SuDS in London - a guide
November 2016 Contents
3 Introduction 2.13 Archaeology 125 Implementation I. Background 2.14 Crime and disorder 6.1 Implementation II. Who is the guidance for? 2.15 Highways and planning 6.2 SuDS design team III. Surface water and SuDS 2.16 Inclusive design 6.3 Drainage hierarchy IV. A SuDS approach V. How should I use the guidance? 29 SuDS components 131 Cost beneft VI. Structure of the guidance 3.1 Which SuDS components are 7.1 Cost beneft suitable for London? 7.2 Methodology 7 Principles of SuDS 3.2 Structures 7.3 Design life 1.1 Planning for SuDS 3.3 Infltration systems 7.4 Cost comparison 1.2 Wider benefts 3.4 Filter strips 7.5 Best value 1.3 The four pillars of SuDS 3.5 Filter drains 1.3.1 Water quantity 3.6 Wet swales and dry swales 137 Appendices 1.3.2 Water quality 3.7 Rills, runnels and Further information 1.3.3 Amenity channel systems Glossary 1.3.4 Biodiversity 3.8 Bioretention systems 3.9 Trees 16 The London context 3.10 Permeable paving 2.1 What is unique about London? 3.11 Detention basins 2.2 The Thames River Basin 3.12 Attenuation and storage 2.3 London’s geological conditions 3.13 Ponds and wetlands 2.4 London’s chalk aquifer 3.14 Management and maintenance 2.5 London’s soils 2.6 Streetscapes of London 65 SuDS on London’s streets 2.7 Townscape 4.1 SuDS and the urban realm 2.8 Retroftting 4.2 Street scenarios 2.9 London’s green infrastructure 2.10 Trees 75 Case studies 2.11 Working with London’s utilities Case study index 2.12 Contamination Introduction 1 Background
The risk of fooding in London increases year on year, with more frequent and intense storms and signifcant quantities of surface water runoff. (This is the movement of rainwater over the surfaces of the city, including the ground, streets, footways and roofs.)
London’s existing network of sewers and drains is at or near capacity in many areas and the issue is exacerbated by a rapidly increasing population. This has already exceeded London's previous peak and is refected in Potters Fields Park the scale of development in the city.
Sustainable drainage systems (SuDS) can help address fooding risks by managing surface water runoff in a way that mimics natural processes, slowing down the runoff rate while providing wider benefts, such as public realm improvements. This is consistent with TfL's overarching 'Healthy Streets' programme.
This guidance seeks to show how SuDS can be incorporated into London’s streets and wider public realm. It highlights potential opportunities and constraints and aims to encourage the relevant authorities across London to consider their streetscape and the Broken kerb detail for bioretention possibilities of successfully integrating SuDS.
4 Introduction II Who is the III Surface water IV A SuDS approach guidance for? and SuDS “SuDS are designed to maximise the opportunities and benefts we can secure Primarily aimed at a non-technical The Mayor’s Climate Change Adaptation from surface water management”. audience, with advice for those who Strategy (GLA 2011) identifed surface CIRIA C753 The SuDS Manual 2015, p6 design, build, operate and maintain water food risk as the greatest short- London’s streets and public realm, this term climate risk to London. This occurs A SuDS approach will: guidance also aims to bring SuDS to a when the rate of fow exceeds what can wider audience, such as design be absorbed either by drainage systems • Manage surface water runoff in a professionals, academics, road user (the sewers) or open ground, and is called way that mimics natural processes groups, local communities, politicians surface water exceedance. and other stakeholders. • Deliver multiple benefts from When the sewer network is full and rainwater, based on the four The Construction Industry Research rainwater cannot get into it fast enough, pillars of SuDS. These are: and Information Association (CIRIA) has fooding occurs (pluvial fooding). This can produced a more comprehensive and occur independently or simultaneously • water quantity technical document: C753 The SuDS with fuvial fooding (where rivers and • water quality Manual 2015 and reference is made to this streams are surcharging). The resultant • amenity document throughout. fooding has a signifcant impact on • biodiversity communities, property and the highway. This guidance should not be an alternative SuDS help reduce the speed and quantity • Work with the natural hydrological to the SuDS manual; it is a companion of surface water fow to the drainage cycle to re-use, reduce and change which seeks to inform and inspire those system. They include above-ground and the fow and quality of runoff interested in delivering SuDS in the below-ground elements and many of the Capital. Although London has its unique above-ground elements are discussed in • Use a holistic, catchment- challenges, the content will hopefully also Chapter 3. This guidance is concerned with based approach be seen as relevant to other UK towns the integration of such measures into the and cities. public realm and therefore looks mainly • Engage with stakeholders and at above-ground measures. communities to share knowledge and change attitudes
• Help address climate change-related issues
5 Introduction V How should I VI Structure of Chapter 5: Case studies Case studies from London, the UK and use the guidance? the guidance overseas show how these principles can be put into practice. The 24 studies identify The guidance should be used to gain a Chapter 1: Principles of SuDS the SuDS teams, set out project objectives, basic understanding of SuDS and how they Sets out the SuDS planning policy illustrate the components and describe the can be applied in London. It should be read environment, the four pillars of SuDS, benefts and lessons to be learned. alongside CIRIA C753 The SuDS Manual the SuDS management train, and the 2015, which provides industry standards in relationship between surface water and Chapter 6: Implementation this area, and other street-related TfL and urban realm. Explains how to form a SuDS design team Greater London Authority (GLA) guidance and develop SuDS designs according to which give a wider understanding of Chapter 2: The London context CIRIA guidance. London’s public realm, including: Identifes the unique London context, including geology, landscape, townscape, Chapter 7: Cost beneft • Streetscape Guidance 2016 heritage and utilities. Reviews cost beneft of SuDS when compared to traditional drainage designs. • London Chapter 3: SuDS components Cycle Design Outlines the surface components of SuDS Appendices Standards 2014 and the design requirements, benefts and Further information relevant to each maintenance implications. Case studies chapter, including references and a glossary • London of SuDS components and links to further of terms. Sustainable guidance are provided. Drainage Action Plan 2016 Chapter 4: SuDS in London’s streets Illustrates how different SuDS components and designs could be integrated and retroftted into typical London streets.
CIRIA C753 The SuDS Manual, 2015
6 Introduction 1 Principles of SuDS 1.1 Planning for SuDs The London Sustainable Drainable Action Ideally, SuDS need to be delivered Plan (LSDAP) also seeks to reduce surface in a coordinated and integrated Controlling stormwater quantity and water water fows into the sewer network manner, subject to the constraints and quality to mitigate fooding and the risk of through a series of wide-ranging actions. considerations set out in this document. pollution respectively are the main drivers for SuDS. SuDS are crucial to help achieve this; The additional benefts that can arise from they also reduce risk and address policies SuDS in the public realm and streetscape Potential fooding is not limited to large dealing with current and future food are discussed throughout this chapter. one in 100 year storms; fooding in urban issues in a sustainable and cost effective They can contribute positively to the areas often results from the more frequent way (London Plan Policy 5.12). character of the streets, open spaces and and intense rainfall we are experiencing in parks in the Capital, as well as address the Capital as a result of climate change. food risk and pollution concerns.
When localised fooding happens, it is usually linked to surface water fows exceeding the capacity of the drainage system. It is therefore important to slow down the fow rate or hold the rainfall back, whether that be within developments or the public realm.
The aim for the reduction in fow rate – or ‘betterment’ – is to achieve levels that emulate a greenfeld site which is supported by the London Plan (Policy 5.13). Although greenfeld rates are not always achievable, the London Sustainable Design and Construction SPD reports that ‘most developments referred to the Mayor have been able to achieve at least 50% attenuation of the site’s surface water runoff at peak times’. Surface water fooding is the greatest short-term food risk to London
8 1 Principles of SuDS 1.2 Wider benefts An important principle which infuences the planning and design process is the The ambition for SuDS in London is not preference that SuDS components are at based solely on reducing water runoff or near the surface. This provides new rates; it is also about the multiple benefts opportunities to integrate SuDS into the that ensue. SuDS can play a signifcant role urban realm, which can include: in enhancing health and quality of life via better air quality, improved surroundings • Creating and enhancing a sense of place and other attributes embedded in TfL’s Health Action Plan. • Water management using the natural hydrological cycle as a baseline SuDS are made up of a sequence of components that: • Enhancing catchment permeability and reducing surface water runoff • Control surface water fow rates • Improving resilience to the • Control fow volumes effects of climate change
• Regulate frequency of runoff • Adaptability in managing rainfall events
• Reduce contaminants to • Improving air quality acceptable levels • Mitigating urban heat island effects CIRIA calls this sequence the SuDS management train and this terminology • Long-term and effective upstream is widely used in the water source control measures management industry. These contributions are encompassed within the four main principles, or ‘pillars’ of SuDS.
SuDS can provide multiple benefts
9 1 Principles of SuDS 1.3 The four pillars of SuDS
SuDS should be based on the four pillars of SuDS design as set out in CIRIA C753 The SuDS Manual 2015. These are: Images courtesy of Jess Bastock Jess of courtesy Images • Water quantity
• Water quality
• Amenity
• Biodiversity Quantity: permeable paving, grit jointing Quality: reed bed planting By managing quality and quantity to meet requirements on the surface, the benefts of amenity and biodiversity generally follow, assuming the SuDS components are well designed.
However, where retroftting SuDS, or where circumstances are particularly constrained or challenging, permeable paving, attenuation tanks and other below-ground features may be the only intervention possible. Of course, in these cases, biodiversity and amenity benefts will be limited.
The following pages describe these four Amenity: community planting Biodiversity: reed bed habitat pillars in more detail.
10 1 Principles of SuDS 1.3.1 Water quantity
SuDS mitigate the impact of everyday rainfall and high-intensity storms by dealing with the same quantity of water over a longer period. This process is called attenuation.
Attenuation aims to limit the rate of runoff to the rate which would have existed before the area was developed (that is a greenfeld rate). Structures, such as inlets, outlets, weirs and spillways can be used to regulate fow.
Water quantity refers to the volume and fow rate of surface water runoff. Restricting the fow of surface water before it can pass through to the next stage of the system alleviates pressure on the sewer system.
A comparison between greenfeld and urban environments which demonstrates this point on the next page.
Quantity: Attenuation, Bo01 Malmö
11 1 Principles of SuDS Comparison between runoff rates for greenfeld and urban environments
Evapotranspiration Evapotranspiration
Surface flow
Interflow
Baseflow Surface flow Interflow Baseflow Greenfield Urban Higher and more rapid peak discharge /s) /s) 3 3
Steeper Lower and less recession Higher baseflow rapid peak Lower Gradual recession baseflow Flow in river (m Flow in river (m
Rainfall event Time Rainfall event Time
12 1 Principles of SuDS 1.3.2 Water quality Improvements to water quality can also contribute to amenity and the potential for Surface water is often polluted. Runoff for biodiversity. Reed beds, for example, from roads, for example, includes which naturally slow and treat water, contaminants from tyre abrasion such provide an active edge to water features as rubber and soot, nickel and chromium and attract a wide range of birds and from brake pad linkings and oil, silt and insects. iron oxide from general traffc use. Designing for water quality must take During warm, dry periods, these account of: substances build up on sun-warmed surfaces and heavy showers can wash • Interception and treatment methods them into the drainage system. This creates to meet CIRIA standards a warm, contaminated, low-oxygen water mix, which fows into watercourses • The quality of surface water and and groundwater. groundwater receiving run-off
Managing the quality of runoff helps • The extent of existing pollution protect the natural environment from control systems in the catchment pollution and SuDS can be crucial in this Reed beds can contribute to water quality respect. The risk of pollution in a SuDS • The extent to which risk management scheme must be assessed and a mitigation measures for spillages of contaminants, strategy proposed to determine the such as oil, are in place • The extent to which the design of required number of treatment stages to the system incorporates sediment ensure water is clean enough to fow to a • The proportion of permeable retention, such as forebays or watercourse. surfaces, green roofs, and/or surfaces hydrodynamic separators discharging to a rainwater harvesting SuDS can also improve the quality of system or soil-based feature • System resilience to cope with future water entering combined sewers, reducing demand, including allowances for pressure on sewage treatment plants. • The proportion of the surface water climate change and urban intensifcation management system that is on or near the surface to facilitate treatment
13 1 Principles of SuDS 1.3.3 Amenity By including surface drainage as part of an integrated urban design approach, SuDS The way London’s public realm looks and can make a major contribution to the feels has a direct effect on people’s quality look and feel of streets and other spaces of life. As London’s population grows, this throughout the Capital. becomes increasingly important.
SuDS may enhance the amenity of London’s public realm in a range of different ways, including:
• Contributing to integrated green infrastructure
• Enhancing character/sense of place
• Improving the quality of space
• Providing a backdrop to existing buildings and streetscape
• Supporting biodiversity
• Reducing air temperature
• Improving air quality
• Reconnecting people with the natural water cycle
• Supporting community involvement and knowledge-sharing though education, Amenity: Thames Path, Richmond engagement and participation
14 1 Principles of SuDS 1.3.4 Biodiversity Although streetscapes can lack the vegetation to absorb and release water London’s natural habitats, catchments and slowly into the drainage network, a key river ecosystems have been disrupted by priority in London is to integrate more urbanisation and intensifcation. SuDS can green infrastructure into development and address this by incorporating and creating a the transport network and opportunities range of habitats that beneft water quality to to this are explored in Chapter 3). and urban wildlife.
Aspects of biodiversity that can be addressed by sustainable drainage include:
• Habitat creation, including the signifcant existing and potential urban forest resource of street trees and parkland trees
• Connectivity and the ability of fauna and fora to move through the city, especially along linear infrastructure such as road, rail and canal corridors
• Source control with living roofs, green walls, trees and other green infrastructure, which can also help intercept rainwater and mitigate the urban heat island effect
• Improvements to air and water quality
Biodiversity in pond Biodiversity at roof level
15 1 Principles of SuDS 2 The London context 2.1 What is unique As London develops and grows, its public The opportunities for SuDS, both above realm needs to work much harder. Not and below ground, will vary across about London? only will it be more intensively used, it London. For instance, in conservation will also need to fulfl multiple demands, areas designated for their landscape, This chapter explains some of the including drainage. architectural and historic interest, there conditions particular to London, although may be more limitations than in an area of some may also be found in other Responsibility for London’s public realm is redevelopment, where a comprehensive metropolitan areas. Some are unique, divided between TfL and 33 local planning approach to water resource management others less so, but all will infuence the authorities, plus other private landowners. may be designed and implemented. integration of SuDS into the public realm. Like most UK cities, much of London’s For the former, and signifcant areas of London is by far the UK’s biggest drainage infrastructure consists of piped central London, this might involve the metropolitan region, occupying an networks. Climate change, population need to retroft SuDS into the streetscape area four times that of Birmingham, increase and densifcation all contribute which is addressed in more detail later in and is experiencing a period of rapid to surface water runoff and increase the this chapter. intensifcation of use and development. pressure on the network. If our drainage The Capital sits within the Thames network is not to exceed capacity or need Other factors also highlighted in this River Basin and contributes the largest total replacement at signifcant cost and chapter, include archaeology and geology. share to the 17% of the Basin’s area which disruption, a long-term approach to surface These can both defne the scope and is urbanised. water runoff management is needed. appropriateness of the scheme and where, with the former, there is over 2,000 years Hand in hand with urbanisation has come The Thames Tideway Tunnel is addressing of history in the heart of the city. population growth. London’s population some of these issues at a strategic level, exceeded its pre-war peak of 8.6 million particularly in relation to events of intense Well-designed and maintained SuDS can in 2015 and is forecast to grow by 100,000 rainfall. Nevertheless, many local SuDS make a major contribution to public realm. per year to 2030. Much of this growth interventions are needed to manage the They can help reduce food risk, improve is expected to be accommodated in the process effectively. water quality, and create a sense of place. existing built-up area, putting increasing This guidance shows how this can be done. pressure on the available water supply and drainage infrastructure in the Capital.
17 2 The London context 2.2 The Thames The Thames River Basin Management Plan Further information: also provides further information on the Thames River Basin Management Plan River Basin catchment-based approach and London’s British Geological Survey local catchment partnerships. London sits in the Thames River Basin District catchment which covers an area of over 16,200km² and where over 15 million people live. The Thames basin includes all water sources including rivers, lakes, groundwater and coastal waters.
Within London there are 32 London boroughs, plus the City of London, eight areas in which catchment-based partnerships operate and 897 sub- catchments.
Reference should be made to the ‘Thames River Basin Management Plan’ to:
• Understand local context
• Target and coordinate interventions
• Identify or access funding for improvements within the catchment
• Ensure objectives of the Thames River Basin Management Plan and local plans are being achieved.
Thames River Basin
18 2 The London context 2.3 London’s Further information: Engineering Geology of British Rocks and CIRIA C753 The SuDS Manual, Chapter 29 Soils – Lambeth Group Aquifer: Status geological conditions British Geological Survey Report 2015, Environment Agency Geology of London (2012), Royse et al Greater London is situated in the London Management of the London Basin Chalk Basin. This is made up of layers of deposits of chalk, clays, sand, and gravel.
Understanding the geological condition of the ground is vital to the implementation Finchley Ridge of SuDS features, as different ground Lea Valley Barnet Plateau Finchley Ridge conditions indicate how SuDS will interact Essex Plateau Essex Plateau
with their local environment. Ruislip Plateau Colne Roding Valley Hampstead Ridge Valley
Barnet Plateau Barnet Plateau
Essex Plateau For example, some of London’s geological Lea Valley North Thames Terraces formations may present risks including: North Thames Terraces Hampstead Ridge North Thames Terraces compressible deposits, collapsible Brent Valley
Colne Valley Lower Thames Floodplain deposits, shrink-swell clays, running sand, Hayes Gravels Hayes Gravels Lower Thames Floodplain soluble rocks and landslides.
Upper Thames
South London Pebbly Sands The British Geological Survey (BGS) can Hounslow Gravels Wandle Valley South London South Thames Clays and Gravels Ravensbourne Heaths and Commons River Valley provide useful preliminary information. River Upper Thames Cray Geotechnical surveys confrm site specifc Valley
South London Pebbly Sands geology. Such information on geotechnical South London Clays and Gravels All London Green Grid properties, such as permeability, porosity Ecological / Landscape Zones Lower North London Downs Dip Slope ChalkChalk soilssoils and soakage, should be gathered as Gravel and SandyChalk soils hilltops Lower North London Gravel and sandyGravel andhilltop Sandy hilltops Lower North London Downs Dip Slope Downs Dip Slope baseline data for any SuDS project. Clays ClaysClays Loams
Upper North London Low level Gravels Downs Dip Slope Loams Loams Flood Plain soils Upper North London Downs Dip Slope LowLow level gravelsGravels Annotated FloodFlood plainPlain soils soilsNatural Signatures - Natural England
The geology of London, All London Green Grid, GiGL
19 2 The London context 2.4 London’s • In areas with high groundwater levels, 2.5 London’s soils water can enter the SuDS component chalk aquifer and reduce its storage capacity London’s soils are derived from the underlying geology. Across London there Beneath London is a large chalk aquifer. • There is a risk of fotation and increased are variously clays, sands and gravels This was substantially depleted during the loads imposed by groundwater which are often found in a river 19th and 20th centuries due to extraction environment. Soil management is by industrial activities. This resulted in • High levels of groundwater can reduce fundamental to the successful the aquifer being depleted to 88m below the infltration rate of SuDS features functioning of SuDS components. sea level. However, in the last 60 years, as industrial activities moved away from • Groundwater can change the stability of SuDS should be designed according central London, the chalk aquifer has underground structures and foundations to the geology and soils of the area. started to rebound by as much as 3m Designs should consider the availability per year. Further information: and properties of existing soils, the CIRIA C753 The SuDS Manual, Chapter surrounding ground and the requirements Some geology in London is susceptible 26 Management of the London Basin Chalk for imported soils. Soils should not be to shrink-swell movement, caused by the Aquifer: Status Report 2015, imported unless this is unavoidable. presence or absence of water. This can Environment Agency. have a substantial effect on underground Soil properties typically infuence: structures and foundations. • Water quantity: the physical properties Since 1992, the General Aquifer Research of soil affect the attenuation Development and Investigation Team capacity as they dictate its drainage (GARDIT) has licensed the removal of and water-holding properties groundwater from London’s chalk aquifer. The aim is to control and eventually • Water quality: the fltration capacity stabilise the rise in groundwater levels. of soils infuence water quality by, for example, affecting the amount The SuDS designer should take account of of elements such as nutrients or the chalk aquifer because: contaminants, taken up by the soil or dissolved into the water Exposed chalk
20 2 The London context • Amenity/biodiversity: the nature Further information: and availability of soil affects plant CIRIA C753 The SuDS Manual, Chapter 29 species selection. Plants’ nutrient or BS3882:2015 Specifcation for Topsoil pH values can vary considerably BS8601:2013 Specifcation for Subsoil and Requirements for Use Soil specifcation should be bespoke Soils and the design process Suitably qualified soil scientists, engineers and to the project in hand. A suitably environmental consultants should be appointed at the experienced soil scientist, engineer and feasibility stage to inform the design process environmental consultant should be Consider key soil properties: sought early in the design process. - Geotechnical - Horticultural - Environmental Soils in new schemes should be tested for Strategic contamination. Testing schedules should Baseline investigation: include parameters from the groups - Assessment of existing ground conditions - Tests listed below (as appropriate): - Presence of underground services
• Geotechnical: permeability; bulk Consider soil requirements for the scheme: - Are existing soils available and do they have potential density; porosity; plastic/liquid Concept for re-use? - Are imported soils necessary? limit; shear strength; California - Is a load bearing system required? bearing ratio (a strength test) - What landscape types are desirable / feasible?
