ctr10114 martin fitzgerald 40125756 dissertation

Investigation into the Success of the Implementation of Sustainable Urban

Drainage Systems in Scotland Honours Project, March 2014

Bachelor of Engineering in Civil EngineeringName: Martin Fitzgerald Student No. 40125756

Supervisor: Mr. Bernard Kamya

Name: Martin Fitzgerald

Student Number: 40125756

Project Supervisor: Bernard Kamya

Submission Date: Friday March 21st 2014

Martin Joseph Fitzgerald

40125756

Investigation into the Success of the Implementation

of Sustainable Urban Drainage Systems in Scotland

Edinburgh, March 2014

Dissertation submitted to the School of Engineering and The

Built Environment, Edinburgh Napier University in partial

fulfilments of the requirements for the Honours Degree in Civil

Engineering.

Edinburgh Napier University,

School of Engineering and the Built Environment,

Department of Civil and Transport Engineering,

Edinburgh, 2014

This dissertation is to be appraised by:

Mr Bernard M Kamya - MBA, C.Eng, MICE, MIStructE



Edinburgh

Along with one other member of the committee charged with

appraising the Civil & Transportation Engineering Year 4 Honours

Project, 2013/2014.

This dissertation was supervised by:

Mr Bernard M Kamya - MBA, C.Eng, MICE, MIStructE



Edinburgh

i Abstract

Abstract

Due to the process of urbanisation, the area of impermeable surfaces on earth has

increased dramatically. This increase in impermeable area has in turn, led to an

increase in surface water runoff. For decades in Britain, traditional drainage systems

such as single and combined sewers were used to convey this runoff to the nearest

watercourse as quickly as possible. However, this was causing a major problem with

downstream flooding as well as immeasurable damage to the environment as often

untreated raw sewage and other contaminants were being discharged into these

watercourses.

Sustainable Urban Drainage Systems (SUDS) were then developed to replace these

traditional drainage systems. SUDS are designed to reduce the impact of new and

existing developments with regard to surface water drainage discharge. SUDS are

being more increasingly used to mitigate the flows and pollution from runoff, by

replicating as closely as possible natural drainage systems that use cost effective

solutions with low environmental impact.

The purpose of this dissertation is to determine how successful the implementation

of these sustainable urban drainage systems has been in Scotland. Whilst there is

no doubting that Scotland leads the way over nations like England and Wales, there

is no hiding from the fact that there is still a long way to go.

Factors for the success of SUDS in Scotland include legislation commanding the

mandatory use of SUDS on all new developments after 2005, extensive research

and detailed monitoring of SUDS. Reasons for doubt however, include adoption and

maintenance issues, poor communication between relevant parties and uncertainty

regarding the responsibility for maintaining SUDS systems.

In this report, a case study of the city of Perth in central Scotland further echoes

these doubts, and until they are resolved, the implementation of SUDS in Scotland

cannot be deemed 100% successful.

ii

Success of the Implementation of SUDS in Scotland

Table of Contents Abstract .................................................................................................................................................. i

Table of Contents ................................................................................................................................... ii

List of Abbreviations .............................................................................................................................. iv

Glossary of Terms ................................................................................................................................. v

List of Figures ....................................................................................................................................... ix

Acknowledgements ............................................................................................................................... ix

Chapter 1 Introduction

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

1.2 Aims & Objectives ....................................................................................................................... 4

1.3 Research Methodology ............................................................................................................... 5

1.4 Brief introduction of the case study ............................................................................................. 6

Chapter 2 Literary Review

2.1 Introduction ................................................................................................................................. 7

2.2 The SUDS Concept .................................................................................................................... 8

2.2.1 What are SUDS? ................................................................................................................. 8

2.2.2 Why do we need SUDS? ..................................................................................................... 9

2.2.3 Integration and Planning .................................................................................................... 11

2.2.4 The importance of the Management Train Concept .......................................................... 12

2.3 Retrofitting ................................................................................................................................ 13

2.4 History & Development of SUDS .............................................................................................. 16

2.4.1 The Traditional Approach .................................................................................................. 17

2.4.1.1 Combined Sewer Systems (CSS) .............................................................................. 17

2.4.1.2 Separate Sewer Systems (SSS) ................................................................................ 17

2.4.2 The EU Water Framework Directive .................................................................................. 18

2.4.3 The SUDS Approach ......................................................................................................... 19

2.5 Economic & Social Effects of Flooding ..................................................................................... 20

2.6 The role of SUDS in reducing flood risk .................................................................................... 21

2.7 Types of SUDS ......................................................................................................................... 23

2.7.1 Prevention ......................................................................................................................... 24

2.7.1.1 Minimise Impervious Surfaces ................................................................................... 24

2.7.1.2 Site Management Measures ...................................................................................... 24

2.7.2 Conveyance ...................................................................................................................... 25

2.7.3 Pre-treatment .................................................................................................................... 25

2.7.4 Source Control .................................................................................................................. 26

2.7.5 Site Control ........................................................................................................................ 26

2.7.6 Regional Control ................................................................................................................ 26

2.7.7 Source Control Devices ..................................................................................................... 27

2.7.7.1 Pervious Pavements .................................................................................................. 27

iii Table of Contents

2.7.7.2 Green Roofs ............................................................................................................... 28

2.7.8 Filtration Devices ............................................................................................................... 29

2.7.8.1 Bio-Retention Areas ................................................................................................... 29

2.7.8.2 Grassed Filter Strips................................................................................................... 30

2.7.8.3 Filter Trench ............................................................................................................... 32

2.7.9 Infiltration Devices ............................................................................................................. 33

2.7.9.1 Infiltration Basin .......................................................................................................... 33

2.7.9.2 Infiltration Trench ....................................................................................................... 34

2.7.10 Other SUDS Techniques ................................................................................................. 35

2.7.10.1 Grassed Swales ....................................................................................................... 35

2.7.10.2 Retention Ponds ....................................................................................................... 36

2.7.10.3 Detention Basins ...................................................................................................... 37

2.7.10.4 Stormwater Wetlands ............................................................................................... 38

Chapter 3 SUDS – the good and the bad

3.1 Introduction ............................................................................................................................... 39

3.2 SUDS – Reasons for success................................................................................................... 40

3.2.1 Legislation ......................................................................................................................... 40

3.2.2 Detailed Research ............................................................................................................. 41

3.2.3 Effective planning and design ............................................................................................ 44

3.3 Engineering Nature’s Way Survey ............................................................................................ 47

3.4 SUDS – Reasons for doubt....................................................................................................... 49

3.4.1 No long-term testing .......................................................................................................... 49

3.4.2 Legislation and confusion over responsibilities .................................................................. 50

Chapter 4 Case Study

4.1 Introduction ............................................................................................................................... 53

4.2 Perth, Scotland ......................................................................................................................... 53

4.3 History of Flooding .................................................................................................................... 55

4.4 What are the issues? ................................................................................................................ 56

4.4.1 Adoption and Maintenance Issues..................................................................................... 56

4.4.2 Communication Issues ...................................................................................................... 57

4.4.3 Responsibility .................................................................................................................... 58

4.5 What is being done to help? ..................................................................................................... 58

4.6 Analysis & Discussion ............................................................................................................... 60

Chapter 5 Conclusion

5.1 Conclusions .............................................................................................................................. 62

5.2 Future Recommendations ........................................................................................................ 63

5.3 End Note ................................................................................................................................... 64

References............................................................................................................................................ i

iv


List of Abbreviations

BMP Best Management Practice

BSI British Standards Institution

CAR Controlled Activities Regulations

CIRIA Construction Industry Research and Information Association

CIWEM Chartered Institution of Water and Environmental Management

COPA Control of Pollution Act 1974

CQA Construction Quality Assurance

ENW Engineering Nature’s Way (Hydro International plc)

EQS Environmental Quality Standard

EU WFD European Water Framework Directive

SCOTS Society of Chief Officers for Transportation in Scotland

SEPA Scottish Environmental Protection Agency

SNIFFER Scotland and Northern Ireland Forum for Environmental Research

SUDS Sustainable Urban Drainage Systems

SUDSWP SUDS Working Party

SW Scottish Water

WEWS ACT Water Environment and Water Services Act (Scotland) 2003

WQO Water Quality Objective

WQS Water Quality Standard

v Glossary of Terms

Glossary of Terms

Aquifer – Layer of rock or soil that holds or transmits water.

Asphalt – European Standard description of all mixtures of mineral aggregates bound with bituminous materials used in the construction and maintenance of paved surfaces.

Attenuation – Reduction of peak flow and increase of the duration of a flow event.

Balancing Pond – A pond designed to attenuate flows by storing runoff during the peak flow and

releasing it at a controlled rate during and after the storm. The pond always contains water. Also known as wet detention pond.

Base Flow – The sustained flow in a channel or system because of subsurface infiltration.

Basin – A ground depression acting as a flow control or water treatment structure that is normally dry

and has a proper outfall, but designed to detain stormwater temporarily.

Bioretention Area – A depressed landscaping area that is allowed to collect runoff so that it

percolates through the soil below the area into an under-drain, thus promoting pollutant removal.

Catchment – The area contributing surface water flow to a point on a drainage or river system. (Can

be divided into sub-catchments)

Construction Quality Assurance (CQA) - A documented management system designed to provide

adequate confidence that items or services meet contractual requirements and will perform adequately in service. CQA usually includes inspection and testing of installed components and records the results.

Control Structure – Structure to control the volume or rate of flow of water through or over it.

Controlled Waters – Waters defined and protected under the Water Resources Act 1991. Any relevant territorial waters that extend seaward for three miles from the baselines, any coastal waters that extend inland from those baselines to the limit of the highest tide or the freshwater limit or any river or watercourse, any enclosed dock that adjoins coastal waters, inland freshwaters, including rivers, watercourses and ponds and lakes with discharges and ground waters.

Conveyance – Movement of water from one location to another.

Design Criteria – A set of standards agreed by the developer, planners and regulators that the proposed system should satisfy.

Detention Basin – A vegetated depression that is normally dry except following storm events constructed to store water temporarily to attenuate flows. May allow infiltration of water to the ground.

Diffuse Pollution – Pollution arising from land-use activities (urban and rural) that are dispersed across a catchment or sub-catchment and which do not arise as a process effluent, municipal sewage effluent or an effluent discharge from farm buildings.

Evapotranspiration - The process by which the Earth’s surface or soil loses moisture by evaporation

of water and its uptake and then transpiration from plants.

Extended detention basin – A detention basin is where the runoff is stored beyond the time normally

required for attenuation. This provides extra time for natural processes to remove some of the pollutants in the water.

Filter Drain – A linear drain consisting of a trench filled with a permeable material, often with a perforated pipe in the trench’s base to assist drainage and store and conduct water, but it may also be designed to permit infiltration.

vi


Filter Strip – A vegetated area of gently sloping ground designed to drain water evenly off impermeable areas and filter out silt and other particulates.

Filtration – The act of removing sediment or other particles from a fluid by passing it through a filter.

First Flush – The initial runoff from a site/catchment following the start of a rainfall event. As runoff

travels over a catchment it will collect or dissolve pollutants and the ‘first flush’ portion of the flow may be the most contaminated as a result. This is especially true for intense storms and in small or more uniform catchments. In larger or more complex catchments, pollution wash-off may contaminate runoff throughout a rainfall event.

Floodplain – Land adjacent to a watercourse that would be subject to repeated flooding under natural conditions.

Flow control device – A device used to manage the movement of surface water into and out of an attenuation facility, for example weirs.

Geomembrane – An impermeable plastic sheet, typically manufactured from polypropylene, high-density polyethylene or other geosynthetic material.

Geotextile – A plastic fabric that is permeable.

Green roof – A roof on whose surface plants can grow. The vegetated surface provides a degree of

retention, attenuation and treatment of rainwater, and promotes evapotranspiration.

Groundwater – Water that has been percolated into the ground; it includes water in both the

unsaturated zone and the water table.

Groundwater protection zone (source protection zone) – Areas that influence water supply

boreholes where groundwater must be protected from pollution. These are defined by reference to travel times of pollutants within the groundwater.

Gully – Opening in the road pavement, usually covered by metal grates, which allows water to enter conventional drainage systems.

Hydrograph – A graph illustrating changes in the rate of flow from a catchment over time.

Hydrology – The study of the waters of the Earth, their occurrence, circulation and distribution, their

chemical and physical properties and their reaction with the environment including their relation to living things.

Impermeable – Does not allow water to pass through it.

Impermeable Surface – An artificial non-porous surface that generates a surface water runoff after

rainfall.

Infiltration (to a sewer) – The entry of groundwater to a sewer.

Infiltration (to the ground) – The passage of surface water into the ground.

Infiltration basin – A dry basin designed to promote infiltration of surface water into the ground.

Infiltration device – A device designed to promote infiltration of surface water into the ground.

Infiltration trench – A trench, usually filled with permeable granular material, designed to promote

infiltration of surface water to the ground.

Integrated management practice – The concept of integrating SUDS into the design of a

development from the feasibility stage so that the development is designed to achieve the best SUDS layout.

Interflow – Shallow infiltration to the soil, from where it may infiltrate vertically to an aquifer, move horizontally to a watercourse or be stored and subsequently evaporated.

vii Glossary of Terms

Initial rainfall loss – The amount of rain that falls on a surface before water begins to flow off the surface.

Lagoon – A pond designed for the settlement of suspended solids.

Micropool – Pool at the outlet to a pond or wetland that is permanently wet and improves the

pollutant removal of the system.

