SUSTAINABLEDRAINAGE IN LEEDS

Supplementary Guidance No. 22

JULY 2004

This guidance provides information for developers on theuse of sustainable drainage techniques in newdevelopments. It expands current City Council policy andGovernment guidance and sets out a procedure fordealing with drainage issues through the planningprocess. It is not intended to provide detailed technicaldesign advice. The guidance is relevant for alldevelopments where buildings and/or hard surfaces willcreate surface water runoff.

Rain falling on buildings and hard surfaces cannotinfiltrate into the ground so it needs to be drainedartificially in order to prevent problems of localisedflooding. The traditional method of dealing with surfacewater has been to pipe it away from developments anddischarge it to the sewerage system or nearbywatercourses. This has implications for water quality, theecology and amenity of watercourses, including canals,and downstream flooding.

It is predicted that climate change, as a result of humanactivity, will result in increased rainfall in the UK as wellas an increase in the frequency of intense rainfall events.This is likely to exacerbate flooding problems.

Sustainable drainage systems provide an alternative tothe traditional approach. Sustainable drainage seeks tomimic more natural drainage processes by allowingrainfall to soak into the ground where possible or bydelaying discharges. This reduces both the volume andrate of surface water runoff to sewers and watercourses.

BACKGROUNDBACKGROUND

Flooding at Ring Road,Wortley, Leeds

Flooding at Ring Road,Wortley, Leeds

The Leeds Unitary Development Plan (UDP) encouragesdevelopment that fulfils the fundamental requirement ofsustainability. This is reflected in Strategic Goal 4:

~ to ensure that development is consistent with theprinciples of sustainable development.

Planning permission considerations are covered bygeneral policy 5 (GP5).

The Leeds UDP Review: first and Revised Deposit -propose policy N39A:

~ Development proposals should, wherever practicable,incorporate sustainable drainage systems.

The Sustainable Development Design Guide(Supplementary Guidance No. 10) includes a sectionon Protecting Water Resources (refer to Appendix B).

Planning Policy Guidance Note 1 General Policy andPrinciples identifies sustainable development as a keyobjective for the planning system.

Planning Policy Guidance Note 25 Development andFlood Risk provides guidance on the promotion ofsustainable drainage systems through the planningsystem. Paragraphs 40 - 42 and Appendix E areparticularly relevant. Appendix E paragraph E14 listsessential considerations early in the planning anddesign stages:

~ Integration of sustainable drainage systems into theoverall site concept and layout;

~ The need for investigation and subsequentremediation of contaminated land;

~ Agreements on adoption, maintenance andoperation of the systems; and

~ The need for monitoring long term performance.

The Building Regulations require that adequate surfacewater drainage is provided. Approved Document Hincludes a priority for soakaways or other infiltrationsystems over drainage to watercourses or sewers.

POLICY CONTEXT

The traditional method of piping surface water awayfrom a development is efficient in preventing localisedflooding on a site but it does cause significantenvironmental and amenity problems. These include:

~ Downstream flooding. Rapid drainage of water fromurban areas can result in flooding elsewhere in thebeck or river catchment.

~ Erosion of watercourses. Artificially high flows canresult in bank erosion which can be detrimental toproperty and the amenity and ecology ofwatercourses.

~ Pollution of watercourses. Surface water runoff cancontain a range of pollutants including oil, silt,organic matter and heavy metals. Householders oftenwrongly connect washing machines and dishwashersto the surface water system which will add detergentsand other agents. All of this has an adverse impact onaquatic plants and animals.

~ Overload of combined sewer systems causingoverflows of foul effluent to watercourses. As well asbeing a health hazard this can also have an adverseimpact on flora and fauna and public amenity.

~ Reduced groundwater recharge. Large areas ofimpermeable surfaces prevent rainwater infiltration.This tends to affect the level of the natural water tableand can have an adverse impact on trees and othervegetation in the immediate area. It can also lead tolow base flows in watercourses as the natural processof infiltration and drainage to the watercourse isdisrupted.

~ Detrimental effects on navigable waterways. Somewatercourses and drains discharge into inlandwaterways and excess flows can cause pollution andundesirable currents, making navigation unsafe.