Produce a soil strategy: • Potential contaminants: heavy - Utilising the site’s existing soils (if available) metals; hydrocarbons; asbestos - The soil requirements of the scheme; including number of soils types required Outline Design - In soft landscape; the soil requirements of each • Horticultural: soil texture; pH value; planting type and species - Imported soil and drainage media requirements fertility status; salinity, phytotoxic - Requirements and selection of load bearing systems in hard landsape (toxic to plants) elements for - Management / maintenance requirements SuDS schemes with planting Detailed Design Construction requirements; • Invasive species, seeds and propagules - Produce a detailed specification
Soils and the design process
21 2 The London context 2.6 Streetscapes In some parts of central London, where throughout central London. In outer space is at a premium, a more innovative London, opportunities for SuDS tend to of London approach is needed to incorporate SuDS be far greater. into the public realm. For example, London’s streetscapes vary considerably opportunities may occur where buildings The relationship between streetscape and across the city, refecting the city’s size, are set back, where historical remnants SuDS elements is examined in more detail historical development and the variety exist and in the open spaces scattered in Chapter 4. of structures and land uses that defne it. Streetscape generally consists of natural and man-made elements. The opportunity for introducing natural elements can be limited, if not missing, in intensely urban areas, but greater in suburban areas. SuDS need to be designed to take account of these constraints.
Depending on specifc conditions, streetscape can impact footfall, accessibility, local economic performance, air quality, public health and sense of place. Designed right, SuDS can contribute positively to all of these.
Streets are often the most resilient feature of the urban fabric. While street patterns may remain unchanged for centuries, streetscapes evolve and respond to new demands and requirements. SuDS can be a part of that process.
In parts of central London, more innovative SuDS solutions will need to be explored
22 2 The London context 2.7 Townscape SuDS interventions need to progressively complement and enhance the townscape Townscape is the mix of physical and and become a fundamental part of the social characteristics that make up the character of London. urban environment. This includes its buildings, landscapes, and the way those Historic England has produced a useful characteristics are perceived. Townscape guide called ‘Streets for All: A guide to the directly contributes to people’s sense of management of London’s streets’ which place and identity. reviews many of these assets.
London has a complex townscape that When working on London’s streets there refects its rich and diverse history, culture are several statutory consultees that and built form. London’s Roman origins need to be engaged. A recommended, but are still visible in the City’s street pattern. not exhaustive list, is contained within Further waves of expansion were created Appendix A. by trade, population growth, industrialisation and transport infrastructure. Having Further information: absorbed formerly separate towns and Historic England (2000), Streets for All: villages, London’s character is inherently A guide to the management of London’s polycentric, with its many separate centres streets, Historic England, London, UK each having their own identities. Jones, E. and Woodward, C. (2013), Guide to the Architecture of London, Weidenfeld & London’s history and character is also Nicolson, London refected in its streetscape. Paving, pillar boxes, street furniture, stone drinking troughs, telephone boxes, sculpture, memorials and other heritage assets all contribute to a strong sense of place. This is enhanced by the Capital’s green and blue infrastructure; its many parks, squares and gardens, the canals, the River Thames and its many tributaries. Borough Road: Victorian street tree planting
23 2 The London context 2.8 Retroftting • Integrated as part of development, redevelopment or regeneration Many of the potential SuDS opportunities in London are retrofts, ie, installing the • As part of investment in the components into the existing streetscape public transport network, and public realm. Depending on the such as station forecourts available space and prevailing condition, existing streetscapes can be adapted or • Improving London’s cycle route retroftted with a variety of interventions, infrastructure, eg, Mini-Hollands. improving the quality of the public realm where possible. • As community initiatives, addressing private households, When retroftting SuDS, it is important to including front gardens consider how the space will be used. If wheeled goods handling, for example, is The opportunities – which will be expected, the design will need to address determined above and below ground this in terms of smoothness, access and – and constraints are illustrated in potential obstruction. Chapter 4. Retroft initiatives, such as Twenty 4 Twenty, Greenstreets, SuDS for The following may offer opportunities to Schools and Life+ Climate Proofng for retroft SuDS: Housing Landscapes, offer partnership opportunities to design and deliver SuDS. • During annual road maintenance works
• During road reconstruction or resurfacing
• As part of road drainage improvements
• As part of planned road modernisation Road closure, permeable surfacing and tree planting in Waltham Forest Mini-Holland
24 2 The London context 2.9 London’s green • space for walking and cycling 2.10 Trees infrastructure • enhancing biodiversity/ London benefts from a legacy of Victorian ecological resilience tree planting that contributes signifcantly London is one of the greenest cities in the to its canopy cover while intercepting world with 47% green space and 22% tree • creating a sense of place rainfall. These trees were established in canopy cover. much more favourable, less engineered, Many of these benefts overlap with the conditions than today’s high-performing The green and blue infrastructure of the aims of SuDS interventions. It is therefore pavements where space above and below Capital includes commons, parks, gardens, vital to protect London’s existing green ground is often at a premium. Tree planting felds, street trees, woodlands, green roofs, infrastructure when designing SuDS in has, however, continued in London with green walls and water bodies, including the the Capital. initiatives such as the Mayor's Street Tree River Thames and all its tributaries. Initiative, where over 10,000 trees were planted in 28 boroughs from 2012 to 2015. Together, these assets defne much of the character of the city. Their environmental, SuDS schemes in London should retain economic and social benefts include: existing trees where possible. Specialist advice should be sought at an early stage. • intercepting rainfall Further information: • attenuating surface water fow Greater London Authority (2015), Natural Capital: Investing in a Green Infrastructure • maintaining soil permeability for a Future London, Green Infrastructure Task Force, London, UK. • reducing urban heat island effect Landscape Institute (2013), Green Infrastructure: An integrated approach to • improving air and water quality land use, Position Statement, London, UK. Treeconomics London (2015), Valuing • food mitigation London’s Urban Forest: Results of the London i-Tree Eco Project, London, UK. • providing amenity space Trees in the public realm of the All London Green Grid SPG 2012. Queen Elizabeth Olympic Park TDAG (2014) Trees and Hard Landscape: A Guide for Delivery
25 2 The London context 2.11 Working with 2.12 Contamination London’s utilities In London, contaminated soil and groundwater is likely to be found when Footway and carriageway space in London installing SuDS components because is limited and often highly congested there are few places that have never been below ground with utilities that supply subjected to some form of development or London’s gas electricity, water, sewerage industrial activity. However, contamination and telecommunications. Much of this should not preclude SuDS. Early in the infrastructure, which was installed in the Below ground infrastructure process, a specialist should be appointed late 19th and early to mid 20th centuries to identify contamination risks and sources is ageing, poorly documented and so an integrated remediation strategy can maintained, although its exact location is be explored. Designers should consider: often diffcult to pinpoint. • The risk of mobilising contamination SuDS designers should work closely with through increased infltration utility providers because utilities can be expensive and disruptive to divert. During • Risk of contamination entering SuDS feasibility and option appraisal stages features and contaminating relatively of SuDS design, the team should apply clean rainwater runoff; this could have to each utility owner for information on adverse effects on vegetation and their assets or associated assets. This materials used within SuDS components information should be validated. • Excavation and disposal of contaminated During feasibility studies and option soils is likely to be expensive appraisal stages of design, it is recommended that high quality surveys • SuDS should not compromise are obtained to identify services and remediation systems in place to protect avoid abortive works later in the project. users from the contamination Underground assets should be recorded and this information given to the relevant Further information: highway authority or landowner. Contaminated soil CIRIA C753 The SuDS Manual, Chapter 26
26 2 The London context 2.13 Archaeology 2.14 Crime London’s history covers millennia of and disorder settlement, with layers of archaeology which can be encountered when All designs should seek to provide safe and excavations occur. secure environments, as outlined in s17 of the Crime and Disorder Act 1998. When working in Greater London, it is advisable to contact Historic England’s TfL’s transport community safety Greater London Archaeology Advisory managers located in the Enforcement & Service (GLAAS) – or in the case of On Street Operations Directorate (EOS) Southwark and the City of London, provide advice to design teams on meeting their own borough archaeology offcers their duties under the Act. – as early as possible to understand what policy and consent requirements During design development, contact a are in place for sites of archaeological police Crime Prevention Design Advisor interest and their settings and designated (CPDA) to understand existing crime archaeological priority areas. All local patterns early in the design process and authorities maintain a record of their ensure risks are mitigated. archaeological priority areas.
Further information: Historic England (2015), Guidelines for Archaeological Projects in Greater London. Greater London Archaeological Advisory Service, London, UK. Communities and Local Government (1990), Planning Policy guidance 16: Archaeology and Planning, UK. National Planning Policy Framework, Department for Communities and Local Well-designed streets provide passive Government, March 2012 surveillance and feel safe
27 2 The London context 2.15 Highways Each highway authority has its own 2.16 Inclusive design restrictions (such as working hours, and planning noisy working, etc). Special consideration Any SuDS measure which infuences should be given to works planned near the public realm should be inclusively When developing a SuDS scheme on a Underground, Cycle Superhighway or designed. Design teams should consider London road or street, contact the borough rail systems. specifc measures, such as raised edge and TfL as appropriate, in their capacity as protection, when the following features the local planning and highways authority. SuDS measures must be designed to are proposed: ensure that maintenance and vehicle The implementation of works which affect access requirements can be met without • Rain gardens infrastructure below ground level are compromising the operation of the subject to the New Roads and Street network in terms of safety and disruption • Swales Works Act 1991, which sets out a code of to all road users. practice for the coordination of works. This • Open rills and runnels is administered by all highways authorities, including TfL. • Gravel flter strips
Under the Traffc Management Act 2004, • Detention ponds traffc authorities must ensure road networks are managed effectively to • Other features with steep minimise congestion and disruption to or sudden drops vehicles and pedestrians. This is necessary to protect vulnerable When working on the TfL Road Network people, including children and visually- (TLRN) or on any borough roads, there impaired pedestrians. Each place must are requirements relating to a range of cater to the needs of all and not restrict its issues, including the extent of the road use by any group or individuals. The design works, the code of conduct, lane rental process must consider the needs of people schemes (in case of TLRN) and highway under the Equality Act 2010. licences/permits.
Accessible environments are inclusive to all
28 2 The London context 3 SuDS components 3.1 Which SuDS components are suitable for London?
SuDS are a combination of components on and off-site that make the most of the benefts described in Chapter 1. This chapter explains the SuDS components that may be appropriate for use in London.
SuDS use a variety of components to manage water quality and volume and deliver amenity and biodiversity. An understanding of topography and local surface water discharge options are critical in identifying the most suitable combination of components, with particular attention to:
• Where the rainwater lands and how it is collected (source)
• Identifying conveyance options (pathway)
• Determining the most appropriate discharge points (receptor)
In general, SuDS should ‘think upstream’ and take advantage of specifc upstream source control measures. Integrated SuDS components: wet Integrated SuDS components: dry
30 3 SuDS components A number of case studies illustrating the • Bioretention systems or bioretention • Pools, ponds, canals, rills and runnels application of various components from rain gardens, including a fltration can be integrated into formal or informal a variety of sources and locations are layer that provides required treatment urban landscapes, depending on design, incorporated within this chapter. and detention before the rainwater and used to store and treat water is discharged at a controlled rate to SuDS components in the street, whether a watercourse or drainage network • Surface water drainage soakaways and TfL or borough-owned, could include any infltration systems; these depend on the of the following depending on the context, • Filter drains to collect water stability of ground conditions, proximity opportunity and site constraints: and treat pollution, particularly to foundations, below-ground structures effective in combination with grass and infrastructure and protection of • Permeable pavements with robust flter strips that trap silt before ground water quality and geology surfaces which allow rainwater to water reaches the flter drain pass through them. Attenuated in Some of these components are granular sub-base material or below • Detention basins to attenuate in shallow, illustrated in indicative street settings in ground structures, this can replenish grassy depressions. These are mostly dry the following chapter. groundwater or discharge at a controlled but can store and treat water at shallow rate into the drainage network depths with vegetation when it rains
• Tree planting to intercept rainfall within • Hard ‘basins’ or lowered areas of hard the tree canopy, beneath which the landscape. These provide attenuation ground surface may be impermeable. and temporary storage of runoff before Trees naturally manage rainwater slow release to the next component through transpiration, increasing in the SuDS management train. This soil permeability and enabling water may be particularly appropriate in to infltrate into the subsurface combined sewer areas where water treatment is less important • Tree trenches connecting below ground rooting zones. This maximises • Swales provide linear attenuation the accessible water and soil that is particularly versatile for volume to rooting systems and highways and the rail network. They is benefcial to the long-term can be designed as a ‘storage swale’ sustainability of trees and planting and/or for water conveyance Rainwater interception over the highway
31 3 SuDS components Some SuDS components are linked to • Water butts and tanks to intercept • Rainwater planters to attenuate buildings and structures that help defne and harvest rainfall by disconnecting in above ground planters, with the public realm. These may include: and diverting downpipes integral storage and slow release
• Living roofs’ (green, brown or blue • Rain gardens to create temporary Other SuDS components can be roofs) to provide source control localised ponding for roof runoff, delivered by better management of allowing plants and trees to existing assets, including: beneft from that ponding • De-paving, bioretention and street tree planting, retroftted as part of already planned annual highways maintenance, repair and improvement programmes
• Re-purposing linear green infrastructure, such as verges and embankments along roads, railways and waterways
• Decompacting existing parkland soils
• Repurposing existing green space for swales, rain gardens and bioretention components
• Protecting existing assets that are already providing a SuDS function, including street trees, parks and gardens, verges and infrastructure corridors
The SuDS components are described in more detail in the order found in CIRIA C753 The SuDS Manual. Retroft cycleway and SuDS in Lyon
32 3 SuDS components 3.2 Structures be proprietary systems with irrigation, or formed over time by planting climbing Roofs and walls can provide the frst plants into the ground that are more point of interception as part of the SuDS self-suffcient. management train. Benefts Living roofs are an effective way to Living roofs and green walls provide integrate green infrastructure, no matter multiple benefts and contribute to the how intense the development. The term Green Infrastructure Vision for London. living roofs include ‘green’ (planted), ‘blue’ They reduce rainwater runoff rates, (water attenuation) and ‘brown’ (recycled offset the urban heat island effect and substrate) roofs. The three types of living flter air pollution. roofs can be characterised by: Benefts include: • Extensive roofs: these have varying substrate depths and • Water quantity: living roofs vegetation that generally includes intercept and attenuate rainwater. Proprietary green wall system grasses and wildfowers, creating They allow a reduced discharge minimal loading on structures rate through evaporation and transpiration. Green walls can use an educational and urban farming • Intensive roofs: these typically recycled water for irrigation resource. Green walls soften the have deeper substrates supporting hard city environment, reducing air a range of vegetation. This puts • Water quality: living roofs treat temperatures while being space effcient larger loadings on the structure water through a variety of physical, biological and chemical processes • Biodiversity: Living roofs safeguard, • Blue roofs: these attenuate within the soil and root uptake zones. enhance, restore and create habitat through vegetated substrate They regulate surface water runoff with no additional land take. They specifcation and drainage design temperature that could adversely provide important habitat stepping affect ecology of local water bodies stones and contribute to London’s Green walls are vegetated walls that are natural capital. In particular, they supported on cables, cellular systems or • Amenity: living roofs can improve provide refuge for rare invertebrates. self-clinging and unsupported. They can the look of roofscapes, while Green walls provide vertical habitats rooftop parks and gardens act as for nesting and food for pollinators
33 3 SuDS components Design considerations • Vegetation: living roofs support a variety • Roof conditions are often hostile, Living roofs can be retroftted or designed of plants for amenity, biodiversity and with high winds, extreme temperatures, as an integral part of a new development. food growing. The species selection, periodic rain and drought. Diverse dry The following aspects of design need to whether seeded, self-seeded, pre-grown meadow mixes, that are naturally be considered: or planted, should be adapted to self-sustaining in exposed environments, microclimate and substrate specifcation can be used. Natural windblown or • Exceedance: design roof drainage bird-borne self-seeding is a viable to cope with excessive rain and economic alternative, naturally adapted, rather than off-the- • Irrigation: rainwater should be shelf, imported monocultures intercepted for irrigation, where possible • Access, safety and edge protection: • Structural resilience: living roofs add outlets and drains should be additional loading to a roof structure, easily accessible for inspection depending on the material used, in the form of a dead load. This is Maintenance typically around 0.7 to 5.0 kN/m, Living roofs require periodic maintenance, with imposed loads up to 10 kN/m including for irrigation, inspection of outlets and removal of invasive plants. • Fire resistance: fre risks can be managed Frequency depends on the type of system. through the use of appropriate materials Green walls formed by climbing plants and design. Vegetation should be kept a may need to be periodically attached minimum distance away from vulnerable to supports. Proprietary products areas such as openings and vents require maintenance of plants and irrigation systems and may require • Substrate: varying depths of substrate, occasional replanting. together with dead wood and aggregates within a single roof landscape, create Useful design guidance: different microclimates and the CIRIA C753 The SuDS Manual, Chapter 12 potential for habitat diversity. Soils CIRIA C644 Building Greener BS 120563: and growing media can be formed 2000. Rainwater outlets gutters of recycled material, which support Living roof: Copenhagen BS EN 13252:2001 different potential for fora and fauna
34 3 SuDS components
Water attenuation performance of the Museum of
London green roof
Case study 1 – The roof area was divided into two by an impermeable barrier, creating two Structures separate sub-catchments. This allowed rainfall runoff measurements on the green Location roof and the existing control roof. The London Wall living roof was better at attenuation than City of London the grey roof.
Date 2011
Water attenuation performance of the Museum of
London green roof SuDS components
Living roof
Objectives • Attenuate rainfall • Improve biodiversity
Outcome London East of University of courtesy Images As part of a sustainability initiative at the Museum of London, a series of living roofs were installed on the museum’s roof as part of waterproofng works.
This installation included a range of roofs, including wildfower and sedum mat systems. The variety of scale, levels, shading and aspect produces a biodiverse urban habitat.
The University of East London has monitored Water attenuation performance of the the living roof’s attenuation performance Museum of London green roof
35 3 SuDS components Case study 2 – Outcome The green wall contributes to a biodiversity Structures network that delivers a range of economic and health benefts, encourages wildlife Location and reduces the risk of fooding; 200 Goods Way linear metres of green walls have been London Borough of Camden planted since 2012. As part of a Living Landscape strategy, these green walls – Date together with the living roofs – minimise 2012 the urban heat island effect by increasing air-plant exchange and contribute to the SuDS components SuDS strategy for the area by intercepting Green wall rainwater. Their contribution to the sense of place is also signifcant. Objectives This new neighbourhood is being built around a green framework where 40% of the 27 hectare development is given to open space. More than 400 new trees are being planted and walls and roofs greened
Planting detail Kings Cross green wall
36 3 SuDS components 3.3 Infltration systems
London’s parks, gardens and green space provide large scale SuDS infltration in the open soil, coupled with the interception that parkland trees provide. Infltration systems also exist at a smaller scale, for example, kerb inlets, grass verges and permeable paving.
Designed infltration systems can include the following sustainable drainage components:
• Soakaways: pits that temporarily provide storage before infltration
• Trenches: linear soakaways and strips of grass that are predominantly dry, but in heavy rainfall, fll up and store water for a period of time before infltration
• Infltration basins: depressions performing the same function as trenches
• Blankets: open, fat areas of grass, allowing infltration over a wider area than a trench or basin. St James' Park: London’s parks allow water to infltrate. Soil compaction through high footfall may reduce permeability
37 3 SuDS components These components are designed to A minimum of 1m from the base of the Maintenance promote infltration where capacity and infltration component to maximum This can usually form part of the wider permeability of soils and the depth of groundwater level is required. Upstream routine landscape maintenance. groundwater allows. However, infltration pre-treatment may be needed to remove Control structures require periodic systems may not be appropriate in many sediment and silt. inspection. Existing parkland, particularly parts of London due to groundwater in critical drainage zones that are extraction issues (see Chapter 2). Performance of SuDS components may subject to intense use, should be be compromised if surface soils become periodically decompacted. Benefts compacted, so should be designed to Infltration components allow groundwater withstand high intensity pedestrian use. Useful design guidance to be replenished. They can incorporate Performance depends on the capacity CIRIA C753 The SuDS Manual, Chapter 13 marginal and wetland habitat. Planting of the soils surrounding the component. slows the fow rate by improving the When rainfall rate exceeds the design drainage properties of the soil, creating capacity, a fow route or temporary storage a more effective SuDS component. should be provided. Infltration can be used to manage overfows from rainwater collection systems, such as Soil infltration can be enhanced by: water butts and runoff from small areas (for example, drives and roofs). • Managing construction traffc to prevent compaction during construction Design considerations Infltration components can be retroftted, • Mixing sand with soil to retain designed as a series of small linked its drainage properties elements, or as a single larger one. • Adhering to tight construction tolerances Runoff fow to be directed to a SuDS infltration component can be collected • Soil decompaction laterally along the edge of an impermeable surface. Kerb openings and roadside lateral • Reusing existing topsoil to allow the inlets help to direct, control and reduce inherent seed bank in the soil to fow velocities. regenerate quickly, reducing erosion and enhancing the potential for infltration
38 3 SuDS components Case study 3 – Infltration systems
Location Streatham Common South London Borough of Lambeth
Date Davies Owen of courtesy Images 2013
SuDS components De-paving Tree planting Kerb inlets Before Objectives Streatham Common South falls within the Streatham Critical Drainage Area (CDA). The project included implementation of a rain garden to alleviate food risk and was completed within a standard highway maintenance scheme.
Outcome Pavement SuDS, where inserted with verges, replaced concrete dished channels. These slow surface water drainage into the sewer system. Modeling undertaken has shown that the grass verge can theoretically remove 6m of surface water runoff in a one in 100 year, six-hour After Kerb inlet and de-pave detail storm event.
39 3 SuDS components Case study 4 – Outcome The paving over of front gardens in Infltration systems London is a major issue and contributes collectively to the risk of surface water Location fooding. Permitted development rights 50 & 60 Reedworth Street have recently been withdrawn for London Borough of Lambeth homeowners wishing to pave a garden
with impermeable surfacing. Ann Bodkin of courtesy Images Date 2012 This project highlighted how hardstanding can be removed without affecting parking. SuDS components Residents were supported in changing Permeable paving materials and provided with tools, technical advice and practical assistance. Objectives The initiative has increased the To increase the permeability of permeability of front gardens and front gardens. improved streetscape aesthetics.