Percentage runoff – The proportion of rainfall that runs off a surface.

Permeability – A measure of the ease with which a fluid can flow through a porous medium. It depends on the physical properties of the medium, for example grain size, porosity and pore shape.

Permeable surface – A surface formed of material that is itself impervious to water but, by virtue of voids formed through the surface, allows infiltration of water to the sub-base through the pattern of voids, for example concrete block paving.

Pervious surface – A surface that allows inflow of rainwater into the underlying construction or soil.

Piped system – Conduits generally located below ground to conduct water to a suitable location for treatment and/or disposal.

Pollution – A change in the physical, chemical, radiological or biological quality of a resource (air, water or land) caused by man’s activities that is injurious to existing, intended or potential uses of the resource.

Pond – Permanently wet basin to retain stormwater and permit settlement of suspended solids and

biological removal of pollutants.

Porous surface – A surface that infiltrates water to the sub-base across the entire surface of the

material forming the surface, for example grass and gravel surfaces, porous concrete and porous asphalt.

Prevention – Site design and management to stop or reduce the pollution of impermeable surfaces and reduce the volume of runoff by reducing impermeable areas.

Proper outfall – An outfall to a watercourse, public sewer and in some instances an adopted highway drain. Under current legislation and case law, having a proper outfall is a prerequisite for defining a sewer.

Public sewer – A sewer that is vested and maintained by the sewerage undertaker.

Rainfall event – A single occurrence of rainfall before and after which there is a dry period that is sufficient to allow its effect on the drainage system to be defined.

Rainwater use system – A system that collects rainwater from where it falls rather than allowing it to drain away, and includes water that is collected within the boundaries of a property, from roofs and surrounding surfaces.

Retention pond – A pond where runoff is detained for a sufficient time to allow settlement and

possibly biological treatment of some pollutants.

Return period – The occurrence frequency of an event. A 100-year storm refers to the storm that

occurs on average every 100 years. In other words, its annual probability of exceedance is 1 percent. (1/100)

Runoff – Water flow over the ground surface to a drainage system. This occurs if the ground is impermeable or saturated, or if rainfall is particularly intense.

Runoff coefficient – A measure of the amount of rainfall converted to runoff.

Sewer – A pipe or channel with a proper outfall that takes domestic foul and/or surface water from

buildings and associated paths and hardstandings from two or more curtilages.

viii


Soakaway – A subsurface structure into which surface water is conveyed to allow infiltration into the ground.

Source control – The control of runoff at or near its source.

Storm – An occurrence of rainfall, snow or hail.

Stormwater hotspot – Stormwater hotspots are defined in the USA as areas where land use or activities may generate highly contaminated runoff, or where groundwater is an important resource for drinking water abstraction.

Sub-base – The unbound layer of aggregate used immediately below the bound layers. It is laid on

the soil (or capping layer) to provide a stable foundation for construction of the road pavement.

Sub-catchment – A division of a catchment, allowing runoff management as near to the source as is

reasonable.

SUDS – Sustainable drainage systems or sustainable (urban) drainage systems. A sequence of

management practices and control structures designed to drain surface water in a more sustainable fashion than some conventional techniques.

Surface water management train – The management of runoff in stages as it drains from a site.

Suspended solids – Undissolved particles in a liquid.

Swale – A shallow vegetated channel designed to conduct and retain water, but may also permit infiltration; the vegetation filters particulate matter.

Time of entry – Time taken for rainwater to reach an inlet into the drainage system after hitting the ground.

Treatment – Improvement of the quality of water by physical, chemical and/or biological means.

Treatment volume – The proportion of total runoff from impermeable areas captured and treated to

remove pollutants.

Turbidity – Reduced transparency of a liquid caused by the presence of undissolved matter.

Watercourse – Any natural or artificial channel that conveys surface and/or ground water.

Weep garden – Bioretention system built into a terrace on a sloping site, where the water is allowed

to seep out of the face of the retaining wall that forms the terrace.

Wetland – A pond that has a high proportion of emergent vegetation in relation to open water.

(Wilson, et al., 2004)

(Nelson & Nelson, 1973)

ix List of Figures

List of Figures

Figure 1.1 Volume of water stored in the water cycle's reservoirs ............................. 1

Figure 1.2 The Natural Hydrologic Cycle A ............................................................... 3

Figure 1.3 The Natural Hydrologic Cycle B ............................................................... 3

Figure 1.4 Map of Scotland ....................................................................................... 6

Figure 2.1 The SUDS Triangle .................................................................................. 8

Figure 2.2 CIRIA Management Train Concept .......................................................... 9

Figure 2.3 Disturbance to the water cycle caused by impermeable surfaces .......... 10

Figure 2.4 Green Roof Garden, Edinburgh ............................................................. 15

Figure 2.5 A retrofit rain garden on an Islington housing estate .............................. 15

Figure 2.6 Management Train Concept [2] .............................................................. 23

Figure 2.7 Common SUDS Techniques .................................................................. 23

Figure 2.8 Permeable Paving .................................................................................. 27

Figure 2.9 Green Roof ............................................................................................ 29

Figure 2.10 Bio-retention area ................................................................................ 30

Figure 2.11 Grassed Filter Strip .............................................................................. 31

Figure 2.12 Filter Trench ......................................................................................... 32

Figure 2.13 Infiltration Basin ................................................................................... 33

Figure 2.14 Infiltration Trench ................................................................................. 34

Figure 2.15 Grassed Swale ..................................................................................... 35

Figure 2.16 Retention Pond .................................................................................... 36

Figure 2.17 Detention Basin .................................................................................... 37

Figure 2.18 Stormwater Wetland............................................................................. 38

Figure 3.1 Hopwood Park MSA, M42, Worcs - Ornamental Pond ........................... 46

Figure 4.1 Banks of the River Tay, Perth ................................................................ 54

Figure 4.2 A view of the River Tay and Perth city centre on a summer day ............. 54

Figure 4.3 Flooding in Gowrie Street/Perth Street, Perth 2011 ................................ 55

Figure 4.4 Flooding in Feus Street, Perth 2010 ....................................................... 55

x


Acknowledgements The work presented in this dissertation has been carried out at the School of

Engineering & the Built Environment in Edinburgh Napier University under the

supervision of Mr Bernard M. Kamya. I am extremely grateful to Bernard for his

valuable guidance and discussions during the process of writing this dissertation.

Thank you also to the staff of Scottish Water and of the Perth and Kinross County

Council who assisted me in my case study of Perth, Scotland.

I would like to thank my colleagues in the Civil Engineering 4th Year class of

2013/2014 at Edinburgh Napier University who made it a very enjoyable year and in

particular to David O’Toole, David Harte, Antòin O’Sullivan, Ken Kennedy, Trevor

Devereux, Brian Kavanagh, Emad Gharib and Terence Connolly who provided an

excellent work environment in which to complete this project.

Next, I would like to thank my family, in particular my parents Michael and Ann. They

encouraged and supported me right from the beginning and during the difficult times

when I was in need of inspiration and encouragement, they were always there to talk

and to keep me focussed and my appreciation for their love and support cannot be

expressed in words.

Finally, there is one person who must get an extra special mention.

Niamh, without you this dissertation would not have been possible. When things

looked bleak and I needed encouragement, you were there every second of every

day to keep me going and I am very grateful for that. I love you very much.

I would like to dedicate this dissertation to my late Grandmother Mary (Ma) Mc

Donnell who sadly passed away during the writing of this dissertation and also to my

late Grandfather James (Jim) Fitzgerald, both of whom always instilled in me the

importance of education and the need to work hard in order to achieve success.

Martin Fitzgerald

Edinburgh, Scotland

March 2014

1 Introduction

Chapter 1

Introduction

1.1 Introduction

“We forget that the water cycle and the life cycle are one”

- Jacques Cousteau

Water, little would argue that this is the key component in supporting life on earth.

Humans use water every single day in some form or another. Billions of litres of

water are used in the running of day to day activities from washing clothes and cars,

recreational purposes, agricultural needs, food processing to drinking.

Water covers approximately 71% of the earth’s surface, yet, it is one of the most

sought after commodities among human life.

Despite the vast quantities of water on earth, only 2.5% of all this water is fresh

water, and 98.8% of that fresh water is made up of ice and groundwater. Less than

0.3% of all freshwater is found in rivers, lakes and the atmosphere, with only 0.003%

found in the biological bodies and manufactured products. (Pidwirny, 2006)

Figure 1.1 Volume of water stored in the water cycle's reservoirs

The water found on earth continuously moves through a natural process called the

Hydrologic Cycle. This cycle refers to the continuous exchange of water within the

hydrosphere, between the atmosphere, soil water, surface water, groundwater and

(Pidwirny, 2006)

2


plants. The water moves through each of these regions through the processes of

evaporation, transpiration, precipitation and finally to runoff.

Precipitation falls in many forms such as rain, snow, sleet etc. and this falls at an

approximate rate of 119 Tt per year over land. (Pidwirny, 2006)

[NOTE: 1Tt = 1012, and 100 = one ton/1000Kg]

It is this precipitation that gives us the need for drainage, particularly in urban areas.

Water has to be sent back to oceans via rivers and streams, and this can only be

done through drainage networks as the process of urbanisation has dramatically

increased the area of impermeable land on earth, thereby increasing runoff.

But, it is not sufficient to just drain this water away, it must also be treated to remove

contaminants and pollutants before it reaches the intended water body and at times

of heavy rainfall, the stormwater must be attenuated until a point when the receiving

watercourse is sufficiently capable of managing the water to prevent downstream

flooding. From the statistics outlined above, it is clear that there are very limited

supplies of fresh water on earth for a population of 7 Billion and growing. For this

reason, pollutants must be removed before it reaches the intended water body and

pollutes a vast volume of our water supply.

For many years, the traditional approach to urban drainage was to collect runoff in

pipes and transport it to the nearest water course as quick as possible. This caused

immeasurable and irreversible damage to the environment as well as major flooding

issues and it soon became apparent a new system was necessary.

It was at this point that Sustainable Urban Drainage Systems (SUDS) were

developed.

Sustainable Urban Drainage Systems are designed to reduce the impact of new and

existing developments with regard to surface water drainage discharge. SUDS are

being more increasingly used to mitigate the flows and pollution from runoff, by

replicating as closely as possible natural drainage systems that use cost effective

solutions with low environmental impact.

The general consensus is that Sustainable Urban Drainage Systems have been a

widespread success. However, this dissertation will take a deeper look at SUDS in

3 Introduction

Scotland and look at the importance of their implementation on the environment and

the lives of people who have to live with flood risk. From this, the author will attempt

to draw a conclusion on the success of the implementation of SUDS in Scotland and

attempt to make recommendations in order to further improve the SUDS experience.

Figure 1.2 The Natural Hydrologic Cycle A

Figure 1.3 The Natural Hydrologic Cycle B

(Pidwirny, 2006)

(Bauder, 2006)

4


1.2 Aims & Objectives

The success of Sustainable Urban Drainage Systems is based on 3 primary factors:

1. Has the quality of storm water on discharge been improved?

2. Has the system provided a wildlife or landscape benefit?

3. Is the area in question still prone to flooding?

As well as the 3 points outlined above, the success of SUDS can be based on

whether or not they have improved the quality of life for those people who have to

live with the stress of knowing their home is at risk of flooding.

In general, Sustainable Urban Drainage Systems have been a great success. Top

water engineering professionals all agree that Scotland is streets ahead of other

nations regarding the implementation of SUDS. However, there is an argument that

a lot more can be done to improve the SUDS experience in Scotland including more

funding for the adoption and maintenance of SUDS and putting more effort into the

retrofitting of SUDS in Scotland.

The aim of this dissertation is to draw a conclusion on the success of SUDS in

Scotland by compiling all of the opinions of top water engineering professionals as

well as the opinion of the author.

The author’s opinion will be based on several factors. These factors include looking

at successful cases of SUDS in Scotland and the reasons for their continued

success but also based on what has not been done and what could be improved.

The author aims to outline a number of areas in which the authorities could improve

in order to make the implementation of SUDS more successful.

The author will also attempt to identify an area in Scotland that is historically prone to

flooding and other drainage issues and investigate what is being done in order to

alleviate the risk of flooding there. This case study will further add to the argument

that more could, and should be done to further the success of the implementation of

SUDS in Scotland.

5 Research Methodology

1.3 Research Methodology

The first step in this dissertation is to gain a greater knowledge of Sustainable Urban

Drainage Systems. This includes researching the following in detail:

1. What are SUDS?

2. The SUDS Concepts

3. Why do we need SUDS?

4. The background leading to the development of SUDS

5. Types of SUDS

6. Advantages and disadvantages of the different types of SUDS

After I have expanded my knowledge of SUDS, I will then look at recent surveys and

publications of some of Scotland’s top water engineering professionals, including

those of consulting engineers, house builders, developers, local authority

representatives, SEPA and Scottish Water. This will be done in order to gain an

insight into their views on the implementation of SUDS in Scotland, whether they

believe SUDS to have been a success or not, and what areas they feel can be

improved.

Next, I will begin to draw up my own argument for the success of SUDS. I will start

by briefly looking at cases where SUDS have been undoubtedly successful and

reasons for their success. This will be done in order to prove that the SUDS model is

indeed, efficient.

After the successful cases have been identified in brief, I aim to identify an area in

Scotland that has been plagued with flooding and other drainage issues over the

past number of years and investigate what the authorities are doing to eradicate this

flood risk. I will then gather the necessary statistics required for this area in order to

understand better the circumstances of the chosen area. This case study will further

add to the argument that there is still a long way to go for SUDS to be considered

100% successful.