CONVENTIONAL DRAINAGE SYSTEMS

Combined sewer outfall entering Wyke Beck, Leeds

High flow in River Aire,Leeds City Centre

Surface Water Management Train Source: Environment Agency

Permeable pavingSource: Environment Agency

SUSTAINABLE DRAINAGE SYSTEMSSustainable drainage systems are designed to address

the problems associated with conventional drainagesystems by controlling both the quantity and quality ofsurface water as close to its source as possible. Theremay also be other benefits of sustainable drainageincluding reduced costs (the need for gullies, drains andextensive piped networks can be reduced or eliminated)and habitat creation (features such as well designed wetbalancing ponds and wetlands can provide valuablewildlife habitats). The Leeds Biodiversity Action Planincludes a great crested newt species action plan whichpromotes the creation of ponds of value for wildlife,especially as part of sustainable drainage initiatives.

A range of sustainable drainage techniques are availableand more than one technique may often be appropriateat a given site. It is good practice to select according tothe following hierarchy in order to achieve reductions inthe total volume of runoff as well as reductions in the rateof runoff.

~ 1. preventative measures - these include rainwatercollection and use for toilet flushing, garden andlandscape watering and other uses. A simpleexample is a water butt but more sophisticatedsystems are available to collect roof water and useit to supplement mains water. As well as reducingthe amount of surface water runoff to be dealt withthere are environmental and economic benefits ofreduced demand for mains water. 'Green'(vegetated) roofs can also reduce runoff.

~ 2. permeable surfaces - these are hard or softsurface treatments which allow water to infiltrate tothe underlying subsoil. Permeable hard surfacesare becoming more readily available commercially.

~ 3. filter strips and swales - these vegetated landscapefeatures collect water from impermeable surfacesand allow it to soak into the ground.

Permeable paving atHawthorn Park, Leeds

Permeable paving at residential development -near Wetherby

~ 4. infiltration devices - structures which drain waterdirectly into the ground. These can be used atsource or the run-off may be conveyed to theinfiltration area in a pipe or swale.

~ 5. detention techniques – basins, ponds, wetlandsand other structures designed to hold water whenit rains and then release it in a controlled mannerto a conventional surface water drainage system.

Infiltration techniques are dependent on the suitability ofsoil conditions. Where surface water is discharged to asewer or watercourse oil and silt separators will berequired as appropriate.

The Construction Industry Research and InformationAssociation (CIRIA) publishes useful guidance includingSustainable Urban Drainage Systems - a design manualfor England and Wales (CIRIA Report 522) andSustainable Urban Drainage Systems Best PracticeHandbook (CIRIA Report 523). Detailed design adviceshould always be sought from qualified and experienceddrainage engineers. In addition, advice regardingsustainable drainage for new developments should alsobe sought from the City Council at an early stage.

The selection of techniques should include considerationof the impact on, and potential benefits to, otherelements of the development. Professional input shouldbe sought (for example from landscape architects,highway engineers and ecologists) to optimise the widerbenefits for the project at an early stage.

Drainage concepts for a site should be agreed inprinciple as early as possible in the planning approvalprocess in order to ensure that sustainable drainagefeatures can be incorporated in the development wherepracticable.

Surface water drainage is a material consideration whendetermining planning applications. Early consideration ofsustainable drainage in the development process isimportant as there may be implications for landpurchase, design concepts and site layout. Conversely itcan be very difficult to incorporate sustainable drainagefeatures if detailed consideration is not given to drainageissues until after the basic concepts of the developmenthave become fixed.

Developers are advised to discuss drainage issues withthe City Council at the pre-application stage. Resolvingdrainage issues at this stage will help to speed decisionmaking when an application is submitted.

In accordance with Council policy and Governmentguidance Leeds City Council will seek to incorporatesustainable drainage systems for significantdevelopments and will encourage sustainable drainagesystems for all other developments.

Early investigation is essential to ensure that the impactof any land contamination on drainage is dealt withcorrectly.

An Indicative Drainage Strategy for the site should besubmitted with outline planning applications. Forsignificant developments a Drainage ImpactAssessment will also be required at this stage (a checklistindicating the minimum information required is includedas Appendix A).

SUSTAINABLE DRAINAGE AND PLANNING APPLICATIONS

Swale Source: Environment Agency

Swale at Refuse CollectionAgency Depot, Leeds

Significant developments are all developments except:

~ individual householder applications

~ developments of less than ten new dwellings (unless asensitive area identified by the Council may beaffected)

~ non-householder extensions under 100 square metres

~ changes to use not involving new buildings on hardsurfacing

~ developments which are part of a larger developmentfor which a Drainage Impact assessment has beenaccepted.

A detailed drainage design will be required with reservedmatters or full planning applications.

A planning application must demonstrate that a viabledrainage strategy is proposed. If it is intended thatdrainage should be to a public sewer then the specificsewer should be identified.