De-paving of private front gardens After with gravel and planting
40 3 SuDS components 3.4 Filter strips Design considerations Filter strip effciency depends on Filter strips are uniformly graded, gently length, width, vegetation cover and soil sloping areas of grass that allow water specifcation. Considerations include: to fow as a sheet towards a swale, bioretention system or flter drain. They • Soil permeability provide a simple form of source control through pre-treatment of water, to protect • Vegetation specifcation swales or flter drains from clogging up with silt. • Height of vegetation and fow depth
Filter strips are effective at intercepting • Peak fow velocity in relation rainwater where the soil is suffciently to particulate settlement permeable. The grass and vegetation slows the water, allowing it to soak into the • Time of travel of runoff ground. The plants help evaporate water across the flter strip and flter out pollution. • Protection of the strip from vehicular Benefts run-over and development Filter strips create soft open space next to impermeable areas. They can either be • Designed for management by standard Filter strip: Parkway retroft seeded with amenity or meadow grass and landscape maintenance machinery managed as long or short mown grass to support biodiversity by providing: Filter strips should be more than 2.5m Maintenance wide, and ideally laid to a 1% slope. This can form part of the wider landscape • Foraging for birds and invertebrates Small flter strips that are 1-2m long maintenance operations, to ensure create effective connections between the feature meets design performance • Habitats for invertebrates broken kerb lines and the side slope standards. Measures to prevent soil of a swale. Lengths of greater than 5m compaction are particularly important. • ‘Stepping stone’ habitats, particularly help improve water quality performance. in the urban environment Filter strips should be shielded with Useful design guidance a kerb or low-level barrier when they CIRIA C753 The SuDS Manual, Chapter 15 are next to a road or car parking.
41 3 SuDS components 3.5 Filter drains
Filter drains are deep, narrow, gravel-flled trenches that collect and move water from the road. They often include a perforated pipe at the base to help drainage. Water fow through the gravel can removes some pollutants.
Benefts Filter drains provide:
• Long and short term water storage during a storm between the aggregate particles
• Silt removal, by eliminating suspended sediment in the water Filter drain: open gravel flled joint • A material that enhances biodiversity by hosting micro-organisms and providing a breeding ground Filter drains can be protected from silt on the highway. Equally, they can be for insects and amphibians by an adjacent flter strip (see 3.4) or integrated as an architectural feature in fow spreader. the public realm. Design considerations Filter drains must be able to accommodate Filter drains are usually 1-2m deep, with a Maintenance high return periods (ie, one in 100 year minimum depth of flter medium beneath Filter drains require routine maintenance events) without suffering damage. A any infow and outfall (0.5m) to ensure to ensure vegetation or debris is removed geotextile (not a geomembrane) below reasonable levels of pollution removal. from the surface. the surface of the aggregate traps silt to prevent it clogging up the drain, while These components can be placed at the Useful design guidance allowing permeability. bottom of embankments to intercept CIRIA C753 The SuDS Manual, surface water runoff or with flter strips Chapter 9 and 16
42 3 SuDS components 3.6 Wet swales Benefts Erosion: swales convey and/or retain Conveyance: swales are a simple and fowing surface water where soft and dry swales effective means of collecting and landscape is likely to erode. Reducing distributing runoff, or as a means of the velocity of water fow limits erosion Swales are linear components that provide conveying runoff on the surface, through the use of measures such slow water conveyance. They provide while enhancing open space or the as weirs, check dams, erosion control fltration, attenuation and storage of roadside environment. matting and planting. surface water runoff from relatively small catchment areas. They can be designed to Filtration: engineered soils can Design considerations accommodate a range of rainfall events. help neutralise contaminants and Swales should be designed to suit the scale sedimentation caused by runoff. Designs and character of the specifc location, taking Generally, swales are sloping sided, fat- can include submerged anaerobic zones to into consideration orientation, aspect and bottomed, vegetated open channels, promote nutrient renewal. proximity to other landscape or townscape constructed at a gentle gradient. Steeper features. The design of soft or hard edges gradients can be accommodated through Attenuation: swales are typically designed depends on the urban design context. the use of check dams. Swale design is to capture a one in 10 year storm event limited by available space and is only by storing water within and on top of effective when close to catchment areas. the fltration media where the water can Swales can be dry or wet. disperse over time.
Dry swales allow surface water to infltrate Amenity: swales provide shallow linear and include a flter bed with an underdrain planted features in the landscape that are to prevent waterlogging. They can be lined space-effcient and adaptable to location. or unlined depending on groundwater levels. They integrate well alongside highways, cycleways or pathways. They allow Wet swales retain water, behaving like bridging structures to enhance spatial a linear wetland. They are best located experience, creating places for play and where sites are level and soils are poorly contact with nature. drained, where they can deliver amenity and biodiversity through specifc wetland Biodiversity: swales can be designed planting. During intense storm events, with a variety of marginal planting and water is retained in the swale before being wildlife meadow that contribute to habitat Dry swale: Upton, Northants conveyed to a downstream outlet. creation and connectivity.
43 3 SuDS components Mini swales can manage small events with Contamination: Where there is ground The selection of vegetation should be from overfow to other SuDS components. contamination on brownfeld sites, native species that provide appropriate incorporate a liner, unless leaching can habitat for indigenous species. Where over- Ground conditions: Examine existing be managed to an acceptable level. The the-edge drainage is required, the grass ground conditions and hydrology to liner level should rest above the level of level should be 25mm below the edge of determine the use of either a wet or dry seasonal high groundwater level. the hardstanding to be drained, to ensure swale. The volume of water to be stored, effective surface fow. or infltration capacity of the soils, Edge protection: as a component that allow the designer to establish the basic typically sits below pavement surface Trees: swales can accommodate trees swale dimensions. levels and can hold standing water, within their design, provided conditions consider the edge detail. needed for growth and the hydrological effects are considered. Swales should Exceedance: swales are designed to respect the presence of existing trees and provide a level of storage that can ensure root systems are not compromised. accommodate a one in 10 year storm event. Proposals should accord with BS 5837:2015 The storage capacity of a swale depends and take account of tree preservation on its size, which depends on the available orders and conservation area designations. space. A swale can overtop during severe storms, so build in contingency fow paths Maintenance and/or provide outfalls. Swales require routine maintenance to ensure effcient operation. Different
Image courtesy Robert Bray Associates Robert Bray courtesy Image Health and safety: swales are shallow swale construction and operation affect surface features and should not present maintenance prescriptions. a danger to the general public. However, risks can be mitigated through design to Useful design guidance address edge conditions or provide shallow CIRIA C753 The SuDS Manual, side slopes and shallow fow depths. Chapter 9.8 and 17 HD 33/06 Surface and Sub-Surface Vegetation: planting in the swale stabilises Drainage Systems For Highways slopes, reduces erosion and slows water fow. Swales provide an ideal location Dry swale for a variety of planting that can provide amenity, habitat and foraging.
44 3 SuDS components Case study 5 – Swale
Location Mill Pond Road,
London Borough of Wandsworth Camlins of courtesy Images
Date 2016
SuDS components Bioretention swales Kerb inlets Tree trench planting
Objectives Mill Pond Road is a new road within a development at Nine Elms. It is constructed with a central planting bed acting as a swale to attenuate surface water.
Outcome The surface water runoff is collected along bespoke broken kerb units and fed into the central planting zone, where it flters through to an underground collection and holding tank before being released slowly into the mains sewer system. Standing water is not anticipated for more than one or two days following extreme rainfall events; plants have been selected to be Bioretention swale Plan tolerant of these conditions.
45 3 SuDS components 3.7 Rills, runnels and Filtration: fow-reducing elements, such as planting, textured paving and other channel systems features provide fltration, treatment and sedimentation from captured surface water. Rills or runnels are small, open-surface water channels within paved construction. Attenuation: rills can attenuate surface They collect water directly from hard water by providing storage and reducing surfaces and convey water, at a reduced discharge rates. fow rate, to, from or between other SuDS components. They come in a variety Design considerations of designs to suit the urban landscape Edge protection: typically sitting below and have formed part of the historic pavement surface level, rills have hard edges streetscape environment for many years. and can hold standing water. Design teams should consider how pedestrians (particularly Rills can be planted, with rainwater visually impaired and older people), cyclists bringing them to life. They provide an and vehicles will interact with them, alternative to piped drainage, allowing especially at crossing points and in relation the captured water to remain at the to pedestrian desire lines and vehicle surface and for easy discharge into other movement, especially in narrow streets. SuDS components. Vegetation: rills can provide an ideal Benefts location for aquatic or sub aquatic planting Rills are an effective way to provide SuDS, for habitat creation. including water treatment if planted, where space is at a premium. Silting: rills can become impaired by silting. This can be prevented by placing upstream Amenity: planted rills, interacting with SuDS components to flter sediment. rainwater, enhance the urban environment. Outlets: Rills typically discharge into other Conveyance: rills are effective at collecting SuDS features and the way in which this and distributing storm water runoff, while occurs dictates the rill’s function. Consider Runnel enhancing and demarcating open space. ways of restricting the fow at outfall, through the use of check dams, weirs and orifces.
46 3 SuDS components Maintenance 3.8 Bioretention Bioretention swales are similar to under Channel systems require routine drained swales with vegetation tolerant maintenance of inlets and outfalls, debris systems of likely inundation occurrences and and management of plant material. pollutants. Rain gardens are localised, Bioretention systems are a planted, soft less engineered systems. They usually Useful design guidance landscaped low-spot, positioned to serve a single roof or small paved area HD 33/06 Surface And Sub-Surface Drainage collect, store, flter and reduce surface and can create an attractive addition to Systems For Highways runoff from frequent rainfall. As a surface the public realm. water management component they are CIRIA C753 The SuDS Manual versatile and can be integrated into public Benefts realm environments through altering Filtration: engineered soil or growing CIRIA publication C698: Site Handbook for street geometry, creative material choices media mixes and flter media can be the Construction of SuDS and planting. designed to enhance bioretention treatment performance. Cambridge City Council, Sustainable Inlets, outlets and control structures are Drainage and Adoption Guide 2010 used to control and reduce the water Attenuation: water can be stored within fow rate through the bioretention system. and on top of the fltration and growing media, allowing rainwater to infltrate over Bioretention systems are used to treat and a period of days. manage storm events by collecting local surface water. Water accumulates on the Conveyance: bioretention features can be surface, before fltering through vegetation gently sloped or terraced to allow water to and growing/fltration media. Here it either be conveyed at a reduced fow through the infltrates or is collected via pipe work use of check dams, weirs and/or vegetation leading to a suitable outfall. to a suitable outfall location.
Bioretention tree pits and trenches can Amenity and biodiversity: bioretention be incorporated into pavements using features can be integrated in many ways soils that intercept, dissipate and cool into the streetscape. Integrating planting rainfall runoff. has multiple benefts, enhancing the attractiveness, diversity and quality of the Rill urban environment, while meeting local Biodiversity Action Plan targets.
47 3 SuDS components contaminants with the use of fltration mediums, normally sand-based material with a source of organic matter to provide nutrients for planting.
Sedimentation: slowing surface water fow allows fne particles to be removed. Design should limit excessive sediment accumulation that could reduce storage volume, fltration and infltration rates.
Exceedance: bioretention systems can deal Bioretention rain garden in Vauxhall with only small catchment areas and are likely to be overwhelmed during heavy storms. The design should therefore allow Design considerations than 350mm. An outfall provides overfow for contingency fow paths and/or Edge protection: typically, bioretention when heavy rainfall means infltration into provide outfall. components are sited below pavement the soil is too slow. surface levels and can hold standing water. Outfalls: if an outfall is required, consider It is therefore important that the interface Erosion: bioretention systems aim to catch the location, particularly the relative with pedestrian and vehicular movement fowing surface water. Soft landscapes level of potential discharge locations, as is carefully considered. Bioretention can may suffer erosion, so design the feature bioretention system outfalls can be deep be profled in various ways, with soft to control the surface water runoff compared to conventional drainage. edges and gentle side slopes, or hard movement through the use of weirs, edges and vertical sides. check dams, erosion control matting Maintenance and planting. Bioretention systems require routine site Inlets: inlets may be necessary, especially maintenance operations to ensure effcient when hard edge protection is required. Pollution/contamination: pollution and operation. Inlets and outfalls require Erosion at inlet points can be prevented by contamination sources affecting surface periodic inspection. reducing the surface water fow velocity and ground water may affect planting, via a sediment trap or a reinforced and so the planting specifcation should be Useful design guidance textured zone. Protection grilles should not designed to meet the site conditions. CIRIA C753 The SuDS Manual, Chapter 18 be used unless the inlet diameter is greater Bioretention systems can remediate water
48 3 SuDS components Case study 6 – Bioretention
Location Swan Yard London Borough of Islington
Date J & L Gibbons of courtesy Images 2013
SuDS components Bioretention planter
Objectives A small offce redevelopment has included SuDS components within a limited space to intercept and attenuate rainwater.
Outcome Previously, roof rainwater discharged directly into the street. The most effective way to incorporate SuDS has been by diverting and disconnecting downpipes to feed rainwater into bioretention planters and water butts for irrigation.
The planting adds a small element of self-sustaining biodiversity in an otherwise hard paved yard.
Before After
49 3 SuDS components Case study 7 – SuDS components Bioretention planter Bioretention De-pave Tree planting Location A24 London Road Objectives London Borough of Sutton To reduce hard paving on a wide pavement and plant trees and perennials Date to aid water attenuation. 2014 Outcome Six areas were de-paved and planted with birch trees and a variety of hardy perennials. This has improved the streetscape and reduced the hard paved area contributing to surface water runoff. Each planting area has been mulched with gravel and contains an outlet. Originally envisaged as rain gardens, the design was subsequently amended to limit surface water runoff into the planting areas by installing a raised edge. The project had Local Implementation Plan (LIP) funding and was delivered by Sutton on the TLRN.
Outlet detail Planting
50 3 SuDS components 3.9 Trees
Trees in the hard landscape, parks, gardens and streets contribute to London’s status as one of the greenest cities in the world. Their SuDS functions include attenuation, interception and soil permeability.
Trees provide multiple ecosystem services and mitigation from the effects of climate change, including cooling and improving air quality. Trees also beneft the urban environment in terms of heritage, amenity, and biodiversity. They reinforce a sense of place and can be used for traffc calming.
Benefts Attenuation: tree pits can store storm water runoff through the use of structural soils or proprietary crate systems. It is, however, seldom possible to create attenuation or infltration areas around existing trees; this may kill them.
Trees draw water from the ground through root systems to their leaves, where it is lost through evaporation.
Interception: trees intercept rainfall and store it. This reduces the amount of water reaching the ground, thereby reducing the volume of runoff. Street trees: biodiversity
51 3 SuDS components Infltration: soil infltration rates are A large species tree, such as an oak, can considered. For a more detailed description improved due to root growth that also host hundreds of different animals, plants of the benefts of large tree species in enhances soil biodiversity. and fungi, with long-term beneft to urban environments, see CIRIA C712. Tree pollinators and the urban ecology. specifcation and soils performance criteria Filtration: soils and geotextiles that should be developed in parallel as an make up the construction of tree pits Design considerations integral part of SuDS component design remove silts and particulates that may Existing trees: existing trees should and long-term vision. be present in runoff water. Through be retained where possible. Proposals ‘phytoremediation’, trees absorb trace should accord with BS5837:2015 and take By combining trees with other SuDS amounts of harmful chemicals – including account of tree preservation orders and components, the volume of rainwater metals, hydrocarbons and solvents – conservation area designations. interception and attenuation can be and transform them into less harmful signifcantly increased. The London i-Tree substances or use them as nutrients. Available space: tree pits require eco project, for instance, demonstrated space below ground to successfully that the combined canopy cover of Amenity: street trees are an important accommodate long-term root growth. Tree London produces an avoided runoff of 3.4 component of London’s townscape. pits and trenches (connected pits) should million cubic metres per year. London’s climate allows for a wide provide adequate soil volume, water and diversity of native and exotic species. For gaseous exchange to the root system. The Soils: where possible, trees should be instance, London’s trees remove over 2,000 location of below ground services and established within soft landscape areas, tons of pollution/ha/year and store 2.3 drainage should be identifed to ensure rather than confning rooting zones to million tonnes of carbon per annum. Tree- root zones, utilities and other below restricted trenches in hard landscape. lined streets also make cycling and walking ground infrastructure are all coordinated. more pleasant, enhancing the health and Protection for both long-term root growth Soil depths: the overall depth of soil wellbeing of Londoners. and below ground infrastructure can be should be appropriate for the tree species. provided with root barriers. Guidance Excessive topsoil depth increases the Biodiversity: trees constitute the largest on delivering trees in hard landscapes is risk of anaerobic conditions (oxygen element of biomass in the city, providing provided by The Trees and Design Action defciency). Topsoil should therefore only signifcant biodiversity value. Trees and Group (TDAG). be used within the upper part of the soil woodlands provide food, habitat and profle, with suitable subsoil in the lower shelter for birds, invertebrates and other Tree specifcation: tree species and layer. The exact depth permissible will be species, some of which are subject to diversity, provenance, mature size, dependent on soil conditions, the tree legal protection. clear stem height, root preparation specifcation and the type of load-bearing and procurement should be carefully system (see soils: Chapter 2).
52 3 SuDS components Where tree planting is incorporated • through channels or rills as direct into hard landscape, the use of load- surface water runoff to a tree pit bearing tree planting systems may be necessary. New and retroft SuDS schemes • via depressions or low points will require these systems, which may directing runoff from impermeable categorise the street as a zone of ‘special surfaces towards the tree pit engineering diffculty’. There are several systems available for planting in hard • via permeable surfaces used to collect landscape, including: and convey surface water to the tree pits
• Cell systems Outlets: tree pits should be well drained as waterlogging during establishment can • Urban tree soil be one of the key reasons for failure. This is best achieved by infltration if the • Raft systems ground properties are suitable. Where infltration is not possible then an outfall • Structural growing media to a surface water drainage network can be used. The discharge should be deep to Infltration rates: the rate of infltration prevent waterlogging. of a tree pit dictates the size of the tree pit required for water storage. Maintenance The construction of the pit can be Trees require a higher level of management altered accordingly. during the frst fve years after planting because roots need to establish good Pollution/contamination: pollution and contact with the growing medium before contamination sources affecting surface they can effciently extract water. and ground water infuences tree growth. Certain species are more susceptible than Useful design guidance others, and species selection should be CIRIA C753 The SuDS Manual, Chapter 19 specifc to each site and SuDS scheme. CIRIA C712 The benefts of large specie trees in urban landscapes 2012 Street trees: biodiversity Inlets: surface water can be introduced to a TDAG (2014) Trees and Hard Landscape: tree in a variety of ways: A Guide for Delivery
53 3 SuDS components Case study 8 – Outcome The plaza was constructed as a single Trees rooting zone below granite paving. This earthen layer consists of an 800mm Location thick base course of boulders that form Hyllie Plaza a structural soil, 60% of which is cavities. Malmö, Sweden Mulch was then watered down into the voids. Twelve parallel slots were cut Date into the paving and planted with beech 2010 trees. The soil in the beds was mixed with pumice, mycorrhiza and charcoal SuDS components to support effective water and nutrient Tree trench attenuation cycling and was informed by biological Tree planting research that determined parameters on how to successfully establish the trees. Objectives To establish a ‘forest’ in the plaza using a species of beech typical of the area with fully integrated SuDS. The forest contributes to regional identity while intercepting and attenuating rainwater.
Surface water drain to root zone Beech planted in tree trenches
54 3 SuDS components 3.10 Permeable products that provide infltration and Silting: permeable paving becomes impaired storage (see 3.11). Care is needed in using by silting, oiling or mudding. Silting can paving proprietary systems as high stresses are be prevented using protective upstream placed on the units and their performance SuDS components, eg, flter strips and Permeable paving comes in various is diffcult to monitor once paving has swales. Intelligent placement and correct forms, including block paving, bituminous been laid. construction methods also reduce silting. materials, grass reinforcement, and bound or unbound gravels. All promote water Conveyance: permeable paving can be Compaction: over-compaction of the sub- infltration, whether through the porous used to convey storm water within its base and subgrade affects the effcient surface of a paving material or through the construction, removing potential overland function of the paving for conveyance and joints between the paving units. fow and puddling. infltration, so take care when installing.
