Non Statutory Technical Standards For Sustainable Drainage .

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NON-STATUTORYTECHNICAL STANDARDSFOR SUSTAINABLEDRAINAGEPractice Guidance

ContentsBackground1Introduction2Process for delivering sustainable drainage4Introduction4Pre Application Discussions5Matters to be discussed6Planning Applications9Statutory Consultations10Non-Statutory Consultations10Conditions and Planning Obligations11Non-Statutory Technical Standards12Introduction12Runoff Destinations14Flood Risk Outside Development16Peak Flow Control17Volume Control19Flood Risk Within Development20Structural Integrity22Designs for Maintenance Considerations23Construction25Appendix A26Appendix B27Non-Statutory Technical Standards for Sustainable Drainage: Practice Guidance

BackgroundSince February 2013 Defra facilitated Task and Finish Groups to provide definition for planning ofdevelopment with respect to surface water management. These groups considered technical andregulatory matters.Defra then established an industry-wide stakeholder group incorporating local authorities, developmentindustry, sewerage undertakers, Highways Agency, Environment Agency (EA) and Water UK to furtherdefine and clarify proposed technical standards in relation to Government’s implementationof sustainable drainage policy.A Steering Group was made up of members of the Task and Finish Groups which has focused on thedevelopment of the practice guidance to provide an interpretation of the non-statutory technical standards.Steering Group members:Bronwyn BuntineOwen DaviesNick HumphreyAndrew LeadbetterKent County CouncilRoyal Borough of GreenwichCamden Borough CouncilPeterborough City CouncilJohn RumbleHertfordshire County CouncilBava SathanSurrey County CouncilKevin TidyMark WelshJohnathan GlerumBracknell Forest CouncilLincolnshire County CouncilAnglian Water ServicesBrian MorrowUnited UtilitiesPaul VodenHouse Builders AssociationRay FarrowHome Builders FederationStephen WielebskiHome Builders FederationNon-Statutory Technical Standards for Sustainable Drainage: Practice Guidance1

Introduction1.1. The Minister announced on 18 December 2014 that sustainable drainagewould be delivered through the planning system. This relies on the NationalPlanning Policy Framework, Planning Practice Guidance and Non-statutoryTechnical Standards (technical standards) for sustainable drainage systems,produced and issued by Government.1.2. Planning applications for major development should therefore be accompaniedby a site-specific drainage strategy or statement that demonstrates that thedrainage scheme proposed is in compliance with the NPPF and the Nonstatutorytechnical standards. The NPPF (and associated PPG) relates toGovernment policy on the provision and long term maintenance of sustainabledrainage systems. The technical standards provided by Government relate tothe design, construction, operation and maintenance of sustainable drainagesystems (SuDS) and have been published as guidance for those designing schemes.1.3. This guidance supports the technical standard in question, and provides a briefexplanation to provide clarification. It will be reviewed periodically to reflect best practice.1.4. Although sustainable drainage systems can be utilised to deliver water quality,amenity, biodiversity and landscape, the technical standards do not considerthese matters which are addressed through planning policy. Water qualityconsiderations are covered by the National Planning Policy Framework (NPPF)and biodiversity, amenity and landscape may be found in local planning policy.1.5. Drainage should be considered as an integral part of the land acquisition duediligence process, that is early in the development planning and designprocess, along with other key considerations such as: LayoutDensitySite accessTopographyGround conditionsDischarge destinations1.6. It is easier and more cost effective to incorporate sustainable drainage systemsalong with landscape design from the earliest stages of planning adevelopment. Even for small developments (one or two houses), cost effectivedrainage solutions are best achieved by integrating components into the overallsite design.1.7. The technical standards and guidance were developed by a multi-stakeholdergroup representing Lead Local Flood Authorities, HBF, HBA and Water andNon-Statutory Technical Standards for Sustainable Drainage: Practice Guidance2

