storm water management

Application of dynamic storm water management modeling for Matara Municipal Council area

Abstract

Urbanization of an area cause to increase the impervious areas in the vicinity of city area that

cause to decrease the infiltration and increase the surface runoff. This cause flash floods in

low land areas. Therefore stormwater management in urban areas should be done with

sufficient attention.

Stormwater drainage problem in Matara Municipality area has become a major problem. This

is mainly because of improper practices adopted while developments are taking place. In this

context alternation made to the surface topography and permeability in property

developments have created a significant impact on increasing the surface run-off rates and

volume. People who live in the close proximity, change the topography to prevent the surface

runoff through their land, thus, effectively changing the natural drainage paths in the

urbanized areas.

This studies mainly focused to develop a stormwater model for Piladuwa area in Matara

municipal council, by the use of EPA SWMM model.

Field visits to the study area were made to collect the input parameter for mathematical

model development. During these field visits stakeholder surveys was done to collect the

data for model verification. A Sensitivity analysis was carried out for the catchment area

in order to identify the catchment parameters that affect the catchment outflow

parameters. Result taking from the model used to take the engineering option for storm

water management in Piladuwa area.

i


Acknowledgements

First and foremost, I would like to express my appreciation to Prof. N. T. S Wijesekera [Final

year Research Project coordinator and my individual Research Project supervisor], for

sacrificing his priceless time of heavily loaded work schedule in order to guide, direct,

advise, comment, correct and criticize me and my research work.

Also there was excellent support from academic staff of the Department of Civil Engineering

University of Moratuwa. I make this an opportunity to extend my humble gratitude to all the

academic staff members in the Department of Civil Engineering.

Special appreciation goes to Mr.Dulanjan Wijesinghe and, Miss.Nimmi sooriyabandara for

helping us in GPS survey .

I would also like to thank my research group members Miss.H.M.D.Harshani,

Miss.K.S.S.Chandrasiri and my batch mates that I closely worked with during the research

work, Mr. Supun rangana, Mr. Susantha Wanniarachchi and Mr.Y.A.Naotuna. Thank you

very much for the eventful, wonderful and most remembered time shared with me during the

final year research project.

At last but not least, I appreciate each and every person who contributes to make my research project a success.

Thank you.

Charithal.R.M.

Department of Civil Engineering

University of Moratuwa.

ii


Table of Contents

Abstract.......................................................................................................................................i

Acknowledgements....................................................................................................................ii

List of Figures...........................................................................................................................vi

List of Tables...........................................................................................................................vii

CHAPTER 01.............................................................................................................................1

1.1 Introduction.................................................................................................................1

1.1.1 Research background...........................................................................................1

1.2 Scope...........................................................................................................................2

1.3 Objectives....................................................................................................................2

1.3.1 Overall objectives of group..................................................................................2

1.3.2 Specific objective.................................................................................................2

1.3.3 Limitation and boundary of the research project.................................................2

1.4 Study Methodology Flow Chart..................................................................................4

1.5 Activities Executed......................................................................................................5

CHAPTER 02.............................................................................................................................7

2.1 Literature review.........................................................................................................7

2.1.1 Brief History.............................................................................................................7

2.2 Stormwater management in urbanized watersheds.....................................................7

2.2.1 Effects of urbanization on watersheds.................................................................7

2.3 Storm water modeling for urban areas........................................................................8

2.4 Different Model available for modeling......................................................................9

2.5 Typical application of SWMM..................................................................................11

2.6 Engineering Guidelines.............................................................................................12

CHAPTER 03...........................................................................................................................15

3.1 Data Collection...............................................................................................................15

3.1.1 General description..................................................................................................15

3.3 Sample calculation.........................................................................................................17

3.3.1 Slope........................................................................................................................17

3.3.2 Area.........................................................................................................................18

iii


3.3.3 Width..................................................................................................................18

3.3.4 Manning roughness:...........................................................................................18

3.3.5 Percentage of pervious and imperviousness......................................................18

3.4 Field work execution.............................................................................................19

3.4.1 Other required data.............................................................................................20

CHAPTER 04...........................................................................................................................21

4.0 Modeling.......................................................................................................................21

4.1 Model selection...........................................................................................................21

4.2 My study area.................................................................................................................21

4.3.1 Schematic diagram for SWMM model........................................................................22

4.3.3 Notations & symbols used.......................................................................................23

4.2.3 Data for model.........................................................................................................23

4.4.4 Design rainfall intensity.............................................................................................25

4.4.5 Input rainfall data....................................................................................................26

4.4.6 Catchment details.......................................................................................................27

CHAPTER 05...........................................................................................................................29

5.0 Model results..................................................................................................................29

5.1 Surface runoff.................................................................................................................29

5.2 Simulation result.............................................................................................................30

5.3 Subcacthment Runoff summary....................................................................................32

5.4 Node depth summary.....................................................................................................32

5.5 Node inflow summary.................................................................................................33

5.6 Node flooding summary................................................................................................33

5.7 Outfall Loading Summary.............................................................................................34

5.8 Link flow summary.......................................................................................................34

CHAPTER 06...........................................................................................................................36

6.1 Sensitivity Analysis........................................................................................................36