Permeable pavements are used as source Simplicity: conventional below ground Ground conditions: consider the control as they manage rainfall where it drainage features, such as gullies and pipes, existing ground conditions and lands. The basic structure of permeable are not needed, thus eliminating cost and hydrology to determine the possibility paving is similar to that of a standard maintenance requirements. of the sub-base of the pavement pavement. However, the sub-base contains functioning as a soakaway. a coarser granular fll and geotextiles that Filtration: permeable paving provides prevent sedimentation. fltration at either surface level or within Exceedance: permeable paving can deal the subgrade. This removes or treats with most storm events but could be Permeable paving can attenuate and sediments, heavy metals, hydrocarbons inundated during big storms (one in 100 convey water to a suitable outfall. In and some nutrients. Paving fltration year). When this happens, and the capacity London, the potential for permeable capabilities are largely dependent on of the pavement is reached, the paving paving is signifcant, provided the the construction, which can have conveys water as a traditional pavement. underlying geology is suitable. differing characteristics. Design should incorporate exceedance fow paths and appropriate outfalls. Benefts Design considerations Attenuation: increasing the depth of the Catchment area: permeable paving Maintenance granular sub-base enables storm water provides source control. With careful Maintenance regimes related to design to be stored beneath the surface, where detailing and design it can manage aspiration and SuDS performance need it can infltrate and/or slowly release to a additional storm water, such as intercepted to be clearly established from the outset. suitable overfow. Geocellular units can be water from adjacent roof structures. Permeable paving can require more care introduced. These are lightweight modular than traditional impermeable surfaces to
55 3 SuDS components maintain its integrity and function. Over The maintenance regime of permeable to be removed from joints, unless time, detritus collects in the upper part of paving is largely dependent on the wildfower establishment is part of the the joint material and surface pores. This construction of the surface course. design concept. build-up can affect infltration capability. Brushing and joint material renewal is The performance and appearance of required, the frequency being determined Useful design guidance permeable surfacing in areas where buses, by local conditions. The exact type of CIRIA C753 The SuDS Manual, Chapter 20 taxis and delivery vehicles stand may be jointing grit will vary depending on the Interpave, the Precast Concrete affected by leaking engine oil. product system and contractors will need Paving and Kerb Association – to take account of this. Weeds will need see www.paving.org.uk
De-paving the margins of an existing pathway to increase permeability
56 3 SuDS components Case study 9 – Objectives on each side of the road, with underground This Thames Water Utilities Limited storage provided by geocellular structures Permeable paving (TWUL) project aims to trial the retroft on one side and aggregate on the other, of SuDS within the highway with a with a fow control outlet to the Location focus on their food risk benefts. existing sewer. Mendora Road Three streets were selected for the trial London Borough of Hammersmith & as part of the Counters Creek SuDS The scheme is lined to ensure monitoring Fulham Retroft Pilot Schemes. data carried out by Thames Water gives an accurate representation of the scheme Date Outcome with no infltration loses. 2016 (under construction) Mendora Road involves the installation of permeable paving within the parking bays SuDS components Permeable paving retroft Images courtesy of Atkins of courtesy Images
During construction After construction
57 3 SuDS components Case study 10 – Outcome The sub-base was designed to support Permeable paving Marshalls Priora permeable concrete blockpaving, using graded crushed rock Location aggregate to provide structural strength, London Borough of Newham integrity and voidage for attenuation. This was placed on a geogrid for additional Date strength. Creating a void at the joint Marshalls of courtesy Images 2012 (Temporary) between the Priora blocks at the surface allowed water to pass through the SuDS components pavement at source. The joint void was Temporary permeable paving installation flled with 2-6mm clean stone to provide a permeability rate of 18,750L/s/ha, to Objectives cope with any storm event. No additional To provide a coach park that would have a positive drainage was required. minimal impact on the environment so the site could be returned to its original use as sports felds after the 2012 Games.
Installation complete Aerial view of site under construction
58 3 SuDS components WATER SQUARE BENTHEMPLEIN Roterdam, the Netherlands
3.11 Detention basins
Detention basins are generally dry, low spots within a landscape. They can be designed as multi-functional spaces during dry conditions. During storm events, water is channelled to these basins where it is ‘detained’ before release at a Urbanstein of courtesy Image controlled rate.
Basins usually require lots of space. However, as they can be designed to provide alternative functions, they can be incorporated into relatively dense urban environments as a soft or hard landscape feature.
Benefts Attenuation: detention basins provide storage for stormwater before slow release through a restricted outlet and fow control. Hard detention basin with multiple functionality for recreation Interception: detention basins provide a large surface and depth for holding surface water runoff. If landscaped with soils that Biodiversity: soft landscaped detention Design considerations are suffciently permeable, they provide basins can be planted with marginal and The form, depth and profle of the interception by infltration of small wetland vegetation to provide habitat and basin depend on topography and rainfall events. a source of food for insects and mammals. existing features, such as trees and Planting that enhances the ecological vegetation. Detention basins’ scale should Amenity: as a multi-functional space, value also increases the drainage complement the landscape and townscape detention basins have a variety of uses, properties of the soil to create a more character. such as car parking, play, public open effective component. space and habitat.
59 3 SuDS components
catchment area of basin 1 catchment area of basin 2 catchment area of the deep basin 3 Two in one The water square combines water storage with the improvement of the quality of urban public space. The water square can be understood as a twofold strategy. It makes money invested in water storage facilites visible and enjoyable. It also generates opportunites to create environmental quality and identty to central spaces in neighborhoods. Most of the tme the water square will be dry and in use as a recreatonal space.
diferent atmospheres for diferent actvites overview of the water sqaure and its basins Sedimentation: fne materials can cause Inlets: inlets into detention basins come sediment accumulation within a detention in a variety of design forms. At pipework basin that can affect storage volume, outfalls, a protection grille should not be fltration and infltration rates. Designers used unless the inlet diameter is greater should create upstream features or than 350mm. forebays that flter out sediments from stormwater before it enters the basin. Filtration: the primary pollutant removal mechanism is settlement. Filtration of Infltration: consider the existing nutrients can also occur through ground material and hydrology to see biological uptake by surface and if the detention basin can function as submerged vegetation. a soakaway. Maintenance Vegetation: when part of a soft landscape, Detention basins require routine site detention basins allow diversity of planting maintenance operations to ensure effcient to providing amenity, habitat, foraging operation. Where the detention basin has a and the potential for community growing. hard surface, additional maintenance may Aquatic vegetation can be used to provide be needed to preserve the amenity value. stabilisation, prevent scour and re- suspension during heavy storms. Useful design guidance CIRIA C753 The SuDS Manual, Chapter 22 Erosion: detention basins can suffer erosion, especially during heavy storms. Storm water velocities can be reduced using weirs, sectioning or graded stone near the inlet.
Compaction: ensure soils are not over- compacted during construction. The compaction of pond soils can negatively impact infltration rates and prevent Detention basis with stepping stones and planting vegetation root penetration.
60 3 SuDS components 3.12 Attenuation and • Storm water from between the one in 10 year and one in 30 year events storage tanks should be managed within the SuDS network. No fooding should occur This is one of the most versatile sets above ground within areas which are of SuDS components because it is less not part of the drainage system dependent on the underlying geology. When the rate of rainfall exceeds the rate • One in 30 year to one in 100 year storms at which water can leave a surface, street should be managed within the SuDS or area, the water is attenuated on site. network or within the site. This must not result in fooding of property, nor should This may happen at-grade or below ground it impact on the function of the street and is often done using soil cells and attenuation tanks, usually located within • Where it is not possible to manage buildings or beneath the public realm. storm water from the one in 100 year These must be connected to mains sewers storm at-grade within the streetscape to provide an overfow. or SuDS network, consider:
Design considerations • below-ground storage in Designers should follow the guidance below: proprietary crates, tanks or pipes • allowing an increased • Rate of runoff from the site discharge rate from the site should target greenfeld runoff rates where practicable Useful design guidance CIRIA C753 The SuDS Manual, • Storm water up to the one in 10 Chapter 21 and 24 year storm event should be stored within SuDS components
Attenuation: soil cells
61 3 SuDS components 3.13 Ponds and Benefts Water quantity: ponds and wetlands wetlands store a lot of storm water. The more water there is, the more time there is Although ponds and wetlands are for sedimentation, biodegradation and commonly used where runoff cannot biological uptake. be managed at source, they can also be used close to source where the benefts Water quality: through the use of derived can be greater. The opportunity engineered soil mixes and additives, for such features tends to be where lots flter media can be created to enhance of space is available; however, there is bioretention treatment performance. considerable value in small ponds and Designs can include submerged anaerobic retention features close to and within zones to promote nutrient renewal. Reed developments. beds are highly effective at bioremediation.
Ponds and wetlands are not limited to Amenity: permanent water features, such the end of the system, where the demand as ponds and wetlands, offer important for storage may be greatest; they can aesthetic and amenity benefts. Integrating have a signifcant contribution at any point an aquatic bench, to create a shallow zone in the management train. They provide for wetland planting, increases aesthetic high value wildlife and amenity benefts value and the potential for biological to an area and effectively treat polluted fltration and habitat. Ponds can water naturally. incorporate features such as islands and shallows that allow greater access Wetlands do not necessarily hold a and interaction. permanent pool of water; this is especially true in dry conditions. The depth of water Biodiversity: design features, such as increases during storm events, attenuating shallow and convoluted edges, uneven and treating surface water runoff before surfaces, woodlands, tussock grass areas outfall at a controlled rate to a suitable and dead wood piles, increase habitat discharge point. diversity. These can provide shelter, food, foraging and breeding opportunities for Pond: high in biodiversity and aesthetic value urban wildlife.
62 3 SuDS components Design considerations vegetation root penetration 3.14 Management Sedimentation: fne materials cause and establishment. sediment accumulation within ponds and maintenance and wetlands, reducing storage volume, Outlets: incorporate a non-clogging, fltration and infltration rates. Mitigation variable fow rate control structure, SuDS components require different measures can be implemented upstream together with an emergency overfow. This inspection and maintenance regimes or by installing a sedimentation area might be a protected orifce, combined with to traditional drainage systems. Like all within the catchment. an overfow channel protected with a weir. drainage systems, life cycle management and maintenance must be considered Vegetation: ponds and wetlands are ideal Inlets: prevent excessive erosion at from the start of the design process. spots for planting, which can provide inlet points. Where pipework outfalls, a Construction design and management amenity and habitat. Native species that protection grille should not be used unless (CDM) must consider the long-term are resilient to local conditions should be the inlet diameter is greater than 350mm. performance of SuDS components as well provided. Aquatic vegetation can provide as the need for maintenance vehicle access. stabilisation, preventing scour and Filtration: ponds and wetlands treat re-suspension during heavy storm events. surface water runoff by sedimentation Close collaboration with local authorities that occurs while water remains in the through the feasibility and design process Edge protection: ponds and wetlands hold pond. Filtration of nutrients can also occur is crucial to successful delivery of SuDS standing water, so consider passing cyclists, through biological uptake by surface, schemes, particularly on adopted highways. motorists, and pedestrians. Trees, woodland, submerged and aquatic vegetation, Local authority engagement should planting, benches or other physical particularly reed beds. inform design decisions and specify asset obstructions provide natural protection. management and maintenance regimes. This Maintenance will ensure that site or street management Erosion: ponds and wetlands are Conduct routine inspection and can deal with SuDS requirements. susceptible to erosion, especially during maintenance to ensure the effcient heavy storms. Stormwater velocities can operation of ponds and wetlands. SuDS maintenance can sometimes be be slowed through planting and low- Maintenance regimes over and above undertaken alongside routine management tech bio-engineering sympathetic to the routine on-site pond maintenance include of the public realm, particularly landscaping character of the SuDS component. water quality monitoring and control of requirements. Many developments include algal bloom. open spaces and many local authorities Compaction: ensure soils are not already manage such areas. All open compacted during construction as this Useful design guidance spaces have opportunities to include can reduce infltration rates, and prevent CIRIA C753 The SuDS Manual, Chapter 23 SUDS in some form.
63 3 SuDS components It is helpful to engage the local community Component specifc maintenance necessary alongside soft SuDS that interface in SuDS development from the outset, Green walls: most versions require with pavements. Where edges adjoin particularly during retrofts. Local irrigation. This must be maintained carriageways or parking bays, high/double knowledge can help shape the design, rigorously. Failure of an irrigation system kerbs and or >450mm wide paved aprons while allowing people to appreciate what will result in the death of the green wall, should be provided for access to parked the SuDS components do. This also reducing the attractiveness of the area cars without walking in the soft feature. offers potential for the local community and increasing replanting costs. Low- to take ownership, by helping to maintenance green walls planted directly Salting: where soft SuDS receive runoff manage and maintain SuDS as part of into the ground can be just as effective. containing de-icing salts, good sub- their neighbourhood. drainage is essential to prevent salt Sweeping: detritus and sediment from accumulation from harming plants. Sub- In London, operational constraints on pedestrian and traffc use can drainage allows most salts to drain through management and maintenance vary accumulate quickly. This can lead to a during the winter months when plants between the busiest streets (managed by build-up of sediments to clog systems, are dormant. Salt tolerant plants should TfL) and the 95% that are maintained by the such as joints for permeable pavements. still be selected and the ground must not boroughs. Not all SuDS features will meet Sweeping regimes need to support the become compacted. the criteria of Local Highway Authorities to SuDS components. adopt maintenance responsibilities, which Geocellular drainage: while useful for needs to include long-term costs. Geotextiles: Many SUDS components creating below-ground surface water incorporate specifc geotextiles to separate reservoirs or rooting zones for street Maintenance requirements can be materials to separate materials to some trees, geocells are complex and potentially simplifed by using well thought-out extent. These tend to blind/clog over dangerous. There are various design, designs. In a rain garden, for example, soil time, reducing infltration/percolation certifcation, supervision, testing and specifcation and plant species selection rates. There is little long-term test data maintenance issues that require emphasis should meet the specifc demands of the from the UK for public/urban situations; if they are to be used safely SuDS, site characteristics and geotechnical designers should be aware of the long- and appropriately. conditions. Maintenance requirements will term maintenance risks that geotextiles vary depending on the time of year. may pose. Highway structures and geo-technical structures must be designed, checked and For a detailed guide to SuDS maintenance, Compacting: for landscaped SuDS to be supervised under relevant eurocodes. Most refer to CIRIA C753 The SuDS Manual, effective, they must be protected from Highway Authorities will wish to manage Chapter 32 (Operation and maintenance). both vehicle and pedestrian overrun. As a this via their Geotechnical and Highways minimum, structural edges are generally Structures technical approvals process.
64 3 SuDS components 4 SuDS in London’s streets 4.1 SuDS and the urban realm
This section shows how SuDS can be integrated into the design and management of some typical London streets. SuDS should be designed in parallel with other urban design considerations, refecting the unique opportunities and constraints created by every London street.
Streets account for 80% of London’s public realm. They are not just corridors for movement; they contribute to the city’s sense of place and identity and often refect London’s diverse communities.
Well designed streets are essential for London’s future growth, both in terms of population level and economic activity. Their function for pedestrians and cyclists, as well as other users, is growing and the Streets are places too design of streets needs to facilitate this.
Improvements to streets can directly SuDS are an important component of across London. Although based on unlock wider benefts beyond movement, this transformation, addressing surface specifc examples of streets in London, including health benefts for London’s water food risk, improving air quality and the illustrations are purposefully generic, growing population. These benefts can be contributing to a higher quality of life. aiming to demonstrate the art of the realised at a variety of levels, from minor possible in a variety of locations and interventions to transformations of large Eight street scenarios are illustrated environments, rather than to provide a junctions and gyratories. below to show how SuDS may be provided strictly applicable set of design criteria. within the many different street types
66 4 SuDS in London’s streets 4.2 Street scenarios
Street scenario 1 A roadway with large tracts of land alongside, between slip roads and interchanges. This expansive leftover space has great potential to incorporate extensive SuDS creating and linking habitats, as well as improving and using adjacent land. 4 Potential SuDS components 8 1. Wet swale, see 3.6 2. Filter drain, see 3.5 9 3. Filter strips, see 3.4 4. Tree planting, see 3.9
5. Ponds, see 3.13 3 6. Retention basins as overfow, see 3.12 5 7. Infltration where conditions allow, 2 see 3.3 6 1 8. Living roofs, see 3.2 7
67 4 SuDS in London’s streets Street scenario 2 A busy road; an important route for buses, cyclists, pedestrians and general traffc. Large areas of traffcked sealed surfaces mean SuDS need to optimise performance within limited space.
Potential SuDS components 1. Tree planting, see 3.9 1 2. Inlets
3. Bioretention, see 3.8 9 4. Soil and drainage material, see 2.5 5. Permeable paving to parking bays, where appropriate, see 3.10 5 6. Maintenance access strips 6 7. Utilities 2 3 8. Geotextile 4 9. Structure (green wall), see 3.2 8
7
68 4 SuDS in London’s streets Street scenario 3 An important focal point for business and culture. High pedestrian fows, with limited motor traffc access. This scenario offers large areas of public realm for integrating a variety of SuDS components with existing mature trees.
Potential SuDS components 9 1. Tree planting, see 3.9 1 2. Structure (green roof), see 3.2 3. Bioretention, see 3.8 11 2 4. Outfall
5. Porous bound gravel, see 3.10 10 3 6. Soil and drainage material, see 2.5 4 7. Utilities 7 8. Geotextile 5 8 9. Existing trees 6 10. Disconnected downpipe and rain planter 11. Structure (green wall), see 3.2
69 4 SuDS in London’s streets Street scenario 4 An important local route with high quality foot and cycle provision. The adjacent park provides particular opportunities for linear SuDS components. Other SuDS features in this street include downpipe 7 2 disconnections from adjacent houses 1 and fats.
Potential SuDS components 1. Green wall, see 3.2 2. Tree planting, see 3.9 9 3. Kerb drainage 4. Permeable paving, see 3.10 5. Dry swale, see 3.6 3 6. Adjacent green space used for SuDS 4 7. Existing trees 5 6 8. Infltration where conditions allow, see 3.3 8 9. Channels to direct fow from downpipes to tree planting, see 3.7
70 4 SuDS in London’s streets Street scenario 5 A well-connected local centre with high footfall from people accessing shops and services. A range of opportunities are illustrated, showing how SuDS can be integrated to enhance the visual coherence and identity of the area, improve air quality and reduce temperature in the context of 2 the street and below-ground structures.
Potential SuDS components 1 1. Existing trees 2. Tree trenches in median, see 3.9 3. Living roof, see 3.2 3 4. Permeable paving acting as an inlet 5 to tree trench, see 3.10
5. Street furniture aligned with SuDS 4 6 components to reduce clutter 8 6. Slab paving 7. Soil and drainage material, see 2.5 7 8. Geotextile
71 4 SuDS in London’s streets Street scenario 6 A traditional, quiet and safe residential street. Pedestrian and vehicular traffc is mostly local, with provision for cyclists. There is potential to integrate many SuDS components in front gardens, as well as 1 the street. 2 Potential SuDS components 1. Existing trees 7 2. Tree trenches, see 3.9 3. Bioretention, see 3.8 4. Permeable paving to parking bays, see 3.10 5. SuDS components aligned to provide traffc calming measures 5 6. De-pave and permeable paving to front 6 gardens, see 3.10 3 4 7. Green wall, see 3.2 8. Soil and drainage material, see 2.5
8
72 4 SuDS in London’s streets Street scenario 7 A local shopping street in a residential area that mainly caters for pedestrian and cycle movement. Restricted access for service vehicles. SuDS components are integrated into the street furniture and public realm, creating an attractive and welcoming place.
