energy costs: USD 2.6 million for construction

of the main system, USD 9,000/year for the O&M and USD 21,000/year for energy costs (in the

first twenty years). The Belt canal system is the opposite: relatively cheap in energy costs and

relatively expensive in construction and O&M: USD 5.5 million for construction of the main

system, USD 22,500/year for the O&M and USD 12,000/year for energy costs. The separated

system is in between: USD 4.2 million for construction of the main system, USD13,500/year for

the O&M and USD 19,000/year for energy costs.

Table 8.4 presents the Net Present Value (NPV) of the construction, O&M and energy costs

over 20 years for a discount rate of 4%. The table shows that the total costs of the belt canal

system and the separated system after 20 years are respectively 2 and 1.5 times the total costs of

the gravity driven system and that the energy and O&M costs are negligible compared to the

construction cost. The gravity driven polder system is the cheapest option and is therefore

recommended. Table 8.5 till Table 8.7 present construction cost for gravity, belt canal and

separated system

Table 8.4. Net Present Value construction and energy costs for 20 years period

Total costs (million USD)

Construction 2.55

Energy 0.30

O&M 0.13

gravity driven system

Total 2.99

Construction 5.48

Energy 0.18

O&M 0.33

Belt canal system

Total 5.98

Construction 4.16

Energy 0.28

Separated system

O&M 0.20


89

Total 4.63

Table8.5. Construction costs gravity driven polder system

unit Quantity Cost per unit (USD) Cost (USD)

weirs:

crest width 5 m 2 25,000 50,000

pumping station

Pumps m3/s 8 250,000 2,000,000

Housing 1 500,000 500,000

Total 2,550,000

Table 8.6 Construction costs Belt Canal system

unit quantity cost per unit (USD)

cost (USD) Remarks

dike along Banger

dike along Banger m 7,000 125 875,000

including land

acquisition

Weirs

crest width 5 m 2 25,000 50,000

pumping station

Pumps m3/s 7.5 250,000 1,875,000

Housing 4 500,000 2,000,000

tidal gate

tidal gate 1 150,000 150,000

parallel channel

Channel m 7000 75 525,000

including land

acquisition

Total 5,475,000

Table 8.7 Construction costs Separated system

unit quantity

cost per unit (USD) cost (USD) Remarks

Channels

channel m 1,000 400 400,000 including land


90

acquisition

Dams

crest width 10 m 2 2,500 5,000

pumping station

Pumps m3/s 9 250,000 2,250,000

Housing 3 500,000 1,500,000

Total 4,155,000

Tidal gate

This part describes the possibility of a tidal gate to discharge the water out of the polder. To be

able to analyse the possibility of a tidal gate, the following parameters are important:

• (tidal) level at sea;

• preferred internal water table (polder level), depended on:

• surface level;

• type of water system.

Figure 8.8 presents the concept of the tidal gate.

Figure 8.8. Tidal gate during low and high tide

Water level Banjir Kanal Timur

In the current situation the water level in the northern part of the Banjir Kanal Timur is deter-

mined by the sea under normal conditions. The water level at the southern boundary of the

Banger Polder (Jl. Brigjen. Katamso) is 2.5 to 3.0 m+MSL. In extreme conditions (T25) the

gradient of the river varies from 1.9 m+MSL at the northern boundary (Jl. Arteri) to 5.5

m+MSL at the southern boundary of the polder.


91

Inside levels

The water tables inside the polder are:

Polder section I: 2.0 m-MSL;

Polder section II: 0.5 m-MSL;

Polder section III: 0.5 m+MSL;

The water table will follow the rate of land subsidence: 9 cm/year in polder section I and 5

cm/year in polder section II and III.

Possibility of a tidal gate in a gravity driven polder system

A gate only functions if the upstream water level is higher than the downstream level. For the

tidal gate this implies that the water level at least has to be higher than the low tide, to discharge

during a part of the tidal cycle. In the Banger, the polder level is 2.0 m-MSL, 1.5 m lower than

mean low tide, see Figure 8.9. This implies that a tidal gate is not possible to discharge the

water. A pump is required to keep the polder level at 2.0 m-MSL. Gravity discharge is only

possible when the water level rises more than 1.5 m during low tide, which will happen only

less than once per 5 years. The water table will be lowered 9 cm/year to follow the land

subsidence. This implies that after 6 years gravity discharge is not possible under any

circumstances. It can be concluded that a tidal gate will probably not be used, or maybe once for

a couple of hours. It is concluded that a tidal gate is not feasible.

Figure 8.9. Tidal gate gravity driven system in 2008

Possibility of a tidal gate in a belt canal system

Because the water level in the Kali Banger is (artificial) higher than low tide, water can be dis-

high tide (+0.5 m

+MSL)

low tide (0.5 m-MSL)

Sea Kali Banger

tidal gate (closed)

surface level Mean Sea Level

1.5 m 2.0 m-MSL

0.5


92

charged to the sea through the tidal gate. Figure 8.10 presents the discharge of the Kali Banger

(as a belt canal) through the tidal gate. It has to be noted that pumping stations are required to

achieve the higher water level in the belt canal. With this system the energy costs are only partly

reduced.

Figure 8.10 Discharge from the Kali Banger by tidal gate

Possibility of a tidal gate in a separated system

The higher lying surface level of the southern are could be suitable for gravity discharge. The

problem in this case is that the water levels in the Banjir kanal are much higher. Table 8.8

present the polder levels in the Banger Polder and the outside water levels of the Banjir kanal

Timur. It can be concluded that gravity discharge is not possible.

Table 8.8. Inside and outside water levels

Polder section Polder level

(m+MSL)

Water level Banjir

Kanal Timur (m+MSL)

Conclusion

I -2.0 -0.5 to +0.5 Gravity discharge not possible

II -0.5 + 2.0 Gravity discharge not possible

III +0.5 + 2.5 Gravity discharge not possible

The following can be concluded from this paragraph:

• Tidal gate is not possible for a gravity driven system;

-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0 12 24 36 48

Time (hours)

wa

ter

lev

el (m

MS

L)

sea level water level Banger Polder

DISCHARGE 10 HOURS


93

• A tidal gate is possible in a Belt-canal system to discharge from the belt canal to the sea.

Pumping stations are required to achieve the higher water level in the belt canal;

• Tidal gate is not possible in a separated system, because the occurring water level in the

Banjir kanal Timur is too high.

For the design works, tidal characteristics as discussed in Table 3.1 are used. The current

surface level and predicted surface level in 2018 and 2028 are presented in Appendix I. The

variation of surface level is from 3.4 m+MSL south, to 0.8 m-MSL north.

Dam in Kali Banger

Figure 8.11. Dam in the Kali Banger

One of the most important components of the Banger Polder is the dam. This dam is blocking

the river (Figure 8.11). The dam protects the Banger Polder from floods, since the sea cannot

flow into the Banger Polder anymore. At the other hand, the dam blocks the discharge of the

Banger Polder. Therefore, the pumping station and water quality control will be required. The

dam will be located under the bridge of Jl. Arteri and will be part of the northern dike.

Estimation of the water table

Drainage depth

The polder level is important because it regulates the groundwater level. The groundwater level

control is important for several functions in the polder:

• green areas, trees: desired water level 1 to 0,5 m-surface (to provide sufficient soil air and

moisture balance);

Current situation


94

• houses: 0.7 m below built-up level and (to enhance the bearing capacity of the building,

to prevent high humidity and unhealthy climate in the basements of buildings);

• roads: 1.0 m below road (to enhance bearing capacity of the road);

• retention: water level as low as possible, to create as much retention as possible.

Polder levels

Based on the surface level (appendix I) and the drainage depth of 1 m, the polder level is

roughly determined for the Banger Polder. Figure 8.12 presents the polder level of the polder

sections, the surface level and the area of the polder sections. The roads and buildings require a

groundwater level of 1.25 to 1.50 m-surface in the wet season. To increase the retention

capacity the water table is determined at 2.00 m-surface. Thus the determination of the water

table is based on retention capacity rather than the groundwater level control.

In the dry season the water table can be controlled at a higher level.

Figure 8.12. Estimation of water tables


95

Note that the lowest polder level is hydrologically an ideal location for retention, because of the

low-lying surface area. In that case, the polder level will have the same level as the adjacent

polder section. See Table 8.9.

Table 8.9. Water tables in the Banger Polder sections

Polder section Water table

(m+MSL)

area Procentage

ha %

I -2.0 370 70

II -0.5 100 19

III +0.5 60 11

Due to land subsidence, the surface level will decrease. The polder level has to follow this

lowering surface level. The water table has to be lowered in accordance to the rate of land

subsidence. This implies the water table has to be lowered 9 cm/year in polder section 1 and 5

cm/year in polder section II and III.