6.2 Sensitivity analysis for Subcatchment 06..................................................................36

6.2.1 Sensitivity of Slope of the catchment....................................................................36

6.2.2 Sensitivity of ” n”pervious......................................................................................37

6.3 Sensitivity analysis for other subcatchment...................................................................39

iv


CHPATER 07...........................................................................................................................40

7.1 Conclusion & Discussion...............................................................................................40

8.0 REFERENCES............................................................................................................viii

9.0 ANNEXES.......................................................................................................................viii

9.1 Annex A........................................................................................................................viii

9.2 Annex B...........................................................................................................................ix

v


List of Figures

Figure 1 – Matara Municipal Council area................................................................................1

Figure 2 – Flood hazards............................................................................................................2

Figure 3 - Catchment areas........................................................................................................3

Figure 4 - Methodology flow chart............................................................................................4

Figure 5 - Surface runoff reducing...........................................................................................13

Figure 6 -Pervious cathbasin....................................................................................................14

Figure 7 - sMap of selected area (Piladuwa)...........................................................................22

Figure 8 - Divided subcatchments..........................................................................................22

Figure 9- SWMM model schematic diagram...........................................................................23

Figure 10 notation used for SWMM........................................................................................23

Figure 11 - Input parameters for the model.............................................................................24

Figure 12- manning’s roughness values...................................................................................24

Figure 13 –Infiltration data......................................................................................................25

Figure 14 - Typical Depression storage values........................................................................25

Figure 15 –Time series editor..................................................................................................26

Figure 16 - Time series............................................................................................................27

Figure 17 - Surface runoff........................................................................................................29

Figure 18 – Subcatchment losses.............................................................................................29

Figure 19 – Schematic diagram of Piladuwa...........................................................................30

Figure 20 - Water elevation profile -at 1.00 hour....................................................................30

Figure 21 – Node depth Vs time..............................................................................................31

Figure 22..................................................................................................................................31

Figure 23 – Water elevation profile -at 15 minutes.................................................................31

Figure 24 – Water elevation profile -at 30 minutes.................................................................32

Figure 25 – Flooding area........................................................................................................40

vi


List of Tables

Table 1 - Model comparison....................................................................................................10

Table 2 - Model comparison....................................................................................................10

Table 3 – Field work execution................................................................................................20

Table 4 – Catchment details.....................................................................................................28

Table 5 – Subcatchment Details...............................................................................................28

Table 6 - Subcacthment Runoff...............................................................................................32

Table 7 - Maximum node depth...............................................................................................32

Table 8 - Node inflow summary............................................................................................33

Table 9 - Node flooding summary...........................................................................................33

Table 10 - Outfall Loading Summary......................................................................................34

Table 11 - Link flow summary.................................................................................................34

Table 12 – Flooding nodes.......................................................................................................36

Table 13 - Subcatchment slope vs peak flow...........................................................................37

Table 14 - Pervious Manning's n vs. peak out flow.................................................................38

vii


CHAPTER 01

1.1 Introduction

1.1.1 Research background

When the history is considered, it can clearly see that the civilization has occurred

around the f flood plains. Matara Municipal Council Area is also situated in a flood plain of

Nilwala River (Figure 1) and has experiencing stormwater drainage problems,such as flash

floods.

Figure 1 – Matara Municipal Council area

Matara municipality area is a very low land area and it is almost a flat terrain .Matara

town rapidly growing since Matara is one of best city in southern province and it possesses

leading schools and infrastructure facilities. Because of above mentioned reasons people

attract to the Matara city and its population density went up and people dwell low land areas

also. With respect to the population increase imperviousness, vegetation removed of the city

limit this created, increase of overland flow as well as speed of the over land flow.

Nowadays Matara municipality area facing storm induced flash flood due to above

mentioned reasons. This is a inconvenience for people, with flood they may have to leave

their houses (Figure1) then government have to give them shelter and food and also when

road are flooded transportation is become vulnerable (Figure 1)so time of people is wasted

and large amount money ,properties of the country wasted productivity of the work force also

affected .This problem is not only facing Matara, lot of cities in Sri Lanka facing this problem

so it is advisable to manage stormwater and overcome this flooding problem.

1

Nilwala River


Figure 2 – Flood hazards

1.2 Scope

The main scope of this study is to develop a mathematical model for the Matara

Municipal Council Area, to provide engineering and management options to mitigate the

stormwater problem.

1.3 Objectives

1.3.1 Overall objectives of group

Overall object of this project is to investigate the existing stormwater related problems

in Matara Municipal Council and develop a mathematical model for storm water management

and find out engineering and management options, that can be implemented, in order to

mitigate the stormwater problem.

1.3.2 Specific objective

1) Identify the watershed using water flow directions

2) Identify the sensitive catchment parameters which affect the outflow from the

catchment to the canal system

1.3.3 Limitation and boundary of the research project

Since Matara Municipal Council area is an ungauged catchment area, no data were

available about the catchment and it was found through the field survey for model calibration

process. Therefore it is difficult to develop a model which generate output with higher

accuracy. Therefore the developed model was calibrated produce the results within a

maximum and minimum values.

2


1.4 Study area

Matara is located at the Southern coast of Sri Lanka. Matara is a well developed

commercial centre. Nilwala River is the main fresh water body at close proximity. In Matara

Municipal area there are three sample areas which were identified for detailed modeling.

