Suds a5 Booklet Final 080408

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Sustainable

Drainage Systems (SUDS)A guide for developers


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We are the Environment Agency. Its our job to look afteryour environment and make it a better place for you, andfor future generations.

Your environment is the air you breathe, the water youdrink and the ground you walk on. Working with business,Government and society as a whole, we are making yourenvironment cleaner and healthier.

The Environment Agency out there, making your

environment a better place.

Published by:

Environment AgencyRio HouseWaterside Drive, Aztec WestAlmondsbury, Bristol BS32 4UDTel: 0870 8506506Email: [email protected]

Environment Agency

All rights reserved. This document may be reproduced withprior permission of the Environment Agency.


3/12A guide for developers 1

The problem

Development can harm our water resources if a traditional approach todrainage is adopted. Removing water from the site as quickly as possiblecauses a range of impacts:

Surface water run-off

increased downstream ood

risk as a result of the run-offfrom roofs and paved areas.This also causes sudden risesin ow rates and water levelsin local watercourses.

rainwater diverted to pipedsystems reduces the amount ofwater soaking into the ground.As a result, ground water levelsfall and dry weather ows inwatercourses are reduced;

surface water run-off cancontain contaminants such asoil, organic matter and toxicmetals. Although often at low

levels, cumulatively they canresult in poor water quality inrivers and streams, adverselyaffecting biodiversity andamenity value. After heavy rain,the rst ush of water throughthe drainage system is oftenhighly polluting;

As a result, many urbanwatercourses are lifeless andunattractive, and are often hiddenin culverts under the ground.Some pollution arising from urbanrun-off may be unavoidable, and

water treatment at every outfallis impractical. But SustainableDrainage Systems (SUDS) cansignicantly reduce the harm to ourwater resources, and improve thequality of our built environments,by moderating ows and lteringrun-off.


4/122 Sustainable Drainage Systems

Towards sustainabledevelopmentSustainable Drainage Systems(SUDS) are designed with threeobjectives in mind:

to control the quantity and rateof run-off from a development;

to improve the quality of therun-off;

to enhance the natureconservation, landscape andamenity value of the site and itssurroundings.

SUDS deal with run-off as close toits source as possible and balanceall three objectives, rather thanfocussing only on ood prevention.

Implementing SUDS contributessignicantly towards achieving

sustainable development.In recognition of this, LocalPlans increasingly state that allapplicants should, in the rstinstance, incorporate SUDS intodevelopment proposals.

SUDS - the benets

Implementing SUDS may leadto cost savings, for example, by

avoiding or reducing the need for: gully pots; surface water sewers; piped connections to

distant outfalls.

SUDS can be cost-effectivelydesigned to work with retained

natural features such as ditchesor ponds, and to form an integralpart of hard and soft landscapedareas. In this way, they cancontribute towards an attractivescheme that enhances the natureconservation and amenity valueof the development, while also

making the best use of the valuablewater resource.



SUDS and the

planning processSUDS include tried-and-testedtechniques that are alreadybeing implemented on a rangeof projects in the United Kingdomand Europe. They incorporatecost-effective techniques that areapplicable to any development

scheme. These range from smalldevelopments to major residential,leisure, commercial or industrialoperations with large areas ofhardstanding and roof. They canalso be successfully retro-tted toexisting developments. PlanningPolicy Statement 25 for England

on Development and Flood Riskemphasises the role of SUDS andintroduces a general presumptionthat they will be used. SUDSare being incorporated in otherplanning policies as they arerevised.

As with other key considerationsin the planning process - transport,landscape, heritage and natureconservation - incorporating SUDSneeds to be considered early inthe site evaluation and planningprocess, as well as at the detaileddesign stage.

Many planning authorities will

expect planning applications,whether outline or detailed,to demonstrate how a moresustainable approach todrainage is to be incorporatedinto development proposals,and for detailed designinformation to be submitted at

the appropriate stage. Planningauthorities may use planningconditions to secure theimplementation of SUDS.

Adoption and futuremaintenance

The arrangements for adoption andfuture maintenance of the systemshould be considered during theearly stages of design. This is likelyto inuence the design just as muchas technical considerations.It is recommended that maintenanceshould be the responsibility of a

publicly accountable body. Thiswill often call for the paymentof a commuted sum or a legalagreement, possibly backed upby the deposit of a nancial bond.The adopting organisation willprobably wish to approve thedesign before construction.



Sustainable DrainageSystems (SUDS)

Sustainable drainage is a design philosophy that uses a rangeof techniques to manage surface water as close to its sourceas possible. To produce a workable and effective scheme, SUDS

must be incorporated into the development at the earliestsite-planning stage.

Permeable pavements

The need for surface water drains

and off-site sewers can be reducedor eliminated where run-off isencouraged to ow through porouspavements made from materialslike concrete blocks, crushed stoneor porous asphalt. Dependingon the ground conditions, thewater may inltrate directly

into the subsoil or be stored inan underground reservoir (forexample, a crushed stone layer)

before slowly soaking into the

ground. If inltration is not possibleor appropriate (for example,because of ground contamination),an impermeable membrane canbe used with an overow to keepthe pavement free from water inall conditions. Pollutant removaloccurs either within the surfacing

or sub-base material itself, or bythe ltering action of the reservoiror subsoil.