Possibility of a tidal gate in a gravity driven polder system

A gate only functions if the upstream water level is higher than the downstream level. For the

tidal gate this implies that the water level at least has to be higher than the low tide, to discharge

during a part of the tidal cycle. In the Banger, the polder level is 0.7 m-MSL, 0.3 m lower than

mean low tide. This implies that a tidal gate is not possible to discharge the water. A pump is

required to keep the polder level at 0.7 m-MSL. However, a tidal gate can function besides the

pumping station to reduce the energy costs of the pumping station. The water table has to be

lowered in accordance to the rate of land subsidence. This implies the water table has to be

lowered 9 cm/year in polder section I and 5 cm/year in polder section II and III.

Water can only be discharged when the water level in the polder is higher than the sea level. To

discharge by gravity, the water level has to be set up for a certain period, to be able to discharge

through the tidal gate. Table 3.1 shows that the lowest surface level in the polder section is 0.1

m-MSL, 0.6 m above the polder level and 0.3 m above low tide. The water level can set up for a

certain period to be able to discharge during low tide. By discharging through the tidal gate, the

water level is lowered from 0.1 m-MSL to 0.4 m-MSL (low tide). Furthermore, the water level

has to be lowered to the level of the polder level: 0.7 m-MSL. This is only possible by pump.


96

Figure 8.13 presents the tidal cycle and the period of discharge.

Figure 8.13. Discharge by tidal gate and pump

Technically it is possible to use a tidal gate to reduce the energy costs of the pumping station.

However it is not advised and is not be feasible for the following reasons:

• the pumping station is always needed to discharge the water between 0.4 m-MSL and 0.7

m-MSL and is needed to discharge during high tide;

• heightening the water level reduces the retention capacity. At a water level of 0.4 m-

MSL, the retention capacity is lowered by approximately 30%, it takes 9 hours (by pump)

to lower the water level to the level of the polder level. At a water level of 0.1 m-MSL the

retention capacity is reduced by approximately 60%;

• to reach the water level of 0.4m-MSL or higher, the rainfall intensity has to be

approximately 45 mm/day or higher. To reach the water level of 0.1m-MSL, the rainfall

has to be approximately 90 mm/day. This rainfall intensity occurs once per year. This

implies the tidal gate can only be used a couple of times per year. Besides, these extreme

rainfall events almost occur during the rainy seasons. In this season, the polder level has

to be at the level of the polder level to have enough retention capacity;

• the polder level is determined at 0.7m-MSL to contribute to the several functions in the

polder.

The possibility of a tidal gate in a belt canal system

Because the water level in the Kali Banger is (artificial) higher than low tide, water can be

discharged to the sea through the tidal gate. Figure 8.14 presents the discharge of the Kali


97

Banger (as a belt canal) through the tidal gate.

Figure 8.14. Discharge from the Kali Banger by tidal gate

Technically it is possible transfer the Kali Banger into a belt canal, with a higher water level, in

order to discharge water from the Kali Banger through a tidal gate. This water system is

considered not to be feasible for the following reasons that the investment costs are much higher

than the gravity driven polder system:

• embankments are required at both sides of the Kali Banger in the north and middle part of

the Banger Polder. Total length of the embankments is approximately 7 km. The height of

the embankments is 1 m;

• in the north and middle part of the Banger Polder all 30 existing gates have to be replace

by an equal number of pumps. To reduce the number of pumps, additional drains have to

be realised.

It can be concluded that tidal gate is considered not to be feasible for the Banger Polder. In a

gravity driven polder system, the polder level is lower than low tide. This implies a pump is

needed to discharge the water. Using a tidal gate besides the pump to reduce energy costs is also

considered not to be feasible. The tidal gate will only be used a couple of times a year, only for

the next 4 to 8 years. After that period, due to land subsidence, the use of the tidal gate is not

possible anymore at any time. The investment costs are higher than the reduced energy costs.

In a belt canal system, the use of a tidal gate is possible. However, this type of water system

requires much more investment costs compared to a gravity driven water system, while at least


98

two pumping stations are needed.

8.3 Polder infrastructure for the Banger Pilot Polder

Retention area

The required retention capacity depends on the discharge capacity of the polder and the safety

level. Furthermore, several retention options will be discussed.

Through a hydrodynamic 1-D simulation, the exact required retention capacity will be

calculated for the polder area. Besides, the retention area of the downstream retention basin

might decrease, because of realisation of retention in upstream parts. Actually, in the ideal

situation the retention is spatial spread, but cooping with the existing urban area, this is not

possible. Table 8.10 presents the run-off area and corresponding run-off coefficient.

Table 8.10. Run-off area and run-off coefficient

Area

(ha)

Run-off coefficient

short period

(-)

Paved 393 0.9

Unpaved 144 0.3

Open water 20 1.0

Total 557

Other considerations are:

• discharge capacity : 6 m3/s;

• safety level: design chance of occurrence: 100 years;

• freeboard tertiary and quartery channels: 30 cm;

• freeboard secondary channels: 50 cm;

• freeboard Kali Banger and fishing ponds: 100 cm.

Retention capacity

An important step in the assessment of the development of the polder is the determination of the

required retention capacity. The retention capacity depends on the safety level and discharge


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capacity of the polder (pump capacity). The relation between pumping capacity, the retention

capacity and safety level is shown in Figure 8.15.

Figure 8.15. Retention capacity versus pump capacity versus design chance of occurrence

The graph shows the guideline for pump capacity for polders in Indonesia: 1 m3/s/100 ha, as

described in the Basis of Design. The graph shows that the guideline pump capacity lies in the

bend of the curve, a lower capacity means an exponential increase of required retention

capacity. A higher capacity has limited impact on the required retention capacity.

According to the Program of Requirements, the pump capacity is 6 m3/s and the safety level of

frequency of occurrence of 100 years, the necessary retention capacity is 855,000 m3.

Retention capacity design chance of occurrence T100

The retention capacity partly already exists in the current drainage system, Kali Banger and the

fishing ponds. Table 8.11 presents the current en required additional retention capacity. 615,000

m3 retention capacity has to be realised, besides the existing retention capacity.

Table 8.11. Existing and required retention capacity T100

Existing drainage system

area (ha) retention capacity (m3)

Total required 855,000

12.0 120,000 Existing Kali Banger fishing ponds channels

6.5 65,000


100

15.0 55,000

Total existing 240,000

To realise 615,000

Retention capacity design chance of occurrence T25

The retention capacity needed to reach a safety level of inundation once per 100 years might be

not doable in the Banger area, due to existing buildings and the planning of realising container

terminals. In the first phase of this project (feasibility phase), the design return period of

occurrence was determined as 25 years. Looking at the necessary retention capacity to acquire a

higher safety level, the return period of 25 years is considered to be feasible.

Table 8.12 presents the current en required additional retention capacity for a design chance of

occurrence of 25 years. 410,000 m3 retention capacity has to be realised, besides the existing

retention capacity.

Table 8.12. Existing and required retention capacity T25

Existing drainage system

Area

(ha)

Retention capacity

(m3)

Total required 650,000

12.0 120,000

6.5 65,000

Existing Kali Banger fishing ponds channels

15.0 55,000

Total existing 240,000

To realise 410,000

Next to that, the following options of retention are discussed:

• retention in fishing ponds;

• water table is the same as Kali Banger (direct connection);

• lower water table to increase retention capacity (discharge by pump);

• retention in inundatable playing fields/green areas;

• controlled inundation.


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The retention options can be combined. In the next part the retention capacity is translated to

retention area. The necessary additional retention capacity for a design return period of 25 years

is used.

Retention in fishing ponds

The necessary retention is realized by creating fishing ponds. The fishing ponds can be used as

normal. The fishing ponds can be made in open connection with the Kali Banger, Figure 8.16.

The retention capacity is limited to the freeboard in the fishing ponds and Kali Banger, because

of the open connection. Because the freeboard is 1 m (same as Kali Banger), the required area

of fishponds is 41 ha. This retention area can be located in Kemijen, next to the existing

fishponds. Figure 8.17 roughly presents the needed retention area.

Lower water table in fishing ponds

To increase the retention capacity of the fishing ponds, the water table can be lowered in the

fishing ponds. A lower water table in the fishing ponds requires a continue discharge by pump

from the fishing ponds to the Kali Banger, as can be seen in Figure 8.18. If for example the

water table of the fishing ponds is 1 m lower than the water table of the kali Banger, the

freeboard is increased from 1 to 2 m. The necessary area of fishing ponds is decreased from 41

ha to 21.5 ha. This relatively low water table affects the groundwater level and will attract

seepage of the surrounding area.