They are listed below.

1. Piladuwa

2. Walgama

3. Thotamuna

Figure 3 - Catchment areas

3

Nilwala River


1.5 Study Methodology Flow Chart

Figure 4 - Methodology flow chart

4


1.6 Activities Executed

Literature survey

Literature surveys done to identify best software package to this project and

also to gain knowledge what have done by other have done relating to our

research project. Literature survey is very important to find manning’s

roughness value, parameters for GREEN AMPT infiltration method etc….

GPS practice

To take the GPS point, photo point and voice cut at the field. GPS points are

very important to identify the path of the river , also we can check that if there

is a deviation with map also and length between nodes can be measures using

GPS points .

Desk study

Desk study is done before every field visit to identify the boundaries of the

area which we are going to be covered at the field and also from where to start

and end the field study. After every field visit desk study done to calculate

catchment slope, width of catchment etc… Data arranging was also done

during this desk study time.

Computer model practicing and identifying the parameters for the model

After choosing the software package for the modeling purpose it was needed

to know familiarize with the parameters that should taken at the field work.

After identifying the parameters a field book was prepared.

Practicing a sample data collection

Before going to the field, it is important to have firsthand experience in how to

take the relevant data accurately and quickly. So

Field visit

Field visits were conducted for collect data of the subcatchment such as

vegetation, ponded areas, geometry of channel, nodes etc…..

Data arranging and summarizing

5


After every field visit it was necessary to arrange and summarize the collected

data for future references.

Calculation other parameters

After every field visit the collected data were entered to the model thus it was

needed to calculate the catchment parameters. These parameters were

calculated using Arc GIS software. Those parameters are essential to develop

the model.

Model development for catchment areas

This research is based upon the model development for subcatchment

areas.After developing the model for this areas evaluation of engineering and

management option can be done.

Calibration and verification of models

Even though we develop a computer model e can’t guarantee that it would

give accurate result as output . To assure reliable output from the model it is

necessary to calibrate the model with the available data for rainfall data and

inundation depths.

Sensitivity analysis

Sensitivity analysis is important to identify which parameter affects mostly

affect to the outflow from the catchment. After identifying those parameters

engineering and management option can be given.

6

CHAPTER 02

2.1 Literature review

2.1.1 Brief History

It is advisable to discuss the problems of existing Nilwala scheme, which was

implemented in 1980 s with technical consultancy of a French company. The strategy of

‘protecting lands by embanking and evacuating storm water by pumping’ was mainly applied

in this scheme. Other alternatives such as diversion, storage, temporary detention, enlarging

river channel etc were not been considered. Flood warning and bypassing system had been

attempted, but failed due to various socio - economic factors.

The Nilwala scheme was subjected to many controversies since the beginning. The

time allocated for planning and design was very limited. The problem was not discussed

widely and the stakeholders and local expertise point of view were not taken in to

consideration. The scheme could not achieve the targeted benefits. Specially the first phase of

the scheme, Kiralakele, was a complete failure and still abandoned after the several attempts

of rectification works. (P.Hettiarachchi)

2.2 Stormwater management in urbanized watersheds

The term "stormwater management" implies a comprehensive approach to the planning,

design, implementation, and operation of stormwater drainage improvements. The purpose of

stormwater management approach is to develop an effective drainage systems that balance

the objectives of maximizing drainage efficiency and minimizing adverse environmental

impacts.

(Municipal Program Development Branch Alberta, January 1999)

2.2.1 Effects of urbanization on watersheds

Urbanization causes a change to natural systems that tends to occur in the following

sequence. First, land use and land cover altered as vegetation and topsoil were removed to

make the way for agriculture, or subsequently buildings, roads, and other urban

infrastructure. These changes, together with and the introduction of a artificial drainage

network, have alter the hydrology of the local area, such that the receiving waters in the

affected watersheds experience radically different flow regimes than it was prior to

urbanization. Nearly all of the associated problems result from one underlying cause: loss of

the water-retaining and evapotranspirating functions of the soil and vegetation in the urban

landscape. In an undeveloped area, rainfall typically infiltrates into the ground surface or is

evapotranspirated by vegetation. In the urban landscape, these processes of

evapotranspiration and water retention in the soil are diminished, such that stormwater flows

rapidly across the land surface and arrives at the stream channel in short, concentrated bursts

of high discharge. This transformation of the hydrologic regime is a wholesale reorganization

of the processes of runoff generation, and it occurs throughout the developed landscape.

When combined with the introduction of pollutant sources that accompany urbanization (such

as lawns, motor vehicles, domesticated animals, and industries), these changes in hydrology

have led to water quality and habitat degradation in virtually all urban streams. (CLAIRE

WELTY, et al., 2008)

The influence of humans on the physical and biological systems of the Earth’s surface is not a

recent manifestation of modern societies; instead, it is ubiquitous throughout our history. As

human populations have grown, so has their footprint, such that between 30 and 50 percent of

the Earth’s surface has now been transformed (Vitousek et al., 1997). Most of this land area

is not covered with pavement; indeed, less than 10 percent of this transformed surface is truly

“urban” (Grübler, 1994). However, urbanization causes extensive changes to the land surface

beyond its immediate borders, particularly in ostensibly rural regions, through alterations by

agriculture and forestry that support the urban population (Lambin et al., 2001)

2.3 Storm water modeling for urban areas

Even though storm water modeling is not much used in Sri Lanka it is widely used in

many other countries. Stormwater modeling is being done very effective for obtaining

management solution for urban area.