Sewerage Companies facilitated by Defra. The standards relate specifically tothe design, construction, operation and maintenance of sustainable drainagesystems and have been published as guidance to those designing schemes.1.8. This practice document is not intended to define the full technical detailand justification for drainage applications. This information is provided in otherdocuments, which are clearly referenced and annotated in this guide.1.9. This guidance document is presented as practice, a “living” documentand therefore will be reviewed annually based upon feedback received fromstakeholders. Comments should be submitted via the LASOO forum onKnowledge Hub.1.10. The imposition of any standard(s) above those now defined by Government, namely S1 to S14inclusive, will need to be evidence based, viability tested and subjected to public consultation before it canbe imposed as local plan policy that has the required weight to be regarded as a material planningconsideration. This is a matter for the Local Planning Authority.Non-Statutory Technical Standards for Sustainable Drainage: Practice Guidance3

Process for deliveringsustainable drainageIntroduction2.1. It is essential that the consideration of sustainable drainage takes place at theland acquisition due diligence stage and that this feeds in to the design process.Drainage information then informs any planning application.2.2. By adopting the principle of ‘working from the whole to part’ and consideringall aspects of the site and the proposed development, this should ensure that themost cost effective, well designed sustainable surface water drainage system isdelivered without compromising project viability.“Delivery of sustainable drainage is different, not difficult”Illustrative Planning Full applicationS106 where orif appropriateConditionsReserved mattersNOTE: Dashed links indicate the optional parts of the processNon-Statutory Technical Standards for Sustainable Drainage: Practice Guidance4

Pre-application discussions2.3. It is highly recommended that pre-application discussions take place before submittingan application to the local planning authority. Ideally, these discussions should start at the landacquisition due diligence stage and continue as part of the pre-planning application process.2.4. The more issues that can be resolved at pre-application stage, the greater the benefits.For their role in the planning system to be effective and positive, statutory planning consulteeswill need to take the same early, pro active approach, and provide advice in a timely mannerthroughout the development process. This assists local planning authorities in issuing timelydecisions, helping to ensure that applicants do not experience unnecessary delays and costs.2.5. At pre-application stage, the applicant should enter into discussions with: The Local Planning Authority (LPA), with respect to Local Plan requirements for SuDSincluding biodiversity, ecology, water quality, open space, maintenance and landscapewhich may impact sustainable drainage delivery; and, The Lead Local Flood Authority (LLFA), with respect to local flood risk and ordinarywatercourses taking into account the technical standards.2.6. The participation of other consenting bodies in pre-application discussionsshould enable early consideration of all the fundamental issues relating towhether a particular development will be acceptable in principle, even whereother consents relating to how a development is built or operated are needed ata later stage. These other agencies or bodies include, but are not limited to: Environment AgencyInternal Drainage BoardCanal and River TrustHighway Authority, andRelevant sewerage undertaker only where a connection to a public sewer is proposed2.7. The applicant should collect all available information pertaining to the site,which may affect the manner in which a drainage solution is proposed. Thisinformation may facilitate pre-application discussions and could include: Strategic flood risk assessmentLocal flood risk management strategySurface water management plansSurface water flood risk mapsLocal flood historyFlood defence asset information2.8. The Local Planning Authority may offer a multi-disciplinary approach to preapplicationdiscussion, which addresses matters collectively.Non-Statutory Technical Standards for Sustainable Drainage: Practice Guidance5