Figure 8.16. Retention in fishing ponds, open connection


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Figure 8.17. Retention area

Figure 8.18. Retention in fishing ponds, lower water table

Retention in play grounds/green areas

Water is temporary stored in playing fields or other green areas. This controlled inundation

occurs with a low frequency (once per 2 or 10 years). During extreme rainfall events, water will

be temporary stored in the playgrounds. When the water level in the Kali Banger is lowered, the

water can flow back by gravity through a gate to the Kali Banger, as shown in Figure 8.19.

Because the freeboard is 1 m (same as freeboard Kali Banger), the required area of play fields is

41 ha. Because the surface level of the playground is equal to the water table, seepage can

occur, especially during the rainy season. The seepage can make the play ground soggy.


103

Figure 8.19. Retention in play grounds or green areas

Controlled inundation

A safety level of a return period of 25 years requires a large retention area. Therefore, a

distinction can be made for the safety level of different types of land use. For example,

inundation of streets causes no damage and if the inundation period is limited, the disruption of

life is limited. Furthermore, in some areas, inundation causes less damage than in other areas.

This area with a lower risk can be used for controlled inundation with a low frequency of

occurrence (5 or 10 years).

Controlled inundation of streets

Streets can be used as temporary retention area. This controlled inundation occurs with a low

frequency (2 or 5 years). It is only possible under the condition that the street level is lower than

the level of the buildings and that the inundation period is limited to a couple of hours. Figure

8.20 presents the concept of controlled inundation of streets. Normally the street level is 10 to

20 cm lower than the level of buildings. If the allowed inundation height is 10 cm and the

duration period is 3 hours, 65,000 m3 can be stored in the streets, requiring an area of 65 ha.


104

Figure 8.20. Controlled inundation of streets

Controlled inundation of other areas

In some areas, inundation causes less damage than other areas. These areas, with a lower risk

can be used for controlled inundation with a low frequency of occurrence (for example: 10

years). If allowed inundation is 20 cm, the required retention area is 63 ha. Besides this

retention area (meant to store between T10 and T25), additional retention is needed to store

water up to T10. The additional storage is 286,000 m3.

Pumping station

The polder has a natural gradient from high to low, which follows the direction South (the

mountains) to North (the sea). The location of the pumping station should therefore be

preferably chosen in the North of the polder. To minimize construction costs, the pumping

station has to be located as close as possible to a suitable receiving body of water. The polder

does not directly border to the sea, so either the Kali Banger (outside the polder) or the Banjir

Kanal Timur can function as receiving body. The discharge capacity of the Kali Banger is

estimated to be very limited, since bund walls of fishponds block its flow. The Banjir Kanal

Timur is therefore a better option. This determines the location of the pumping station to be in

the Northeast corner.

Realizing the pumping station does not decrease the flood related problems, since dikes are not

yet constructed and the Banger area is not yet protected. By constructing the pumping station

end of this year/beginning of 2008 an expectation is raised (among residents in particular) that

flooding will be reduced. It will therefore become even more important to follow-up with the

construction of dikes, because until that time the pumping station will have no function.


105

Obviously it is in the interested of all stakeholders that this pumping station will not become

some kind of ‘stranded Ark’. Proposed location of the pumping station is presented in Figure

8.21.

Figure 8.21. Proposed location of pumping station

In order to determine the hydraulic head of the pumping station, the suction and delivery level

have to be known.

Intake level

The water table will be approximately 0.7 m-MSL. To increase the retention capacity, the pump

has to be able to lower the water level till 1.7 m-MSL. As a conservative approach in this stage

of the project, an intake level of 2 m-MSL is used.

Delivery level

The delivery level at construction (in 2008) and the delivery level at the end of the pump’s

lifetime differ, primarily due to the high rate of land subsidence. Therefore both a level for 2008

and for 2028 is given.


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The discharge point level in 2008 is 1.25 m+MSL and in 2028 is 3.12 m+MSL. This level is

calculated as indicated in Table 8.13.

Table 8.13. Calculation of discharge point

2008 2028

Mean high water spring (MHWS)

Wind set up

Storm surge

Sea level rise

Land subsidence

+0.50 m

+0.40 m

+0.20 m

0.006 m

0.09 m

+0.50 m

+0.40 m

+0.20 m

0.126 m

1.89 m

Level at discharge point +1.25 m +3.12 m

Consolidation of the top layers has not been taken into account because this consolidation

should have occurred before the construction of the pumping station by applying a preload on

location. An overview and the system are presented in Figure 8.22 and Figure 8.23 respectively.

Figure 8.22. Overview of 2008 and 2028 delivery levels

Figure 8.23. Water management system


107

The hydraulic head is the delivery level minus the intake level. For 2008 the hydraulic head is

3.25 m (+1.25 – -2.0 m), for 2028 the hydraulic head is 5.12 m (+3.12 - -2.0 m).

Water quality

The discharge consists partly of unscreened wastewater. Black and grey water are screened by

local septic tanks, from which the water flows to a trickling filter plant. However, water from

the open street gutters is unscreened and may contain oils, solids and stringy materials like

plastic bags. The discharges from the trickling filter plant, the street gutters and subsurface

drains are all collected in the primary drain, and therefore this discharge as a whole can be

considered unscreened. The quality of the area by the coastline of Semarang city is poor with

chloride content > 600 ppm (Said and Sukrisno, 1984).

Energy supply

A local transformer station will be constructed near the pumping station. In order to guarantee a

reliable and continuous supply of electricity in case of a power failure, the installation shall

include an emergency power supply by means of a diesel generator set. Both the transformer

station and the emergency power supply should be placed at save and dry level so the pump still

can be operated normally.

Peripheral conditions

The projected housing area will surround the pumping station at a distance of approximately 40

m. Therefore the noise level of the pumping station at the parcel boundary should not be higher

than 50 dB(A).

Underground conditions

Since the north project area is newly reclaimed no pipes or cables are present yet in the

underground, while in the middle and south part and the boundary of project area there should

be infrastructures (gas, telecommunication, PDAM, electricity) are present in the underground.

The details of installed underground infrastructures must be determined.


108

Lifetime

The design lifetime for the pumping station is 50 years. The technical lifetime of the (screw)

pumps is 20 years. Given the high rate of land subsidence after 20 years a pump with different

specifications needs to be selected, based on the land subsidence rate at that time.

Required pump capacity

Required pump capacity is 6 m3/s. This capacity is needed during storm weather conditions with

a chance of occurrence of 1 year. With this capacity, a 1 year rainfall event can be discharged

within 24 hours.

At dry weather conditions the discharge is 43,100 m3/day or 0.50 m

3/s. This capacity is

determined by:

• domestic wastewater production of 15,500 m3/day;

• small – medium scale industries 2,600 m3/day;

• flushing capacity of 25,000 m3/day (based on a retention time of 10 days, a water depth of

1.0 m and an area of 25 ha).

Average rainy season capacity

The average system discharge 74,100 m3/day or 0.9 m3/s. This capacity is based on:

• domestic wastewater production of 15.500 m3/day;

• small – medium scale industries 2,600 m3/day;

• average rainfall 10 mm in rainy season, 56,000 m3/day.

Pump configuration

Pumping of polder water to the Banjir Kanal Timur can be done with the help of Archimedean

screws pumps or with centrifugal pumps. In case of application of screw pumps it may be

expected that more units shall be installed next to each other in one common concrete structure.

If centrifugal pumps will be applied, they shall be of an axial flow propeller type or a normal

centrifugal propeller type. In a further design phase shall be investigated and decided which

type of pump and the exact number of pumps will be the best choice in the present case.

A spare pump is required. This spare pump is standby and can be taken in operation if one of the


109

others is in failure.

Dirt screening

Especially axial flow propeller pumps are sensible for pollution and clogging of the impeller. To

prevent that larger parts are entering this pump type, a fine bar screen shall be installed in the

water inlet structure just before the pumps. Since this screen shall have small openings between

the bars, it shall operate automatically. In case of application of ‘normal’ centrifugal pumps a

manual cleaned screen can be applied. This screen shall be provided with larger openings

between the bars. The same can be done for a pumping station with Archimedean screws.

Gate or weir

Check valves shall be placed for additional safety and protection against wave run-up during

extreme storms.

Pump selection

The relatively large maximum difference between the lowest intake level of -2.00 m+MSL and

the highest discharge level of 3.12 m+MSL can technically be covered by a single Archimedean

screw pump. The use of centrifugal pumps is also considered as possible, with the prerequisite

that a bar screen is installed in front of the pumps.