The final step is to draw an overall conclusion to the success of SUDS in Scotland.

This will be done by taking a general outlook on both successful and unsuccessful

cases as well as looking at whether the systems have met the criteria set out by the

EU Water Framework Directive.

6


1.4 Brief introduction of the case study

As part of this dissertation, an area of Scotland with notable flooding and other

drainage issues is to be looked at in detail. This will be done in order to gain an

insight into what is being done in Scotland to alleviate the drainage issues for areas

like this.

The area chosen for this case study is Perth which lies within the Tayside region of

Scotland, under the control of the Perth and Kinross County Council. This area, in

recent years has had well-publicised issues with flooding including major floods in

1993, 1999, 2010, 2011 and 2012,

As of a 2002 SNIFFER (Scotland and Northern Ireland Forum for Environmental

Research) Report, Perth had 32 SUDS sites; undoubtedly that number has risen in

the years since that survey. What this dissertation aims to do is look at Perth in more

detail and discover the reason for the continued flooding as seen in 2010,11 and 12.

This could be down to the SUDS in operation there being unsuccessful, they might

be a part of small development sites, or it could be due to the obvious need for a

major, public SUDS system to be put in place.

Chapter 4 of this dissertation will outline the results of my investigation, also

including the views of a senior flood engineer from the Perth and Kinross County

Council who has co-written many published journals and is highly-respected water

engineering professional.

Figure 1.4 Map of Scotland

Perth, Scotland

(Scotland Channel, 2014)

7 Introduction

Chapter 2

Literary Review

2.1 Introduction

The purpose of this chapter is to look at SUDS in more detail in order to gain a

greater understanding of their history and how they work. This will enable the author

to be in a greater position to make a judgement on the success of SUDS

implementation in Scotland and draw a conclusion on the matter in the final chapter

of this report.

Outlined in this chapter are the SUDS Concepts, the history and development of

SUDS, the problems associated with flooding and why SUDS are necessary to

alleviate these problems and finally a description of the various types of SUDS

techniques in use in Scotland today.

The SUDS concepts include the aims and objectives of SUDS and how they can

effectively be integrated into new and existing developments by means or integration

and planning from the beginning of the design process or through retrofitting. Also

described in this section is the CIRIA management train concept and its importance

in delivering effective SUDS techniques to new developments.

The history and development of SUDS is a closer look at why SUDS were necessary

to be developed. This section will outline the traditional means of urban drainage, the

legislation that paved the way for change and the SUDS solution and how it differs

from traditional drainage methods.

Finally, this chapter will give a brief outline to the different SUDS techniques

available in Scotland today. They will be classed in order of preference according to

the CIRIA Management Train Concept, most preferential being source control

measures, with the least preferential being site and regional control measures.

8


2.2 The SUDS Concept

2.2.1 What are SUDS?

Sustainable drainage systems (SUDS) are increasingly being used to mitigate the

flows and pollution from runoff. The philosophy of SUDS is to replicate as closely as

possible the natural drainage from a site before development and to treat runoff to

remove pollutants, so reducing the impact on receiving watercourses. This requires a

reduction in the rate and volume of runoff from developments, combined with

treatment to remove pollutants as close to the source as possible. They can also

provide other environmental benefits such as wildlife habitat, improved aesthetics or

community resource. (Wilson, et al., 2004)

Figure 2.1 The SUDS Triangle

In essence, the SUDS approach to drainage involves controlling the runoff from

development sites so that it mimics green field runoff and maintains the natural

drainage patterns, as well as enhancing the local environment.

More often than not, one individual SUD system cannot tick all three of the boxes

required in the SUDS concept. As a result, a treatment or management train is

required that comprises of one or more technique. The management train may also

include techniques such as good site management to prevent pollution. Several

SUDS techniques will be needed to reduce the volume of runoff and treat pollution.


9 The SUDS Concept

Figure 2.2 CIRIA Management Train Concept

2.2.2 Why do we need SUDS?

There are a large number of human and non-human activities that can destabilize

the hydrologic cycle. One of the major human activities to have the greatest impact

on the hydrologic cycle is the process of urbanisation.

When rain falls on undeveloped land, the vast majority of the water will soak away

into the topsoil and it will slowly make its way through the soil to find the nearest

water course. Approximately 15-20% of this rainfall becomes direct surface runoff,

which will slowly make its way to the nearest watercourse over the rough ground

which will most likely contain vegetation hence removing pollutants. This means that

the effect of rainfall, be it a small shower or even a short, heavy storm, will be spread

out over a number of hours, meaning there will be little impact on flow rates for the

receiving water course because a lot of the water will have absorbed into the ground.

However, when a large number of people move to an area and that area of land is

developed, the area of impermeable surfaces massively increases due to tarmac

roads, pavements, roofs and driveways. As well as this, most areas of a site are

excavated before construction and better quality material is compacted in layers to

reduce settlement of buildings after construction has been completed. As a result of

these compacted layers of soil, water is impeded from draining through the it, making

the soil almost as impermeable as the roads and pavements.

(CIRIA, 2000)

10


The water that would have previously been able to infiltrate the soil now runs off the

surface, creating a greater volume of water, which ends up flowing to areas of a

lower topographical level, generating floods.

In developed sites, direct runoff can increase to more than 80% of the total rainfall

volume, compared to a figure of 15-20% for an undeveloped site (Sieker, 2010). On

top of this, paved surfaces are smoother than the previous condition of a site where

vegetation may have been present, meaning that the surface runoff may travel over

that surface much faster, thereby reaching the watercourse quicker.

The greater volume of water and higher flow rates mean that receiving waters are

more sensitive to rainfall intensity and volume in a developed site as opposed to an

undeveloped site. Because of the increased volumes and flow rates of runoff on

developed sites, peak flow rates can increase by a factor up to ten, meaning streams

and rivers have to cope with larger and often sudden runoff flows. Often what

happens is the streams and rivers cannot cope with this added pressure and flooding

occurs. It is for this reason that drainage is required, and where the idea of

Sustainable Urban Drainage Systems (SUDS) comes into play.

Figure 2.3 Disturbance to the water cycle caused by impermeable surfaces

(Sieker, 2010)

11 The SUDS Concept

2.2.3 Integration and Planning

One of the main philosophies of SUDS is “prevention is better than cure”. If SUDS

are only considered as an after-thought to a conventional site design, more often

than not the results are unnecessarily large and costly.

For this reason, a successful SUDS design requires the drainage to be carefully

integrated into the site while taking the original green field drainage patterns into

consideration. SUDS designs that integrate the features into the overall site design

generally result in smaller, more cost-effective solutions. (Minnesota Metropolitan

Council, 2001)

In order to effectively integrate SUDS into the initial site design, the following factors

should be taken into consideration:

1) Reduction of impervious surfaces can be achieved by simple street design. If

a site is correctly laid out, length of roads can be minimised as well as the

width of roads being kept to the absolute minimum consistent with achieving

safe traffic management. The edge of streets can be constructed using

pervious surfaces to reduce runoff. Also cul-de-sac turning areas can be

designed to use the minimum required turning circle and the use of

hammerheads is also beneficial in reducing the area of impervious surfaces.

2) Raised kerbs and gutters should be avoided wherever possible as they

amplify stormwater volume and velocity (Minnesota Metropolitan Council,

2001). Also roads without raised kerbs and gutters tend to be less expensive

at construction stage, but it is important that roads without these features

should be designed with detailed edges so as to collect water into the SUDS

feature as opposed to flowing back into the road construction and weakening

it.

3) Reinforced grass can be used wherever possible for overspill car parking

areas and parking space dimensions minimised.

4) The landscaped areas associated with roads and car parks can be placed so

that they act as filter strips, swales etc.

5) Most importantly, the site layout and levels should be designed to follow the

existing site topography as much as possible. This helps to preserve natural

12


hydrology and drainage pathways on the site and assists with overland flood

routes. (Atlanta Regional Commission, 2001)

(Wilson, et al., 2004, pp. 33-34)

2.2.4 The importance of the Management Train Concept

The management train concept is fundamental to designing a successful SUDS

scheme and addresses the quality and quantity of runoff at all stages of a drainage

system. It uses drainage systems in series to improve the quality and quantity of

runoff incrementally, by reducing pollution, flow rates and volumes.

The management train provides a list of the following techniques, listed in order of

preference according to CIRIA C609 – Sustainable Drainage Systems

1) Prevention – The use of good site design and housekeeping measures on

individual sites to prevent runoff and pollution (for example, sweeping

impervious surfaces to remove dust and grit) and rainwater reuse, rainwater

harvesting.

2) Source Control – Control of runoff at or very near its source (through the use

of pervious pavements or green roofs for example)

3) Site Control – Management of water from several sub-catchments (by

routeing water from building roofs and car parks to one large soakaway or

infiltration basin for the whole site)

4) Regional Control – Management of runoff from several sites, typically in a

detention pond or wetland.

The SUDS management train is summarised in Figure 2.2 CIRIA Management Train

Concept. From this diagram, it is clear that prevention and source control are the

preferential options when it comes to choosing a suitable SUDS technique. These

two options should always be considered before site or regional controls. Water

should only be conveyed elsewhere only if cannot be dealt with on site (lack of space

for example). Conveyance between individual parts of the management train should

also be considered.

13 Retrofitting

An effective SUDS management train should take the following points into

consideration:

a) Dealing with runoff at source is generally more effective as you are dealing

with lesser volumes of runoff and pollutants tend to be less concentrated in

the stormwater stream (Wilson, et al., 2004, pp. 33-35).

b) According to the Building Regulations, Part H, infiltration of runoff is preferred

over discharge to watercourses. Discharge to sewers should be used only

when no other option is available.

c) Before treatment, it is vital for SUDS techniques employed to be able to

remove gross silt or sediment loads, so as to ensure the long-term

effectiveness of all techniques (Wilson, et al., 2004, pp. 33-35).

d) The treatment system should comprise of a series of features that

complement each other, such as filter strips and infiltration trenches.

e) The more techniques used in a system, the better performance is likely to be.

This is because the use of more than one technique reduces the risk of

system failure.

2.3 Retrofitting

Under current legislation, SUDS must be considered in the planning of all new

development sites. For new development sites, the easiest option is to provide a

management train which attempts to mimic the natural drainage of that site.

However, new developments only form a small part of the current urban areas and

the question then arises over all existing developments that don’t have any SUD

system in place. The answer is to retrofit SUDS to these existing developments. If

retrofit SUDS can be incorporated into existing development areas, then the

opportunities for delivering sustainable solutions that offer multiple benefits will be

much greater.

SUDS techniques can be retrofitted to existing sites to reduce the risk of flooding in

receiving waters or to reduce pollutant levels in runoff. It is often easier to retrofit an

individual technique, rather than to provide a management train like for new

developments (Wilson, et al., 2004, pp. 38-39).

14


Retrofitting surface water management measures will deliver:

i. Drainage systems that mimic natural drainage processes

ii. Management of pollution alongside flood risk

iii. The ability to adapt and manage extreme events

iv. Extra benefits from better amenity, improved biodiversity and greater

resistance to climate change

v. Integration with urban design to create better places to live (Digman, et al.,

2012)

One issue with retrofitting SUDS is space requirements. Unlike in new developments

where SUDS are planned for from the beginning, in existing developments they are

merely an afterthought. As a result, the space necessary to construct the desired

SUD system is more often than not, not available.

On existing developments, more often than not the conventional approach to

drainage is in place, i.e. collect runoff in pipes and discharge it to the nearest

watercourse as quick as possible. However, many opportunities to retrofit measures

can be exploited if conventional thinking is challenged and an innovative approach to

surface water management is adapted (Digman, et al., 2012).

There are many examples of retrofit SUDS to be seen all over Scotland, and to a

great extent they have been a great success. Examples of retrofitted SUDS are not

only to be seen in private developments however, they can, and are, being

effectively integrated into public realms also. Many examples from around the world

are on show at present which solidify the argument that reducing surface water from

entering existing drainage systems, through retrofitting of SUDS, can be more cost

effective than increasing the drainage capacity (eg Green City, Clean Waters in

Philadelphia and the Green Streets approach in Portland Oregon). (CIRIA, 2012)

In Scotland, there are also many successful examples of retrofit SUDS to be seen.

Some examples include rain gardens in Islington and green roof gardens in

Edinburgh.

15 Retrofitting

Figure 2.4 Green Roof Garden, Edinburgh

Figure 2.5 A retrofit rain garden on an Islington housing estate

According to CIRIA C713, 2012 – Retrofitting to manage surface water, retrofit

measures could look like:

a) Existing buildings will be fitted with green roofs and rainwater harvesting

systems

b) Roads will have rain gardens in their verges, collecting and storing runoff,

removing pollutants and calming traffic

c) Some roads, paths and spaces between buildings will be reshaped to carry

surface water, and during extreme events act as “blue” flood pathways when

the capacity of drainage is exceeded

(Wakeham, 2009)

(Digman, et al., 2012)

16


d) Open areas such as parkland and car parks will be designed and designated

to act as temporary flood storage

e) At the same time they will provide green infrastructure benefits such as

creating places for recreation and reducing urban heat islands

f) Surface water management will be an integral component of urban design,

providing a host of benefits such as enhancing amenity, increasing

biodiversity and enhancing land value

g) Local flood protection measures will be installed to make buildings more

resistant to flooding (Digman, et al., 2012).