Potential SuDS components 1. Existing trees 2. Tree trenches, see 3.9 3. Bioretention planters to the base of 2 disconnected downpipes, see 3.8 4. Channel to bioretention, see 3.7 1 6 5. Slab paving 3 6. Permeable paving to discrete areas, 7 see 3.10 4 7. Porous surfaces over existing trees
8. Bioretention, see 3.8 8 5 9. Cell systems, see 3.11 9 10. Soil and drainage material, see 2.5 10
73 4 SuDS in London’s streets Street scenario 8 A civic square. This is a place of street activity with a high concentration of cultural, commercial and entertainment uses. A place with restricted vehicular access, providing the opportunity for a wide range of large and small scale SuDS components, carefully considered in respect of the heritage setting and signifcance. 1 Potential SuDS components 1. Existing trees 2. Permeable paving where appropriate, see 3.10 3. Amenity areas acting as detention basins, see 3.12 2 8 4. Outfall 3 5. Soil and drainage material, see 2.5 7 4
6. Geotextile 5 6 7. Attenuation tanks, see 3.11 8. Bioretention planters to the base of disconnected downpipes, see 3.8
74 4 SuDS in London’s streets 5 Case studies Case study index London under 500m² 5.1 Priory Common 85 m² 5.2 Upminster Bridge swale 400 m² The following case studies include local 5.3 Kenmont Gardens 435m² and strategic examples of SuDS to show the versatility of sustainable drainage London under 2000m² in various contexts. Most are examples 5.4 Derbyshire Street 765m² from London, but there are also exemplar 5.5 Renfrew Close 900m² national and international studies which 5.6 Islington Town Hall 1000m² may have some application in the Capital. 5.7 Rectory Gardens 1000m² They are described and ordered by size. 5.8 Talgarth Road 1200m² 5.9 Mile End Green Bridge 2000m²
London over 0.2ha 5.10 Queen Caroline Estate 0.23ha 5.11 Bridget Joyce Square 0.26ha 5.12 Crown Woods Way 0.26ha 5.13 Hackbridge 0.27ha 5.14 Goldhawk Road 0.27ha 5.15 Firs Farm 0.48ha 5.16 Salmons Brook 0.77ha 5.17 LuL depot roof, Middlesex 125m² 5.18 Coulsdon Bypass 34ha 5.19 London Sustainable Industries Park, Dagenham 142ha
National & international 5.20 Great Kneighton/Clay Farm, Cambridge 109ha 5.21 Alnarp, Sweden 0.37ha 5.22 Benthemplein, Netherlands 0.95ha 5.23 Rue Garibaldi, Lyon, France15ha 5.24 Bo01, Malmö, Sweden 85ha
76 5 Case studies 5.1 Priory Common rain meadow
Location Summary Priory Common Green space enhancement and London Borough of Haringey re-purposing for surface water Extent interception and infltration. 85m² Cost Project description £48,000 (construction only) Next to Priory Road is a linear green space Date with mature plane trees planted along 2016 the roadside. The verge is about 75m long Credits and was highlighted as a site to deal with London Borough of Haringey surface runoff from the road, via a sewer Thames21 connection directly to the River Moselle. Robert Bray Associates This project is part of a suite of SuDS SuDS components schemes locally that will cumulatively Filter strip improve water quality. Infltration basin Channels Objectives • Intercept road runoff pollutants at source and use the existing landscape to allow ‘interception loss’ (ie, prevent water from reaching the ground) for everyday rainfall
• Clean and cool runoff during summer when the watercourse is most susceptible to the effects of pollution and water temperature increases (which inhibit the ability of Love the Lea campaign, Thames 21 water to carry dissolved oxygen) Priory Common after installation
77 5 Case studies Actions and results • Surface dressing with topsoil and low • Monitoring will show the extent of • Runoff is diverted at the surface into a earth banks (bunds) has minimum impact interception loss and the protection gully in Redston Road and collected in on the trees, with simple wildfower offered to the River Moselle a fve-sett channel that directs water meadow seeding for open soil areas onto the grass verge along Priory Road Lessons learned • The river is within the sub-catchment • Importance of contractor selection • Verge re-profling carries water for its area of the line and, to a lesser extent, full length until it reaches the sewer nearby roads. This has implications • The value of expert supervision both for pollution and bank stability • Early observations indicate that of the River Ingrebourne as well • How sites, that might otherwise water fows quickly into the rain as the reliability of the line be considered unsuitable for meadow but slows as it travels SuDS, can provide benefts with through the grass, soaking into the • High intensity summer storms will minimum intervention tree-lined verge before reaching the be diverted from the sewer and letterbox outfall to a road gully cooled before release to the river
• Performance will improve as the meadow grows
• The client partnership with Thames21 and Haringey Council are considering monitoring opportunities
Benefts • This simple SuDS retroft shows how an existing urban green space
can bring signifcant benefts to Associates Robert Bray of courtesy Images unprotected urban watercourses
• Surface collection of runoff avoids any signifcant excavation or spoil for removal Conveyance of water through the scheme
78 5 Case studies 5.2 Upminster Bridge swale
Location Summary Upminster Bridge Swale construction for increased on-site London Borough of Havering attenuation and water treatment. Extent 400m² Project description Cost Upminster Bridge Station serves the Trial scheme District Line and is 3.5km west of the Date M25. The adjacent River Ingrebourne 2015 is vulnerable to fooding and has been Credits deemed an at-risk river by the London Underground Environment Agency. The river is within Environment Agency the sub-catchment area of the line and No disruption to service during construction Green Infrastructure Agency to a lesser extent, nearby roads, with Environmental Scientifcs Group Environmental Protection Group implications for both pollution and bank SEL Environmental stabilisation of the River Ingrebourne and ITM Monitoring reliability of the line. SuDS components Swale A London Underground Power Upgrade Outfall/runoff interception Project, involving the construction of a new substation, presented the opportunity to trial an experimental SuDS scheme. This included two swales with associated tanks and v-notch weirs. One receives water from the new substation roof, the other from adjacent London Underground tracks. Funding was provided by the Environment Agency with a London Underground Limited contribution in kind. 400m2 swale under construction
79 5 Case studies Objectives • Improved water quality • Any outfow from the scheme is • Manage water quality by improving conveyed to River Ingrebourne, remediation capabilities • Reduced waste from building not to rail infrastructure SECTION AA demolition through the reuse of • Mitigate rail infrastructure food risk waste rubble for swale construction • Enhanced local biodiversity
• Enhance local biodiversity • Enhancement of outlook over rail Lessons learned
infrastructure from residentialCRUSHED BRICKareas • Design required an interface with BENTONITE SEAM Ø225MM DRAINAGE PIPE Actions and results Depth varies 0.87-1.00m conventional drainage systems • Surface water from the railway lines and from the outfows of the sub- RAMP SECTION AA APRON station roof is attenuated. This has enhanced the site’s food resilience and reduced saturation of the soil on EXISTING CONCRETE SLAB CRUSHED BRICK BENTONITE SEAM the slopes by the River Ingrebourne. Ø225MM DRAINAGE PIPE Slope stability has improved as a result Depth varies 0.87-1.00m RAMP APRON • Monthly remote monitoring provides EXISTING CONCRETE SLAB data on water quantity. DataSECTION loggers BB are attached to sampling chambers. These contain water chambers which house water level sensors SECTION BB Ø450MM DRAINAGE PIPE Depth varies 0.87-1.00m (FUTURE CONNECTION TO TRACK DRAINAGE)
BENTONITE SEAM Protection Infrastructure LU of courtesy Images • Plant establishment is being monitored
Ø450MM DRAINAGE PIPE Depth varies 0.87-1.00m (FUTURE CONNECTION TO TRACK DRAINAGE) • Water quality is being sampled monthly BENTONITE SEAM from fve locations and analysed. EXISTING CONCRETE SLAB Benefts EXISTING CONCRETE SLAB • Ability to withstand a one in 100 year food event of 59L/sec Swale sections
3rd foor Albany House, 55 Broadway Project title Drawn Date Revision SW1H 0BD, London UPMINSTER BRIDGE SUBSTATION SWALES MM 11/06/2015 Contact: Melina Kakouratou 80 5 Case studies Tel: 020 7027 8137| Mobile: 0792 140 3141 AS BUILT Checked Scale Ref. 3rd foor Albany House, 55 Broadway E-mail: [email protected] title f.gov.uk 1:100@A3 Drawn Date Revision SW1H 0BD, London UPMINSTER BRIDGE SUBSTATION SWALES MM 11/06/2015 Contact: Melina Kakouratou Tel: 020 7027 8137| Mobile: 0792 140 3141 AS BUILT Checked Scale Ref. E-mail: [email protected] 1:100@A3 5.3 Kenmont Gardens
Location Summary Actions and results Kensal Green Transformation of highway to • Surface fow is directed towards London Borough of Hammersmith & Fulham neighbourhood garden. rain gardens and trees Extent 435m² Project description • Trees are planted in linked trenches that Cost The garden was previously a carriageway incorporate below-ground attenuation £300,000 (total scheme) that had been pedestrianised. The Date carriageway still existed, but had been • Water fow is held and slowed within 2015 closed off with bollards. attenuation features before passing Credits through control chambers and into London Borough of Hammersmith & Fulham The project is a Neighbourhood and the existing drainage system Project Centre Ltd Corridor Scheme, developed to incorporate FM Conway SuDS. It is funded through a combination • Permeable paving allowing infltration Green Blue Urban of TfL LIP Funding and Lead Local Flood SuDS components Authority Funding. • Community involvement throughout Permeable paving the project, with concept designs Rain gardens Geocellular storage Objectives sent out for public consultation in Tree planting • Improve an under-used area through September 2014, from which a positive public realm works, including planting, response was received and a preferred paving and lighting improvements option selected. A dialogue was maintained with College Park Residents • Incorporate SuDS features Association (CoPRA) and Kenmont within the design Primary School throughout the process
• Retroft SuDS to the existing drainage Benefts system of a deep combined storm • The design restricts runoff to greenfeld and foul sewer, fed by gullies that rate for events up to the one in 10 were formerly in the carriageway year average recurrence interval (ARI) with exceedance routes
81 5 Case studies • CoPRA and Kenmont Primary School were heavily involved in the latter stages, with pupils of the school creating clay tiles under the supervision of a professional potter, which were then installed in the new space
• Engagement throughout the
process and a planting event Warren George of courtesy Images ensured community buy-in
Community planting workshop After
Plan After After
82 5 Case studies 5.4 Derbyshire Street Pocket Park
Location Summary Bethnal Green Transformation from roadway into London Borough of Tower Hamlets community shared space. Extent 765m² Project description Cost Derbyshire Street is in a densely populated £120,000 (total scheme excluding offcer time) part of east London, next to a park and Date the Oxford House community and arts Associates Greysmith of courtesy Images 2014 centre. Before the redesign, the street was Credits a dead-end with parking issues, anti-social London Borough of Tower Hamlets behaviour and fy-tipping. Greysmith Associates Before Oxford House The potential of the site’s south-facing Mayor of London’s Pocket Park Initiative JB Riney aspect, existing trees and community The Grass Roof Company involvement helped develop a consensus Thames Water Utilities for streetscape improvement. A key aspect RBMP of delivery was the partnership between SuDS components the local highway authority, the food Permeable paving management teams and the community. Bioretention basins This grassroots approach enabled funding Green roofs from the Mayor of London’s Pocket Park Tree pits initiative.
Objectives • Improve facilities for community use
• Onsite water management through SuDS
After
83 5 Case studies Actions and results Benefts • Green roofs on bike sheds and a bin • Inhibits the fow of storm water runoff store increases the attenuation storage into the combined sewer system capacity, improving the streetscape’s ability to mitigate impacts during high • Community partnerships have and/or prolonged peak fow events safeguarded future management and maintenance • Disconnecting downpipes on Oxford House increased attenuation storage • New community resource created capacity by redirecting water away from the combined sewer overfow • Native and edible plants promote and conveying it into bioretention biodiversity and a social capital basins and a new swale • Able to withstand a one in • Permeable paving allows water 100 year rainfall event to seep into the ground. During high and/or prolonged peak fows, Lessons learned additional runoff is attenuated by • Active engagement between the the surrounding SuDS scheme community and local authority has social and economic value • A network of rain gardens, swales and engineered tree pits has • SuDS can help defne and enhance increased the attenuation storage public realm improvements that relate capacity of the streetscape to pedestrian and cycle routes
• A bespoke information board • Permeable block paving is susceptible to communicates the streetscape and gathering litter fragments, so the jointing community benefts of the scheme of paving systems needs consideration leading to continued community buy-in to the maintenance and • Connectivity with Weavers Field could monitoring of the scheme have further enhanced the scheme Community event
84 5 Case studies 5.5 Renfrew Close
Location Summary London Borough of Newham Transformation of green space to multi- Extent functional green infrastructure for the estate. 900m² Cost Project description £43,000 (construction only) An existing communal green space between Date residential blocks was retroftted with a
2015 SuDS scheme. The rain gardens receive water Associates Robert Bray of courtesy Images Credits from hard surfaces at roof and ground level Groundwork and from soft surfaces at ground level. Environment Agency Robert Bray Associates Objectives Greatford Garden Services • Provide a sustainable drainage SuDS components function and alleviate fooding Detention basins Bioretention basins • The rain gardens should create Tree planting Channels attractive, productive and biodiverse Downpipe disconnection green spaces for the residents Swales Actions and results • Bioretention basins designed to take road and roof runoff
• Downpipes and rainwater conveyed to swales and bioretention basins
• Swale network to accommodate different sized rainfall events Channel outfow into swale and bioretention basin • Visual amenity provided by rain gardens
85 5 Case studies Benefts • Can withstand a one in 100 year + 30% storm event
• Runoff from 750m² of roof and 165m² from roads are attenuated in the scheme
• 12-hour delay between rainfall event and pressure recording in the basin
• 16-hour delay between peak rainfall and peak pressure in rainfall basin for frst event
Lessons learned After • Monitoring system installed and used to support the design of future SuDS retroft projects should try to direct fows from known problem areas into bioretention basins to prevent surface fooding
• Maintenance agreements need to be in place along with a clear method of reporting
Channel detail
86 5 Case studies 5.6 Islington Town Hall
Location Summary Objectives Upper Street Transformation of a car park into a • Enhance the town hall’s setting London Borough of Islington green public space for community and as a key civic location Extent ceremonial events. 1,000m² • Provide a high quality public Cost Project description realm on Upper Street £100,000 Islington Town Hall is on Upper Street Date which is populated by shops, bars and • Address car parking issues, 2011 cafes and attracts heavy footfall. Before while maintaining a suitable Credits the redesign, the forecourt of the town setting for ceremonial events London Borough of Islington hall was a car park with impermeable J&L Gibbons surfaces. This had implications for the • Plant large species trees SuDS components management of stormwater runoff for long-term beneft Permeable paving onto Upper Street’s carriageway and for Large specie tree planting combined sewer overfow. Actions and results De-paving • Permeable paving surfaces allow water A political incentive to ‘green’ the town to seep directly into the sub-base, hall forecourt initiated the scheme as part thereby redirecting excess and polluted of Islington’s sustainable agenda. water away from the combined sewer
This was coupled with recognition of • Trees and planting provide canopy the poor presentation of the building to cover, increasing the interception of the street. These were key factors in the rainwater and enhancing biodiversity project gaining support. • De-paved and planted surfaces It shows how small public realm increases attenuation by interventions can address car parking maximising areas for infltration issues and storm water runoff, while Before transforming a space and improving the public realm.
87 5 Case studies Benefts • Increased attenuation storage capacity
• Improved water quality
• Enhanced public realm and green infrastructure
Images courtesy of J & L Gibbons of courtesy Images • Enhanced civic function of the forecourt
• Tree-planting for improved air quality
Lessons learned • Permeable surface treatments can successfully address shared space requirements
• An integrated SuDS scheme can have environmental and economic beneft
After After
88 5 Case studies 5.7 Rectory Gardens
Location Summary • In System B, runoff travels along a Hornsey Retroft and transform green space to grass channel, which is planted so London Borough of Haringey manage road runoff. oils and silts are concealed but is Extent easily accessible to remove solids 1,000m² Project description Cost Runoff fows directly to the River Moselle • The ‘source control’ features are £80,000 via a surface water sewer connection. followed by wildfower meadow Date basins that can hold signifcant 2016 An existing local park was identifed for amounts of reasonably clean runoff Credits accommodating SuDS components that to the one in 10 year return period Haringey Council enhanced amenity and biodiversity value. Robert Bray Associates • An under-drain below the basins Thames21 Objectives allows water to leave the site at a Hugh Pearl (Land Drainage) Ltd The project aims to collect all the runoff greenfeld rate. This fow is governed by SuDS components from a defned road catchment and show a protected orifce control chamber. Retention basins how the full SuDS aspiration of ‘managing Detention basins Planted channels quality and quantity aspects of runoff • In larger storms, up to the one in 100 year while delivering amenity and biodiversity return period, with a 30% allowance for benefts’ can be met in an existing urban climate change, these basins overfow park setting. into further grass storage basins. The second basins are managed as amenity Actions and results grass so are accessible most of the time • Runoff from the road is collected in three bespoke, cast iron inlets that • The wildfower meadow basins replace gully pots and perform like chute have balance beams so that even gullies, delivering the dirty surface water when wet or flled with water they into two SuDS management drains can be used for adventure play
Plan • System A to the west, delivers runoff Benefts to a silt interception forebay basin
89 5 Case studies • Retroft demonstrates how polluted Lessons learned runoff can be practically managed in an • The project was undertaken with the existing local park or urban green space, Priory Common rain meadow (case while enhancing amenity and biodiversity study 5.1) and therefore benefted from sharing expert site supervision • The small interception forebays provide and a knowledgeable contractor a simple way of trapping and removing pollutants, such as silt and heavy oils • Protecting planted channels where water entered the SuDS and the relatively fat • The changes of level in the park basins reduced erosion to a minimum
landscape enhance the quality Associates Robert Bray of courtesy Images of the space, while defning the • Physical protection of the basins was SuDS and biodiversity features considered but not used for reasons including visual quality, risk of vandalism • The under-drain ensures the basins are and cost. It may be necessary to After dry most of the time, but the rainwater overseed the basins when germination irrigates both trees and the meadow, of the wildfower seed is inspected particularly in summer when many urban park landscapes suffer drought • The client partnership (Thames21 and Haringey Council) are currently • Water-play in a safe place helps considering monitoring opportunities the community relate positively to normal rainfall and to appreciate • It would be useful to estimate natural the impact of heavy storms in losses at different times of year in summer when the basins fll different weather conditions
• Signs provide information about • The quality of runoff should be easy the components and benefts to assess by collecting it as it passes of SuDS to passers-by through the control chambers
Swale
90 5 Case studies 5.8 Talgarth Road
Location Summary Actions and results Talgarth Road Green infrastructure enhancements on the • Some trees along this stretch were London Borough of Hammersmith & Fulham highway to improve air quality. in a poor state and needed to be Extent replaced. Others were removed to 1200m² Project description allow a cycle path to be repositioned Cost This project saw green infrastructure £240,000 (total scheme) installed alongside a footway and cycle • A 26m section of the roadside planting Date path along Talgarth Road between has been designed to accept runoff from 2016 Butterwick and Shortlands, to the the highways and footway, thus reducing Credits north of the Hammersmith Flyover. The the surface water fow to the combined London Borough of Hammersmith & Fulham project intends to reduce the exposure sewer and providing additional capacity FM Conway of pedestrians and cyclists to the poor within the Counter's Creek Catchment SuDS components air quality in Hammersmith town centre, Bioretention basin while incorporating SuDS and providing • The bioretention basin will be deeper Tree planting a safe and secure setting. The aim is than the other stretches of planting to replicate this approach elsewhere to provide underground attenuation in the borough. for the surface water fows, with a controlled release to the sewer Objectives • Improve air quality with integrating SuDS • Exceedance fows, during extreme events, are directed towards • Planting Miscanthus (silvergrass) to the existing road gully act as a flter to traffc emissions. This grass grows to 1.8m and provides • Roadside bioretention basins a soft, visibly permeable border, incorporate bespoke roadside inlets to ensure a sense of safety • A border of herbaceous groundcover will be planted between the Miscanthus and the bicycle path
91 5 Case studies Benefts • Air quality monitors, placed on either side of the grass, measure particulate matter and nitrogen dioxide levels, to demonstrate the extent of air quality benefts from the greening.
Lessons learned
• The bioretention basin will include the Warren George of courtesy Images same plant species as the rest of the roadside planted areas to test how these species perform when experiencing runoff from the surrounding area, compared to conventional planting beds
• Should the species thrive in this environment, the aim is to repeat this along other stretches of highway within the borough to help tackle air quality and fooding issues
Under construction Complete
92 5 Case studies 5.9 Mile End Green Bridge
Location Summary Actions and results Mile End Road Reinstatement of soils and planting on • The soil required de-compacting London Borough of Tower Hamlets green bridge. and amelioration to increase Extent its capacity to retain water 2000m² Project description Cost The bridge provides a key connection • Soil depths were increased by 250mm £75,000 within Mile End Park by spanning the Mile to allow for greater root-zone and Date End Road. better plant establishment 2010 Credits As part of High Street 2012 works, the • Trees were planted at a high Design for London existing green bridge was rejuvenated to density to improve their resilience London Borough of Tower Hamlets incorporate more planting. to the shallow soil profle Mile End Park muf architecture/art Tim O’Hare Associates The proposals had to consider the • The central median was removed J & L Gibbons requirements of the A11 below. Traffc to create greater openness fows on this part of the TfL road network SuDS components Green roof/bridge could not be impeded during the works Benefts Tree planting or maintenance operations once planting • The young plant stock established faster Soil amelioration was established. than previous semi-mature tree planting
Objectives • The dense blocks of planting and mix of • Enhance park connectivity species provide increased biodiversity
• Increase the impact of the planting from • The planting had immediate impact due the road below and the parkland above to its density and educational interest as an emerging ‘upland’ ecology • Improve soil infltration • The bridge is more successfully • Encourage biodiversity integrated into the park landscape
• The planting creates a distinctive feature and is more visible from the A11 below 93 5 Case studies Lessons learned • Stability of high level planting, achieved through young stock able to adapt rooting structure to specifc soil depths
• Parapet planting proposals have to take into account the restricted access for planting and maintenance Images courtesy of J & L Gibbons of courtesy Images • Early engagement with TfL necessary to prevent contract delays
• Early engagement of soil scientist to avoid delays due to soil testing Before
Green Bridge from the Mile End Road After
94 5 Case studies 5.10 Queen Caroline Estate
Location Summary Hammersmith Estate regeneration through integrated London Borough of Hammersmith & Fulham SuDS design. Extent 0.23ha Project description Cost Queen Caroline Estate is bound by the Groundwork of courtesy Images £226,000 (total scheme) River Thames and the Hammersmith Date Flyover. The estate is a mixture of paved 2015 carriageway surfaces for access and Credits parking, plus grassed areas. The challenges Groundwork of the site made it an appropriate London Borough of Hammersmith development for the LIFE+ Climate Garage green roof & Fulham proofng social housing project that Greater London Authority EU LIFE+ Programme provides low cost, retroftted SuDS to improve community resilience to SuDS components climate change. Green roofs Bioretention basin Detention basin Objectives Permeable paving • Reduce surface water food risk and frequency
• Improve the condition of the estate’s infrastructure
• Address deprivation and vulnerability to climate change on the estate
After
95 5 Case studies Actions and results • Run off from 900m² of impermeable • Green roofs were installed to increase surface has been conveyed into a SuDS attenuation storage capacity where it has not been possible to disconnect • A community growing area of downpipes that run internally. The 32m² has been created green roofs were installed on bin stores and pram sheds; these are visible Lessons learned at ground level and from above • Engaging residents in the development of proposals ensured a detailed • A bioretention basin was built to understanding of how the streetscape attenuate rainwater. This fow comes functioned, thereby maximising from surrounding impermeable surfaces the reach of project benefts and from the roof of an adjacent building • Despite CAT and radar scans, some • Permeable paving has increased the below ground services were not volume and rate of infltration into identifed and required designs to the subsurface, helping to maintain be revised to accommodate them the effectiveness of bioretention and detention basins by limiting the water fowing to them
Benefts • The works were delivered at the same cost as conventional landscape improvement when compared to other housing estate works
• Landscape has been transformed into multi-functional space
• 142m² of green roof has been Paving strip installed, improving biodiversity Bioretention basin outside homes
96 5 Case studies Susdrain – SuDS and placemaking 01/10/2015
Kenmont Gardens Australia Road Goldhawk Road
Melina Road Edith Road
Talgarth Road Cheeseman’s Terrace Queen Caroline Estate Mendora Road Stevenage Road
Maystar Estate
Australia Road
5.11 Bridget Joyce Square, Australia Road
Location Summary White City Transformation of the road into a shared London Borough of Hammersmith & Fulham ‘urban oasis’ for pedestrians and cyclists. Extent 0.26ha Project description
Cost Australia Road is in the heart of the White Warren George of courtesy Images £950,000 (total scheme) City Housing Estate, in the northern Date section of Shepherds Bush, south of the 2015 A40 Westway. Credits London Borough of Hammersmith & Fulham This stretch of Australia Road has a school Robert Bray Associates on one side and playgrounds on the Before Thames Water other – potentially hazardous for children TfL GLA crossing the road between parked cars. McCloy Consulting F M Conway The street lies within the Counters Creek SuDS components Sewer catchment, which is exceeding Permeable paving its capacity, resulting in the fooding of Bioretention basins properties downstream. Hydrological Rills modelling of the borough has also shown Rain gardens that this stretch of Australia Road is Tree planting susceptible to signifcant surface water Downpipe disconnection food risk.