Where drainage details are subject to a planningcondition Planning Services will consult Land Drainageofficers on the adequacy of the design of proposeddrainage systems in order to ensure that they are inaccordance with sustainable drainage best managementpractices. The full impact of proposals on other elementsof the development, such as greenspace and existingtrees, should be demonstrated.

National Building Regulations (Approved Document H)also has an influence on the positioning and designcriteria of drainage infrastructure. Planning Servicesofficers will liaise with Building Standards regarding thesuitability of connections to the drainage system anddischarges in relation to ground conditions.

Swale at the Eden Project,Cornwall

SoakawaySource: Environment Agency

Unlike traditional piped drainage systems there iscurrently no guidance on who should be responsible forthe operation and maintenance of sustainable drainagefeatures.

The City Council will insist on clear-cut provisions for thefuture maintenance of all on-site drainage infrastructure.Future management arrangements may be required inrespect of both on and off site features to ensure futuremaintenance.

Building Regulations (2000) Approved Document H.

CIRIA (2000) Sustainable Urban Drainage Systems:Design Manual for England and Wales. Report C522.

CIRIA (2001) Sustainable Urban Drainage SystemsBest Practice Manual. Report 523.

DETR (2001) Planning Policy Guidance (PPG) 25 –Development and Flood Risk

Leeds City Council (1998) Sustainable DevelopmentDesign Guide. Supplementary Guidance No. 10.

Leeds City Council (2001) Unitary Development Plan

Leeds City Council (2003) Unitary Development PlanReview: First Deposit

Leeds City Council (2004) Unitary Development PlanReview: Revised Deposit

National SUDS Working Group (2003) Framework forSustainable Drainage Systems (SUDS) in England and Wales

Scottish Environmental Protection Agency, EnvironmentAgency & Environment and Heritage Service SustainableUrban Drainage Systems: An Introduction

FUTURE MAINTENANCE REFERENCES

Balancing pondSource: Environment Agency

Balancing pond at Thorpe ParkBusness Park, Leeds

Construction Industry Research & InformationAssociationwww.ciria.org.uk

Environment Agencywww.environment-agency.gov.uk

Leeds City Councilwww.leeds.gov.uk Drainage pages

Office of the Deputy Prime Minister (PPG25)www.odpm.gov.uk

Scottish Environment Protection Agencywww.sepa.org.uk/guidance/urban-drainage/index.htm

Development Department Planning ServicesThe Leonardo Building2 Rossington StreetLEEDSLS2 8HD

Tel: 0113 147 8000Fax: 0113 247 4117Email: planning@leeds.gov.uk

Development Department Land Drainage TeamRing RoadMiddletonLEEDSLS10 4AX

Tel: 0113 247 8790Fax: 0113 247 4117

USEFUL WEBSITES CONTACTS

Balancing pond at the David Lloyd Centre, Leeds

Green roof at residential developmentin Chapel Allerton, Leeds

APPENDIX A PLANNING APPLICATIONS - DRAINAGE EF

Permeable paving for residential

development in Leeds

Permeable paving Source: Environment Agency

Significant developments are all developments except:

identified by the Council may be affected)

FECTIVENESS AND IMPACT ASSESSMENT PROCEDURE

PROTECTING WATER RESOURSES

UDP Policies: N39 culverting and canalisation ofwatercourses

The impact on the water environment should be aconsideration at the site identification stage. Thisincludes impacts on water quality, protecting the floodcapacity of watercourses and protecting features such asponds and wetlands.

The site layout should seek to minimise impacts on thewater environment by reducing the quantity andimproving the quality of surface water run off. Developerswill be expected to make provision for the long termmanagement of water conservation measures.

NB: Illustrative guide only. Each site should beconsidered individually. A combination of measures may be used.

APPENDIX B ~ EXTRACT FROM SUSTAINABLE DEVELOP

AREA SERVED (HECTARE)<2 2-4 4-7 7-9 9-15 >15

Dry extended detention pond ? Wet extended detention pond ? Wet pond ? Infiltration trench ? Infiltration basin ? ? Porous pavement ? ? Grassed swale ? Filter strip ?