With today’s advances in computer technology, many cities in the developed countries

manage local and minor flooding problems using computer based solutions. This involves

building computer models of the drainage/sewer system, for instance by using software like

MOUSE (Lindberg et al., 1989); Info Works (Bouteligier et al., 2001) and the SWMM

models (EPA SWMM, MIKE SWMM, and XP SWMM), (Huber and Dickinson, 1988).

These types of models are used to understand the frequently complex interactions between

rainfall and flooding. Once the existing conditions have been analyzed and understood,

alleviation schemes can be evaluated and the optimal scheme implemented. Nevertheless, at

present there are few studies on urban flooding that O. Mark et al. / Journal of Hydrology 299

(2004) 284–299 285deal with both the conditions in the surcharged pipe network and the

extensive flooding on the catchment surface. Even fewer projects have dealt with modeling

urban flooding in developing countries. Some of the few case studies dealing with of

modelling of urban flooding which both includes the pipe system and extended surface

flooding are: Bangkok (Thailand) (Boonya-Aroonnet et al., 2002); Dhaka City (Bangladesh)

(Mark et al., 2001); Fukuoka and Tokyo (Japan) (Ishikawa et al., 2002); Harris Gully (USA)

(Holder et al., 2002); Indore (India) (Kolskyet al., 1999) and Playa de Gandia (Spain)

(Tomicˇic´ et al., 1999). These studies treated urban flooding as a one-dimensional (1D)

problem. Schmitt et al. (2002) considered a 2D model as a benchmark for 1D model. A

model, which dynamically couples a 1D pipe flow model with a 2D hydrodynamic surface

flood is currently under development (Alam, 2003).

Many numerical models available today adopt numerical schemes to the solutions of full de

Saint-Venant equations. For instance, models like SWMM-EXTRAN (Huber and Dickinson,

1988)

2.4 Different Model available for modeling

There are 8 models specially design for urban stormwater modeling They are listed below:

1 DR3M-QUAL

1. HSPF

2. STORM

3. MIKE_SWMM

4. SWMM level1

5. QQS

6. WALLINGFORD MODEL

7. BRASS

Table 1 - Model comparison

(Review of storm water models by Christopher zoppou)

SWMM free and it can use for planning and designing urban models.

Table 2 - Model comparison

Georgia Stormwater Management Manual

The storm water management model(SWMM) was developed for the Environmental

Protection Agency in 1969 – 1971 as a singel event model for simulation of quantity and

quality processes in combined sewer systems.It has since been applied to virtually every

aspect of urban drainage,from routine drainage design to sophisticated hydraulic analysis to

non-point source runoff quality studies, using both single event and continous

simulation.Through subdeviding large catchments and flow routing down the drainage

system.SWMM can be applied to catchments of almost any size ,from parking lots to

subdevision section to cities. (philip B.Bedient, 1992)

The EPA Storm Water Management Model (SWMM) is a dynamic rainfall-runoff simulation

model used for single event or long-term (continuous) simulation of runoff quantity and

quality from primarily urban areas. The runoff component of SWMM operates on a collection

of subcatchment areas that receive precipitation and generate runoff and pollutant loads. The

routing portion of SWMM transports this runoff through a system of pipes, channels,

storage/treatment devices, pumps, and regulators. SWMM tracks the quantity and quality of

runoff generated within each subcatchment, and the flow rate, flow depth, and quality of

water in each pipe and channel during a simulation period comprised of multiple time steps.

2.5 Typical application of SWMM

Since its inception, SWMM has been used in thousands of sewer and stormwater studies

throughout the world. Typical applications include

Design and sizing of drainage system components for flood control

Sizing of detention facilities and their appurtenances for flood control and water

quality protection

Flood plain mapping of natural channel systems

Designing control strategies for minimizing combined sewer overflows

Evaluating the impact of inflow and infiltration on sanitary sewer overflows

Generating non-point source pollutant loadings for waste load allocation studies

Evaluating the effectiveness of Best Management Practices for reducing wet weather

pollutant loadings.

2.6 Engineering Guidelines

Detained water contributes to runoff and therefore detention ponds or basins must have an

outlet and outfall system . A gravity outfall should be used whenever feasible. Pumping

should only be used where there is no other practical way of handling the excess runoff.

(Highway Design Manual )

Detention pond designing

Detention ponds are the most commonly used form of runoff control, Outlet facilities for

ponds can consist of a concrete weir, a berm with culverts at several levels, a mid-pond

draw-off, or any one of a variety of other outlet structures. Side slopes are typically

grassed. However rip rap or gabion erosion protection shall be used where erosive wave

action is a concern. Various edge treatments are also used to minimize onshore weed

growth and maintain aesthetics. The pond side slopes are normally kept flat, typically

between 5:1 (H:V) to 7:1 (H:V), to reduce the risk of slipping on wet grass and falling

into the water.(Storm water management Guidelines for the Province of Alberta)

Detention

Detention refers to holding or storing stormwater and releasing it over a set period of time

to avoid high peak flows in the receiving water. Generally, detention is employed

through the use of excavated or constructed basins, often referred to as dry detention

basins or dry basins, which drain completely between storms. Dry detention basins are

effective at reducing the peak flow of stormwater from a drainage area and have the

advantage of causing the least rise in temperature in the receiving water, thus helping

protect temperature-sensitive aquatic species .Properly designed dry basins can be

aesthetically pleasing. Some commercial office buildings have well-kept grassed

detention basins that serve in dry weather as lunchtime gathering areas for employees.