Conventional SUDS design usually follows a pre-determined design criteria;

however, the design process for retrofit SUDS works in reverse. Starting with a set of

existing site constraints, the designer should determine the best stormwater control

or treatment obtainable, even if it does not fully comply with current design standards

(Wilson, et al., 2004, pp. 38-39).

As can be seen above, there is a lot of research and investigation in the possibility of

retrofitting SUDS by many major water engineering companies like CIRIA and The

Environment Agency. In chapter 3, potential retrofitting issues will be discussed in

greater detail in conjunction with the findings by these companies and a conclusion

will be drawn onto the overall success of retrofit SUDS in Scotland.

2.4 History & Development of SUDS

The increase in surface water runoff due to urbanisation often leads to the overflow

of gullies, ditches, streams and rivers, creating the problem of riverside flooding. This

flooding poses risks to people’s health and wellbeing as well as greatly reducing their

quality of life. This is not to mention the billions of pounds worth of damage it causes

each year worldwide, destroying entire communities and leaving millions homeless.

In this section, the traditional approach to surface water runoff drainage will be

outlined as well as the negative effects it had and continues to have on the

environment. Then we will look at the legislation that forced the change from this

system, and ultimately to the development of SUDS.

17 History & Development of SUDS

2.4.1 The Traditional Approach

Many of the UK’s urban drainage systems date back to the 19th Century. They were

initially built in the central areas of large towns and cities, and were intended to carry

surface storm runoff, industrial effluent and domestic foul sewage. These systems

were soon followed by sewage treatment works introduced to improve the quality of

the wastewater being discharged to local watercourses. However, the capacities of

these systems and treatment facilities were often insufficient to deal with the demand

created by rapidly growing cities. (Swan, 2002)

There are two types of traditional drainage systems; The Combined Sewer System

(CSS) and the Separate Sewer System (SSS). These systems solved the issue of

urban drainage by removing the stormwater runoff from the impermeable surfaces as

quickly as possible, usually by collecting it in pipes. The priority of this approach to

drainage was to minimise the risk of flooding in that area, without any consideration

for downstream flooding, water quality damage being caused to the environment.

2.4.1.1 Combined Sewer Systems (CSS)

Combined sewers usually operate on a single pipe, where sewage and surface

runoff are carried together. Most of these combined sewers were constructed at a

time where it was acceptable to discharge raw sewage directly into rivers. Nowadays

however, these combined sewers carry the runoff and sewage to a water treatment

plant, usually of limited capacity.

At times of heavy rainfall, the wastewater treatment plants typically lack the capacity

to treat all of the sewer system influent, and as a result the excess flow is discharged

directly into the receiving watercourse. This issue was overlooked for decades, as

authorities believed the sewage was being sufficiently diluted, first by the rainwater in

the pipe, and then being further diluted by the watercourse.

2.4.1.2 Separate Sewer Systems (SSS)

Separate sewer systems were developed to deal with some of the hydraulic and

environmental issues caused by the combined sewer systems. In these systems,

18


sewage and runoff are carried in separate pipes, sewage to a treatment plant and

runoff to the nearest and most suitable watercourse. On the surface, it appeared

separate sewers had solved the problems of the combined sewer; however, this was

not the case.

As it flows across the impermeable surfaces, the surface runoff water can become

contaminated by numerous pollutants. These pollutants include tiny metal fragments,

greases, oils, petrol/diesel from road vehicles, silt and dust, pesticides and

detergents from gardens and car washing, and often in poorer, less developed

countries, human and animal waste. Because the surface runoff was being

discharged directly to the nearest watercourse without any treatment, this meant the

pollutants being picked up from the impermeable surfaces were being discharged

into the watercourse.

Up to the 1990’s, these two systems remained in use with the objective of increasing

water flow efficiency. Apart from the problems outlined above regarding combined

and separate sewers, there were other issues to contend with. These included health

issues, aesthetic issues and environmental issues.

As urban areas expanded, the area of impermeable land increased, which meant

new points of flooding were observed. This, in turn meant that larger means of

channelling water were required. However, the natural hydrologic cycle had already

been altered, meaning a whole new system was needed. Unfortunately, the process

of increasing the water flow efficiency remained a priority with the authorities, despite

the problems that came with it.

It wasn’t until the EU Water Framework Directive was introduced that this new

system that was so badly needed, was introduced.

2.4.2 The EU Water Framework Directive

For decades, there was a lot of uncertainty regarding water management. The

reason for this is there was a lot of inconsistent European Legislation that didn’t

clearly lay-out ways of protecting our water sources and the environment. The EU

Water Framework Directive introduces a simpler approach to water management

19 History & Development of SUDS

and provides better environmental protection. As a result of the WFD, a number of

existing European Directives have been or will be replaced (Environment Agency,

2014).

In October 2000 the WFD was adopted and it came into force in December of that

same year. The purpose of the Directive is to establish a framework for the

protection of inland surface waters (rivers and lakes), transitional waters (estuaries),

coastal waters and groundwater. It will ensure that all aquatic ecosystems wetlands

meet “good status” by December 2015 (Joint Nature Conservation Committee,

2010).

[Good Status being defined as a slight variation from undisturbed natural conditions]

The EU Water Framework Directive has been incorporated into Scottish law by the

Water Environment and Water Services Act of 2003 (WEWS Act). This legislation

promotes the use of SUDS in Scotland and has been a major factor in the successful

implementation of SUDS in Scotland as will be seen in Chapter 3.

This promotion of the use of SUDS in the WEWS Act is a major reason for the

further studies and development of SUDS, and ultimately the replacing of the

traditional approaches to urban drainage that has caused so much harm to the

environment as seen earlier in this section.

2.4.3 The SUDS Approach

SUDS are more sustainable than traditional drainage methods because of the

following reasons:

They manage runoff and flow rates from impermeable surfaces, thereby

reducing the impact of urbanisation on flooding

They protect or enhance water quality by reducing pollution from surface

runoff

They protect natural flow regimes in watercourses

They provide amenity or wildlife habitat which is beneficial to wildlife and the

local community

They provide opportunities for evapotranspiration from vegetation and surface

water in ponds for example

20


They encourage groundwater recharge wherever possible

They create a better environment to live, work and play. (CIRIA, 2012)

2.5 Economic & Social Effects of Flooding

In a 2007 survey conducted by the Scottish Executive, 1223 people were surveyed

from seven locations in Scotland including Brechin, Edinburgh, Forres, Elgin,

Hawick, Glasgow and Perth. Of the 1223 people, 633 came from households that

had been flooded and 590 from households not flooded but located in areas that had

been flooded over a 12 year period from 1993-2005.

In the surveyed locations, rivers that burst their banks was the most common cause

of flooding at 85%, followed by surcharging sewers and overland flow at 10% and

coastal storms at 5%. The flood waters analysed were nearly always contaminated

with mud and/or sewage.

Of the flooded households surveyed, a mere 42% received some kind of warning,

one third of which provided more than 3 hours’ notice of the impending flood. The

most common form of warning was word of mouth among neighbours and just over

51% of flooded households had received an official warning.

The most common immediate responses to a flood warning were to deploy

sandbags or floor guards, move vehicles, remove possessions from the ground floor

of houses and vacate properties.

Direct economic losses for households averaged around £32,000 for damage to

buildings and around £13,500 for contents damage. Approximately 10 days leave

from work (paid and unpaid) was required to deal with the immediate aftermath of

being flooded. (Werritty, et al., 2007)

Aside from the economic losses associated with flooding, there is also the emotional

and psychological trauma that is caused to flood victims and in some extreme cases,

there is the tragic loss of life which leaves families and whole communities torn

apart. Although in recent decades, fatalities associated with flooding have been rare,

there are still cases where loss of life has occurred. In the January 2005 flood in

Scotland, 5 fatalities occurred in the Outer Hebrides. (Werritty, et al., 2007)

21 The role of SUDS in reducing flood risk

Households with insurance registered higher stress levels regarding living with flood

risk than those without insurance. This was in part due to the thought of having to

deal with loss adjustors and builders whilst having to live in temporary

accommodation.

Households with an annual income of less than £20,000 also reported high levels of

stress and anxiety and in some cases, more adverse health impacts.

In this report by the Scottish Executive, the trauma of being flooded and its

immediate aftermath was the most significant impact reported, chiefly among the

elderly and most vulnerable. Some participants reported how difficult it was to

maintain family cohesion when children have to live in hotels or with grandparents,

and as a result their education suffered. Also it was reported that relationships within

the family were severely tested whilst living in temporary accommodation and

dealing with contractors. (Werritty, et al., 2007).

As the above facts outline from the 2007 survey conducted by the Scottish

Executive, living with flood risk is an anomaly that hundreds of thousands of Scottish

citizens have to live with and the effects of living with flood risk not only accounts for

the economic end of things, but also it has a great effect on their health and mental

health. It is for this reason that flood relief measures and systems that can

successfully alleviate the flood risk are so important; and this is where the

importance of SUDS becomes most apparent.

2.6 The role of SUDS in reducing flood risk

As can be seen in the previous section, there are many severe consequences of

flooding. These range from the economic implications where it costs flood victims

and the Scottish Government millions of pounds every year to the emotional and

psychological trauma it inflicts on flood victims. And in some cases, it takes much,

much more.

With traditional drainage techniques, there are no provisions in place to protect

against flooding. When excessive rain falls, the systems become overloaded and

22


cannot handle the sheer volumes of runoff it has to deal with. This leads to polluted

water being released into the watercourses and also flooding in low-lying areas.

With SUDS techniques, if they are properly designed, constructed and maintained,

they can mitigate many of the adverse effects of urban stormwater runoff on the

environment (Wilson, et al., 2004, p. 29) as well as giving peace of mind to potential

flood victims.

As seen earlier in this chapter, the 3 main aims of SUDS can be summed up in the

SUDS Triangle. These 3 aims are to reduce quantity, improve quality and provide

amenity or wildlife habitat. This is done through providing a management train of

techniques, each of which contribute to meeting these 3 aims.

By reducing peak flows to watercourses at times of exceptionally heavy rainfall, the

risk of downstream flooding is greatly reduced. There are a wide number of SUD

systems in use today that are predominantly used to attenuate stormwater, and then

release the water at a controlled rate so as to not overload the receiving

watercourse.

The improvement in which SUDS provide to the lives of potential flood victims is

immeasurable. With the peace of mind knowing their properties are safe from the

risk of flooding, stress levels are reduced, the cost of insurance policies are reduced

and the resale value of properties remains consistent.

23 Types of SUDS

2.7 Types of SUDS

The CIRIA Management Train concept divides SUDS techniques into different

categories, beginning with the most preferential option going to the least preferential.

Figure 2.6 Management Train Concept [2]

Figure 2.7 Common SUDS Techniques

Prevention Conveyance Pretreatment

Site management measures

Pervious pavements

Green roofs

Bioretention

Filtration

Grasses filter strips

Grassed swales

Infiltration devices

Infiltration basin

Filter drains

Ponds

Stormwater wetlands

On-/off-line storage

Pipes

Source

Control

Techniques Regional

Control

Site

Control

Site layout design to

minimise impervious areas


(Wilson, et al., 2004, p. 37)

24


2.7.1 Prevention

According to CIRIA C609 (2004), prevention or good site practice is the most

effective way to deal with stormwater issues. Prevention methods include efficient

site design which minimises the area of impermeable surfaces, thereby reducing

runoff volumes and good site management measures including regular sweeping of

impermeable surfaces, minimised use harmful chemicals and separation methods

which limit the potential for runoff and pollutants to come into contact.

2.7.1.1 Minimise Impervious Surfaces

By reducing the area of impermeable surfaces on a development site, the volume of

runoff is therefore greatly reduced. This can be done by carefully designing streets

and car parking spaces to minimise impermeable area by optimising the use of

hammerheads and T-shaped turning heads. Another way to reduce impervious

surfaces is to maximise the use of pervious surfaces where possible and by

connecting roof drainage to infiltration devices so that the runoff does not affect the

watercourses.

2.7.1.2 Site Management Measures

There are many effective site management methods which can be used in order to

prevent the adverse effects of stormwater on the receiving watercourse. These

methods include:

Regular sweeping of impervious surfaces to reduce pollutant build up, and

thereby reducing pollutant loads entering the SUDS scheme. As a minimum,

pavement should be swept twice a year, once in spring and again in autumn

to remove leaf fall (Wilson, et al., 2004, p. 133).

Winter de-icing of pavements can be a major contributor to pollutant loading.

Chlorides and other contaminants are unlikely to be substantially reduced by

SUDS techniques; therefore prevention is the best way to reduce their impact

on receiving waters.

25 Types of SUDS

Landscape management is a substantial area when it comes to site

management measures. Landscapes should be designed to reduce sediment

load, avoid the over application of fertilisers and avoid the over application of

pesticides.

Control of construction site runoff and chemical storage and avoidance of

chemical spillages are also importance site management measures in

avoiding pollution to receiving watercourses.

2.7.2 Conveyance

The transfer of surface water runoff (conveyance) across the site, between

components is essential. There are a variety of approaches that can be used;

underground through pipes with little control or water quality treatment, or through

vegetated channels on the surface providing some treatment and attenuation and

through more engineered canals or rills. The preference in terms of delivering

sustainable drainage objectives is the conveyance of water through vegetated

channels or swales. Uncontrolled conveyance to a point of discharge into the

environment is discouraged (CIRIA, 2012).