Four screw pumps may be expected with a discharge capacity of 2.0 m3/s each. Three screw

pumps shall be as a maximum in duty, the fourth one is standby and can be taken in operation if

one of the others is in failure. So a total of 6 m3/s capacity is always available in the pumping

station. It is suggested that the use of a low and high-speed operation mode, whereby the

capacity at low speed can be chosen approximately 50% of the design capacity. With this

provision a range in capacity of 1 – 6 m3/s can be realized during operation.

If centrifugal pumps will be chosen and to minimize total construction costs we advice pumps in

a submersible construction. It may be expected that from a point of view of lowest total

construction and operation costs installation or five or six pumps from the same type and size is

the optimal choice, or one or two smaller pumps in combination with two or three larger pumps.

In case of five pumps from the same size (+ 1 stand-by) the capacity of each pump shall be 1.2


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m3/s. In case of application of some smaller pumps and some larger pumps, the capacity of the

smaller pumps can be chosen as desired (for example 0.5 m3/s). The capacity of the larger

pumps can be determined for example at 1.5 m3/s.

Screw pumps can be manufactured and installed by the company PT Ruhaak at Jakarta, other

manufacturers for screw pumps are for example Spaans Babcock and Landustrie in the

Netherlands. Submersible pumps are manufactured and supplied by the most leading suppliers

of submersible pumps in the world, such as Nijhuis, Flygt, ABS, Hidrostal and KSB.

Considerations for pump choice

The static head can vary significantly, because of the level change in the pumping and/or

retention basin, and the long-term land subsidence. The dynamic head is small, due to minor

resistances in the outlet pipe. The capacity of screw pumps is in principle not dependent on the

water level on both sides of the pumping station, and thus the total delivery head. For the first

period a design can be chosen with a lower (temporary) discharge point. In this case can be

saved on the energy consumption.

The capacity of an axial flow propeller pump is in a high degree dependent on the total delivery

head. In this situation because of the variation in water level at suction side (Banger river side)

and at discharge side (Banjir Kanal Timur side). Depending on the pump characteristics, the

actual pump capacity of an axial flow propeller pump at high water inside the polder can be

more than 1.5 times that of the design capacity. Therefore the required area of the pump basin

must be 1.5 times bigger than that of a screw pump. Roughly the same can be said for another

type of centrifugal pump. The actual efficiency of an axial flow propeller pump (and other type

of centrifugal pump) will be lower than the optimum during a rather long time, as a result of the

variable working point (see Figure 8.22). For screw pumps the performance decrease is less

significant, provided that the intake water level will be equal or higher than the filling point.

The technical life cycle of axial flow propeller pumps is approximately 10 years, while that of

screw pumps is 20 years. The initial construction costs for screws may be a little bit higher, but

the yearly costs for energy, operation and maintenance will be lower. A present worth cost

capitalization is appropriate to assess the most economic solution.

Archimedean screw pumps are reliable, less prone to clogging than the centrifugal pumps, and


111

easy to inspect. And always with a constant capacity (independent from water levels).

Figure 8.22. Characteristics axial flow propeller pump

A submersible pump cannot be designed with a high and low speed switch. In case variable

speed pumping is chosen, adjustable frequency converters will be required. This is an advanced

technique that is less suitable within the Indonesian market and which will increase the demands

set on the operation and maintenance staff.

Assessment of alternatives

Table 8.14 presents scores and cost estimates and is intended to give more insight in the

advantages and disadvantages of the two alternatives mentioned in the preceding paragraph.

Table 8.14. Score table of pump station alternatives

Criterion Option 1

Screw pump

Option 2

Submergible pump

Investment costs

Technical design lifetime (years)

Efficiency (related to energy costs)

Durability

Accessibility and ease of maintenance

Hands-on knowledge staff

Performance with heavy pollutes water

Adaptability delivery head 1

-

20

+

++

++

++

++

+/0

+

10

+/-

-

-

-

-

+

1 Adaptability of screw pump possible by means of an adjustable upper casing screw


112

Archimedean screw pumps have the highest score in respect to durability, accessibility, ease of

maintenance, and performance with heavier pollution, but Archimedean screws are expensive in

construction. An additional disadvantage of the screw pump is the technical complexity of

design and construction, especially when compared to submergible pumps. Submergible pumps

only require the construction of a pump-pit and an upper structure to support the pump. There is

a preference for axial flow pumps above propeller pumps, since axial flow pumps are less

susceptible for clogging and failure due to floating garbage and stringy materials in the water.

Centrifugal pumps can be either submergible or in dry operation. For comparison with the

submergible axial/propeller pumps, we have assumed a similar submergible installation.

Centrifugal pumps have the advantage above propeller pumps that they are less sensitive for

clogging and a slight advantage in operation with a head that increases over the years. In respect

of investment costs submergible propeller or axial pumps are the preferred choice.

DPU has selected propeller pumps in light of the lower investment cost and in light of the fact

that they have good experience with this type of pump in this area. DPU already purchased 2

pumps with a capacity of 1.5 m3/s each (3.0 m3/s in total) and is tendering another 3 pumps of

the same type.

Pumping basin

The Banger River will be lead directly to the pumping station and will have a sufficiently large

wet perimeter to be able to function as a size pumping basin, and prevent level fluctuations and

on-off cycling of the pumps.

Discharge channel and outlet structure

A drain pipe will discharge the water into the outlet structure. Between the drain pipe and the

concrete structures (collecting pit and outlet structure) a ‘compensator’ shall be placed, which

allow a certain settlement difference. At the end of the drain pipe at the outlet structure a steel

grating must be installed for safety reasons. The concrete outlet structure shall be provided with

closing provisions. The height shall be equal to the height of the dike along the intersecting

drain. For safety a railing shall be placed. In front of the outlet structure the intersecting drain

shall have slope- and bottom protection to maintain stability and to prevent erosion.


113

Operation

In the dry period, one pump shall operate periodically to discharge light domestic water. In case

of screw pumps, one screw pump shall operate then in low/high speed. In the wet period, more

pumps shall operate regularly continuously until certain moment. In the occasion where heavy

rainfall occurs, the last pump shall support for the occurrence of 1 year chance of occurrence.

8.4 Landscape and land use planning in the Banger Pilot Polder

Landscape and land use planning in the Banger Pilot Polder are based on the Master Plan of the

municipality of Semarang. The master plan 2000-2010 the following land use and functions are

envisaged:

• kelurahan Kemijen and Rejomulyo: the function of this area is trading supported by

particular facilities, residential area and industry; development towards grocery trading and

warehouses; a container terminal is planned in the area owned by PT Kereta Api Indonesia

(PT KAI, Indonesian Railway Company) in Kemijen;

• kelurahan Mlatibaru and Mlatiharjo: predominant function of this area is housing, supported

by trading area and home industry area;

• kelurahan Kebonagung and Bugangan: predominant land use is trading and services,

residential area and industrial area;

• kelurahan Sarirejo an Rejosari: land use in this area is for trading, services and residential

area supported by home industry; development into non-grocery trading and home industry;

• kelurahan Karangturi and Karang Tempel: land use is trading and service with residential

area; development directed towards non-grocery trading.

The Banger Polder consists of one sub-district (Kecamatan Timur) and the following 10 villages

(kelurahan) and comprises 84,000 inhabitants. Besides residential area, the land in the project

area is used for small trading, small service industries and small industries. In the north area

(kelurahan Kemijen) the land is used by the railway company, an oil company (Pertamina),

fishponds and a part of this area is unused. Table 8.1 shows the land use of the villages.

Table 8.15. Current land use in ha

Kecamatan

housing water other total

Kemijen 42 9 45 96


114

Kecamatan

housing water other total

Rejomulyo 38 0 2 40


Mlatibaru 35 2 3 40

Bugangan 34 2 10 46


Sarirejo 40 0 6 46

Rejosari 55 3 10 68



Total

415 20 92 527

8.5 Boundary conditions for the design of water management and flood protection for the

Banger Pilot Polder

Two main boundary conditions have to be considered, i.e. land and water boundary conditions.

Land boundary conditions, these boundaries can be described by the dikes.

Due to land subsidence, the crest level of the dikes decreases rapidly, which has an impact on

the design lifetime. Because longer design lifetime requires more investment costs, the design

lifetime is an important parameter. Therefore, possible future extensions of the polder area are

explored. These future extensions are likely, because from the viewpoint of flood protection, the

locations of the dikes of the Banger polder are not optimal. If an extended polder area will be

realised in future, some dikes will loose its function. In order to realise no-regret measures and

to determine the design lifetime, possible extensions of the polder area are examined.