Pollutant removal and aesthetic qualities can be enhanced by extending the time the

stormwater is held, which creates a small permanent wetland. Plants in the wet area hide

the sediment and debris accumulated near the outlet. Disadvantages include moderate to

high routine maintenance needs, infrequent but expensive sediment removal, and

nuisance problems including weeds, odors and debris collection. Dry basins are

considered unsightly at least in part because the accumulated sediment and debris are

visible between rains.

Surface runoff reducing

On-site (Lot-level) Controls

On-site (Lot-level) controls are practices that reduce the quantity of stormwater runoff

and improve the water quality before the runoff reaches the conveyance system. These

practices are applied at a single lot level or multiple lots in a small area.

Reduced Lot Grading

The development standards require a minimum lot grade of two per cent to ensure

adequate drainage of stormwater away from the buildings. In order to avoid foundation

drainage problems, grading within two to four meters of buildings should be maintained

at two per cent or higher. In areas outside this envelope, grading can be flattened to 0.5

per cent. A reduction in the lot grading should be evaluated if the land is flat. In hilly

areas, alterations to natural topography should be minimized. Areas outside this envelope

should be graded at less than two per cent (Figure 5). Reduced lot grading can be

implemented where soils have an infiltration rate of ≥ 15 mm/h and it is applicable to all

soils coarser than loam; clay soils are usually not suitable. In areas where reduced lot

grading is implemented, roof leaders should extend two meters away from the building to

discharge to the surface.

Figure 5 - Surface runoff reducing

Pervious Catchbasins

Pervious catchbasins are designed to convey the road drainage and these systems

have large sumps that are physically connected to an exfiltration storage medium.

The storage medium is located below or beside the catchbasin. Pervious

catchbasin details for road drainage are shown in Figure6

Figure 6 -Pervious cathbasin

CHAPTER 03

3.1 Data Collection

3.1.1 General description

Field visits conducted to collect subcathment parameters such as vegetation, ponded

areas, geometry of channel, nodes etc….. These field-collected data are very important for

model calibration and verification in case of ungauged catchments. SWMM software was

practiced before the field visit to familiarize with the input parameters. Before going to the

field locations in Matara, a preliminary field visit was conducted at Molpe- Katubedda area to

gain experience on field parameter capturing. Also a GPS survey was done in the university

premises to familiarize with the instruments.

It is important to know about parameters that must be collected at the field for model

development. For model calibration and verification purpose at least the upper limit and the

lower limits of the water flow in conduits must be known in the case of unavailability of

exact measurements.

To obtain maximum outputs from a field visit, it is important to study the area using maps.

These maps were very important to identify the boundaries of the catchment areas.

Responsibilities were allocated to each person, regarding with data collecting, asking

questions from stakeholders, taking relevant photographs, tabulating all data and as well as

the careful looking at the instruments. Since responsibilities were changed during the field,

all members practice each and every activity. At the end of each day, a small discussion was

done to ensure the successful data collection.

3.2 Field data

At the field following data were collected.

Canal geometry (shape, width etc….)

Canal bank condition(concrete, gabion etc…)

Position of nodes

Length between nodes

Maximum depth of canal at nodes

Photos of the field

GPS locations

Data from stake holders

3.3 Sample calculation

After every field visit desk study was carried out to complete the calculation accordingly. The

sub catchments slope, area, width, manning’s roughness and percentage areas of pervious

and imperviousness, were calculated using collected data, 1:10,000 topographic sheets, and

Arc GIS software. Infiltration model choose for computation was the Green-ampt model.

Required data for this method can be found in SWMM help manual, provided the soil type is

known.

3.3.1 Slope

If contours are present and we can recognize water flowing paths can be recognized then

water path length and contour intervals were measured to calculate the slope.

Considering all, Final Slope = (0.07x516.38+0.044x443.31+0.0896x294.65)

1254.34

= 0.0654

3.3.2 Area

Subcatchments of the study area was divided according to the contour pattern of that area.

Using Arc GIS software, areas of each subcatchment were calculated by creating a polygon.

3.3.3 Width

This is given by the subcatchment area divided by the maximum overland flow length.

Maximum overland flow length was taken as the length of the water path that starts at the

most far end of the sub catchment.

3.3.4 Manning roughness:

Values of Manning’s roughness for over land flow used as in the manual of the SWMM and

checked the values with the literature available value( Applied Hydrology by Chow V.T.)

Weighted average method was used to achieve a representative roughness value since land

cover changes within the area.