KEY Feasible? Marginal - needs careful design

Not feasible

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MENT DESIGN GUIDEThe following guidelines should be considered:

~ the culverting and canalisation of watercourses shouldbe avoided wherever possible, and opportunities to re-establish natural watercourses, channels, margins andwetlands should be maximised;

~ the amount of non-porous hard surfacing should beminimised to enable infiltration;

~ downstream watercourses should be protected fromthe adverse effects of excess surface water run-off,both in quantity and quality;

~ landscape areas should incorporate such features asswales and filter strips to reduce the volume of pipedsurface water run off;

~ infiltration methods, such as soakaways, should beused wherever possible and where soil conditionspermit;

~ where surface water cannot be absorbed on siteprovision should be made for open balancing ponds(NB. These should be designed to maximise theirwildlife value);

~ where site drainage is to a combined sewer the impactof any increased flow on combined sewer overflowsshould be considered and minimised;

~ install oil interceptors and silt traps to improve thequality of any surface water discharge to watercoursesand/or soakaways;

~ provide facilities for rainwater collection for re-use;

~ where possible, site landscaping should utilise plantspecies which do not require a lot of water.

Roadside swale

ENVIRONMENT AGENCY (EA)The EA is a statutory consultee regarding any planningapplication and it is the relevant land drainage operatingauthority for main rivers, which in Leeds are the riversAire and Wharfe, Collingham Beck, Cock Beck andOulton beck. The EA may advise that sustainabledrainage principles be used in connection with anysignificant development in order to protect againstflooding and pollution on a catchment wide scale.However, it is unlikely to have detailed knowledgeregarding the potential effects of surface water run-offon local non-main river streams and becks, for which therelevant land drainage operating authority in Leeds is theCity Council.

The EA is also unlikely to have sufficient resources tocheck developers' drainage proposals in detail to ensurethat they comply with sustainable drainage bestmanagement practice.

The legal basis of water pollution control in England andWales is the Water Resources Act 1991 (as amended).The regulation of the quality of surface water dischargesis a discretionary power, and the EA seeks instead toencourage the adoption of good practice (through theplanning process) so that most discharges need not besubject to a formal discharge consent regarding thequality of the discharge, which in most cases it would beimpracticable for the Agency to police. There is nomechanism by which the EA can restrict the quantity ofsurface water discharges and this must be achievedthrough planning conditions, as emphasised by PPG25.Surface water discharges to soakaways are not subject toa formal discharge consent.

APPENDIX C ~ ROLES OF RELEVANT AGENCIES

Floodied beck in Leeds

LAND DRAINAGE AUTHORITYThe flood defence operating authority for all non-mainriver watercourses in Leeds (with the exception of a smallarea in north east Leeds which comes under MarstonMoor and North Wharfe Internal Drainage Boards) is theCity Council, these functions being administered by theDevelopment Department, Land Drainage Team. Thereare some 500 km of non-main river watercourse withinthe Leeds district compared with 100 km of main river.

The Land Drainage Team has detailed knowledge of thecondition of and possible local effects on thesewatercourses of proposed surface water discharges. Theyhave undertaken some detailed studies of the conditionand capacity of watercourses and are responsible fordeveloping sustainable drainage policies for everycatchment in Leeds.

They advise Planning Services on the restrictions whichshould be placed on surface water discharges inplanning conditions and scrutinise developers' detaileddrainage plans and designs to ensure that they complywith sustainable drainage best management practices.They are also able to advise on a suitable point ofconnection to the watercourse system, the need for workson the receiving watercourse and therefore fordevelopers to be required to contribute to those works.

The Land Drainage Team also controls the culverting ofnon-main river watercourses (note that the consent of theEnvironment Agency is also required for culverting thesewatercourses).

BUILDING STANDARDSNational Building Regulations lay down technicalrequirements for below ground drainage systems andtheir discharge to a suitable point of disposal. BuildingStandards officers can also provide advice on localground conditions.

SEWERAGE UNDERTAKERYorkshire Water is a consultee to the planning process. Itcan advise on the adequacy of the existing sewerageinfrastructure, which can be a material considerationunder PPG23 and PPG12 (paragraph 6.15).

Yorkshire Water may impose a limitation on the flowwhich can be discharged to existing sewers. Sustainabledrainage techniques can be helpful in enablingcompliance with such restrictions.

Yorkshire Water will be happy to discuss sustainabledrainage proposals with the developer. Tel. 0113 2354154.

HIGHWAY AUTHORITYThe City Council as Highway Authority is responsible foragreeing the design of roads to be constructed inconnection with new developments and adopted by theauthority under Section 38 of the Highways Act. The useof sustainable drainage techniques needs to beconsidered in relation to the provision of highway surfacewater drainage, which may utilise a common surfacewater drainage system with the rest of the development.

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