Objectives • Create a landscape that serves a vital drainage function in providing food resilience against surface water and sewer fooding issues and that provides After George Warrenclimate – Londonchange adaption Borough benefts of
97 5 Case studies Hammersmith & Fulham 14 • Instill a sense of pride within • Flow controls are designed to restrict the local community fows to below 1 L/s (less than the 5 L/s generally adopted by industry) and retain • Provide a multi-functional space that fows on site for longer. This is achieved, could be used for a variety of events in part, by designing drainage outlets that minimise the risk of blockage, • Provide educational potential, yet ensure easy access and safety for while being safe for the children council staff to inspect and maintain who use the site on a daily basis • Interpretation boards explain the Actions and results design; monitoring equipment • Permeable block paving (1,320m²) provides performance evidence allowed retention of existing site levels, negating the need to excavate Benefts the existing concrete road slab. • Carriageways adaptations have made The 180mm permeable pavement the use of community assets safer depth can cater for heavy loads • Reduction in local and wider food risk • The permeable paving and the After disconnected downpipes from the • The attenuation of water and its surrounding school and playground associated vegetation have contributed buildings direct rainwater to heavily to air quality (principally NOx and • Annual fow volumes into the planted bioretention basins and PM) and water quality (hydrocarbons combined sewer overfow rain gardens, providing over 55m and total suspended solids) have been reduced by 50% of additional attenuation • The ecological considerations Lessons learned • The scheme uses sculpture to (hydrological and vegetative) have • Supervision of SuDS construction replace traditional downpipes to provided a site for biodiversity that by designers was essential make the scheme distinctive. The will increase as the scheme matures, to successful delivery sculpture also provides an important while providing an educational security deterrent against those resource and community buy-in • Involvement of the construction trying to access the school roof to monitoring and maintenance contractors early in the design process ensures the best outcome
98 5 Case studies 5.12 Crown Woods Way
Location Summary Eltham Enhanced streetscape and food risk London Borough of Greenwich resilience through bioretention. Extent 0.26ha Project description Cost Crown Woods Way is a residential street, £23,000 (total scheme) south of the A2 East Rochester Way and Date is within a high food risk area. Narrow 2015 grass verges and a crematorium next to the Credits site made limited contribution to water London Borough of Greenwich management. The proximity of a busy Trees for Cities carriageway also meant the site SuDS components was subject to high levels of noise and De-paving air pollution. Kerb drainage Bioretention basins The programme to address these conditions was fronted by a partnership between the Royal Borough of Greenwich and Trees for Cities, who adopted a holistic approach to improve the function and quality of the streetscape.
Objectives • Reduce food risk
• Address concerns about the environmental impact of air and noise pollution After
99 5 Case studies Actions and results • Trees were planted within the de-paved Benefts • Two rain garden bioretention basins rain garden areas. This addressed • Reduces street food risk by increasing have increased the attenuation storage the hydrological balance of the attenuation storage capacity capacity of the streetscape, reducing site and the impact of noise and air the likelihood of water being conveyed pollution by providing a physical noise • Reduces noise and air pollution to the combined sewer overfow. barrier and zone for air exchange and This measure allowed 30% more particulate accumulation. Special • Establishes a new carbon sink water to infltrate into the subsurface, consideration was given to the drainage through tree planting compared with a conventional and growth capacity of each tree grassed area of comparable size Lessons learned Modest public realm improvements can promote partnerships between a range of stakeholders
After After
100 5 Case studies 5.13 Hackbridge
Location Summary Actions and results Hackbridge Transformation of street function • Bioretention basins, including tree London Borough of Sutton and traffc fow with integrated green planting, provide attenuation for runoff Extent infrastructure. from the reconfgured streetscape 0.27ha Cost Project description • Rills and flter drains with fow £920,000 (total scheme) The public realm around the junction control devices regulate the fow Date of Hackbridge Road and London Road of water into tree-rooting zones 2014 was previously dominated by busy that provide bioretention Credits carriageways, with pedestrians confned London Borough of Sutton to narrow footways fronted with shops. • Permeable paving allows for water Civic Engineers Traffc on the carriageway was fast-moving, infltration into the subsurface, Adams & Sutherland adding safety concerns to those around improving capacity during prolonged SuDS components noise, air pollution and health and safety. or high peak fow rainfall events. Up Permeable paving The low-lying topography of the area to 40% of the carriageway has been Bioretention basins meant the site was susceptible to surface reallocated to permeable paving Tree planting Filter drains & rills water fooding. Downpipe disconnection • Reduced traffc speeds have also Objectives improved the pedestrian environment • Reconfgure the streetscape to make it safer and better for pedestrians Benefts • Traffc calming; shop • Manage water runoff by installing SuDS frontage enhancement
• Mitigate air and noise pollution • Surface water fooding in the area has not been observed since the scheme was installed
101 5 Case studies Lessons learned • Detailed surveys of underground services and features are necessary in retroft situations
• A project approach that can adapt to unforeseen constraints makes the construction process more effcient Images courtesy of Civic Engineers of courtesy Images • Crossings and parking bays should be clearly marked
Tree planting along the carriageway Permeable paving
102 5 Case studies 5.14 Goldhawk Road
Location Summary • During heavier rainfall, when the tree Shepherd’s Bush Tree trench planting for attenuation. pit flls above the weir level, the water London Borough of Hammersmith & Fulham fows into a sub-base replacement layer Extent Project description covering the rooting zone just beneath 0.27ha Street tree planting within the pavement the paving build-up. This distributes Cost on a busy London high street using a modular the water over the whole rooting zone, £100,000 (construction only) structural tree soil system, combined with allowing it to infltrate into the soil Date kerb inlets and fow-control devices. 2015 • Specialist soil with a 25% void Credits Objectives ratio allows rainwater storage London Borough of Hammersmith & Fulham To provide SuDS functionality and to Robert Bray Associates protect the combined sewer. • Perforated pipes in the base of the McCloy Consulting construction collect water and direct GreenBlue Urban FM Conway Actions and results it to a fow control chamber, which • Each tree is planted within a 1.8m x 1.8m discharges to the combined sewer. SuDS components tree pit with tree grille, located within The fow control chamber allows Kerb inlets Tree pit attenuation a much larger soil-flled rooting zone water to build up in the rooting zone Flow control beneath the pavement, aiming to provide when it rains to be released slowly between 10-20m³ of soil per tree once the peak in runoff has passed
• Runoff from the adjacent road and • Integrated protected overfows ensure the footpath fows directly into the tree pit system can discharge freely to the sewer at road level, via a custom kerb inlet once storage capacity has been reached. Flow rates are designed to reduce the • The soil level in the tree pit is lower than risk of combined sewer overfow events the road. It is surrounded by a raised polypropylene weir to allow initial water storage. This ensures the trees get water Image courtesy of George Warren George of courtesy Image Under construction every time it rains and allows sediments and litter to drop out of the water
103 5 Case studies Benefts • Combines benefts of large tree rooting zones with their ability to store runoff, with little modifcation
• SuDS scheme introduced in a LBHF of courtesy Image demanding, fully-paved urban location
Lessons learned • Detailed surveys of underground services and features and careful analysis is essential in retroft situations Image courtesy of Robert Bray Associates Robert Bray of courtesy Image
Tree pit details Plan showing modular soil system Completed scheme
104 5 Case studies 5.15 Firs Farm Wetlands
Location Summary Actions and results Winchmore Hill Open space transformation with wetland • Northern and southern branches of Moore London Borough of Enfeld habitats to improve water quality outfow. Brook are diverted from their culverted Extent courses to three combined wetland cells 0.48ha Project description Cost The main driver for the wetland creation • Cells channel the water for £900,000 (total scheme) was Enfeld Council’s desire to improve treatment through fow paths Date water quality in Pymmes Park Lake, where 2016 Moore Brook outfalls before entering • A watercourse downstream connects Credits Pymmes Brook. Moore Brook is a lost to a fourth cell which is built as a pond, Enfeld Council watercourse within a surface water sewer. before continuing downstream in an Environment Agency Firs Farm was identifed as a space suitable open channel to the original culvert Thames Water for the creation of a wetland scheme. The TfL Sustrans watercourse was de-culverted and diverted • Surface water is treated at the surface GLA to a series of open watercourses, wetlands before re-entering the culvert downstream, Thames 21 and ponds to improve water quality. improving the quality of the water Friends of Firs Farm which outfalls at Pymmes Park Lake SuDS components Objectives Ponds and wetlands • Improve water quality alongside food • A further diversion to four more wetland alleviation, habitat enhancement, cells at Pymmes Park upstream of community space provision the lake provides further treatment and creating cycleway links Benefts • Provide intensive monitoring programme • Water quality improvements to be carried out by Thames21/Enfeld before discharge to river further Council over next two to three years down the catchment to determine the impact of wetlands on reducing diffuse urban pollution. • A surface system allows for issues to be This data will be used to optimise identifed and easily dealt with due to the future management of the two sites size and location of the SuDS elements
105 5 Case studies • Transformation of a previously underused open space to an area with an enhanced natural habitat and for the local community to focus activities. A local ‘Friends’ group and a waterway charity Thames21 have generated community-based interest in the site. This included help with consultation, volunteers for planting and outdoor learning, and assisting in future funding bids
• A range of amenity areas, including seating, an outdoor classroom and dipping ponds Plan • Opportunity for many disciplines to work together across the council and other organisations
• Provided opportunities to combine other objectives, such as the provision of cycleway transport infrastructure
• Biodiversity enhancements
Lessons learned Campbell Graham of courtesy Images • Importance of working alongside other land uses, in this case sports pitches
• Pre-treatment measures upstream of the wetland would be benefcial Wetland basins and planting Outlet into wetland area
106 5 Case studies 5.16 Salmons Brook Glenbrook Stream
Location Summary • Enable the community to access and Salmons Brook Transformation of existing green beneft from their local waterway London Borough of Enfeld space into wetlands. Extent • Assess the impact of the scheme 0.77ha Project description on Salmons Brook and surrounding Cost Salmons Brook is a tributary of the infrastructure in the catchment £15.3m (Total scheme) River Lea that fows through wasteland, Date industrial parks and Deepham Sewage Actions and results 2014 Treatment Works. Salmons Brook receives • Bioretention basins were integrated and Credits polluted wastewater from misconnected existing features improved. This has Thames 21 plumbing and road runoff from residential made the existing wooded landscape Environment Agency and industrial sources within the more effcient at attenuating and slowing Enfeld Council catchment. This jeopardises the quality of the conveyance of water. The wetland Robert Bray Associates Maydencroft the watercourse and those downstream basins also encourage the growth of and affects the Salmons Brook’s ability to plant and bacterial communities, which SuDS components alleviate fooding in surrounding streets. helps remediate polluted water Bioretention basins Kerb Inlets Swale EU water quality standards were not • Weirs allow control of water fow through Weirs being achieved so the Environment the SuDS scheme and any subsequent Agency and Thames21 devised a scheme discharge into Salmons Brook. to improve the watercourse. • The base level of the area has been Objectives lifted to further control fow; this • Create a wetland system to treat increases the effectiveness of the and remediate polluted water sub-catchment via the wetland before it enters Salmons Brook bioretention basin system.
Image courtesy of Thames 21 of courtesy Image • Promote change through education • By raising the base level, opportunities for Roadside swale at The Spinney about the urban water cycle stepping stone and weir crossing points were created. This has improved access.
107 5 Case studies • Swales slow the fow of water through Lessons learned the system and ensure that, with • The value of local community the weirs and wetland bioretention involvement basin, the higher concentrated polluted water is discharged into the • Managing woodland structure is crucial wetland, rather than Salmons Brook in ensuring that light levels are suffcient for the establishment of vegetation • Kerb inlets allow rainwater to be conveyed away from the combined sewer overfow and into the
Image courtesy of Robert Bray Associates Robert Bray of courtesy Image swales and through the network of weirs and wetland basins
Benefts Weir detail at Grovelands Park • Salmons Brook water quality improved
• Flood risk reduced and road Chaoming Li of courtesy Image runoff management improved
• An area of greater recreational value created
• Reduction in house insurance costs for surrounding properties
• Public awareness of the reality of waste and pollution in their environment that
Image courtesy of Robert Bray Associates Robert Bray of courtesy Image might otherwise remain unnoticed
• A sense of ownership has been fostered through scrub clearance Treatment wetland at Grovelands Park and wetland planting days Swale incorporating existing mature trees
108 5 Case studies 5.17 LuL depot roof, Middlesex
Location Summary Actions and results Ruislip Depot Retroft green roof and monitoring • Biodiverse extensive green roof Middlesex of source control. types, each 18.5m x 3.3m, have been Extent installed on a section of fat roof 125m² Project description Cost A small-scale trial to evaluate the • One section (south) has a drainage £30,000 (Trial project) effectiveness of retroftted green roofs, board with 65mm of extensive Date for LUL depot environments. From the green roof substrate. The other 2012 results it will be decided whether LUL section (north) uses recycled wool Credits could beneft from a broader application. fbre instead of drainage board London Underground Limited GLA Objectives • Both roofs are vegetated with sedum University of East London • Introducing environmentally- cuttings and seeded/planted with GRC friendly measures to address annual and perennial wildfowers SuDS components runoff from depot roof Green roofs • The two trials are separated by an • Achieve low maintenance impermeable barrier to facilitate the measurement of runoff. Total • Address Mayoral policy for SuDS by saturated loading is less than 100kg/m² installing a green roof source control • With the assistance of the University • Ensure retroftting on operational of East London, monitoring devices railway followed the rigorous have been installed in two downpipes assurance and safety procedures of a green roof and two downpipes of London Underground, without of a conventional control roof to interruption of service measure water attenuation
• GLA support has been provided After Installation through Drain London. A small fund enables monitoring performance
109 5 Case studies Benefts • LUL will examine the process of installation, maintenance and performance and the cost-beneft analysis in terms of waterproofng performance and drainage control for a larger scale application
• LUL will also assess: longevity of the waterproofng layer; improved working ambiance and environment; structure insulation; air quality improvements; Images courtesy of LU Infrastructure Protection Infrastructure LU of courtesy Images biodiversity enhancements
• The trial will allow better understanding of the mechanism and potential areas for improvement
Lessons learned • The use of wool as a recycled drainage material was an important outcome
• Monitoring of water attenuation is complete and will inform future green roof schemes
• Organic material used as a drainage board has performed consistently better than the conventional plastic one
• Maintenance is minimised due to Programme of monitoring Early green roof growth within 6 months planting selection of wildfowers
110 5 Case studies 5.18 A23 Coulsdon Bypass, Farthing Way
Location Summary • To the west of the new A23, the Coulsdon Highway runoff attenuation. existing ground rises steeply; being London Borough of Croydon chalk downland, there is likely to be Extent Project description signifcant runoff when it rains heavily. 34ha A groundwater extraction borehole at A separate system, not linked to the Cost Smitham Pumping Station is located in highway drainage, collects this runoff £33m (Total scheme) Coulsdon Town Centre. The new section and discharges it into soakaways Date of A23 between Marlpit Lane and Smitham 2006 Station passes across the inner Source • Non-piped drainage components Credits Protection Zone (SPZ) for the extraction within the site principally relate to TfL borehole and has been designed to direct linear soakaways at the bottom of the Atkins runoff appropriately. embankment adjacent to footways SuDS components where water is caught at a low point Kerb drainage Objectives Soakaways • The drainage design redirects Benefts Filter strip runoff fowing from the new • The design maintains the Filter drains A23 away from the inner SPZ fow of previously-existing drains and watercourses • Attenuation was needed to ensure the area receiving the runoff can cope with • The design of the drainage components the volume of water it now receives allows them to be maintained in a safe and effcient manner Actions and results • The new A23 is drained, via a piped • Surface water is able to drain into system with kerbs and gullies, into soakaways on adjacent land spillage containment devices and a full retention fuel/oil separator, Lessons learned before discharging into soakaways • Localised design changes were Filter strip gravel necessary, due to the unexpected presence of services
111 5 Case studies • The specifed kerb drains were made smaller during construction due to the high retaining wall footing and the 600mm wide narrow verge
• Deep-bored soakaways were used extensively throughout the project. During the construction of some soakaways, the piling contractor met some obstructions. This was overcome by relocating the soakaways, but only small changes in the positions were needed
Carriageway flter strip Surrounding carriageway context Plan
112 5 Case studies 5.19 London Sustainable Industries Park, Dagenham
Location Summary Actions and results Dagenham An integrated water management and • Swales and bioretention basins allow London Borough of Barking and Dagenham infrastructure plan for an industrial park. water to be conveyed from roofs, roads Extent and other features into a system of 142ha Project description components with a high attenuation Cost The London Sustainable Industries Park storage capacity. This limits the outfow £30m (Total scheme) (LSIP) is part of the Thames Gateway of water into Gores Brook at a rate Date regeneration at Dagenham Dock in East of 12 L/s/ha during prolonged and/ 2009-10 London. It is an international exemplar, or high peak fow rainfall events Credits created with the goal of making Thames Civic Engineers Gateway the UK’s frst Eco Region. • Water quality is improved by allowing T. R. Collier & Associates The site is south of the A13 and close to suspended solids to settle out and other Sergison Bates Dagenham Dock Railway Station and the pollutants, such as hydrocarbons, to Vogt Landscape Price & Myers Barking Reach Power Station. The Gores be treated or their discharge limited URS Brook receives outfow from the site GHP which then discharges into the River • Attenuation tanks allow rainfall SuDS components Thames. Consideration of the hydrology to be recycled for use by services Swales of the site was crucial to achieving a that use ‘grey’ water Managed wetland and woodland successful scheme. Bioretention Benefts Water recycling Objectives • Negates the need for costly remediation • Install a water management systems, such as petrol interceptors system for the LSIP • The volume of low water quality • Transform the existing infrastructure run off from carriageways and onsite to create a self-sustaining other built infrastructure on the exemplar of green infrastructure industrial park has been reduced design and planning • BREEAM ‘Excellent’ rating achieved (2010)
113 5 Case studies • The cost of utilities and maintenance has been reduced
• Enhanced ecological value
Lessons learned The installation of an adaptable and resilient water drainage network can provide infrastructure for a range of future uses depending on plot uptake and industry requirements.
Aerial visualisation
Plan Cross-section
114 5 Case studies 5.20 Great Kneighton / Clay Farm, Cambridge
Location Summary Cambridge Holistic integration of water management Extent into major new development. £45m
Cost Project description Simon Bunn of courtesy Image 109ha Great Kneighton, previously Clay Farm, Date is former green belt land 4km south Final phase: 2020 of Cambridge. The site is typical for Credits Cambridgeshire – fat, low-laying terrain, Cambridge City Council crossed with brooks and land drainage Countryside Properties channels. The mixed use development site Bovis of Great Kneighton suffered from poorly Cala Homes draining clay soils and a high water table, Crest Nicholson Skanska 1m below ground. The site is within the Aecom catchment of the historic Hobson’s Conduit, PEP which dictated stringent control measures BBUK Studio for runoff from the development. James Blake Associates Environment Agency Cambridge City Council, along with project Hobson’s Conduit Trust partners, wished to install an integrated SuDS components water management system within a Soakaways designated strategic open space that forms Detention basins Permeable paving and tree planting Bioretention basins part of the Cambridge Green Corridor. Swales Rills Objectives • Withstand one in 100 year Permeable paving • Control outfow into Hobson’s food event, with 30% extra to Rainwater harvesting Brook at 2l/s/ha allow for climate change Green/brown roofs • Install a SuDS code of conduct • Provide amenity and ecological across the development site value to development
115 5 Case studies Actions and results • Swales increase the attenuation storage Benefts • Plot-wide rainwater harvesting capacity of the scheme and provides • Impact of development on system intercepts rainwater, reducing vegetated landscape of hydrological, surrounding drainage infrastructure the amount being conveyed to the aesthetic and biodiversity value is minimised through the subsequent stages of the SuDS scheme management of water on site • Hydrodynamic vortex separators • Detention basins increase the attenuation inhibit the discharge of sediment • Outfow of water quality storage capacity of the scheme and and hydrocarbons into the Hobson’s and volume controlled slows water fow, particularly during Conduit outfow. This is of particular prolonged and/or high peak rainfall note due to the downstream function • Can withstand a one in of Hobson’s Conduit in Cambridge 100 year food event
• Bioretention basins allow water to • Predominantly above-ground nature be attenuated on the east side of of the SuDS features contribute Hobson’s conduit, preventing low to the recreational and aesthetic quality water from discharging into value of the development the watercourse. Water is conveyed from the development to the west, • 20,000m² of wetland habitat created underneath Hobson’s Conduit into the
Image courtesy of Tim Crocker of courtesy Image bioretention basins, creating a series of • Installation of a landscape ponds and wetlands of hydrological, of multiple benefts recreational and ecological value Lessons learned • Permeable paving increases the • Engaging developers and project teams permeability on the site, where early in the development process allows below-ground conditions allow the benefts of SuDS to be shared
• Sub-catchments syphons underneath • Treat each site within the development the brook discharge into a series individually to capture the variations of ponds and detention ponds in soil type and topography
Completed residential unit • Pre-cast concrete rills convey water into bioretention basins in the local square
116 5 Case studies 5.21 Alnarpsgården Swedish University of Agricultural Sciences
Location Summary Actions and results Alnarp Campus courtyard redevelopment to focus • Water from downpipes is collected in Sweden on sustainable drainage while creating a channels running along the facades, Extent social hub. then led to a retention basin (a former 0.37ha manure container). At the bottom of Cost Project description the concrete basin are ‘seams’ in which £170,000 (construction only Alnarpsgården is a rural campus hosting aquatic plants grow in a strict pattern. Date the Institution of Landscape Architecture, From the retention basin, water runs 1997 Planning and Management at the Swedish in a ditch towards the Íresund coast Credits University of Agricultural Sciences (SLU). Anders Folkesson, Part of a historic estate, it consists of • Grit-jointed granite setts form permeable Landscape Architect LAR/MSA buildings converted from agricultural paving, over-seeded with wildfowers Vasajorden AB use and new builds, set within a forested SuDS components landscape. The focus of the campus Benefts Ponds and wetlands is the inner courtyard, which has been • The courtyard design repurposed Disconnected downpipes redeveloped with SuDS principles in mind. existing features, such as the Permeable paving Channels & rills old manure container and dung Retention basin Objectives grooves, as SuDS features • Slow water runoff from roofs and hard surfaces of Alnarpsgården • The redevelopment of the courtyard has created a social hub, well • Provide a frst step of water cleaning used by students and visitors
• Enhance the appearance of the yard • The success of the SuDS components of the courtyard make them a • Demonstrate an open stormwater valuable educational tool system to the landscape architect students of SLU Wildfower seeded joints
117 5 Case studies Lessons learned • Previously, the yard’s ground was slightly concave, the middle of the yard being slightly lower than the ground along the facades. To channel all the stormwater from the yard to the gutters along the facades, the middle of the yard was raised. Adjusting the topography has affected the quality of the space Images courtesy of Anders Folkesson of courtesy Images
Threshold detail SuDS pond acting as a central recreational feature
118 5 Case studies 5.22 Benthemplein (Water Square)
Location Summary Actions and results Rotterdam Multi-functional public realm regeneration. • Detention basins increase the Netherlands attenuation storage capacity of the Extent Project description site to 1,700m³. Uniquely, the three 0.95ha Benthemplein is in central Rotterdam, detention basins provide a recreation Cost north-east of Rotterdam Centraal station. space that is transformed as water £3.175m (Total scheme) It is bounded by major city roads and is attenuated in the basins Date enclosed by medium rise buildings. 2013 • Rills convey water from the surrounding Credits The low permeability paving of the site ground surfaces and buildings into City of Rotterdam meant it was not fulflling its potential the detention basins. Each basin has Schieland and Krimpenerwaard of relieving localised fooding in adjacent its own sub-catchment taking runoff Urbanstein areas. This put pressure on the combined from certain surfaces and buildings and Wallaard ACO sewer overfow of the Nieuwe Maas. incorporates waterfalls, fountains and an Topcourts outside baptistery for use by the church Due to the proximity to areas of fooding SuDS components Detention basins and the opportunity for restructuring Benefts Rills of space, the City of Rotterdam and • Water management has the stakeholders, including church and student added beneft of creating a novel communities, looked to re-imagine the multiple-use public realm space function of the square, as part of the Rotterdam Climate Initiative. • Approximately 4,000m² of existing parking and street access has been Objectives kept to allow space for vehicles • Reduce food risk • Interventions such as the baptistery, • Provide recreational opportunities sports goals and shaded seating has allowed for a range of stakeholders’ needs to be addressed
119 5 Case studies WATER SQUARE BENTHEMPLEIN Roterdam, the Netherlands Lessons learned • Attention to detail during planning and design phases and supervision during construction is crucial in achieving a scheme with complex sub-catchments R N N T • By fulflling city authority climate
objectives, it is possible to receive Urbanstein of courtesy Images extra funding for similar schemes. Rotterdam raised an extra £700,000
Overview of completed scheme
catchment area of basin 1 catchment area of basin 2 catchment area of the deep basin 3 Two in one Detention basin CatchmentThe water square areas combines water storage with the improvement of the quality of urban public space. The water square can be understood as a twofold strategy. It makes money invested in water storage facilites visible and enjoyable. 120 5 Case studies It also generates opportunites to create environmental quality and identty to central spaces in neighborhoods. Most of the tme the water square will be dry and in use as a recreatonal space.