3.3.5 Percentage of pervious and imperviousness

By observing the satellite images of the area those percentages were calculated.

percentage of impervious area

Roof area = 192m2

Houses = 62

Total roof area = 11904m2

Galle road = 4339.37m2

Subroad1 = 1180.38m2

Subroad2 = 603.3m2

Percentage of impervious = 18027.05 x 100% = 9%

= 200290.8

Percentage N pervious

Marshy land area 1 = 22221.96m2

Marshy land area 2 = 7259.09m2

Areas from trees = 67263.19m2

Areas for earth soils = 5169 m2

N values for short grass = 0.15

Light under bush = 0.4

Fallow soils = 0.05

So percentage N pervious = 31585.88/200290.89=0.16

All the calculations were done as mentioned above for all sub catchment.

3.4 Field work execution

Number Date Location Work done

01 06/11/2009 Walgama Identify the main canals at the field and note down shape of the canal segments and identify the canal bank types (as concrete, gabion or vegetation) and took photos of each nodes and important places. At the nodes points maximum depth were measured. When there is a flow we used a float and found the flow velocity of the water. Also got GPS

point of the path. From the peoples asked about rain and flood height and frequency and maximum flow of canal and minimum flow.

0204/03/2010

Piladuwa “

03 Thotamuna “

04 13/03/2010 Thudawa “

0514/03/2010

Kunu Ela “

06 Brownshill “

Table 3 – Field work execution

3.4.1 Other required data

Other required data were gathered from following sources

1:50000 digital maps – Survey department of Sri Lanka

1:1000 digital maps – Survey department of Sri Lanka

Satellite imaginary developed at 2007 - Survey department of Sri Lanka

Runoff coefficient – Ven Ti Chow open channel hydraulics book

Rainfall data - Irrigation Department

Manning roughness values – SWMM help

CHAPTER 04

4.0 Modeling

4.1 Model selection

We used EPA SWMM software use to model the catchment in our research work because of

the following reasons.

1. SWMM is dynamic rainfall-runoff model used for single event or long term

(continuous) simulation of runoff quantity and quality from primarily urban areas.

2. Specially design for urban watersheds.

3. Handles drainage networks of any sizes

4. Accommodates various conduit shapes as well as irregular natural channels

5. Spatially and time varying rainfall can use in model

6. Infiltration and evaporation can be include with model

7. Can use for flood plain mapping

8. GIS point can insert to the model

4.2 My study area

Piladuwa area is I selected and it is situated very close to Nilwala River, which is a

one of boundary for my catchment. This area is having bund, which was constructed in the

Nilwala scheme. My study area having three major canals. Piladuwa area is highly populated

area.

Figure 7 - sMap of selected area (Piladuwa)

4.3.1 Schematic diagram for SWMM model

Figure 8 - Divided subcatchments

4.3.2 Schematic of model

Figure 9- SWMM model schematic diagram

4.3.3 Notations & symbols used

There are some notations which are used to indicate the symbols in the model. Those

notations can be changed by varying the default values of the model. Following are the

notations which are used for this study.

S – Subcathment

C – Conduit (canal)

J – Nodes

Out – Outfall

RG – Rain gauge

Figure 10 notation used for SWMM

4.2.3 Data for model

For familiarize with EPA SWMM, installed the software and practice the tutorial given along

with the software .By doing that identified the following parameters which should input to

the model.

Figure 11 - Input parameters for the model

4.4 Input data for the model

4.4.1 Manning’s roughness

Figure 12- manning’s roughness values

Manning roughness for the open channel flow for a particular cannel section is in over a range. As an example for lined canals filled with vegetal, value fluctuating between 0.03 – 0.4. If the canal filled with more vegetal the roughness is selected near to the upper bound of 0.4. This is because high vegetal means disturbance to the flow is very much and the roughness vale must be high. Like that the values must have to be selected between lower bound and upper bound.

4.4.2 Infiltration data

Figure 13 –Infiltration data

4.4.3 Depression storage data

Figure 14 - Typical Depression storage values

4.4.4 Design rainfall intensity

Rainfall data were collected from the Irrigation Department. These rainfall data had been recorded at three hour intervals. If those data were input to the time series of the model, All the values will be it was taken as for one hour. So those data should be converted into one hour rainfall data.

Rainfall intensity was calculated using rainfall Intensity- Duration –Frequency relationship.

I = Intensity of rain in inches/hr

D = duration of storm in minutes

X & Y are two constants as given below.

According to the map of hydrological stations and Zones Matara is located at zone 3. Then for 10 year return period the Intensity become 0.845 inches/hr.

(Design of irrigation head works for small catchment, ponraj)

4.4.5 Input rainfall data

Figure 15 –Time series editor

Figure 16 - Time series

4.4.6 Catchment details

Catchment Area (km2)Length of the

Longest Stream(km)