These can be created as featureswithin the landscaped areas of thesite, or they can be incorporatedinto ornamental, amenity andscreen-planted areas where theywould be looked after as part ofthe normal maintenance contract.They provide temporary storagefor storm water, reduce peakows to receiving waters andfacilitate the ltration of pollutants(deposited and incorporated into

the substrate). They also encouragemicrobial decomposition andallow water inltration directly intothe ground. Swales and basinsare often installed as part of adrainage network connecting to apond or wetland, prior to dischargeto a natural watercourse. Theymay be installed alongside roadsto replace conventional kerbs,therefore saving construction andmaintenance costs.

Swales and basins

Other techniques which reduce owrates and improve water qualityinclude green roofs and rainwaterreuse. Green roofs can reducepeak ow and the total volumedischarged and improve water

quality. In addition, theycan improve insulation and

increase the lifespan of the roof.Rainwater reuse (or harvesting)involves the collection of therainwater on site and its use asa substitute for mains water, forexample, in watering a garden

or ushing toilets.

Green roofs and rainwater reuse



Inltration trenches are stone-lledreservoirs to which stormwaterrun-off is directed, and from whichthe water gradually inltrates intothe ground. Their longevity is

enhanced by incorporating a lterstrip, gully or sump pit to removeexcessive solids at the inow.Filter drains (sometimes knownas French Drains) are widely usedby highway authorities. They aresimilar to inltration trenches

with a perforated pipe whichcarries ow along the trench. Thisenables the storage, ltering andsome inltration of water passingfrom the source to the discharge

point. Pollutants are removed byabsorption, ltering and microbialdecomposition in the surroundingsoil. Systems can be designedto successfully incorporate bothinltration and lter systems.

Inltration trenches and lter drains

SUDS can be very effective on browneld sites. But the use of inltration-based solutions requires careful thought where there is a risk ofenvironmental damage from land contamination. The focus must be toavoid mobilisation of contaminants.

SUDS on browneld sites



Although these can be designedas wet or dry ponds, or wetlands,they are most likely to contributeto visual amenity and biodiversitywhere they include a permanentwater body. Ponds or wetlandscan be designed to accommodateconsiderable variations in waterlevels during storms, therebyenhancing ood-storage capacity.

The level of solids removal can besignicant when enough time fordetention is allowed. The algaeand plants of wetlands provide aparticularly good level of lteringand nutrient removal. Ponds andwetlands can be fed by swales,lter drains or piped systems, andthe use of silt traps will help tomanage sedimentation.

Ponds and wetlands

Ponds or wetlands can be designed to accommodateconsiderable variations in water levels during storms,thereby enhancing ood-storage capacity.



SUDS during constructionThe early implementation ofappropriate SUDS techniquescan prevent the pollution ofwatercourses during construction.

Choosing the right

SUDS systemThe choice of SUDS system willdepend on a number of factors:

the pollutants present in run-off;

the size of and drainage strategyfor the catchment area;

the hydrology of the area and

inltration rate of the soil; the presence of Groundwater

Source Protection Zones orcontaminated land.

Large-scale ponds and wetlandsare generally more appropriate forsites larger than 5ha. Inltration

trenches, swales, lter strips andporous pavements are suitablefor both large and small sites. Thebest drainage solution for a sitewill often incorporate a mix ofmechanisms.

Soil permeability andhydrology

Soil permeability can have asignicant effect on selecting theright SUDS techniques for a site.

Inltration techniques may not beeffective if the inltration rate isbelow 10mm/hr for the upper soillayers. Swales and ponds, workingby a combination of ltration andinltration, are more tolerant ofpoor soils. In highly permeablesoils, wet ponds need to be lined.Near old mine workings, SUDS

must be designed to avoid linkingto underground workings.

It is important, therefore, fordevelopers to establish the soilconditions and hydrology of theirsite at an early stage in the site-planning process. The results of

such investigations should beprovided to the planning authorityas background to the proposals fora drainage system included withthe planning application.


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Acknowledgements

Oxfordshire County Council for the photograph on page 4

Further information

Sustainable Drainage Systems an introductionEnvironment Agency

SUDS Manual C697, CIRIA ISBN 978 0 86017 697 8

Tel: 020 7549 3300Also see CIRIA website on SUDS: www.ciria.org/suds

Designs that hold water Sustainable Urban Drainage

Systems explained, a 25-minute DVD or videoEnvironment Agency/SEPA

Environment Agency Internet address:www.environment-agency.gov.uk/suds

For further information about Groundwater Source ProtectionZones, call us on 08708 506 506


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Environment rst: This publication is printed on paper made from 100-per-centpreviously used waste. By-products from making the pulp and paper are used forcomposting and fertiliser, for making cement and for generating energy.

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Would you like to nd out more about

us, or about your environment?

Then call us on08708 506 506 (Mon-Fri 8-6)

[email protected]

or visit our website

www.environment-agency.gov.ukincident hotline 0800 80 70 60 (24hrs)oodline 0845 988 1188

Suds a5 Booklet Final 080408

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