diferent atmospheres for diferent actvites overview of the water sqaure and its basins 5.23 Rue Garibaldi
Location Summary Objectives Lyon Transformation of an urban motorway • Minimise runoff into the France to a planted boulevard and high quality combined sewer overfow by Extent civic space. installing a SuDS scheme 15ha Cost Project description • Improve connection between districts £19.3m (Total scheme 1st phase) Rue Garibaldi, east of the River Rhine, is bordering Rue Garibaldi by design and Date a north to south six-lane carriageway, planning consideration, within the 1st phase 2014 constructed in the late 1960s. It is fronted wider green space context of the area Credits with high storey buildings and features that Grand Lyon were characteristic of an urban motorway. • Reduce maintenance and utility costs Atelier des Paysages The environment for pedestrians and by installing a water recycling system SuDS components cyclists is hostile. Retention basins • Reconfgure carriageway function Swales The confguration and high capacity of the by installing separate carriageways Soakaways streetscape exacerbated the effects of for public transport, pedestrians, Depaving urban heat island. Air (principally NOx and cyclists and other vehicles PM) and water quality was low (principally hydrocarbons and total suspended solids). • Improve management of water quality and mitigate urban heat Runoff into the combined sewer overfow island effect by planting trees was high, particularly during heavy or and installing a SuDS scheme prolonged peak rainfall, considering the sub-catchment area of 65,000m². Actions and results • Retention basins were created from These conditions, coupled with a the redesign of an existing underpass. carriageway reconfguration proposal, An automated pumping system was presented the opportunity to reconsider installed to allow water to be recycled Integrated cycleway and SuDS hydrological management of the 2.6km for street cleaning vehicles and stretch of highway irrigation for public realm planting.
121 5 Case studies This has reduced local authority Benefts utilities and maintenance costs and • Reconfguration of carriageway increased the attenuation storage to align with Grand Lyon’s capacity of the streetscape. Water sustainability objectives treatment capabilities also feature, due to the oxidative capacity and • Provision of extra parking for taxis, bacterial activity of the retention basin deliveries and public road users
• Swales with 4,500m³ of vegetation • Creation of new green links through Lyon increase the attenuation storage capacity. These have been integrated into • Re-purposed existing infrastructure the reconfguration of the carriageways to create vegetated separation between • Peak outfow into the combined carriageways with different functions. sewer system is 5 L/s/ha This has signifcantly enhanced biodiversity in the streetscape • Monitoring during the frst phase of construction has helped inform the • Soakaways have increased the infltration development of phases two and three rate by aiding conveyance of water into the ground, contributing to the 1300m • On-site availability of recycled attenuation capacity of the scheme water for street cleaning
• Trees have mitigated urban heat island • Automated irrigation reduces effects by increasing the interception maintenance commitment and cost of solar radiation and increasing evapotranspiration. Tree planting has • Water and air treatment capability contributed to the effectiveness of the SuDS scheme and helped reconfgure Lessons learned the streetscape by creating a separation • Ensure clear agreement between local between carriageways and enhancing authority services for management the sense of place. Sensors have and maintenance responsibilities Rill and de-paving been installed to quantify the cooling on cyclical and periodic regimes effect provided by the vegetation
122 5 Case studies
5.24 Bo01 Võstra Hamnen
Location Summary • Use a scoring system to achieve balance Malmö Transformation of an industrial site to a between development demands Sweden neighbourhood with integrated off-grid Extent sustainable water management. Actions and results 85ha • Swales and bioretention basins created Cost Project description high attenuation storage capacity and £3.3m (landscape construction only) The city of Malmö has developed SuDS made an off-grid drainage system possible. Date schemes since the late 1990s. The Võstra 2001 Hamnen area is on a former industrial site • The network of swales and basins Credits and is in a key strategic location to complement the well-connected City of Malmö accommodate city growth. The site was streets and spaces that characterise the Government of Sweden prone to fooding and its soil foot and cycle networks in the area. Sydkraft AB (E.ON Svergie) contaminated. The international housing Lokala Investeringsprogram exposition, Bo01, framed the frst phase • Meadows, woodlands, seashore and European Union of development and allowed the City marine biotopes serve hydrological Lund University of Malmö to instigate an exemplar in functions in relation to the SuDS and SuDS components sustainable urban regeneration. The added a variation in site conditions 3Downpipe disconnection project featured a new housing district for an abundance of species of 500 apartments, with the public realm a signifcant contributor to achieving sustainability goals.
Objectives • Manage food risks with an open storm water system
• Create an exemplar in sustainable urban design Permeable shared surface Rill • Achieve off-grid sustainable drainage
123 5 Case studies Benefts • Off-grid SuDS system – no pressure on existing drains
• A cross-disciplinary approach during development allowed for the revision of planning tools
• Popular contribution to the character and function of the public space
• Innovative scoring system used to quantify greenspace factors and give weight to ecological and aesthetic considerations
• The scoring system used to quantify green space factors works in a UK context
Lessons learned • Development-wide consideration of topography crucial to success
• Incorporation of water features such as fountains can be achieved by recycling water collected by SuDS
Retention pond
124 5 Case studies 6 Implementation 6.1 Implementation 6.2 SuDS In Chapter 3, the range of components design team which can be used in London were explored, while Chapter 4 illustrated how The SuDS design team must be assembled at these might be applied to a variety of project inception and operate collaboratively. indicative street scenarios. Although much The team is likely to include: of this guidance highlights opportunities to implement SuDS in London, this chapter • Highways engineer for the planning, describes the requirements for a SuDS design, construction, operation and team and recommends the design process maintenance considerations to follow. • Landscape, urban design and landscape Much of the detail can be found in the management to guide the form, shape Meadow planting: low maintenance, high CIRIA 753 The SuDS Manual, from and long-term sustainability of features, biodiversity, deep rooting erosion control, which the design process diagram has particularly early in the process less mowing and less compaction been adapted. • Drainage engineer to ensure the proposed design will Multi-disciplinary collaboration is provide effective drainage fundamental to achieving integrated and sustainable drainage within London’s • Ecologist and/or arboriculturist streets. It ensures innovative ideas can to enable maximum biodiversity be tested and assessed, while minimising beneft to be delivered impact on the decision-making process and maximising opportunity and benefts. This • Soil scientist, in particular to examine requires a range of specialists, technical the potential of existing soils to staff and stakeholders to work together. accommodate SuDS infrastructure and street tree planting. This will also The team can be led by the highway inform the below-ground specifcation engineer, landscape architect/urban designer, or drainage engineer working with specialist consultants. Schemes that form part of wider initiatives can be led by a
126 6 Implementation private developer’s team, working with To start, the design process should the Highways, Planning and Lead Local consider the various site-specifc Flood Authorities. constraints, as these will be one of the biggest design drivers. Baseline data will The Surface Water Management (SWM) be vital, possibly requiring the need to objectives should be set and commission surveys and investigations. underpinned by: These will infuence design consideration of source control, pathway and receptor • SuDS design principles (see Chapter 2).
• Townscape and landscape character Community engagement is a vital part of a successful project. Working with • Local planning policy communities through the design, planning and delivery processes is essential for Kings Cross LWT: Camley Street • Functional demands of the street fnding the best design and building support for the project. Community • Evaluation of any existing SuDS features engagement can also act as a catalyst for partnership, working to beneft long- • A long-term outlook term management and maintenance mechanisms, as well as funding regimes. The planning and drainage design process should include: The aim should be to achieve the maximum beneft, accepting that there • Agreeing with the planning authority the will be practical constraints to consider. level of detail required and any aspects This is particularly relevant as SuDS that require a planning condition is an evolving practice, with complex regulations and potentially high numbers • Identifying a way to ensure the designs of stakeholders involved. are delivered according to specifcation Refer to CIRIA C753 The SuDS Manual, • Community and stakeholder engagement Chapter 7 for a detailed description of the A soil scientist is part of the SuDS team SuDS design process.
127 6 Implementation Design process diagram adapted from CIRIA C753 The SuDS Manual
National/local SuDS Local planning policies guidance & standards Environmental Impact Assessment
Pre-application Set strategic surface water (directly influencing drainage design) discussions management objectives Stakeholder engagement Site Flood Risk/ Consequence Assessment Development Conceptual drainage masterplanning design Initial data collection & analysis Outline planning Outline drainage design permission & conditions
Community engagement Detailed data collection and analysis Full planning Detailed drainage permission design
Key
Building regulators Drainage system approvals Planning process and Drainage design and approval & construction consents requirements construction processes
Planning processes Drainage design and and requirements not construction processes Construction, Satisfactory scheme usually relevant for not usually relevant for inspection & approval construction small sites small sites
Planning data inputs Data inputs for drainage and construction Drainage system Planning data inputs processes management not always required
128 6 Implementation 6.3 Drainage hierarchy
SuDS designs should generally be developed according to the CIRIA process diagram on the previous page. This process may vary, depending on local conditions
When working in London, water should be managed by using the following drainage hierarchy, as described in the London Plan:
1. Intercept and store rainwater for later use: examples of this include water tanks 2. Grit jointed permeable paving and butts, or as well as abandoned and repurposed subterranean pedestrian passageways below urban roadways.
2. Use infltration techniques, such as permeable surfaces: these offer simple and relatively low cost surface water 1. Disconnected downpipe to water butt absorption capacity. Permeable surfaces collect, store and release water at different rates, depending on the sort of 3. Attenuate rainwater in ponds, green soil present. Local geological makeup and or blue roofs or open water features for hydrology should take account of buried gradual release: ponds, linear wetlands infrastructure (such as that associated with and basins can create attractive features London Underground) to ensure chambers that provide ecological habitat as well as do not become water conduits. amenity. There is also scope to incorporate SuDS into green space alongside London’s highways. 3. Attenuation in planted rill
129 6 Implementation 4. Attenuation in tree trenches 5. Discharge to watercourse 6. Surface water sewer outfall
4. Attenuate rainwater by storing in tanks, 6. Discharge rainwater to a surface water sealed water features, permeable paving sewer/drain: this has traditionally been and tree trenches for gradual release: London’s default approach to rainwater Although these systems can be confgured management. However, London’s sewer to suit a variety of below-ground conditions, network is so intertwined with the foul carefully consider utilities to avoid damaging network that there is a need to segregate long-term tree-rooting potential. Surface conveyance systems to minimise water can potentially be re-used in tree contamination and effuent trench planting. treatment costs.
5. Discharge rainwater directly to a 7. Discharge rainwater to the combined watercourse: this can offer a low-cost sewer: the economic justifcation needs to option for surface water dispersal, be set exceptionally high to mitigate the provided the surface water is pollutant- commercial demand for such a choice. In free. Liaise closely with water body retroft scenarios, the combined sewer may authorities as they may put limits on how be the only option. If so, control of discharge much water can be discharged into the rate and water quality will be critical. 7. Combined sewer outfail conveyancing system.
130 6 Implementation 7 Cost beneft 7.1 Cost beneft for large-scale and widespread excavations Four cost beneft references are: in many streets, and the need to work in The Greater London Authority’s (GLA’s) and around other buried infrastructure. • CIRIA’s SuDS Tool (BeST) which document ‘Natural Capital Investing in a provides monetised values to tangible Green Infrastructure for London’ highlights Green infrastructure and sustainable and intangible benefts applicable two key challenges: drainage (as opposed to hard-engineered to the UK’s drainage systems techniques) have many benefts, such as 1. Unseen value (usually expressed reducing air pollution, reducing noise, • i-Tree Eco, a system related to valuing environmentally or socially, rather improving biodiversity, reducing summer trees in terms of ecosystem services. than monetised, typically regarded urban heat island effects and creating This has estimated, for instance, the as intangible) places with identity and character. economic value of London’s urban forest 3 2. A lack of a revenue-raising at almost 3.5million m /annum of storm mechanism to offset management These benefts can be challenging to water alleviation, worth £2.8m/annum and maintenance. monetise. Some evaluation tools use an ecosystem services framework as • TfL’s Valuing the Urban Realm The emphasis of the London Sustainable a starting point to convert beneft Toolkit. This has identifed a positive, Drainage Action Plan (LSDAP) has been to to monetised outcomes. The City of signifcant and consistent relationship ‘identify opportunities for implementing Philadelphia, for instance, has identifed between the quality of streetscape sustainable drainage techniques that the net beneft of using surface drainage and benefts for users and property have limited fnancial impact’. This focuses techniques at almost $3bn compared owners. For further information, on situations where other works are to $100m for the piped alternative. The contact [email protected] likely to be undertaken. Integrating SuDS $3bn includes benefts such as changes would therefore be a component of a to property value, green job creation, • The Government’s Natural Capital wider project. reduction in greenhouse gas Committee which has developed emissions and reduced crime through an accounting framework. This The LSDAP also notes that options to an improved environment. is currently being trialled. increase London’s drainage system capacity using conventional underground piped networks, such as the Thames Tideway Tunnel (under construction), are becoming increasingly complex and prohibitively expensive. This is due to the requirement
132 7 Cost beneft 7.2 Methodology • In a conventional drainage system, this • costs are pro rata, therefore could be provided through provision of would have no bearing upon Cost beneft estimates have been made approximately 35m³ of proprietary tank the percentage range based on the eight street scenarios in system (assumes 90% free volume) • costs will vary between schemes Chapter 4 and, without a specifc design, • The proposed SuDS components a fgure could not be applied Models of conventional drainage and SuDS could provide an equivalent storage components are considered for each of the capacity and would therefore negate Exclusions apply, including construction eight scenarios illustrated in Chapter 4. The the need for any conventional overheads, fees, VAT and infation. Site- following assumptions have been made: drainage or storage systems specifc costs, such as those relating to statutory costs, utility and below ground • The scheme constitutes new • Both systems are subject to the same infrastructure works, are also excluded. development – retrofts are access constraints and require the generally more expensive same amount of traffc management
• There is no upstream source control • Surface water fows to a surface water sewer • The total area under consideration is 1,000m² • The ground is unsuitable for infltration
• A single gully will typically • The same number of trees, where the provide adequate drainage SuDS option counts for an integral tree capacity for an area of 200m² pit providing 30% water attenuation capacity, and the conventional is • The volume of attenuation required based on a proprietary tank system to achieve 50% improvement, as defned by CIRIA, for the one in 100 • The SuDS technologies under year event, plus climate change storm consideration are dry swales, permeable event for an area of 1,000m2, would paving and bioretention components For be approximately 31m³ of water the direct cost comparison some other costs have been excluded, because:
133 7 Cost beneft 7.3 Design life 7.4 Cost comparison • Density of planting and trees including existing trees, which Delivering Benefts Through Evidence – Designing and constructing surface might require specifc attention Cost estimation for SuDS’ was published drainage systems involves a lot of by the Environment Agency in 2015. It variables, all of which have a bearing on • Specifc utility requirements and examines the design life of SuDS. cost, including: other below ground structures
This shows that most SuDS have a long • The site, whether retroft, re- • Proximity to receiving design life. However, their component development or new development watercourse or sewer parts, such as control mechanisms and infltration surfaces, need replacing • The location and geotechnical context • Amenity, public education between fve and 50 years. Specifc to which the solution is being applied. and safety requirements maintenance, such as decompaction, may also be required. Replacement depends on Each scenario within a given streetscape Rates applied to the components are site characteristics, system design and the will be bespoke, considerations being: presented as a range. This is due to degree of maintenance undertaken. the variances of procurement, ie, type, • Scale and size of development contract, market conditions, location There is relatively low risk of structural and time. It also takes into account failure occurring. This contributes • Hydraulic design criteria, ie, volume of the differences of each street scenario signifcantly to the SuDS design life. storage, impermeable catchment area where relevant, ie, size and economies of scale, bespoke nature of the location, • Inlet/outlet infrastructure, ie, volume and surrounding infrastructure, buildings and velocity of anticipated fows, capacity ground conditions. of the drainage system beyond site The comparison between conventional • Water quality design criteria drainage systems and SuDS is expressed as an indicative percentage range, rather than • Soil types, ie, permeability, absolutes. The fgures on the next page in depth of water table, porosity, red brackets show potential percentage load bearing capacity savings in implementing SuDS over conventional drainage; black text indicates • Materials potential percentage cost increase.
134 7 Cost beneft 4.4 LANDSCAPE WATER MANAGEMENTSTRATEGY
Street scenario 1 (55%) – (49%) Nine Elms linear park: SuDS as part
4.4.1 WATER MANAGEMENT Street scenario 2 (32%) - (5%) of wider development proposals Street scenario 3 (20%) – (4%) An in tegrated approach to water management in Nine 4.4 LANDSCAPE WATER MANAGEMENTSTRATEGY ElmsParkside could realise signi cant environmental Street scenario 4 bene(38%)terms – of (3%) water conservation, waste minimization and pollution control. The purpose of the strategy is to establish a hierarchy of interventions Street scenario 5 that(26%) optimises the– conservation(25%) and management of water within the wider environment, and future community. The key interventions to be incorporated Street scenario 6 are(29%) as follows: – (1%)
Street scenario 7 (20%)Podium – Level (30%) Courtyards - Potential permeable paving using drainage mats (indicative) 4.4.1 WATER MANAGEMENT Image courtesy of Camlins of courtesy Image Permeable Surface/ Planting area - Rain Street scenario 8 (9%)water – will (5%) be absorbed, no water to enter into underlying controlled waters
Swale - Water collected locally from roads and This analysis indicates that pathsthe and connecting into wider drainage An in tegrated approach to water management in Nine system ElmsParkside could realise signi cant environmental implementation of SuDS is Attenuationpotentially Basin - Overfow storage system bene terms of water conservation, waste more cost-effective than conventionalfor rainfall event in excess of 1 in 30 year storm minimization and pollution control. The purpose of the strategy is to establish a hierarchy of interventions drainage in construction costUnderground terms Storm Cell - Attenuating rainfall that optimises the conservation and management from roof and paving before water enters the of water within the wider environment, and future alone. The range in the percentagesdrainage system. This is can due reduce peak runoff community. The key interventions to be incorporated fows to the allowable green feld run-off rate primarily to variables in the costs of paving are as follows: specifcations. Podium Level Courtyards - Potential permeable Many schemes within London will require paving using drainage mats (indicative) retroftted design solutions. In these cases, Permeable Surface/ Planting area - Rain costs may be incurred in removing or water will be absorbed, no water to enter into underlying controlled waters adapting existing infrastructure. Illustrative Scheme Masterplan, 2016 Swale - Water collected locally from roads and paths and connecting into wider drainage SuDS projects60 often form part of system wider development proposals, where Attenuation Basin - Overfow storage system the cost of sustainable drainage would for rainfall event in excess of 1 in 30 year storm be integrated from the start and economies of scale apply. In all situations, Underground Storm Cell - Attenuating rainfall from roof and paving before water enters the adjacencies create variability when dealing drainage system. This can reduce peak runoff with different ownerships and boundaries. fows to the allowable green feld run-off rate
135 7 Cost beneft
Illustrative Scheme Masterplan, 2016
60 7.5 Best value
Natural capital is defned by the Natural Capital Committee (NCC) as ‘those elements of nature which either directly provide or underpin human wellbeing’. Liveability and wellbeing infuence how value for society is perceived.