2.7.3 Pre-treatment

Components of pre-treatment consist of grassed filter strips, grassed swales and

filter drains. These devices fall under the category of Source Control and

conveyance devices also, meaning they are preferential when choosing SUDS

techniques to be implemented on new development sites.

Pre-treatment involves the removal of pollutants from stormwater runoff from

impermeable surfaces. They were originally used as a treatment process in the USA

to deal with polluted runoff from agricultural areas but were developed for use in

urban areas also. Nowadays, they are often deployed as a pre-treatment technique

before other SUDS techniques to reduce the risk of silting.

26


2.7.4 Source Control

Source control, also known as Best Management Practices (BMP’s), is the preferred

option when it comes to the design of any SUDS scheme and should always be

considered first. The reason for this is simple and logical; controlling stormwater

runoff at its source results in relatively small catchment areas where the volume of

runoff and pollution are not concentrated into the surface water stream, thereby

reducing the consequences of failure. Where possible, the use of infiltration and

planting should be optimised so as to encourage evapotranspiration. Rainwater

harvesting can also be used as a means of reducing runoff volumes from a site.

There are numerous source control techniques and they are listed below (Wilson, et

al., 2004, p. 36).

2.7.5 Site Control

Where source control is not feasible or additional control of runoff is required, then

site control measures can be used. In this case, the runoff from several sub-

catchments within a site are brought together and dealt with by features such as

ponds, basins and wetlands. Care must be taken when using site control measures

however, as the effect of concentrating runoff increases volumes and can increase

pollutant concentrations. As a result, the consequence of failure would be greater

within a site than source control, for example.

2.7.6 Regional Control

Regional control is similar to site control, but the overall catchment tends to be larger

as it deals with water from several sites and the same site control techniques are

used as seen in Figure 2.7 Common SUDS Techniques. Regional control features

should not be used on their own without some form of source control feature in place

within individual developments.

27 Types of SUDS

2.7.7 Source Control Devices

2.7.7.1 Pervious Pavements

Pervious surfaces can be either porous or permeable. Porous surfacing is a surface

that infiltrates water across the entire surface whereas permeable surfacing is

formed of material that is itself impervious to water but, by virtue of voids formed

through the surface, allows infiltration through the pattern of voids (CIRIA, 2012).

Pervious surfaces are suitable for pedestrian pavements and roads as they allow

rainwater to infiltrate through the surface into the underlying layers. This water can

then be temporarily stored before infiltration into the ground, reused or discharged to

a watercourse or other drainage network. (CIRIA, 2012)

Advantages

Reduced peak flows to

watercourses reducing risk of

flooding downstream

Reduced effects of pollution in

runoff on the environment

Allows duel use of space so

there is no additional land take

Eliminates surface ponding and

surface ice

Resilient to lack of maintenance

Disadvantages

Cannot be used where large

sediment loads may be present

Risk of long term clogging and

weed growth if poorly

maintained

In the UK, currently being used

on roads with low traffic

volumes, low axle loads and

speeds less than 30mph

Figure 2.8 Permeable Paving

(Harrison, 2011)

28


2.7.7.2 Green Roofs

Green roofs comprise a multi-layered system that covers the roof of a building with

vegetation or landscaping. The roof more often than not consists of an impermeable

layer, a substrate or growing medium and a drainage layer although the drainage

layer is not always required.

Green roofs are designed to intercept and retain precipitation, reducing the volume

of runoff and thereby attenuating peak flows. As roofs are one of the most significant

contributors to rainfall runoff, optimising the use of green roofs means other SUDS

techniques can be significantly reduced in size.

There are two types of green roofs; intensive and extensive. Extensive green roofs

are most appropriate for the use in SUDS as they are simpler, light-weight, cost-

effective and can be used in a wide variety of locations with minimal maintenance

required (Wilson, et al., 2004, p. 152).

Pollutant – removal mechanisms include filtering and absorption by the substrate

and drainage layers and retention by plants. The removal efficiency depends on

plant layer, season, nature of pollutants, temperature and light level.

Advantages

Good removal capacity of

atmospherically deposited

urban pollutants

Can be used in high density

developments

Can be retrofitted

Provides ecological, aesthetic

and amenity benefits

No additional land take

Disadvantages

Cost is high when compared

with a conventional roof

Not applicable to steep roofs

Retrofitting opportunities may

be limited by roof structure

Maintenance requirements

Damage to waterproof

membrane likely to be critical

29 Types of SUDS

Figure 2.9 Green Roof

2.7.8 Filtration Devices

2.7.8.1 Bio-Retention Areas

Source Control

A bio-retention area is a shallow depressed landscape area that is under-drained

and relies on enhanced vegetation and filtration to remove pollution and reduce

runoff volumes. Pollution is removed from runoff by a combination of sedimentation,

filtration, adsorption and biological action. The bio-retention area is only used for

treating the water quality volume and is normally placed off-line. The water quality

volume of runoff is diverted into the bio-retention area and allowed to pond.

Bio-retention areas are ideally suited to car parks and roads as no extra land take is

required. Maintenance requirements include monthly inspections, monthly litter

removal, annual weeding, annual replacement of top mulch layer, annual

replacement of damaged vegetation and finally pruning every two years.

(Green Roof Technology, 2014)

30


Advantages

Improved aesthetics

Reduces volume and rate of

runoff

Very effective pollutant removal

Flexible layout to fit into

landscape

Suited to impervious areas such

as car parks without additional

land take

Disadvantages

Cannot be used to treat large

drainage areas (unless split into

sub-catchments)

Susceptible to clogging

Can take up space

Construction cost higher than

other basic techniques

Figure 2.10 Bio-retention area

2.7.8.2 Grassed Filter Strips

Pre-treatment or Source control

Filter strips are wide, gently sloping vegetated strips of land that provide

opportunities for slow conveyance and infiltration (where appropriate). They are

designed to accept runoff as overland sheet flow from upstream development and

often lie between a hard-surfaced area and a receiving stream, surface water

collection, treatment or disposal system.

They treat runoff by vegetative filtering, and promote settlement of particulate

pollutants and infiltration.

(SVR Design, 2013)

(Wilson, et al., 2004, pp. 162-172)

31 Types of SUDS

Advantages

Well suited to implementation

adjacent to large impervious

areas

Encourage evaporation and can

promote infiltration

Easy to construct and low

construction costs

Effective pre-treatment option

Easily integrated into

landscaping and can be

designed to provide aesthetic

benefits

Disadvantages

Not suitable for steep sites

Not suitable for draining hotspot

runoff or for locations where

there is a risk of groundwater

contamination, unless infiltration

is provided

No significant attenuation or

reduction of extreme event

flows

(CIRIA, 2012)

Figure 2.11 Grassed Filter Strip

32


2.7.8.3 Filter Trench

Source control or site control

Filter trenches are shallow excavations filled with rubble or stone that create

temporary subsurface storage of stormwater runoff. These trenches can be used to

filter and convey stormwater to downstream SUDS components.

Ideally they should receive lateral inflow from an adjacent impermeable surface, but

point source inflows may be acceptable.

Advantages

Important hydraulic benefits are

achieved

Can be incorporated easily into

site landscaping and fits well

beside roads

Disadvantages

High clogging potential without

effective pre-treatment – not for

sites with fine particled soils

(clays/silts) in upstream

catchment

Build-up of pollution/blockages

difficult to find

High historic failure rate due to

poor maintenance

Limited to relatively small

catchments

High cost of replacing filter

material should a blockage

occur

Figure 2.12 Filter Trench

(CIRIA, 2012)

33 Types of SUDS

2.7.9 Infiltration Devices

2.7.9.1 Infiltration Basin


Infiltration basins are designed to store runoff and infiltrate into the ground. They

operate in the same way as infiltration devices except they are open, uncovered

areas of land.

Basins can be formed by excavating depressions into the ground or by forming an

embankment to impound the stored runoff water. They store the runoff on the

surface and then infiltrate it gradually into the ground. They are normally dry, except

in times of heavy rainfall (Wilson, et al., 2004, p. 218).

Advantages

Reduces the volume of runoff

from a drainage area

Can be very effective at

pollutant removal via filtering

through soils

Contributes to groundwater

recharge

Changes in performance easy

to observe

Disadvantages

Potentially high failure rates due

to improper siting, poor design

and lack of maintenance,

especially if appropriate pre-

treatment is not incorporated.

Comprehensive geotechnical

investigation required to confirm

suitability for infiltration

Requires a large, flat area

Figure 2.13 Infiltration Basin

(CIRIA, 2012)

34


2.7.9.2 Infiltration Trench


Infiltration trenches are shallow excavations with rubble or stone that create

temporary subsurface storage of stormwater runoff, thereby enhancing the natural

capacity of the ground to store and drain water. Infiltration trenches allow water to

exfiltrate into the surrounding soils from the bottom and sides of the trench.

Ideally they should receive lateral inflow from an adjacent impermeable surface, but

point source inflows may be acceptable. (CIRIA, 2012)

Advantages

Infiltration can significantly

reduce both runoff rates and

volume

Infiltration provides a significant

reduction in the pollutant load

Can be incorporated easily into

site landscaping and fits well

beside roads

Disadvantages

High clogging potential without

effective pre-treatment

Build-up of pollution difficult to

see

High historic failure rate due to

poor maintenance

Limited to relatively small

catchments

Figure 2.14 Infiltration Trench

(CIRIA, 2012)

35 Types of SUDS

2.7.10 Other SUDS Techniques

2.7.10.1 Grassed Swales

Conveyance and source control

Swales are shallow, broad and vegetated channels designed to store and/or convey

runoff and remove pollutants. They may be used as conveyance structures to pass

the runoff to the next stage of the treatment train and can be designed to promote

infiltration where soil and groundwater conditions allow.

Swales are typically located next to roads but they can also be constructed in

landscaped areas within car parks etc. They can replace traditional pipe drainage

and should remove the need for kerbs and gullies.

Advantages

Easy to incorporate into

landscaping

Good removal of urban

pollutants

Reduces runoff rates and

volumes

Low capital cost

Maintenance can be

incorporated into general

landscape management

Disadvantages

Not suitable for steep areas or

areas with roadside parking

Limits opportunities to use trees

for landscaping

Risks of blockages in

connecting pipe work

Pollution and blockages are

visible and easily dealt with

Figure 2.15 Grassed Swale

(CIRIA, 2012)

36


2.7.10.2 Retention Ponds

Retention ponds are basins with a permanent of water in the base. Temporary

storage is provided the level of the permanent pool and the primary pollutant removal

mechanisms are the settling out of solids and biological activity in the pond (which

removes the nutrients). Temporary storage is usually designed to promote pollutant

removal, with the resistance time being the key factor in the level of treatment

obtained. Typically a residence time of 24-48 hours provides a sufficient balance

between pond size and treatment level (Wilson, et al., 2004, p. 229).

Advantages

Can cater for all storms

Good removal capability of

urban pollutants

Can be used where

groundwater is vulnerable, if

lined

Good community acceptability

High potential ecological,

aesthetic and amenity benefits

May add value to local

properties

Disadvantages

No reduction in runoff volume

Anaerobic conditions can occur

without regular inflow

Land take may limit use in high

density sites

May not be suitable for steep

sites, due to requirement for

high embankments

Perceived health and safety

risks may result in fencing and

isolation of the pond

Figure 2.16 Retention Pond

(CIRIA, 2012)

37 Types of SUDS

2.7.10.3 Detention Basins

Detention basins are surface storage basins or facilities that provide flow control

through attenuation of stormwater runoff. They also facilitate some settling of

particulate pollutants.

Detention basins are normally dry and in certain situations the land may also function

as a recreational facility. However, basins can also be mixed, including both a

permanently wet area for wildlife or treatment of the runoff and an area that is usually

dry to cater for flood attenuation.

Basins tend to be found towards the end of the SUDS management train, so are

used if extended treatment of the runoff is required or if they are required for wildlife

or landscape reasons.

Advantages

Can cater for a wide range of

rainfall events

Can be used where

groundwater is vulnerable, if

lined

Simple to design and construct

Potential for dual land use

Easy to maintain

Safe and visible capture of

accidental spillages

Disadvantages

Little reduction in runoff volume

Detention depths may be

constrained by system inlet and

outlet levels

Figure 2.17 Detention Basin

(CIRIA, 2012)

38


2.7.10.4 Stormwater Wetlands

Site control or regional control

Stormwater wetlands are specifically constructed to treat pollutants in runoff by

facilitating adhesion to vegetation and aerobic decomposition. They are one of the

most effective SUDS techniques regarding pollutant removal and also offer a

valuable wildlife habitat. They are not normally designed to provide significant

attenuation but if required to act as a water detention device, the temporary storage

may be provided above the level of the permanent storage (Wilson, et al., 2004, p.

251).

Advantages

Good removal capacity of urban

pollutants

Can be used where ground

water is vulnerable, if lined

Good community acceptability

High potential ecological,

aesthetic and amenity benefits

May add value to local property

Disadvantages

Land take is high

Requires baseflow

Limited depth range for flow

attenuation

May release nutrients during

non-growing season

Little reduction in runoff volume

Not suitable for steep sites

Performance vulnerable to high

sediment inflows

Figure 2.18 Stormwater Wetland

(CIRIA, 2012)

39 Introduction

Chapter 3

SUDS – the good and the bad

3.1 Introduction

As chapter 2 has outlined, there has been a lot of developmental work in the area of

sustainable urban drainage. Every element of SUDS has been carefully planned and

approached in a way that will produce optimum results in a more cost effective way

than traditional means of drainage.

SUDS have been implemented in Scotland for over 20 years now and there are

many points of view and arguments towards the success of their implementation.