Slope (%) Width

Overall Study Area 0.568 0.36 0.003 96.8

Sub Catchment 1 0.0348 0.17 0.002 128.2

Sub Catchment 2 0.0213 0.24 0.002 47.9

Sub Catchment 3 0.0113 0.16 0.004 55.5

Sub Catchment 4 0.009 0.12 0.0028 129.6

Sub Catchment 5 0.0159 0.19 0.005 291.1

Sub Catchment 6 0.0539 0.33 0.0004 93

Sub Catchment 7 0.0307 0.45 0.002 141

Sub Catchment 8 0.063 0.16 0.0029 76.5

Sub Catchment 9 0.0121 0.25 0.0045 54.05

Sub Catchment 10 0.0136 0.26 0.0024 163.3

Sub Catchment 11 0.0426 0.24 0.0026 183.7

Sub Catchment 12 0.0437 0.36 0.0012 110

Sub Catchment 13 0.0394 0.25 0.0025 122.4

Sub Catchment 14 0.0306 0.33 0.007 130.7

Sub Catchment 15 0.0425 0.37 0.009 137.8

Sub Catchment 16 0.0509 0.3 0.002 176.6

Sub Catchment 17 0.053 0.36 0.003 1301.7

Table 4 – Catchment details

SubcatchmentN-

ImperviousN-perv S- Imperv S-Perv %zero

1 0.0125 0.15 2.5 5 102 0.0125 0.15 2.5 5 103 0.0125 0.4 1.25 5 24 0.014 0.4 2.5 5 205 0.015 0.4 1.25 5 256 0.015 0.24 2.5 2.5 27 0.014 0.6 2.5 7.5 48 0.014 0.8 1.25 7.5 59 0.012 0.4 2.5 4.5 510 0.011 0.24 2.5 4 1011 0.011 0.15 1.25 5 512 0.011 0.24 1.25 5 513 0.012 0.15 1.25 5 2014 0.012 0.41 1.25 1.25 1015 0.0125 0.8 1.25 7.5 1016 0.0125 0.8 5 7.5 1017 0.011 0.13 2.5 5 5

Table 5 – Subcatchment Details

CHAPTER 05

5.0 Model results

After modeling and calibration the mathematical model, it can be use to take number of out puts such as flow simulations, subcathment runoff, infiltration etc. Some results are given below which generate for the Piladuwa (My catchment).

5.1 Surface runoff

Figure 17 - Surface runoff

Figure 18 – Subcatchment losses

5.2 Simulation result

Figure 19 – Schematic diagram of Piladuwa

Figure 20 - Water elevation profile -at 1.00 hour

From this animated results clearly shows that this canal is not going to flood with the design rainfall since it is not flooded after one hour.

Figure 21 – Node depth Vs time

Node9

Node 7 &8

Node 5

Node6

Node depth vs time graph can use to identify that maximum depth of the water level at any

node .

Figure 22

Figure 23 – Water elevation profile -at 15 minutes

Figure 24 – Water elevation profile -at 30 minutes

Node15 Node15

Node15

These animated results shows that this canal in my catchment flooded within 1st 15 minutes, so this canal system flooded with design rainfall input.

5.3 Subcacthment Runoff summary

Table 6 - Subcacthment Runoff

5.4 Node depth summary

Table 7 - Maximum node depth

5.5 Node inflow summary

Table 8 - Node inflow summary

5.6 Node flooding summary

Table 9 - Node flooding summary

5.7 Outfall Loading Summary

Table 10 - Outfall Loading Summary

5.8 Link flow summary

Table 11 - Link flow summary

From the field data ,calculated data and output from the result following maximum and

minimum values can be identify.

Largest subcatchment = 0.06 km2

Smallest subcatchment = 0.009 km2

Maximum slope of the catchment = 0.009 km2

Minimum slope of the catchment = 0.0004km2

Maximum out flow from the catchment = 0.249 m3

Minimum out flow from the catchment = 0.029 m3

Maximum runoff coefficient = 0.989

Minimum runoff coefficient = 0.568

CHAPTER 06

6.1 Sensitivity Analysis

At the field we identify the flooding location, from the model we got those area getting

flooded, after calibration of the model. These flooding nodes as below:

Flooding Node Related subcathment

J1 S6

J15 S11

J16 S14

J17 S12

Table 12 – Flooding nodes

So it is needed to do a sensitivity analysis for above mentioned subcatchments to identify

sensitive parameters.

6.2 Sensitivity analysis for Subcatchment 06

6.2.1 Sensitivity of Slope of the catchment

Graph 1 - Subcatchment slope vs peak outflow

% slope % change of

slope

Peak

runoff(m3/s)

peak runoff%

change

0.0025 -50 0.195 4.4

0.005 0 0.204 0

0.0075 50 0.209 2.4

Table 13 - Subcatchment slope vs peak flow

6.2.2 Sensitivity of ” n”pervious

Graph 2 - Pervious Mannig’s N vs peak out flow

Pervious Manning’s N = Manning’s roughness coefficient for pervious area

Manning's "n" % change of "n"Peak

runoff(m3/s)

Peak runoff

%change

0.24 0 0.204 0

0.36 50 0.194 4.9

0.48 100 0.187 8.33

0.8 233 0.176 13.7

Table 14 - Pervious Manning's n vs. peak out flow

6.3 Sensitivity analysis for other subcatchment

Tab

le 1

5 -

Sen

siti

vity

an

alys

is r

esu

lts

CHPATER 07

7.1 Conclusion & Discussion

The output from the SWMM model and field observations are matching so SWMM

can use to model this catchment area. In Piladuwa area major problem is blockage of water

by the bund which was built under Nilwala scheme. This causes to flooding in the area

marked in below figure. Also capacity of this canal is very much low consider to the in flow.