CIRIA Research Project RP993 states that best value is not about cheapness. It is the opportunity to seek and obtain best overall value.
A SuDS approach can be cheaper than piped solutions; it can also deliver considerable wider benefts, as this guidance illustrates. Sustainable surface water management can contribute to a step-change in the resilience of London’s drainage infrastructure and the quality of its urban realm.
Further information: London Sustainable Drainage Action Plan CIRIA C753 The SuDS Manual Chapter 35
Ashwin Street: SuDS components contribute to the quality of the urban realm
136 7 Cost beneft Appendices Further information Defra (2010) Environmental Permitting GLA (2010) Mayor’s Transport Strategy Guidance: Water Discharge Activities para 528, 555, 62 B Woods Ballard, et al CIRIA C698 Site (England and Wales) Regulations Handbook for the Construction of SuDS GLA (2011 updated 2015) London Plan Policy 6.2 Defra (December 2011) National Standards Bartens et al. (2008) Can Urban Tree Roots for sustainable drainage systems, GLA (2011 updated March 2015) London Plan Improve Infltration through Compacted Designing, constructing, operating and Soils for Storm Water Management?: http:// maintaining drainage for surface runoff GLA (2012) All London Green Grid SPG www.ncbi.nlm.nih.gov/pubmed/18948457 Defra / Environment Agency (October GLA (2015) London Infrastructure Plan British Geological Survey, Natural 2013) Delivering Benefts through 2050, Consultation report Environment Research Council: Evidence, Rainfall Runoff Management for https://www.bgs.ac.uk Developments Report SC030219 GLA (2015) London Sustainable Drainage Action Plan Draft Consultation Cambridge City Council, Cambridge Drain London: https://www.london.gov. Sustainable Drainage Design and uk/what-we-do/environment/climate- GLA (2015) Natural Capital Green Adoption Guide changeweather-and-water/drain-london Infrastructure Task Force Report Centre for Ecology & Hydrology (1999 Environment Agency (2009) Thames updated May 2016) Flood Estimation Catchment Flood Management Plan GLA A Barry, Letter to Defra, Consultation Handbook of National Standards for SuDS Environmental Agency (2013) Groundwater CIRIA (2015) CIRIA C713 Retroftting to Protection: Principles and Practice GP3 GLA Economics (June 2003) Valuing Manage Surface Water Greenness, Green Space House Prices and Flood & Water Management Act 2010 Londoners’ Priorities CIRIA (2015) CIRIA The SuDS Manual C753 Forestry Commission, Forest Groundwork Climate Proofng Housing CIRIA (October 2013) CIRIA Research Research(2010) Benefts of Green Landscapes: http://www.groundwork.org. Project RP993, Demonstrating the multiple Infrastructure. Hydrological Benefts. uk/Sites/london/pages/lifeplus-lon benefts of SuDS – A business case URGP Evidence Note 005 (Phase 2) Draft Literature Review City of Highways Authority and Utilities Philadelphia, City of Philadelphia Green GLA (2009) London Regional Flood Risk Committee (HAUC) Advice Note 2009/07, Streets Design Manual Appraisal Special Engineering Diffculty Section 63 and Schedule 4
138 Appendices i-Tree Eco Project (2015) Valuing London’s Old Oak and Park Royal Development TfL (October 2012) Code of Practice Urban Forest: http://www.forestry.gov.uk/ Corporation (February 2016) Integrated Fourth Edition, New Roads and Street Water Management Strategy Works Act 1991 International Institute for Sustainable Development, Water Quality Monitoring RSPB / WWT (December 2012) Sustainable TfL response to Roads Task Force (July Systems Design (2015) Chapter 6: http:// Drainage Systems, maximising the potential 2013) Delivering the vision for London’s www.iisd.org/library/water-quality- for people and wildlife: http://www.rspb. Streets and Roads monitoringsystem-design org.uk TfL Roads Task Force (April 2015) Interpave (May 2014) SuDS Permeable Paving Susdrain (Fact Sheet January 2015) Designing progress report Attenuation Storage for Redeveloped Sites J D Phillips (2007) Fluvial Sediment Storage Thames Water Wastewater services: http:// in Wetlands no. 89007 Water Resource Bulletin T Armour et al (2012) CIRIA C712 The www.thameswater.co.uk/developers/592. benefts of large specie trees in urban htm Thames21 SuDS Highway (formerly K V Heal and S J Drain (2003) Sedimentation landscapes: a costing and Greenstreets): http://www.thames21.org.uk/ and Sediment Quality in Sustainable Urban management guide greenstreets/ Drainage Systems TDAG (September 2014) Trees and Hard UK Groundwater Forum: Kennedy et al. (2005) ‘Psychological’ traffc Landscape A Guide for Delivery: http:// http://www.groundwateruk.org calming, TRL Report TRL641 www.tdag.org.uk United States Environmental protection Landscape Institute (2014) Technical Thames Catchment Based Agency (EPA 832-F-99-012) Storm Water Guidance: Management and maintenance Approach Group: http://www. Technology Fact Sheet Bioretention of Sustainable Drainage Systems (SuDS) catchmentbasedapproach.org/thames landscapes Interim Technical Guidance Water UK (2013) Sewers for Adoption Note 01/2014 TfL (2015/16) Surface Transport Plan 7th Edition
Liu Jia et Al (2014) Review and Research TfL (2016) Streetscape Guidance Third Wildfowl & Wetlands Trust (WWT) Needs of Bioretention Used for the Edition V1 Environment Agency Thames Water, SuDS Treatment of Urban Stormwater for Schools Project: http://sudsforschools. TfL (March 2014) Roads Task Force wwt.org.uk/theproject/ NHBC (November 2015 | Issue 19) progress report Technical Extra
139 Appendices Glossary A ground depression acting as a fow A site that has been previously developed. Amenity control or water treatment structure that Catchment The quality of a place being pleasant or is normally dry, but is designed to detain The area contributing surface water fow attractive, ie, its agreeableness. A feature storm water temporarily. to a point on a drainage or river system. that increases attractiveness or value, Beneft cost ratio (BCR) Can be divided into sub-catchments. especially of a piece of real estate or a The net present value divided by the costs geographic location. (normally the capital and operational CIRIA The Construction Industry Research and Anaerobic costs). Information Association. An absence of oxygen Biodiversity Combined sewer Anthropogenic soil profle The diversity of plant and animal life in a A sewer designed to carry foul sewage and Where the upper profle of soil is changed particular habitat. surface runoff in the same pipe. by human intervention and activity. Bioretention area Contaminated ground Appraisal period A depressed landscaping area that collects Ground that contains substances that, The agreed time over which the costs and runoff and percolates it through the soil when present in suffcient quantities or benefts are assessed and then discounted. below the area into an underdrain; this helps remove pollution. concentrations, can have detrimental Attenuation effects on the surrounding area. An intervention to reduce peak fow and Blue infrastructure Control structures increase the duration of a fow event. Describes all waterways, both natural and man-made, in and around towns and cities. Components of a SuDS scheme which Attenuation tank control the rate at which water fows along A vessel which retains excess water and BREEAM and out of the system. slowly releases it in a controlled discharge The Building Research Establishment’s Conventional drainage to a combined drain or watercourse. Environmental Assessment Method. It sets best practice standards for the The traditional method of draining surface Base fow environmental performance of buildings. water using subsurface pipes to remove The normal level of subsurface water. water as quickly as possible. Brownfeld site Basin Conveyance
140 Appendices Movement of water from one location Detention pond/tank Environment to another. A pond or tank that has a lower Both the natural environment (air, land, outfow than infow. Often used to water resources, plant and animal life) and Depositional environment prevent fooding. the habitats in which they live. Describes the combination of physical, chemical and biological processes Diffuse pollution Erosion associated with sediment. Pollution arising from land use activities The group of natural processes, including (urban and rural) that are dispersed across weathering, dissolution, abrasion, Design codes a catchment, or sub-catchment. This is corrosion, and transportation, by Detailed guidance to infuence the designs different from process effuent, municipal which material is worn away from the of building and public realm; may be sewage effuent, or an effuent discharge earth’s surface. enforced as a planning condition. from farm buildings. Evapotranspiration Design criteria Drain London The process by which the earth’s surface A set of standards agreed by the developer, London Mayoral programme which helps or soil loses moisture by evaporation of planners and regulators that the proposed to predict and manage surface water food water and by uptake and then transpiration system should satisfy. risk in London. from plants.
Designing for exceedance EA Everyday events An approach that aims to manage The Environment Agency. Events with a return period of less than exceedance fows during periods of heavy one year (100% chance of occurring in any rainfall, eg, the use of car parks during Ecology one year). extreme events. All living things – such as trees, fowering plants, insects, birds and mammals – and Exceedance Detention basin the habitats in which they live. When heavy or extreme rainfall causes a A vegetated depression that is normally fow that is greater than the capacity of dry except following storm events. Ecosystem the drainage system. Constructed to store water temporarily to A biological community and its attenuate fows. May allow infltration of physical environment. Extreme events water to the ground. Events of greater than 30 year return Ecosystem services period (3.3% chance of occurring in any The resources and processes that are one year). Can often lead to major fooding supplied by natural ecosystems. with substantial damage.
141 Appendices Filter drain Geocellular structure degree of retention, attenuation and A linear drain consisting of a trench flled A plastic box structure used in the ground, treatment of rainwater, and promotes with a permeable material, often with a often to attenuate runoff. evapotranspiration. Sometimes referred to perforated pipe in the base of the trench as a green, blue or brown roof. to assist drainage. Geographical information A system designed to capture, store, Green space Filter strip manipulate, analyse, manage and present The ‘green lungs’ of towns and cities, land A vegetated area of gently sloping ground, data about the planet’s natural and man that is that is wholly or partly covered with designed to drain water evenly off made features. vegetation. impermeable areas and to flter out silt and other particulates. Geotechnical survey Grey infrastructure Information on the physical properties of Sometimes referred to as hard or Filtration soil and rock. traditional infrastructure, are man-made, The act of removing sediment or other engineered components of a system such particles from a fuid by passing it through Green corridor as drains and gutters. a flter. A strip of land in an urban area that allows wildlife to move along it and can support Groundwater Flora habitats. Typically includes cuttings, Water that is below the surface of the The plants found in a particular embankments, roadside grass verges, rights ground in the saturation zone. physical environment. of way, rivers and canal banks. Gully pots Flow paths Green infrastructure Part of a surface water drainage system; The course rain water takes naturally. A network of green spaces, trees and large containers that remove solids green roofs that is planned, designed from runoff. Forebay and managed to provide a range of A small pool located upstream of a larger benefts including amenity, healthy living, Habitat body of water, designed to act as a buffer, biodiversity enhancement and ecological The area or environment where an trapping sediment and silt resilience (natural capital). organism or ecological community normally lives or occurs. Interception forebay Living roof A small basin or pond upstream of the A roof with plants growing on its surface, main drainage component which traps which contributes to local biodiversity. sediment. The vegetated surface provides a
142 Appendices Heat island Impermeable Micropool Describes urban built up areas that are A material that does not allow liquids or Pool at the outlet to a pond or wetland signifcantly warmer than surrounding rural gases to pass through it. that is permanently wet and improves the areas. pollutant removal of the system. Impermeable surface Highways Agency A surface that does not allow water to Mini-Hollands The government agency responsible pass through it, thus generating a surface TfL programme to transform three outer for strategic highways in England, ie, water runoff after rainfall. London boroughs (Enfeld, Kingston & motorways and trunk roads. This function Waltham Forest) to prioritise walking and is devolved to Transport Scotland, Infltration (to the ground) cycling while improving the quality of the Department of Economy and Transport The passage of surface water into urban realm. in Wales and the Northern Ireland the ground. Roads Service. Monetised costs & benefts Infltration basin These are easy to understand and measure Highways authority A dry basin designed to promote fnancially, eg, the price of A local authority with responsibility for infltration of surface water to land or reduced damage (tangible) costs to the maintenance and drainage of highways the ground. property. maintainable at public expense. Inundation Monitoring plan Hydrodynamic vortex An overwhelming amount of water Sets out the approach, timing and Storm water management device that uses resulting in a food. resources to monitor measures adopted. cyclonic separation to control water pollution. It uses fow-through Linear assets Multifunctional space structures with a settling or separation Linear infrastructure such as pipes, roads, An area that has more than one use, one unit to remove sediment from surface rail, canals, etc. being to manage surface water. water runoff. LUL National Standards for Hydrology London Underground Limited. Sustainable Drainage The branch of science concerned with A regulatory document providing the properties of the earth’s water, Media standards and guidance on the design, and especially its movement in relation Natural topsoils, subsoils and construction and maintenance of SuDS to land. manufactured soils. for approval and adoption by the SuDS Approval Body.
143 Appendices Natural capital The road or car park surface and Pluvial fooding Natural assets which include geology, soil, underlying structure, usually asphalt, Flooding that results from high intensity, air, water and all living things within an concrete or block paving. Note: the path extreme rainfall-generated surface ecosystem. next the road for pedestrians is the water fow. ‘footway’ (the UK colloquial term being Net present value (NPV) 'pavement'). Pollution The difference between the discounted A change in the physical, chemical, costs and benefts over the appraisal period. Percentage runoff radiological, or biological quality of a The proportion of rainfall that runs off resource (air, water or land) caused by NOx PM a surface. man’s activities that is injurious to existing, Oxides of nitrogen particulate matter, intended or potential uses of the resource. especially atmospheric pollutants as a Permeability result of fuel combustion. A measure of the ease that fuid can fow Pond through a porous medium. It depends on Permanently wet depression designed Opportunistic retroftting the physical properties of the medium, eg, to retain storm water above the Where the opportunity to retroft storm grain size, porosity and pore shape. permanent pool and permit settlement of water management arises on the back of suspended solids and biological removal of other drivers, such as regeneration or small Permeable pavement pollutants. scale improvements. These may occur A permeable surface that is paved and within a neighbourhood, or locally on a drains through voids between solid parts Porosity plot level. of the pavement. The percentage of void space in a material. Orifce control chamber Permeable surface A chamber within a drainage system which A surface that is formed of material that Porous paving controls discharge rates. is impervious to water but, by virtue of Surfacing material that contains voids, voids formed through the surface, allows allowing water to pass through it. Pathway infltration of water to the sub-base through The route by which potential contaminants the pattern of voids, eg, concrete block paving. Potable/mains water may reach targets or by which water (and Water company/utility/authority drinking pollutants) are conveyed either below or Phytoremediation water supply. above ground. Use of living plants to clean up soil, air, and water contaminated with Pavement hazardous chemicals.
144 Appendices Prevention Rainwater harvesting or rainwater Risk assessment Site design and management to stop or use system A carefully considered judgment requiring reduce the occurrence of pollution of A system that collects rainwater from where an evaluation of the consequences that impermeable surfaces; to also lower it falls, rather than allowing it to drain away. may arise from the hazards identifed, the volume of runoff, by reducing It includes water that is collected within combining the various factors contributing impermeable areas. the boundaries of a property, from roofs to the risk and then evaluating their and surrounding surfaces. signifcance. Public sewer A sewer that is vested and maintained by Receptor Runnel the sewerage undertaker (see s 219(1) of the A location that is subject to an impact, A small river channel or course. Water industry Act 1991). either through fooding or pollution. Certain types of measures can be Runoff Quietways retroftted at such locations. Water fow over the ground surface to the Proposed network of radial and orbital drainage system. This occurs if the ground cycle routes through London, linking key Recharge is impermeable, saturated or if rainfall is destinations via direct back-street routes, The addition of water to the groundwater particularly intense. through parks, along waterways or tree- system by natural or artifcial processes. lined streets. Soakaway Retention pond A subsurface structure that surface water Rain garden A pond where runoff is detained long is conveyed into, designed to promote A planted basin designed to collect and enough to allow settlement and biological infltration. treat surface water runoff. treatment of some pollutants. Source control Rain meadow Rill The control of runoff at or near A feld or drainage reserve that is capable A shallow channel or watercourse. its source. of fooding to absorb excess rainfall. Risk Stockholm soil Rainwater butt The chance of an adverse event. The Soil made from angular rock, specifed soil Small scale garden water storage device effects of a risk is the combination of the mix and water. that collects rainwater from the roof via probability of that potential hazard being the drainpipe. realised, the severity of the outcome if it is, and the numbers of people exposed to the hazard.
145 Appendices Storm events Surface water Waste Events occurring between one in a year Water that appears on the land surface, Any substance or object that the holder (100% chance of occurring in any one year) ie, lakes, rivers, streams, standing water discards, intends to discard, or is required and one in 30 years return period (3.3% and ponds. to discard. chance of occurring in any one year). These events are typically what urban drainage Swale Water Framework Directive (WFD) systems (below ground) are designed up A shallow vegetated channel designed to European Community Directive (2000/60/ to, and at which fooding occurs. conduct and retain water, but may also EC) of the European Parliament and Council, permit infltration. The vegetation is able designed to integrate the way water bodies Strategic Flood Risk Assessment (SFRA) to flter particulate matter. Treatment are managed across Europe. It required all Provides information on areas at risk from improving the quality of water by physical, inland and coastal waters to reach ‘good all sources of fooding. The SFRA should chemical and/or biological means. status’ by 2015, through a catchment-based form the basis for food risk management system of River Basin Management plans, decisions and provides the basis from which SWM incorporating measures to improve the to apply the sequential text and exception Storm water management. status of all natural water bodies. test (as defned in CLG, 2010) in development allocation and development control process. TfL Watercourse Transport for London. All rivers, streams, ditches, drains, cuts, Sub-catchment culverts, dykes, sluices and passages that A division of a catchment, to allow TLRN water fows through. runoff to be managed as near to the Transport for London Road Network. source as is reasonable. Water table Topographical survey The point where the surface of groundwater SuDS Used to identify and map the contours of can be detected. The water table may Sustainable drainage systems; a sequence the ground and show all natural and man- change with the seasons and annual rainfall. of management practices and control made features on the surface of the earth or structures designed to drain surface water slightly above or below the earth’s surface. Wetland in a more sustainable fashion than some Flooded area where the water is shallow Treatment stage conventional techniques. enough to enable the growth of bottom- A component of a sustainable drainage rooted plants. SuDS management train system that improves the quality of the The management of runoff in stages as water passing through it. it drains from a site. This is CIRIA’s preferred term.
146 Appendices Team
The guidance has been produced by Kevin Reid, Greater London Authority J & L Gibbons with Civic Engineers, Robert Bray Associates, Tim O’Hare Associates, George Warren, London Borough DWD and Jackson Coles for Transport for of Hammersmith and Fulham London (TfL). A steering group provided support, with representatives from Editing: TfL, Robin Buckle and appropriate parts of TfL and the George Weeks following external stakeholders: Additionally, we are grateful to Nick Ayling, Thames Water, Paul Shaffer and Suzanne Simmons from CIRIA for their advice and Owen Davies, Royal Borough support on this project. of Greenwich
Dave Hobbs, Environment Agency
Peter Massini, Greater London Authority
Neil Monaghan, Environment Agency
147 Appendices Photo credits
All photographs and graphics by J & L Gibbons, except:
6 CIRIA C753 The SuDS Manual, 2015 CIRIA 8 Surface water fooding Robin Buckle 10 Amenity: community planting Jess Bastock 19 The Geology of London All London Green Grid, GiGL 22 Exposed Chalk Creative Commons licence 24 Waltham Forest Mini-Holland Robin Buckle 28 Accessible environments TfL 35 Museum of London (x2) University of East London 39 Streatham Hill (all) Owen Davies 41 Reedworth Street (x2) Ann Bodkin 44 Dry swale Robert Bray Associates 45 Bioretention swale (x2) Camlins 57 Permeable pavnig x2 Atkins 58 Permeable pavnig x2 Marshalls 59 Hard detention basin Urbanstein 60 Detention basin George Weeks 77 Love the Lea campaign Thames 21 77 Priory Common after installation Robert Bray Associates 78 Conveyance of water through the scheme Robert Bray Associates 79 No disruption to service during construction TfL 79 400m2 swale under construction TfL
148 Appendices Photo credits
80 Swale sections TfL 82 Kenmont Gardens (all) George Warren 83 Derbyshire Street Pocket Park Greysmith Associates 85 Renfrew Close Robert Bray Associates 89 Rectory Gardens Robert Bray Associates 90 Rectory Gardens Robert Bray Associates 92 Talgarth Road George Warren 95 Queen Caroline Estate (x2) Groundwork 96 Queen Caroline Estate (x2) Groundwork 97 Bridget Joyce Square, Australia Road George Warren 98 Bridget Joyce Square, Australia Road George Warren 102 Hackbridge x2 Civic Engineers Goldhawk Road George Warren 103 Tree pit details Robert Bray Associates 104 Plan showing modular soil system Robert Bray Associates 104 Completed scheme George Warren 106 Firs Farm Wetlands (all) Graham Campbell 107 Roadside swale at The Spinney Thames 21
149 Appendices Photo credits
108 All Robert Bray Associates 113 After Installation TfL 114 Programme of monitoring TfL 114 Early green roof growth within 6 months TfL 115 Permeable paving and tree planting Simon Bunn 116 Completed residential unit Tim Crocker 117 Wildfower seeded joints Anders Folkesson 118 Threshold detail Anders Folkesson 118 SuDS pond acting as a central recreational feature Anders Folkesson 120 Overview of completed scheme Urbanstein 120 Detention basin Urbanstein 120 Catchment areas Urbanstein 128 Design process diagram CIRIA 130 Combined sewer discharge TfL 135 Nine Elms Linear Park Camlins
150 Appendices