There is no doubting the fact that they have improved the status of all water bodies

in Scotland and are well on track to achieving “good status” by 2015, an objective set

out in the EU Water Framework Directive. There are many reasons for this success.

These reasons include:

a) Powerful legislation introduced in Scotland in accordance with the EU Water

Framework Directive which has made the use of SUDS mandatory on all new

developments after 2005.

b) Monitoring of SUDS performance and the further developmental work and

improvement of SUDS techniques carried out by establishments such as

Scottish Water, SEPA, CIRIA and SNIFFER.

c) Improved communication between major governmental bodies including local

authorities, SEPA, Scottish Water and developers.

However, there is an extensive argument brewing in recent times questioning their

total success. People have argued a lot has been done in regard to the

implementation of SUDS, but there is still a vast amount of work to be done in order

to make SUDS in Scotland 100% successful.

In this chapter, the opinions of Scotland’s leading water engineering professionals

will be compiled and the reasons for success and opportunities to improve the SUDS

experience in Scotland will be outlined.

40


3.2 SUDS – Reasons for success

SUDS were charged with the task of replacing traditional means of drainage. They

were introduced to be more sustainable and beneficial to the environment than

traditional systems; hence the name Sustainable Drainage Systems and little would

argue that in that respect, SUDS have been an undisputed success.

There are many other contributing factors to the success of SUDS however. These

factors include strict legislation, vast amounts of research and development and

improved communication between the relevant parties.

In this section, the reasons for the success of the implementation of SUDS in

Scotland will be outlined in greater detail.

3.2.1 Legislation

In October 2000, the EU Water Framework Directive was adopted and it came into

force in December 2000. As seen in 2.4.2 The EU Water Framework Directive, the

purpose of the Directive is to establish a framework for the protection of inland

surface waters (rivers and lakes), transitional waters (estuaries), coastal waters and

groundwater. It will ensure that all aquatic ecosystems wetlands meet “good status”

by December 2015.

The EU Water Framework Directive was incorporated into Scottish Law by The

Water Environment and Water Services (Scotland) Act 2003 (WEWS Act). The

WEWS Act in its part 2 introduced new provisions into existing Scottish legislation.

These changes were to the Water (Scotland) Act 1980 and the Sewerage (Scotland)

Act 1968 in which the amending provisions deal with construction standards and

vesting conditions for the adoption by Scottish Water of privately constructed water

or sewerage, including drainage, infrastructure (Scottish Executive, 2007).

In the WEWS Act, and thus for the purposes of the 1968 Act as amended, a SUD

system is defined as a drainage system which “(a) facilitates attenuation, settlement

or treatment from two or more premises, and (b) includes one or more of the

following: inlet structures, outlet structures, swales, constructed wetlands, ponds,

41 SUDS – Reasons for success

filter trenches, attenuation tanks and detention basins (together with any associated

pipes and equipment)” (Scottish Executive, 2007).

According to the Avoidance sub group of the Flooding Issues Advisory Committee

(FIAC) set up by the Scottish Executive in 2005, SUDS can play a major part in a

sustainable flood management strategy. As a result of this, the Scottish Executive is

committed to promoting the use of SUDS, both in public open spaces and within

private curtilages, and has given effect to this policy with the introduction of General

Binding Rule 10 (d)(i) in the Controlled Activities Regulations (2005, amended in

2007).

In other words, the Water Environment (Controlled Activities) (Scotland) Regulations

of 2005 imposed a mandatory use of SUDS within new or brownfield sites. This has

restricted developers from opting for cheaper, traditional means of drainage as they

had done in the past, which has resulted in beneficial effects on the environment.

The pollution levels have decreased in Scotland’s aquatic ecosystems, wildlife

habitats have prospered and downstream flooding has been reduced significantly.

The common belief among those involved in the water industry in some capacity is

that these changes to the legislation in Scotland are the primary reason for the

success of the implementation of SUDS in Scotland. Later in this report, the results

of a survey conducted in late 2013 of 151 of the top water engineering professionals

in Scotland asking their opinions on the success of the implementation of SUDS in

Scotland will be outlined in greater detail. The standout statistic from the survey is

that the overwhelming majority of the participants, 96.8% of them to be exact,

believe Scotland has successfully implemented SUDS since the implementation of

the WEWS Act in 2003. This is conclusive proof that the implementation of SUDS in

Scotland has been a success, and that the legislation that was introduced to promote

the use of SUDS is a direct reason for their success.

3.2.2 Detailed Research

As is obvious from this report alone with the vast amount of cited sources, there has

been a great deal of research conducted and reports published on SUDS in the past

42


two decades. The vast majority of this research has been carried out by the same

establishments, some of which are listed below:

a) CIRIA – Construction Industry Research and Information Association

CIRIA have published many reports and written many books in relation to

sustainable urban drainage. The most prominent books they have published include

The SUDS Manual C697 and Sustainable Drainage Systems C609, both are which

taken as industry standard for SUDS in Scotland and C697 is the book SEPA refers

people to who have queries regarding SUDS. Recently, CIRIA has launched a

website purely dedicated to SUDS called susdrain, available at

http://www.susdrain.org/.

b) Hydro International (including Engineering Nature’s Way)

Similar to what CIRIA have done, Hydro International established Engineering

Nature’s Way, which is a dedicated resource for people working with SUDS and

flood risk management in the UK. In late 2013, Engineering Nature’s Way conducted

a major survey of 151 Scottish water engineering professionals, in order to gain their

perspective on SUDS in an attempt to improve the SUDS experience in Scotland.

The ENW website is available at http://www.engineeringnaturesway.co.uk/.

c) SEPA – Scottish Environmental Protection Agency

SEPA could be considered the main body in implementing SUDS in Scotland. The

WEWS Act of 2003 requires any actively likely to cause pollution to be authorised

beforehand. SEPA’s principal role relating to flooding and pollution is in monitoring

rainfall and water quality. The statistics gathered by SEPA regarding water quality

are used by other establishments to look at SUDS performance and ultimately used

to further develop and improve SUDS performance. SEPA is the statutory consultee

for planning applications on developments where there may be a risk of flooding, as

well as being the enforcers of the Controlled Activity Regulations, enacted in 2007, in

order to protect the water environment and water quality (McLellan, 2008).

d) Scottish Water

Scottish Water is the drainage authority throughout Scotland and they therefore

share responsibility with the councils for quantity and quality of surface runoff being

http://www.engineeringnaturesway.co.uk/


discharged to watercourses. As of the technical guideline on sewerage infrastructure

- Sewers for Scotland – 2nd Edition, Scottish Water was made responsible for the

future maintenance and capital replacement of shared public SUDS systems and

these changes were brought in through the WEWS Act of 2003. Where SUDS are in

public spaces and the standards are satisfactory in line with 'Sewers for Scotland

2nd Edition', they should be adopted by Scottish Water and maintained as part of the

sewerage network. Such public systems should be an integral part of the SUDS

provision for which several bodies are responsible (Scottish Water, 2007). As far as

Scottish Water’s contribution to SUDS research goes, they have amended the

Sewers for Scotland – 2nd Edition technical guide to include the design and

construction standards of the systems that will ultimately become public SUDS. Also,

Scottish Water have assisted in the writing of many reports relating to the

development of SUDS, particularly reports on retrofitting SUDS in Scotland.

e) University of Abertay, Dundee and Coventry University

Sustainable Urban Drainage Systems Network (SUDSnet) is a network jointly co-

ordinated by the Urban Water Technology Centre (UWTC) at the University of

Abertay Dundee and Coventry University. SUDSnet provides a UK-wide network for

developers, relevant agencies, researchers and water engineering practitioners as

well as all other interested in SUDS. The network focuses on various SUDS issues

including best management practices (BMP’s), monitoring programmes, lessons

learned from existing SUDS schemes, development of design procedure etc.

The network is run in partnership with multiple organisations including CIRIA, SEPA,

Scottish Water, SNIFFER, greenbelt, The Scottish Executive and the Environment

Agency among others. Available at: http://sudsnet.abertay.ac.uk/index.htm.

f) SNIFFER – Scotland and Northern Ireland Forum for Environmental

Research

Sniffer is a registered charity which delivers knowledge-based solutions to resilience

and sustainability issues. According to their website, they create and use ground-

breaking ideas to make Scotland a more resilient place to live, work and play.

Through innovative partnerships approaches, Sniffer share good practice, synthesise

and translate evidence, commission new studies and target communications,

http://sudsnet.abertay.ac.uk/index.htm

44


guidance and training. In July 2002, Sniffer published the report SP(02)09, entitled

SUDS in Scotland – the Scottish SUDS database in which it accurately details all of

the SUDS sites in Scotland at that time, and examines the increasing growth of the

use of SUDS in Scotland. Other notable publications relate to the retrofitting of

SUDS in 2009 and a report on the Monitoring Programme of March 2004 carried out

by Scottish Universities.

g) The SUDS Working Party (SUDSWP)

The SUDS Working Party is a group of stakeholders who regularly meet to discuss

the key issues regarding SUDS. The group comprises of representatives from

Homes for Scotland, Landscape Institute Scotland, RIAS, Scottish Enterprise,

Scottish Government, Scottish Water, Heads of Planning Scotland (HOPS), SEPA

and the Society of Chief Officers for Transportation in Scotland (SCOTS). When

SUDS were introduced to Scotland, it was obvious that national promotion was

necessary to raise the profile of SUDS. SEPA was set up around this time and the

formation of the SUDS Working Party was driven by SEPA so as to include other key

stakeholders. SUDSWP and SCOTS contribution to the development of SUDS came

in the form of developing a whole life costing and whole life carbon tool for SUDS.

This tool is free of charge to be used by the water industry. The tool allows

designers, developers and local authorities to cost and compare the construction and

maintenance costs as well as the carbon emissions of various SUDS for Roads

Schemes. Available at:

http://www.sepa.org.uk/water/water_regulation/regimes/pollution_control/suds/suds_

working_party/whole_life_cost_and_whole_life.aspx

3.2.3 Effective planning and design

There are multiple examples to be seen in Scotland at present where there is

evidence of good planning and design. The results that indicate good planning and

design are the performance stats that have been published in several reports. In

essence, what these reports outline is that the correct SUDS techniques are being

used in the correct places in order to gain optimum results.


In many case studies undertaken, results have been positive regarding 4 key aims of

SUDS; these are reduced water quantity, improved water quality, amenity or wildlife

habitat have been provided and finally the cost of maintenance, in some cases has

come in under budget. The details of some of these reports are laid out below.

In an older report, published in 1999 and written by a University of Edinburgh

student, Kate Heal, the performance of SUDS ponds that had been constructed in

Scotland since the mid-1980’s were analysed. At that time (1999), ponds accounted

for 17% and wetlands for 5% of all SUDS constructed in Scotland (McKissock, et al.,

1999). The majority of these SUDS ponds had been constructed in road systems

(13), housing systems (9) and retail developments (5). SUDS ponds are primarily

constructed in Scotland because the wet climate and low hydraulic activity of soils

limits infiltration options at many sites (Heal , 1999). Even in 1999, there was

evidence of good planning of SUDS as seen in the facts above. The use of ponds

was optimised in order to suit the climate and hydraulic conductivity of soils, meaning

there were beneficial results. The results for this report come from the SEPA and

Scottish Universities SUDS Monitoring Programme started in 1996, up to that point

in 1999 (a report which will be summarised in the next section). What the author of

this report outlines from the SUDS Monitoring Programme is that some of the key

aims of SUDS were met (The SUDS Triangle).

Monitoring of flows at the inlet and outlet of SUDS ponds shows that these

structures do attenuate floods. Claylands Pond, which receives runoff from

the M8 motorway was monitored during a storm event in June 1998, showed

a reduction in peak flow from the inlet to the outlet, signalling effective

attenuation of stormwater.

Newbridge Pond, which receives runoff from the M9 motorway, was observed

in May 1999. Readings from the inlet to the outlet of this pond showed

improvements in water quality, by means of reduced turbidity and removal of

heavy metals.

According to the author of the report, the results of the monitoring programme

up to that point had indicated successful peak flow attenuation and water

chemistry improvement in SUDS ponds in Scotland.

(Heal , 1999).

46


In a case study presented at the 11th International Conference on Urban Drainage in

Edinburgh in 2008, the performance and maintenance of SUDS was monitored for a

motorway service area. The study was carried out between 2000 and 2008 in order

to try and solve the well-documented problems with lack of knowledge on

performance and maintenance of SUDS. The study was carried out on 4 SUDS

management trains constructed in 1999 at the Hopwood Park Motorway Service

Area in central England.

Some might wonder what this study has to do with the success of the

implementation of SUDS in Scotland. But it is important, as it is the statistics in this

report that has given more of a feeling of confidence to stakeholders and developers

regarding SUDS performance and maintenance requirements in Scotland. The

results of the report, in the words of the author; demonstrate the benefits of a

management train approach over individual SUDS units for flow attenuation, water

treatment, spillage containment and maintenance. Peak flows, pond sediment depth

and contaminant concentrations in sediment and water decreased through the coach

park management train. Also in this report, maintenance costs were noted. Of the

£15000 annual landscape budget allocated for the entire site, the maintenance costs

for SUDS only accounted for a mere £2500 compared to £4000 for conventional

methods of drainage. As well as this, since sediment was attenuated in the

management trains, the cost of sediment removal after the recommended period of 3

years was only £500 and another positive point made is that in future, less frequent

removal will be required (Heal, et al., 2008).