In phase I of this project, the boundaries of the project area were already determined. The

project area is, based on hydrological and administrative data, slightly changed at the southern

boundary. The project area enclosures Kecamatan Timur and protect this whole sub-district

from flooding. Figure 8.23 shows the boundaries of this polder. The project area is relatively

small and requires a relatively limited length of dike. For a pilot, this is crucial, because then,


115

the polder can be realised relatively easy and fast.

Figure 8.23. Boundary of the Banger polder

As presented in Figure 8.23, the boundaries of the drainage system that flows to Kali Banger

are:

• north Boundary : Jl. Arteri/Jl. Peta;

• south Boundary : Jl. Brigjend. Katamso;

• west Boundary : Jl. M.T. Haryono - Jl. Ronggowarsito;

• east Boundary : Tanggul Banjir Kanal Timur.

The northern dike of the Banger Polder is extended to Banjir Kanal Barat by the Urban

Drainage Plan Kali Semarang (UDPKS), see Figure 8.24. This project is executed by PCI

Consultants in assignment of Directorate General Cipta Karya.


116

This northern dike, together with the dikes along Banjir Kanal Barat and Banjir Kanal Timur

pro-tects the area between the two channels. Therefore a western dike of the Banger Polder is

not necessary. The safety level of the dike along the Banjir Kanal Barat must be the same as the

other dikes around the Banger area.

Figure 8.24. Urban drainage plan kali Semarang

Location of the dikes

Northern dike

The dike is designed between Banjir Kanal Timur and Kali Baru. Only the part between Banjir

Kanal Timur and jl. Ronggowarsito is part of the Banger Polder. The western part of the

Jl.

Ro

ng

go

war

sito

Dike Banger Polder

Dam in kali Semarang+

pumping station Dam in kali Baru+

pumping station

Ba

nji

r K

an

al

Ba

rat

Ban

jir K

an

al

Tim

ur

Dike UDPKS

Dam+pumping station

Northern dike

Eastern dike (along Banjir Kanal Timur)

Western dike (along Banjir Kanal Barat)

Project boundary Banger Polder

Dam in kali

Banger+

pumping station


117

northern dike shall be constructed by UDPKS. The design is extended to Kali Baru for a

comprehensive assessment on the two options for the location of the dike.

The dike crosses two main junctions: jl. Ronggowarsito and jl. Mpu Tantular. Both roads are

main entrances to the harbour.

Options for location of northern dike

The northern dike and dam can be constructed north or south of jl. Arteri, see Figure 8.25 and

Figure 8.26. The location of the dam is related to the location of the dike, because the dike

cannot cross the road (since a distance of 15 m should be kept from the road). If the dike is

located north of jl. Arteri, the dam is also located north. And vice versa: a dike southern option

is combined with dam, south of jl. Arteri.

This section assesses these two options for the dike + dam. Before starting the Detailed Design,

it should be decided upon by the Municipality of Semarang, which option will be applied.

Option north

The alignment of option north is presented in Figure 8.25. It is not allowed to cross the jl. Arteri

with a dike. However, it is allowed to connect the dam to the eastern dike by a sheet pile con-

struction under the bridge over the Kali Banger. This sheet pile construction is relatively

expensive. Summarised, this option comprises three elements:

- dike (bundwall);

- dam (bundwall);

- connection dam-eastern dike (sheet pile construction).

This option protects jl. Arteri. The dike is located on land owned by the harbour authority (PT.

Pelindo). In the Banger Polder 24 houses will have to be removed. Between jl. Ronggowarsito

and Kali Baru 18 company buildings will have to be removed. Some buildings are already

empty and inundated. The required area for the dike comprises 2.0 ha in the Banger Polder and

2.0 ha in the area west of the Banger Polder (to Kali Baru).


118

Figure 8.25. Option north

Option south

The alignment of option south is presented in Figure 8.26. Both dike and dam are located south

of jl. Arteri. The space for the dam south of jl. Arteri is not sufficient to realise a stable

bundwall dam. Therefore sheet piles are incorporated in the design to realise a stable dam. This

option comprises two elements:

- dike (bundwall);

- dam (sheet pile construction).

This option does not protect jl. Arteri and is located in residential area. In the Banger Polder 23

houses will have to be removed. Between jl. Ronggowarsito and Kali Baru 56 houses will have

to be removed. The required area comprises 2.0 ha.

Jl.

Ro

ng

go

wars

ito

Jl.

Mp

u T

an

tula

r

Dam in kali Banger

Jl. Arteri

kali Banger

Kali B

aru

Ban

jir

Kan

al

Tim

ur

Connection dam-eastern dike

dike


119

Figure 8.26. Option south

Comparison between options

Table 8.16 presents the assessment of the two options. Both options of the northern dike will

affect existing infrastructure, buildings and other structures. The southern option involves more

houses to be removed and private property and therefore has more negative social impact. The

northern dike protects more area and more assets (jl. Arteri) and has less social impact, be-cause

the land is owned by the harbour authority.

The investment costs of the northern option are IDR 9 billion higher than the southern option.

The dam of the northern option is very expensive because it requires steel sheet piles.

Table 8.16. Assessment location northern dike (and dam)

Northern option Southern option

Banger

Polder

Jl.Ronggowar-sito-

K. Baru

Banger Polder Jl.Ronggowar-

sito-K. Baru

Land acquisition [ha] 2.0 2.0 2.0 2.0

Houses to be removed 24 28 (company

buildings)

23 56


120

Land ownership PT.

Pelindo

PT. Pelindo private private

Protecting jl. Arteri included included not included not included

Costs dike+dam (IDR) 21 billion 11 billion 10 billion 13 billion

The northern option is recommended, because in contrary to the southern option, it includes the

protection of a large asset: the jl. Arter. Furthermore land acquisition is easier, since only one

party is involved. The social impact is less, because the buildings to be removed mainly

involves companies of which most are already empty (due to flood).

Eastern dike

The eastern dike of the Banger Polder is the embankment of the Banjir Kanal Timur (BKT).

This embankment needs to be heightened to fulfil the requirements. The eastern dike is referred

to as BKT dike.

Location and segments BKT dike

The existing BKT dike is located between the crossing of the Jl. Arteri in the north and Jl. Brid-

gend Katamso in the south. The length of the dike is 5.427 km (BKT Km 1.341 – BKT Km

6.768). The dike needs improvement between BKT Km 1.341 – BKT Km 5.471 (4.130 km).

The southern part near jl. Bridgend Katamso is sufficiently high for the next 20 years. Based on

their typical cross sections (which is determined by the different water levels in the BKT), 5

segments can be distinguished (see Figure 8.27):

- segment 1: Jl. Arteri;

- segment 2: Jl. Kaligawe;

- segment 3: Jl. Sewah Besar;

- segment 4: Jl. Citarum;

- segment 5: Jl. Kartini.


121

Figure 8.27. Location BKT dike

General design aspects

The total width of the dike should be kept as limited as possible in order not to narrow the

flood-plain of the Banjir Kanal Timur too much. Decreasing the floodplain decreases the

discharge and retention capacity of the Banjir Kanal Timur. The reduction of retention and

discharge capacity leads to higher water levels during extreme discharge events. A minimum

crest width of 1 m is considered to be sufficient for inspection and maintenance by foot.

Hydraulic design BKT dike

The BKT dike has to withstand the static water load form the Banjir Kanal Timur and is not

prone to waves.

Crest level

The design water level along the BKT dike is determined by the Banjir Kanal Timur. The water

level gradient is increasing in southern direction.

1

2

3

4

5

1: jl. Arteri

km 1.341-1.940

2: jl. Kaligawe

km 1.941-2.722

3: jl. Sewah

Besar

(km 2.722-3.203

4: jl. Citarum

km 3.204-4.017)

5: jl. Kartini

km 4.018-5.472

No improvement

of existing BKT

dike


122

The crest level is determined by the design water level of the Banjir Kanal Timur plus freeboard

of 0.5 m. The magnitude of this safety margin is determined according to the Dutch guideline on

the design of dikes along rivers.

The current and required crest levels and the year in which improvement is required are pre-

sented in Table 8.17. The segment south of segment 5 is added to show improvement is not re-

quired for that particular segment. Segment 1-3 need immediate improvement. The total length

of these segments is 1.862 km. Segment 4 and 5 need improvement in respectively 2016 and

2022.