Figure 25 – Flooding area

From the sensitive analysis result we can conclude followings

Subcatchment 14 is the most sensitive for the catchment slope catchment

Subcatchment 6 is the most sensitive for the N pervious value of the catchment

Subcatchment 14 is the most sensitive for the percentage imperviousness of the

catchment

Change of slope have high effect on out flow from the catchment.

Manning’s roughness coefficient for pervious area and percentage of pervious area

are sensitive for out flow from the catchment.

By having thick vegetation will increase the Manning’s roughness coefficient and

decrease the surface runoff.

8.0 REFERENCES

Philip B.Bedient, W. C. (1992). hydro;ogy and flood plain analysis. addison-wesley .

Lewis,A, March 2008 Storm Water Management Model User’s manual Version 5.0,

U.S. Environmental Protection Agency, Cincinnati.

Ponrajah, A.J.P 1989, Technical Guide Lines for Irrigation Works. 1st ed. Irrigation

Department.

Wijesekera,N.T.S 2009, Preparation of the storm water drainage plan fornMatara

Municipal Council area, University of Moratuwa, November1998.

David, E, Farley.J & Haynes,C Design and routing of storm flows in an urbanized

watershed without surface streams, Journal of Hydrology, Department of Civil and

Environmental Engineering, Duke University USA.

Chouli.E, Aftias,E & Deutsch,J.C 2005, Applying storm water management inGreek

cities: learningfrom the European experience, Science Direct, Faculty of Civil

Engineering, National Technical University of Athens.

Trommer,J.T, Loper,J.E & Hammett,K.M, Evaluation and Modification of Five

Techniques for Estimating Stormwater Runoff for Watersheds in West-Central

Florida, U.S. Geological Survey.

May 1, 2001, Highway Design Manual, Storm Water Management.

Marsalek,J, -CisnerosB.E.J, Karamouz,A & Chocat.B, 2006, Urban water cycle

processes and interactions, International Hydrological Programme, Technical

Documents in Hydrology No. 78,UNESCO.

Mendham, NJ Municipal Options for Storm water Management, ResourcePaper,

Association of New Jersey Environmental Commissions.

The National Academy of Sciences, 2008, Urban storm water Management in the

Unites states, National Academy of Sciences.

Chow, V. T., Maidment, D. R. & Mays, L. W. (1988) Applied Hydrology, New York

etc., McGraw-Hill. (0-07-010810-2)

Maidment, D.R. 1993, Hand Book of Hydrology. 1st ed. New York: McGraw Hill

Book Company.

Storm water Drainage manual - Planning, Design and Management, Drainage Service

Department - Government of the Hong Kong.

Dutta, D., Alam, J., Umeda, K., Hayashi, M., Hironaka, S. A two-dimensional

hydrodynamic model for flood inundation simulation: a case study in the lower

Mekong river basin. Hydrologic Processes 21 (9) (2007): 1223 – 1237.

http://www.ec.gc.ca/

http://en.wikipedia.org/wiki/Storm_Water_Management_Model

http://www.wpmpl.com.au

http://sc.water.usgs.gov/projects/bmp/

http://www.ene.gov.on.ca/cons/4328e.pdf

http://www.environment.gov.au/coasts/publications/stormwater/pubs/stormwater.pdf

tp://www.environment.gov.au/coasts/publications/stormwater/index.html

http://www.environment.gov.au/coasts/publications/stormwater/pubs/stormwater.pdf

http://www.ene.gov.on.ca/cons/4328e.pdf

http://sc.water.usgs.gov/projects/bmp/

http://www.wpmpl.com.au/

http://en.wikipedia.org/wiki/Storm_Water_Management_Model

http://www.ec.gc.ca/

9.0 ANNEXES

9.1 Annex A

Photos taken at the field

9.2

Annex B

Date 08/04/2010 Location: (Piladuwa)Chainage

(m) Geometry Roughness Nodes Remarks

shape No. Top Maximum L/B R/B Bed Invert Maximumbarrels width(m) depth(m) level depth

0 rect. 1 0.4 0.6 conc conc conc3.1 rect. 1 0.4 0.8 conc conc conc6.8 rect. 1 1.0 1.0 conc conc conc 0.87515.7 rect. 1 2.3 1.35 conc conc conc 1.46 1.2320.4 rect. 1 2.5 1.45 conc conc conc25.1 rect. 1 2.5 1.5 conc conc conc 1.52 1.3333.6 rect. 1 2 1.5 conc conc conc38.9 rect. 1 2 1.5 conc conc conc43.2 rect. 1 2 1.8 conc conc conc 1.46 1.28 In front of hospital54.3 rect. 1 1.8 1.8 conc conc conc67.8 rect. 1 1.8 1.8 conc conc conc 1.61 1.4279.1 rect. 1 1.5 1.6 conc conc conc 1.55 1.5787.4 rect. 1 1.6 conc conc conc98.9 rect. 1 3 1.6 conc conc conc111.2 rect. 1 3.5 1.8 conc conc conc 2.1 1.5120.8 rect. 1 3 1.75 conc conc Muddy 1.2 0.9150.7 rect 1 2.5 1.8 Vege Vege Muddy160.5 rect. 1 1.9 Vege Vege Muddy172.7 rect. 1 3.8 1.8 Vege Vege Muddy

storm water management

Documents

catchment area

area cause

study area

piladuwa area

research work

matara municipal council

matara municipality

research background