Figure 3.1 Hopwood Park MSA, M42, Worcs - Ornamental Pond

(Graham, et al., 2012)

47 Engineering Nature’s Way Survey

In March 2004, SNIFFER published Report(02)51 entitled SUDS in Scotland – The

Monitoring Programme of the Scottish Universities SUDS Monitoring Group. This

report compiled the information gathered by various Scottish Universities on the

monitoring of SUDS performance over an 8 year period from 1996 to 2004. The

report found that over the period of monitoring, very little maintenance was required

on the systems that were monitored; minor maintenance included the trimming of

vegetation on ponds, detention basins and swales to maintain a pleasant

appearance. However, a number of incidents requiring major attention were noted

during the monitoring period, down to construction deficiencies (Jefferies, 2004).

These concerns and other maintenance issues will be discussed later in this chapter.

From the evidence outlined above, it is clear that a lot has been done in order to

ensure the success of the implementation of SUDS in Scotland. In many respects,

the implementation of SUDS in Scotland has been done very successfully

considering how little information was available in the 1980’s and 1990’s when a lot

of systems were initially installed. However, there are concerns that there is still a lot

of work to be done in order to improve the SUDS experience in Scotland. A 2013

survey of Scottish water industry professionals outlines some of these concerns and

they will be discussed in the next section.

3.3 Engineering Nature’s Way Survey

A recent survey, conducted by Engineering Nature’s Way who are an initiative of

Hydro International, in association with British Water and The Chartered Institution of

Water and Environmental Management (CIWEM), interviewed 151 professionals

involved in the specification, design, delivery and approval of SUDS in Scotland. The

survey is entitled SUDS in Scotland – Experience and Opportunity and was

conducted in September and October of 2013. The aim of the survey was to

investigate how successful professionals believe Scotland has been in delivering

SUDS and to what extent legislation has helped to drive this success (Engineering

Nature's Way - Hydro International plc, 2013). A snap-shot of the results from the

survey are as follows:

48


Of the 151 participants, 96.8% of them believe Scotland has successfully

implemented SUDS since the implementation of the WEWS Act of 2003.

84.7% agreed that legislative drivers have helped Scotland to make more

effective progress with SUDS than England and Wales.

However, many concerns were raised. 61.1% believe affordability of SUDS

presents a barrier to SUDS design and implementation on new developments.

81.3% agree more could and should be done to retrofit SUDS in Scotland.

77.2% agreed that the requirements for design and implementation of surface

water treatment are clearly defined by regulation and guidance in terms of an

‘effective treatment train’

However, the vast majority believed that the regulations and guidance for

SUDS maintenance and adoption was not clear and requires further

classification.

The majority (65%) of those with experience believe that SEPA’s policy to

classify proprietary systems as a level of treatment only in “exceptional

circumstances” was a barrier to design of effective SUDS solutions.

69.2% believe that the proprietary SUDS features either require the same

maintenance or are easier to maintain than natural SUDS features with only

30.8% believing they are harder to maintain.

77.8% felt there was inadequate funding for both the adoption and

maintenance of SUDS in Scotland.

The most overwhelming statistic however, was the percentage of participants

who believe the implementation of SUDS was 100% successful in Scotland.

Of the 96.8% of those who agreed, it was successful, only 2.4% believe it was

totally successful.

(Engineering Nature's Way - Hydro International plc, 2013)

The doubts outlined above are a clear indication more must be done to improve the

SUDS experience in Scotland. In the next section, the doubts outlined above from

the survey are looked at in more detail.

49 SUDS – Reasons for doubt

3.4 SUDS – Reasons for doubt

Despite the vast strides forward that Scotland have made in the past two decades

regarding the implementation of SUDS, there is no disputing the fact that there are

still areas that could be improved on. The concept of questioning SUDS success is

relatively recent. In the short-term, they were viewed as a success, but little or no

thought was given to the long-term maintenance of SUDS. This section aims to

outline the areas where the question marks lie within the Scottish SUDS experience.

3.4.1 No long-term testing

The number of studies into SUDS greatly increased when they were initially

introduced in each country/region (from the mid 1990’s to the mid 2000’s in the UK).

However, once SUDS had become more widely accepted and integrated into

Scottish legislation in 2005 by the Controlled Activities Regulations, there was less of

an incentive to study the long-term performance and requirements for maintenance

of the SUDS techniques being installed. As a result, there is now a vast amount of

knowledge about SUDS and their effectiveness in flow attenuation, improvement of

water quality and providing amenity or wildlife habitat, but a lack of knowledge about

their long-term performance and maintenance requirements. This lack of knowledge

is one of the main reasons, as outlined in the ENW Survey of 2013, for slow adoption

of SUDS techniques by developers and the authorities.

After the ENW Survey was conducted in September and October of 2013, a debate

was set up in which 18 people closely involved in Scottish SUDS policy working

groups representing SEPA, the Scottish Government and Scottish Water as well as

consulting engineers, local authority representatives and house builders in order to

discuss the findings of the survey. Andy Hemingway, SEPA’s representative at the

debate commented that the design and construction of SUDS in Scotland is more

often than not, very good. However, he stated that Scotland’s downfall is the long-

term maintenance issues that have been raised and he also commented that SEPA

should be concentrating on the long term, not 1 or 2 years, but 20 or 30 years down

the line, which is the expected life expectancy of these systems.

50


This uncertainty relating to the long-term effectiveness of SUDS has left the

authorities and developers with doubts and unanswered questions. As a result of

this, the adoption of SUDS by Scottish Water is based on some very strict

guidelines, limiting options to the designer and developer. The design and

construction of SUDS is relatively easy to calculate, however it is the lack of

knowledge regarding the long-term performance and maintenance requirements of

SUDS techniques that leads to difficulty for developers and stakeholders in

estimating the costs associated with these elements. The questions that arise

regarding maintenance are quite simple questions, yet remain unanswered. These

questions include the frequency at which a system must be maintained, whether it

be; regular, occasional or remedial maintenance, the type of maintenance required

such as; sediment removal, litter removal, landscaping, inlet/outlet maintenance etc.,

the cost of maintenance and finally who the responsibility lies with to maintain a SUD

system. In an effort to rectify the uncertainty regarding maintenance, SEPA has

advised CIRIA to modify the chapters on maintenance in The SUDS Manual C697,

which is the industry standard book in terms of best practice, SUDS design and

maintenance that SEPA refers people to when they have queries regarding SUDS.

Modification of these relevant chapters, SEPA representative Andy Hemingway

hopes will eradicate confusion in this area and lead to clearer, more precise

guidelines for developers and designers to work to.

3.4.2 Legislation and confusion over responsibilities

Legislative drivers are given the vast majority of the credit for the success of the

implementation of SUDS in Scotland. However, legislation is also an area which is

holding back SUDS from developing further. The current legislation, as being

implemented by SEPA, according to Ron Jack of Walker Group (Scotland) Ltd is

restricting the flexibility of approach that you can have for selecting SUDS measures.

As outlined in the ENW Survey, 61.1% of the participants believe that affordability of

SUDS presents a barrier to SUDS design and implementation on new developments.

To counteract this, developers wish to use proprietary systems; however this

pathway is blocked by SEPA as under current legislation, proprietary systems are

only classified as a level of treatment in “exceptional circumstances”. As a result,

51 SUDS – Reasons for doubt

designers and developers feel frustrated by the limitations on specifying proprietary

systems as imposed by SEPA (Engineering Nature's Way - Hydro International plc,

2013).

Ron Jack also commented that at the time of SUDS inception, they were governed

by the Planning Advice Note Pan 62, which stated that above ground SUDS were to

be adopted by local authority and below ground SUDS by Scottish Water. However,

this was merely an advice note, and as a result, it was ignored by local authorities as

it had no legislative “muscle”. The result was above ground SUDS were not adopted.

This problem was exasperated when Sewers for Scotland 2 was introduced in the

mid 2000’s; however it only really allowed for basins and ponds above ground.

Under Sewers for Scotland 2, Scottish Water were charged with adopting SUDS, but

since 2006/2007, when this document was published, Scottish Water, until

November 2013, had adopted only 7 SUDS systems in Scotland, leaving an

estimated 1500 systems un-adopted. The problem with this is the responsibility to

maintain these systems is being left to the developers. A consulting engineer present

at the ENW debate commented that the constraints put in place by Scottish Water

and the local councils as to what they are willing to adopt makes it difficult to use the

full range of SUDS features available.

John Millar of the West Lothian Council thinks the local authorities need to improve

their way of thinking. He said that in future, when a development is completed and

the local authority adopts the relevant parts, they need to have a better

understanding as to what is involved in terms of the maintenance responsibilities

because in the past, they believed once the water had drained into a SEPA

controlled sewer, it was no longer their responsibility. Mr. Millar, when speaking of

his own experience in the house building sector, also stated that he often

encountered issues getting approval and getting issues adopted and he believes that

this is still the main barrier to a more successful implementation of SUDS in

Scotland.

The argument exists that in order to solve the adoption and maintenance issues in

Scotland, relevant parties must make a better effort to communicate with each other.

A consulting engineer at the debate stated that in his experience, there were always

issues associated with the interaction of local authorities and Scottish Water

52


regarding the maintenance of SUDS systems. This needs to be rectified as a

significant responsibility is being placed on the home owner and property occupiers

according to Neil McLean of MWH. He believes that it is unfair that the home owner

is being charged for the removal of both foul and surface water from their properties

by the Water Authorities, especially since this water is being directed into SUDS

systems and local authority sewers, yet the local authorities are receiving no

payment for this. The homeowner is already paying sewerage charges and council

tax, and it is unfair and unjust for them to be expected to pay for additional drainage

charges.

One possible solution to this problem would be to transfer some of this duty to the

local authorities, and in return they receive payment for their services. As a result, a

revenue stream would be created for the local authority, thereby encouraging them

to adopt and maintain more SUDS systems, and hence pave the way for a more

successful future regarding the implementation of SUDS in Scotland.

In order to meet the guidelines set out in the EU Water Framework Directive in 2000

where all water bodies must achieve ‘good status’ by December 2015, no country

can afford to neglect an area. In the next chapter, a case study will be undertaken on

Perth, in the Tayside Region of central Scotland, an area with much publicised

issues with flooding in the past number of years. An investigation will be carried out

to see what the authorities are doing to alleviate this flood risk and by doing so,

improving the lives of the people of Perth as well as the numerous environmental

benefits which come with that. The results of this investigation will add to the author’s

final conclusion on the success of the implementation of SUDS later in this report.

53 Introduction

Chapter 4

Case Study

4.1 Introduction

In this report, the reasons for and against the success of the implementation of

SUDS in Scotland have been outlined. There is no doubting the fact that SUDS have

been implemented successfully, more successfully than England and Wales.

However, it is blatantly obvious that there is work still to be done in order to improve

SUDS further, and this means tackling the adoption and maintenance issues as well

as improving the communication between the relevant parties and clearer legislation

relating to where the responsibility lies among the various agencies.

In this chapter, a case study of Perth, Scotland will be carried out in order to

investigate what the authorities are doing to solve the drainage issues Perth have

experienced in past years. Perth has had a well-documented problem with flooding,

with major floods occurring in 1993, 1999, 2010 and 2011, and from the authors

point of view, this is a city that is being neglected in its quest to solve these drainage

issues. This case study will investigate precisely what is being done to reduce the

flood risk for Perth and also investigate if the use of SUDS are being optimised or

ignored.

4.2 Perth, Scotland

Perth is located on the banks of the River Tay, and falls into the catchment known as

the River Tay Catchment. In 1975, Perthshire and Kinross-shire came together to

form a single district in the Tayside Region of Scotland and is now run by the Perth &

Kinross County Council.

54


Figure 4.1 Banks of the River Tay, Perth

Figure 4.2 A view of the River Tay and Perth city centre on a summer day

The climate of Perth is broadly similar to the rest of the British Isles and Scotland, a

maritime climate with cool summers and mild winters. The pictures above are of

Perth on a summer’s day with the River Tay flowing as normal. However, despite this

climate, in the past Perth has experienced its fair share of major rainfall events and

unfortunately, as will be outlined in the next section, Perth doesn’t always look so

pretty.

(Trek Earth, 2014)

55 History of Flooding

4.3 History of Flooding

Unfortunately, in recent times, this has become a more common sight in Perth:

Figure 4.3 Flooding in Gowrie Street/Perth Street, Perth 2011

Figure 4.4 Flooding in Feus Street, Perth 2010

There have been many well-documented cases of flooding in Perth in the past two

decades. These include floods in January 1993, September 1999, December 1999,

January 2011, July 2011 and July 2012.

During these floods, residential and commercial properties were damaged causing

hundreds of thousands of pounds worth of damage to both the home owner and the

local authorities. The 2007 survey exploring the social impacts of flood risk and

flooding in Scotland conducted by the Scottish Executive focused on 7 cities of

Scotland, Perth being one of them. The details of this survey, as seen in Economic &

Social Effects of Flooding in chapter 2, noted that flooding, not only had an economic

effect on Perth, but also a psychological effect on the people who have been flooded

Source: thecourier.co.uk

Source: thecourier.co.uk

56


in the past or the people who day to day, have to live with the knowledge that their

home is at risk of flooding. The next section highlights what the authorities are

currently doing to mitigate this flood risk, but also the barriers the author encountered

whilst trying to obtain information.