Table 8.17. Required crest levels

Design Current Segment

Water

level

[m+MSL]

Free-

board

[m]

Crest level

[m+MSL]

Crest level

[m+MSL]

Land

subsidence

[m/year]

Improvement

[year]

1 Jl. Arteri +1.6 0.5 +2.1 +1.9 0.09 2008

2 Jl. Kaligawe +2.5 0.5 +3.0 +2.8 0.07 2008

3 Jl. Sewah Besar +2.7 0.5 +3.2 +3.0 0.06 2008

4 Jl. Citarum +3.0 0.5 +3.5 +4.0 0.06 2016

5 Jl. Kartini +4.8 0.5 +5.3 +6.0 0.05 2022

Jl. Bridgend Katamso +5.4 0.5 +5.9 +7.1 0.05 2032

Figure 8.28. Existing embankment Banjir Kanal Timur


123

Critical items

Harbour of Semarang is not protected

The location of the northern dike is not optimal from viewpoint of flood protection. Normally

the dike would be located along the sea, to protect as much area as possible. The project area

does not include the harbour, while it has a high economic value and is vital for the economy of

Semarang. However, the advantage of the location of the dike of the Banger polder is the

limited length (1100 m), which is practically ideal for implementation.

Water boundary conditions

Three water boundary conditions can be mentioned, i.e.:

• tidal water fluctuation at the downstream boundary;

• discharge from upstream part of the rivers;

• run-off from the rainfall in the polder area.

8.6 Design approaches and design standards applicable to the Banger Pilot Polder

Safety level of the polder

In the Banger-polder, flooding is caused by two mechanisms:

• sea;

• rainfall within the polder area.

Safety principle flooding caused by the sea

In history the safety definitions of a flood defence were mainly formulated by the ‘highest

known water level’. The flood defence was designed at that level plus a certain margin.

However, the level of safety of the polder is related to the exceedance frequency of the high

water level. This design water level is a function of the economic value of the polder (housing,

people, environment etc.) and the accepted risk to human life. In the Netherlands where the

polder concept has been applied for centuries, the flood defence of these polders must be able to

withstand extreme hydraulic conditions that may occur once per 1,250 year (primary river dikes

which does not have to withstand extreme wave conditions). This standard is the result of


124

comprehensive cost benefit and safety analysis. The Banger polder will mainly protect

residential and commercial functions. Flooding will cause a lot of damage to these functions and

even can take human lives. The design chance of occurrence of the dike is 1,000 years (instead

of 1,250 years), because the wind setup cannot be determined for a longer chance of occurrence

of 1,000 years. The difference between the height of the dike with a design chance of

occurrence of 1,000 and the height of the dike with a design chance of occurrence of 1,250 is

only a couple of cm, which is negligible, compared to the land subsidence.

Safety principle of flooding caused by rainfall

The damage of a flooding caused by the rainfall is limited (to the rainfall within the polder area)

and will not take human lives. In the Netherlands inundation of urban areas, caused by extreme

rainfall, may occur once per 100 year. For the Banger polder a design chance of occurrence of

inundation of 100 years is recommended.

Crest level dikes

Several parameters, but primary land subsidence during the design lifetime determine the design

crest level. Table 8.18 shows the design crest level for a design lifetime of 10 and 20 years.

After the design lifetime period, the dike has to be heightened to pace with the land subsidence

and sea level rising.

Table 8.18. Design crest level for a design lifetime of 10 and 20 years at northern area (after

residual settlements)

Parameter 10 years 20 years

Highest High water Spring 0.50 m+MSL 0.50 m+MSL

Storm surge +0.20 m +0.20 m

Wind setup with a design chance

of occurrence of 1,000 years

+0.40 m +0.40 m

Sea level rising +0.06 m +0.12 m

Freeboard +0.50 m +0.50 m

Land subsidence +0.90 m +1.80 m

Total 2.56 m+MSL 3.52 m+MSL

Design lifetime and crest level of the dikes


125

Design lifetime

The design lifetime is the period in which the dike fulfils its function: withstanding extreme

conditions at sea with a design chance of occurrence of 1,000 years. So, during the design

lifetime period, the chance of failure is once per 1,000 year. In this project the design lifetime is

an important parameter, because the design lifetime of the dikes is related to the land

subsidence. Due to land subsidence, the crest level of the dike will decrease, which influences

the lifetime.

The expiration of the design lifetime does not mean that the dike has lost it function. The

protection by the dike becomes less. Failure of the dike will occur more than the defined safety

level. By heighten the dike in the second phase, the dike can again fulfils its function.

Design lifetime dikes Banger Polder

In phase 1 of this project, it was concluded that a design lifetime of 20 years is considered to be

feasible for the Banger Polder area. But even a design lifetime of 20 years may not be feasible

because of the following reasons:

• the design lifetime is primary determined by the land subsidence. However, the rate of

land subsidence is uncertain. This means that also the lifetime of the dike is uncertain. For

this reason it is advised to design for a limited lifetime of 20 years or less and to monitor

the actual land subsidence of the dikes;

• the future planning of the surrounding area is uncertain. Within the next twenty years,

maybe the polder concept will be implemented in the harbour, north of the project area or

in the area west of the project area. If this is the case, the dikes of the harbour will protect

also the project area. The dikes of the current project area loose its function;

• if in the next 20 years no measures are taken in the surrounding area of the project area,

the surrounded area will be inundated. This makes the Banger Polder inaccessible and

isolated.

After the expiration of the design lifetime the dike can be heighten in a second phase. In the

design, spare room for future heightening will be taken into account. When making a dike, it is

important to take no-regret measures. In the previous part, some possible future extensions are

described, more or less based on the ring dike concept. When a ring dike will be constructed, for


126

example to protect the harbour, some dikes of the Banger polder will lose its functions. Figure

8.29 presents the dikes of the Banger polder and the dikes of the dike-ring concept. In this figure

it can be seen that the dike along the Banjir kanal Timur, is part of the ring dike concept. This

dike (along the Banjir kanal timur) is a not-regret dike, because by possible future extension,

this dike will not lose its function. In the figure it also can be seen that when the polder will be

extended to the ring dike, the northern and western dike of the Banger polder will lose its

function.

Figure 8.29. Dike Banger polder and Ring dike

For the design lifetime of the Banger polder dikes, a distinction will be made between dikes,

which are also part of a possible future ring dike, and Banger polder dikes that will lose its

function, when a ring dike will be realized. For the Banger polder dikes, which are part of the

ring dike, a design lifetime of 20 years is recommended, the same design lifetime as considered

to be feasible in phase 1 of this project. For the dikes, which are not part of the ring dike, a

design lifetime of 10 years is recommended, because it can be expected that within the next 10

years the polder will be extended.


127

Water management system

First, all the water management components (canals, infrastructures, retention and detention

basins) were calculated based on steady flow computation. This preliminary design will be

checked and improved by using an unsteady flow computation.

For this Banger polder system, two different systems will be simulated, they are:

• with tidal gate at the downstream boundary;

• with pumping station at the downstream boundary.

Next to this, for operation and maintenance of the water management system purposes, similar

unsteady flow model can also be applied.

Schematisation of the model

Schematisation of the model should be based on the physical conditions of the prototype. In the

schematisation, it should be clear where the water level and discharges would be calculated.

Initial condition

As initial condition to the model, stationary condition of the system can be used. This stationary

condition can be obtained by the steady flow computation. Initial conditions must cover both

flow parameters (water level and discharges) at all computation points/grids.

Boundary conditions

Upstream river discharges, lateral discharges from river tributaries and water level fluctuations

at downstream boundary will be needed as boundary conditions for the unsteady model

simulations.

Analysis and evaluation

Based on the mathematical model simulation results and its hydraulic performance will be

analysed and evaluated according to the design standard. In this phase an iteration process of the


128

modelling activities will be the case.

8.7 Impacts of subsidence and sea level rise on water management and flood protection for

the Banger Pilot Polder

The impact of land subsidence and sea level rise will amplify to each other and the result is

creating more constraint to the drainage capacity of the water management system in one hand

and to the design of the flood protection in another (dikes and outlet structures). Next to that

they will also affect the salinity intrusion in the groundwater system as well as open water

system (in case of no dam at the mouth).

Land subsidence processes have to be stopped and controlled from now on. Special control

measures have to be set up (structural and non-structural).

8.8 Mitigation measure

Lowering of the groundwater level is needed to acquire better living conditions (dry house,

better bearing capacity of the roads). The lowering of groundwater level leads to additional

settlement. However, the rate of settlement can be reduced by a good and proper groundwater

control. By controlling a higher water table in the Kali Banger in the dry season, the impact on

the settlement will be reduced while the groundwater level is kept low enough to serve its

functions (houses and roads). A water table of 1 m below surface level (1 m higher than in the

wet season) is possible. In the dry season less retention capacity will be required and

groundwater levels are lower.

Different water tables in the dry and wet season demand other specifications for the pumping

station and the weirs and the operation of the hydraulic control structures. This mitigation

measure should be worked out in the design report.