4.4 What are the issues?

4.4.1 Adoption and Maintenance Issues

As part of this case study, the local authority in-charge of Perth was contacted (Perth

and Kinross County Council) as well as Scottish Water. This was done in an attempt

to gain a better understanding of the situation in Perth regarding what SUDS are in

place and what is being done to alleviate the flooding problems experienced there.

In a 2002 SNIFFER Report entitled SUDS in Scotland – the Scottish SUDS

database, it states that as of July 2002 as seen in Table 4.1 SUDS sites present in

SEPA Environment Regulation Areas, there were 32 SUDS sites.

Table 4.1 SUDS sites present in SEPA Environment Regulation Areas

Without doubt, the number of SUDS sites has risen from 32 since that time in 2002

until the present day. However, unfortunately this is the most recent survey of SUDS

sites available. Nevertheless, when Scottish Water were contacted in February 2014

asking how many SUDS sites were in their control as of that time, the response I

received further echoed the sentiments of the ENW Survey. Their response informed

me that there are currently no SUDS sites under the control of Scottish Water in

(Wild , et al., 2002)

57 What are the issues?

Perth and at an absolute minimum, there are 32 SUDS sites based on the most

recent survey, and not one has been adopted. When Sewers for Scotland 2 was

introduced in 2007, it stated that Scottish Water was to adopt all SUDS systems in

Scotland, yet in the intervening 7 years, they haven’t adopted one in Perth. I was

informed by Scottish Water that all systems in place in Perth still belong to the

developers. This leads to the obvious conclusion that the developers are being left to

maintain these systems themselves.

4.4.2 Communication Issues

During the undertaking of this case study, there were numerous occasions where

poor communication was noted.

The first issues with communication were between myself (the general public) and

the Perth & Kinross County Council (the authorities). During numerous attempts to

obtain information regarding SUDS in Perth from the council through emails and

phone calls, I was told to refer to their website where there was no relevant

information to answer my queries. 7 emails were unanswered and on the phone, I

was put on hold all bar one occasion. Eventually, I managed to obtain a personal

email address to one of the senior flood engineers on the council who, to his credit,

was very helpful. But regardless of that, attempting to gather information from local

authorities proved to be very difficult.

The next instance where poor communication was noted was when I spoke to a

representative of Scottish Water. This time, the poor communication was between

Scottish Water and the local authorities of Perth. When attempting to gather the

necessary information from Scottish Water, their response was to tell me they had

no knowledge of what SUDS systems are installed in Perth under the control of the

local authority. This proves there is no continuity among Scottish parties who are

supposed to have the common aim of more successful SUDS delivery in Scotland.

58


4.4.3 Responsibility

This issue became apparent when Scottish Water informed me that up to this point,

they have not adopted any SUDS schemes in Perth, despite it being their duty

according to the legislation Sewers for Scotland 2. The result of this is the

developers who constructed the systems, are still responsible for their maintenance.

It is this lack of responsibility on behalf of Scottish Water that is blocking the way for

smoother delivery of SUDS.

In July of 2011, during one of Perth’s most devastating floods of recent decades, the

onus of protecting properties from the risk of flooding was laid on the homeowner.

According to a report at that time, the drainage systems of Perth were regularly

overpowered by heavy rainfall over a 12 month period. Two particular areas at

affected were Feus Road (as seen in Figure 4.4 Flooding in Feus Street, Perth 201)

and the Fairfield housing estate, where the residents believe they have been ignored

by the authorities. The lack of communication between Scottish Water and the Perth

& Kinross Council were to be seen when they attempted to resolve the situation. A

spokesperson for the council stated they had raised the issue with Scottish Water,

whilst also encouraging them to take action. However, Scottish Water responded to

this by claiming they had already dealt with the drainage issues in the area, despite

this obviously not being the case. Both companies, did however agree, that the

primary responsibility for protecting properties rested with the owners. In the opinion

of the author, if the homeowners are already paying council tax and water charges,

the very least the authorities should be doing is protecting their homes from such

flooding events. This can be done by retrofitting SUDS systems in the areas worst

affected by flooding to attenuate stormwater during major rainfall events.

4.5 What is being done to help?

Due to the pleas of the residents of Perth, Scottish Water and the Perth and Kinross

Council have pledged to help solve the problem of flooding in some of Perth’s

‘hotspots’. In recent years Cromlix Road, Feus Road and Crieff Road have become

major flooding hotspots in Perth. Due the repeated requests of the locals, the

authorities have decided to launch a full joint investigation of the drainage and

59 What is being done to help?

waste-water systems of these areas. At the time of writing this report, a solution has

yet to be found. Whilst the authorities claim to be working as one unit in solving this

problem, the council still claim primary responsibility for protecting of home lies with

the homeowner as the authority has limited resources. As well as this, the council

stated that all the drainage systems in Perth have a finite capacity and during some

weather events, this capacity is often exceeded. This is a clear indication that the old

traditional systems of drainage currently in place need to be replaced with SUDS,

systems capable of dealing with excess stormwater.

In an attempt to solve the drainage issues for Almondbank, an area 7 miles North-

West of Perth city centre (falls under the control of the Perth & Kinross County

Council) the local authorities have published their plans for the Almondbank Flood

Protection scheme in November 2013, and the Government quickly responded by

approval of £9.6 million in funding for the project in January 2014. The scheme has

been developed to protect Almondbank from the River Almond and East Pow Burn

by constructing a series of flood defences along the these rivers. In order to gain a

greater understanding of this project, I contacted a senior flood engineer on the

Perth & Kinross Council to ask him a few questions. One of the main questions I

asked was the use of SUDS being optimised in the scheme. His reply was that the

Almondbank Scheme is predominantly a fluvial flood scheme (i.e. it only protects

from river flooding) and although there are minor surface water drainage elements,

the use of SUDS has not been utilised. Nevertheless, this is a sign of progress on

behalf of the authorities and installing a flood defence system is a major step in

eradicating the flood risk in Scotland.

The Almondbank Flood Defence Scheme is indeed a sign of progress, however,

there is no denying the fact that a similar scheme is needed to protect Perth City

centre from the River Tay. Maybe such a scheme will be developed in the future, but

as the locals have said already, sooner rather than later is better.

60


4.6 Analysis & Discussion

Undertaking this particular case study aided the author in developing an opinion on

the success of SUDS’ implementation in Scotland. Whilst it is apparent Scotland

have done a lot to positively deliver SUDS since the introduction of the EU Water

Framework Directive, it is clear there is a long way to go, and the case study of Perth

has only solidified that opinion.

The only SUDS currently being used in Perth are those belonging to private

developers, SUDS systems which have not been installed to mitigate flood risk, but

merely as a way of preventing further flooding. In my opinion, a system like the

Almondbank Scheme would also be necessary to alleviate the flood risk in Perth city

centre as well further utilisation of SUDS.

The outcomes of this case study have mirrored the sentiments expressed in the

Engineering Nature’s Way survey of 2013 in that, the areas outlined to be in need of

improving, are the same areas the author found difficulties when undertaking the

case study. These areas are; where the responsibility lies among Scottish Water and

the local authorities in maintaining SUDS systems that are already installed, the

need for improved communications between these parties and finally how the

adoption of SUDS schemes has been practically non-existent in recent years.

The study of Perth also gave the author an example of how devastating flooding can

be on the lives of the people it affects. There are areas of Perth that have gained the

label of “flooding hotspots” in recent years due to the regularity of flooding events. It

is a traumatic experience for these people who have to constantly live with the fear

of flooding, and to add insult to injury, the authorities have assigned responsibility to

these people for protecting their own homes.

Despite the regularity of floods, the traditional means of drainage continues to be

used, and the unfortunate reality is; these systems cannot cope with the volumes of

water it has to deal with. These flooding hotspots, such as Feus Road, are classic

examples of areas that would be suited perfectly to the retrofitting of SUDS systems.

Although it is accepted that the implementation of a SUDS management train would

be almost impossible, the use of systems like permeable pavements and perhaps a

61 Analysis & Discussion

pond or a wetland would be suited to this area to attenuate stormwater until the

receiving watercourse is sufficiently capable of taking the excess water.

For Perth, source control measures could be better utilised in homes close to the city

centre. This would relieve some of the flooding hotspots from such vast volumes of

stormwater and reduce the severity of floods. However, should this option prove to

be too costly, although not as desirable, the local authority could construct some site

and regional control measures on the city outskirts as a place to drain water to

during heavy rainfall as a means of attenuation and in some cases, they would

provide aesthetic benefits to the area.

62


Chapter 5

Conclusion

5.1 Conclusions

Firstly, it can be concluded that the implementation of SUDS in Scotland has been a

success. There are elements that deserve recognition for the efforts that the

authorities have made in implementing SUDS, one being introducing strict legislation

imposing the use of SUDS on all new developments after 2005. This has been a

major factor in their success. Other factors include the Monitoring Programme

undertaken by the Universities of Scotland to gather vital performance statistics of

existing SUDS used to aid the further development of future systems.

The doubts regarding SUDS were raised only quite recently. These doubts include

the maintenance issues that have arisen due to the lack of long-term performance

testing of SUDS, poor communication among the relevant parties, lack of options

available to designers and developers regarding cheaper proprietary systems due to

the restrictions imposed by SEPA, lack of funding for adoption of SUDS and the cost

of installing a SUDS management train. Other doubts have been raised over the

sustainability of SUDS and where the responsibility lies among Scottish Water and

the local authorities over who must maintain the SUDS already installed.

From the case study undertaken in this report of Perth, Scotland, the results

obtained echo the opinions of the 151 water engineering professionals who

participated in the ENW survey in 2013. One cannot argue that SUDS have come a

long way and in regard to meeting the aims of the EU WFD, they can be considered

a success as they are streets ahead of nations such as England and Wales.

However the doubts cannot be ignored. In order for the implementation of SUDS in

Scotland to be considered a 100% success, these issues must first be addressed.

In the next section, a series of recommendations are made for the future installation

of SUDS in Scotland.

63 Future Recommendations

5.2 Future Recommendations

1. Since the success of the implementation of SUDS in Scotland is clouded by

this issue of whose responsibility is it to adopt and maintain the SUDS

systems in place, the author thinks that in order to solve this issue, perhaps

the responsibility should be given to one single authority to adopt and

maintain SUDS. In other words, don’t have split duties among Scottish Water

and the Local Councils; give the duties to one or the other.

When Sewers for Scotland 2 was introduced in 2007, that power was given to

Scottish Water but as the debate about the Engineering Nature’s Way survey

in November of 2013 outlined, this had been a glorified failure. According to

one participant, only 7 systems had been adopted by Scottish Water in those

intervening 6 years, leaving some 1500 un-adopted.

It is clear the current system is not working and it is blocking progress for the

development of SUDS in Scotland. One possible option to solve this issue

would be a review of Sewers for Scotland 2 or else a stricter adherence to it.

2. In a 2007 survey of Scottish residents whose homes have been flooded in the

past or whose homes are at risk of flooding, it was established that more

needed to be done to warn people of impending floods so they can

adequately prepare for it. Up to that point, only 51% of participants who had

been flooded had received official warning of the impending flood. In the

author’s opinion, this number needs to be 90-100%. All homes that are at risk

of flooding should at least be entitled to warning as in almost all cases; the

flooding can be easily predicted by the authorities. The SEPA Floodline is one

service that needs further development and improvement.

3. To echo the sentiments of point 2 above, there should in-fact be no necessity

for flood warnings as the necessary systems should already be in place to

deal with flooding; be it flood defence systems or SUDS systems which are

capable of attenuating stormwater during major rainfall events. The argument

exists that there is simply inadequate funding for flood defence systems,

however, the author disagrees. According to Greenbelt – the UK’s leading

property and land management company, an estimated 170,000 residential

and commercial properties are at risk of flooding in Scotland, costing a

potential £31.5 million annually (Greenbelt, 2013). If the necessary flood

64


defence systems and SUDS are put in place, this flood risk will be significantly

reduced, and ultimately reducing the annual economic cost of flood damage.

The money invested to construct these flood defence systems will be saved in

the long run in flood damage costs, so it is the obvious choice.

4. As outlined in the ENW survey in late 2013, those with relevant experience

(developers etc.) believe that SEPA’s policy to classify proprietary systems as

a level of treatment only in “exceptional circumstances” was proving to be a

significant barrier in the designing of effective SUDS. The author believes the

legislation SEPA are implementing needs to be adjusted accordingly to meet

the needs of the developers and relevant parties it is affecting.

5. As seen in chapter 4, it is clear that the adoption and maintenance issue of

SUDS is a significant barrier in Perth. Other barriers include poor

communication among the relevant parties and between the authorities and

the general public. I think Scottish Water and the local authorities in particular

need to make a better effort in communicating with each as those are the two

parties that the successful delivery of SUDS depends upon.

6. As time was a major factor in the writing of this report, there were a lot of

areas in which it was impossible to explore. If time had of been available to

me, I would have liked to have undertaken a monitoring programme of the

private SUDS systems in place in Perth on new developments. This would be

done to gather water quality statistics and also to see if they are effectively

doing their job which is not further adding to the flooding issues of Perth as

was the aim when they were installed.

5.3 End Note

Should the issues clouding the success of the implementation of SUDS in Scotland

be addressed by the authorities and a better effort made by Scottish Water, SEPA

and the local councils in the future, the author is sure that the results of the next

Engineering Nature’s Way survey will have a much different look to them.

For now, the author signs off by making the conclusion that the implementation of

SUDS in Scotland has been a great success; however it is not totally successful due

to the concerns raised. When these concerns are addressed, I’m sure the

implementation of SUDS in Scotland will be considered 100% successful.

i

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