9 Construction aspects of water management and flood protection for the Banger Pilot Polder

129

9 Construction aspects of water management and flood

protection for the Banger Pilot Polder

9.1 Dike, outlet and inlet structures

Possible future extensions

In this part possible future extensions of the polder area are explored. In future, these extensions

are likely, because the dikes of the Banger polder are, from the viewpoint of flood protection

and Water management, not at the right location. However for a pilot, the boundaries of the

Banger polder are well chosen, because it limited the length of the dike and the polder area.

First, the ring dike concept will be described. In the second and third paragraph, two possible

extensions are examined.

Ring dike concept

In the Netherlands, the ring dikes are along rivers and the sea, to protect as much land as

possible. The area protected by the ring dike, can contain several polders. Figure 9.1 presents

the ring dike principle.

Figure 9.1. Ring dike principle

Following this principle, the ring dike around the project area would be along Banjir Kanal

Timur, the sea, Kali Baru and Kali Semarang, as presented in Figure 9.2.


130

Figure 9.2. Ring dike principle around project area

Following the ring dike principle around the project area (see Figure 3.2), the harbour of

Semarang will be protected. The harbour has a big economic value and is vital for the economy

of Semarang. In the harbour, the Master plan for land reclamation can be incorporated in the

boundaries (dikes) of the polder. As presented in Figure 9.2, the boundaries of ring dike are as

follows:

• north boundary : Java Sea;

• south boundary : Jl. Brigjend. Katamso;

• west boundary : Kali Baru, Kali Semarang;

• east boundary : Tanggul Banjir Kanal Timur.

Table 9.1 presents some parameters of this alternative extension.


131

Table 9.1. Parameters possible future extension I

item Sub item unit Quantity

area Area ha 1176

Inhabitants # 119,000

Industries/companies - Pertamina, PLN, Sriboga

Stakeholders

Facilities - PTKA, Pelindo

North km 11,000

West km 3,400

Length of

dike

Total km 14,400

1 - Dike crosses the railway at 2 locations Critical items

2 - Construction of the northern dike is costly

because it has to be built as quay and as sea

defence. Implementation of polder system

will take more time

This dike will be realized in the sea. The location of the dike is shown in Figure 9.3. This

possible future extension only requires some land acquisition of fishing ponds at the eastern

part.

Figure 9.3. Possible location of the dike at the north side

The length of the dike at north side is 11,000 m. The dike has to be constructed as a quay wall

(at the harbour) or as a sea dike.


132

Western dike

The western dike consists of three parts:

• along Kali Baru;

• along Kali Semarang;

• the dike along Kali Baru can be realised at the location of the road.

Eastern dike

The eastern dike is the same as the Banger polder. Next to that possible future extension II are:

Extension west

This option covers the possible future extension extends only west part. At the west side, the

dike will follow the ring dike principle, but not at the north side. In this possible extension, the

western dike lies along Kali Baru and Kali Semarang. Figure 9.4 shows the boundaries of this

polder. As presented in Figure 9.4, the boundaries of this alternative extension are:

• north boundary : Jl. Arteri;

• south boundary : Jl. Brigjend. Katamso;

• west boundary : Kali Baru Kali-Semarang-Jl. Haryono;

• east boundary : Tanggul Banjir Kanal Timur.

Table 9.2 presents some parameters of this alternative extension.

Table 9.2 Parameters possible future extension II

Item Sub item Unit Quantity

Area area ha 703

inhabitants # 106,000

industries /

companies

- Pertamina

Stakeholders

facilities - Railway Company

north km 2,000 Length of

dike west km 3,400


133

total km 5,400

1 - dike crosses the railway at 2 locations

2 - possible piping, due to non-uniform land subsidence

northern dike, caused by foundation Jl. Arteri

Critical items

3 - harbour, with high economic value not protected

Figure 9.4. Boundary of possible future extension II

Location of the dike at the north side

The eastern part of the northern dike (east of Jl. Ronggowarsito) is similar to the northern dike

of the Banger polder. The northern dike, west of Jl. Ronggowarsito is shown in Figure 9.5. The

total length of the northern dike (including the eastern part) is 2,000 m.


134

Figure 9.5. Location of the dike at the north side, west of Jl. Ronggowarsito

The western dike is the same as described in the possible future extension I.

Location of the eastern dike: The eastern dike is the same as the Banger polder.

9.2 Water management system for the Banger Pilot Polder

Rivers around Banger area

The rivers around banger area are presented in Figure 9.6 and Table 9.3 reports the

characteristics of these rivers.


135

Figure 9.6. Kali Banger and rivers around Kali Banger

Table 9.3. Characteristics of rivers

Length

(km)

Basin area

(ha)

Maximum

discharge

(m3/s)

Maximum.

water level

(m+MSL)

Kali Banger 6.5 527 17*

Banjir canal Timur 17.8 5517 295 1.1

Kali Baru 0.8 150 24 1.1

Kali Semarang 1280 40* 1.1

* estimation of maximum discharge


136

10 Management, operation and maintenance of the water management and flood protection system for the

Banger Pilot Polder

137

10 Management, operation and maintenance of the water

management and flood protection system for the Banger Pilot

Polder

10.1 Operation of the structures

When there are water control structures in the secondary canals these will preferably have to be

operated according to the guidelines as given in Volume III: Technical Aspects, unless there is a

general agreement among those stakeholders concerned that another operation rule will have to

be followed. Question is then when the normal operation rules can be followed, and when one

can speak of an extremely dry or an extremely wet period. It is recommended that the normal

operation rules will be followed and that only the rules for extreme dry or wet conditions will be

followed when this is at least agreed by the concerned Polder Authority included representative

of the stakeholders, PemKot Semarang and Dinas PU Pengairan Semarang.

The major problem in Banger Polder associated with the operation of hydraulic structures is

debris and sediment, which decreases the flow capacity of the structures and even damages

the structures. Due to natural and human activities in the headwater areas, large amounts of

debris and sediments are deposited around hydraulic structures, which in turn have a

negative effect on its operation. In order to cope with this problem, time estimation of the

debris and sediment accumulation around the structures will be needed in relation to a

proper operation of the structures. An example of improper maintenance of the system is

shown in Figure 10.1.

Figure 10.1. Improper maintenance of a polder system


138

Operation of the structures will cover the following water management system components:

• pumping stations;

• sliding gates;

• retention and detention basins.

10.2 Maintenance of the water management and flood protection system for the Banger

Pilot Polder

Maintenance of the water management system should cover three types of maintenanc3, i.e.:

• routine maintenance;

• periodic maintenance;

• emergency maintenance.

Frequent and timely maintenance is of importance for obtaining the benefits of the systems.

Especially in urban polder canals, or canal sections with low flow velocities re-growth of weeds

may be very fast, and can quickly reduce the already low flow velocities to practically zero with

detrimental consequences for water quality and drainage capacity.


regular removal of weeds from canals and embankments, it includes minor repairs and servicing

of O&M equipment and facilities. Routine maintenance activities can be planned and budgeted

in advance on the basis of the estimated labour, cost and required frequencies of the works.

Removal of debris in front of gates, and greasing, oiling and cleaning of structure components

are part of the regular duties of the O&M staff and gate operators. Except for the cost of

materials (grease, oil, cleaning tools), no separate budgets are required. Other routine

maintenance works are carried out either by the farmers themselves, by the O&M staff, by

labourers under supervision of the O&M staff, or by contractors.

Canal cleaning

Aquatic weeds are not expected to pose a constraint in the primary canals due to the depth and

the high flow velocity in these canals. For the removal of aquatic weeds in the secondary and

tertiary canals the use of manual labour is preferred. Weed removal from the secondary canal

beds is required at regular intervals. During each round of maintenance the following activities


Banger Pilot Polder

139

need to be carried out:

• cutting loose and removing floating and submerged plants and algae from the canal bed

and canal side slopes; the weeds must be cut as low as possible near the base of the stem

using a sickle, cutlass, scythe or mechanically;

• the weed debris must be removed from the canal bed by hand or using a rake, and be

deposited and burned behind the embankment;

• weed clearance in the secondary and tertiary canals can best start at the downstream end,

and proceed in upstream direction. Preferably the maintenance of the canal beds should

be carried out synchronous with the maintenance of the banks;

• obstructions for the water flow like tree trunks, fishing nets, or temporary checks would

have to be removed to ensure the free flow of water.

Minor repair and shaping of embankments

Erosion gullies caused by rainfall, cracks caused by drying out and shrinking of the soil and

potholes made by traffic in embankments will have to be repaired timely because this type of

damage tends to expand rapidly. The dikes and embankments need to be inspected at regular

intervals and each year the following repair activities will have to be carried out:

• erosion gullies, soil cracks and potholes in the dike have to be cleared of weeds, mud,

debris and other material;

• the holes have to be filled-up and compacted; the top of the soil fill need to be shaped

convex, so that runoff of rainfall is ensured;

• holes in the embankment, made by rats, crabs or other animals, need to be closed.

Maintenance of structures and buildings

Water control structures need to be cleared from weeds at weekly intervals. Obstructing debris,

hampering operation, is to be removed daily. The structures have to be regularly inspected and

any malfunction is to be reported. It is of importance that repair is being done at short notice.

Moving parts need to be greased every two months. Hinges and groves oiled every two months,

every four months old grease and oil need to be cleaned using diesel.

Once per year, in the dry season, the concrete of the structure will have to be cleaned from dirt

and algae. The steel parts need to be cleaned and re-painted. Missing bolts, nuts and padlocks


140

need to be replaced. Small cracks in concrete walls and stone masonry of the structure will have

to be plastered with concrete mortar.



have to be replaced. The offices and housing of O&M staff need to be tarred, painted and

whitewashed.

Major damages to structures and buildings will have to be reported and repaired under the

periodic maintenance program. However, in case of emergencies immediate repair will have to

follow.

Periodic maintenance

Periodic maintenance, also called incidental or regular maintenance, consists of desilting and re-

profiling of canals and repair of embankments, structures, buildings, equipment, etc. These

activities need to be identified and quantified on the basis of yearly inspections and quantity

surveys. The activities cannot be determined in advance from project inventories. Although

some periodic maintenance needs can be estimated from the supposed lifetime of structures or

facilities, the precise volume and location of the works and which structures or equipment need

to be replaced, will vary from year to year.

Emergency maintenance


collapse of embankments or structures, damage caused by flooding, etc. To prevent further

damage, immediate action will generally be required and other ongoing maintenance activities

may have to be interrupted to make all manpower and equipment available for the emergency

maintenance. This maintenance is also needed in case of minor damage to structures and

surrounding earthworks, which impede the structure operation. For example the breakdown of

moving parts like winches and cables by which gates are opened and closed. Such damage will

severely affect the on-farm O&M and may result in crop damage. Urgent repair is then needed.


be made available, or funds from ongoing contracts can be made available by postponing some


Banger Pilot Polder

141

less important works.

Solid waste management

The improper way to do open dumping of solid waste cannot be tolerated anymore. It is clear

that they may create environmental and flood problems. The institutional of the solid waste

management should mainly consider the way to transport the waste to the final deposition

location. The main considerations are:

• in line with the requirement from the people in the area;

• in line with the social culture and environmental conditions of the area;

• sustainable because based on the request of the local people and their financial capacity

and management.

Basically, the operation and management of the solid waste should involve the following:

• RT/RW or Karang Taruna (young people organization);

• private sector;

• shop association;

• NGO;

• recycling organization;

• Polder Authority;

• Local Government.

Dredging of water management systems

Two levels:

• urban polder water management system;

The maintenance of urban polder water management should be carried out by the Polder

Authority.

• river systems.

The maintenance of the river systems will be too difficult for the Polder Authority. It

needs significant budget for that where the Polder Authority cannot do it. Also based on

the Undang Undang No. 4 year 2004, river systems will be managed by the Ministry of

Public Works. It means that in this case the maintenance and dredging of the river

systems should be carried out by PemKot (DPU) in coordination with the Central

Government i.e. Ministry of Public Works.


142

10.3 Institutions and their responsibilities for operation and maintenance of the water

management and flood protection system for the Banger Pilot Polder

Several institutions will be involved in the operation and maintenance of the Banger pilot

polder, i.e.:

• Polder Authority

• BAPPEDA

• PemKot Semarang

• Dinas PU Pengairan, Semarang

• Home Affairs Ministry

10.4 Stakeholder participation in operation and maintenance of the water management

and flood protection system for the Banger Pilot Polder

Participation by the affected parties including consumers, water users, land owners and non

government organisations in the decision making and implementation process has generally

resulted in better compliance with the laws. The Polder Authority should compose of all the

representatives of the stakeholders and they should be at the operational level. Stakeholder

representatives should act in one hand as steering committee, advisor and especially in the

decision-making processes and in charge in operation and maintenance activities in another

side.

The participation of stakeholders should also be in the dissemination and discussions, which

cover, technical as well as social, economy aspects of the Banger polder development.

In the dissemination part, the involvement of the stakeholders should include to:

• socialize the Government Planning in relation to the management of the Banger Polder;

• inventarize and accommodate all ideas from all the key persons in relation to the general

development of the Banger Polder;

• evaluate the perception and motivation of all the non-governmental organizations in side

the Banger Polder in relation to the flood control and protection programme of the Polder

authority in relation to the public social welfare;

• settle the commitments among all the involved parties included stakeholders in relation to

the operation of the Banger Polder.


Banger Pilot Polder

143


144

References

145

References

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Batjjes, J.A. Short waves. Lecture Notes. IHE. The Netherlands. 19...

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2006

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Duivendijk van. Manual on planning of structural approaches to flood management (ICID, New

Delhi, India, 2005

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modelling of urban water systems. Monograph 15. CHI, Guelph, Ontario, Canada, 2006.

Luijendijk, J., E. Schultz and W.A. Segeren. Polders. Development in Hydraulic Engineering.

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Mays, L.W. Urban storm water management tools. McGraw-Hill, London, 2004.

Oki T. and S. Kanae, 2006, Global Hydrological Cycles and World Water Resources, Science,

vol. 313, 1068-1072.

Osman Akan A. and R.J. Houghtalen. Urban hydrology. hydraulics, and urban polder water

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Shanks, R.L. (chief ed). Pumping station design. Butterworths, UK, 1989

Smedema, L.K., W.F. Vlotman, D.W. Rycroft. Modern land drainage. Planning, design and

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1988

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MASMA Urban Storm Water Management, Laman Web Rasmi Jabatan Pengairan & Saliran


146

Malaysia, http://www.water.gov.my

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management. Edward Elgar, UK, 2006.

ANNEX I. Glossary

147

ANNEX I. Glossary


BoD Basis of Design

BOD Biochemical Oxygen Demand mass concentration of dissolved

oxygen consumed under specified

conditions by the biological

oxidation of organic and/or

inorganic matter in water

Bappeda Badan Perencanaan Dearah regional planning agency

Calibration experimental determination of the

relationship between the quantity

to be measured and the indication

of the instrument, device or

process which measures it

Coliform organism microorganisms found in the

intestinal tract of humans and

animals

Data collection process of collection, storage and

processing of data up to data

dissemination, with emphasis on

the type of data, the storage and

transfer facilities and procedures

and the QA/QC routines of the

processed data.

DPU Dinas Pekerjaan Umum regional Public Works

DGCK Directorate General Cipta Karya Director General of public works

DTK Dinas Tata Kota City planning Service, Ministry of

Public Works

KAI Kereta Api Indonesia Indonesian Railway Company

Monitoring: continuous or frequent

standardised measurement and

observation of the environment,

often used for warning and control


148


NPV Net Present Value

O&M operations and maintenance

Pathogens microorganisms that can cause

disease in other organisms or in

humans, animals, and plants

PB Polder Board

PDAM Perusahaan Daerah Air Minum Local Drinking Water Company

PELINDO Perusahaan Pelabuhan Indonesia Indonesian Harbour Company

PLN Perusahaan Listrik Negara State Electricity Company

PoR Program of requirements

PSDA Pengelolaan Sumber Daerah Air Regional department of water

resources management

PU Departmen Pekerjaan Umum Indonesian Ministry of Public

Works

PusAir Puslitbang Air water section of research and

development centre

PfW Partners for Water

TelKom Telekomunikasi Tele-communication company

ToR terms of reference

UDPKS Urban Drainage Plan Kali Semarang

UNESCO-IHE Institute for water education,

Delft, the Netherlands

VAT

V&W Ministry of Public Works,

Transportation and Water

Management

Dutch Ministery van Verkeer en

Waterstaat

VROM Ministry of Housing, Spatial

Planning and the Environment

Dutch Ministery van

Volkshuisvesting, Ruimtelijke

Ordening en Milieubeheer,

Wastewater a combination of liquid and water-

carried pollutants from homes,

businesses, industries, or farms; a

mixture of water and dissolved or

suspended solids

ANNEX I. Glossary

149


Water quality

standards

specific levels of water quality

which, if reached, are expected to

render a body of water suitable for

its designated use

W+B Witteveen+Bos