Matters to be discussed2.9. Each development is individual, and pre-application discussions which look atthe particular site, its surroundings and constraints will help to ensure that whenthe application is made, relevant information is submitted to enable the localplanning authority to determine the application.2.10. It is not possible to produce an exhaustive list of issues that may need to bediscussed, however the following are principal matters which will generallyneed to be considered as part of the pre-application process, for example whensubmitting an outline planning application: Existing topography - how water naturally flows on and/or through thesite, including land drainage flows in general Hydrogeology (i.e. groundwater considerations) – consideration to begiven to groundwater levels and the transient nature of groundwater Proposed land re-grading/earthworks which may affect natural and/or proposed drainage Proposed site remediation/de-contamination works and any proposalsunder consideration for soil improvement, i.e. lime, cement stabilisation Constraints on and off the site Phased, one-off or cumulative development Proposed destination(s) for surface water post-development and any possible constraints Surface water storage volumes and locations Permissible or allowable peak flow rate Existing or proposed watercourses, and potential capacity limitationsincluding third party consents to discharge Existing or proposed surface water sewers and/or pumping stations Flood risk to and from the site with proposed mitigation Offsite works which may be required to provide surface water drainage Temporary drainage during construction Presence of any sensitive receptors, e.g. SPZ or sensitive off-site thirdparty assets Existing and proposed highways Future maintenance and possible adoption arrangements as required in the NPPF Consents required Possible designation of flood features by the LLFA/EA How the Planning Practice Guidance (PPG) and technical standards will influence the design Possible conditions or planning obligations Environmental and ecological considerationsNon-Statutory Technical Standards for Sustainable Drainage: Practice Guidance6

2.11. If the pre-application discussions are to lead to a full planning application being made,the following additional issues may also need to be considered, particularly with regard to meetingthe technical standards: Surface water storage volumes and locations, Sub-catchment areas If appropriate, treatment train components Proposed landscaping and/or vegetative systems Design calculations for:- greenfield run-off- brownfield run-off- infiltration rates where required- peak flow rates- surface water volume(s)- attenuation/storage requirements- drain down times Multi-use areas Exceedance routes Temporary drainage during construction Climate change allowances Future development allowances, if appropriate2.12. Relevant questions to ask during the pre-application discussion are:a. Location of the final discharge destination in relation to the hierarchy of discharge.Has this been considered?b. If the surface water infiltrates to the ground have discussions taken place with the EAand/or sewerage undertaker in relation to pollution risk to any underlying aquifers?Have such proposals been considered alongside the agreed/approved remediationstrategy for the site? What is the risk of infiltration drainage mobilising relict contaminantsin an otherwise benign environment? Reference should be made to relevant infiltrationmapping e.g. British Geological Survey (BGS) maps and EA monitoring data.c. If the surface water discharges to a water body, have discussions taken place on theconsent or rights to discharge?d. If the surface water discharge is to a sewer or highway drain, have discussions takenplace with the appropriate sewerage undertaker and Highways Authority?e. There may be a number of constraints within or outside of the development that mayhave an impact on the SuDS scheme which could include; issues around soil geology,topography, ground water, remediation etc. Have all these issues been identified?Non-Statutory Technical Standards for Sustainable Drainage: Practice Guidance7

f. Have all the drainage components/connectivity of the system been determined withinthe development and outside the development?g. Are there any off site issues for the surface water discharge? Have these been considered?(e.g. access across third party land, or offsite works to proposed destinations).h. As part of the development and the SuDS scheme are there any environmental or ecologicalissues that need to be considered? (e.g. water quality or biodiversity issues).i. Will the SuDS scheme require phasing?j. Are there any cumulative effects from development to be taken into account?k. The topography of a development is an important factor of the SuDS scheme, is thereany substantial re-grading of the development which will affect the SuDS scheme?l. What is the anticipated development programme for the site?m. Are there any temporary arrangements that you are aware of for the drainage that needsto be discussed?n. Have discussions taken place with the Highways Authority around the interaction of managingthe surface water?o. Have discussions taken place regarding how the planning practice guidance and technicalstandards will influence the design?p. Have matters surrounding accessibility and future maintenance been incorporated into the design?q. Has the need for a maintenance plan been considered, which takes into account the drainagedesign and components being proposed?r. What conditions or planning obligations may be required?s. Will there be any flood risk features which will require designation?(Note: the likely range of questions will vary depending upon whether the preapplicationdiscussions are intended to lead to an outline or full planning application being made).Non-Statutory Technical Standards for Sustainable Drainage: Practice Guidance8

Planning Applications2.13. Planning applications may be made either as an Outline application with one or morematters reserved for later determination, or as a Full 4. The level of information which would need to be submitted for each type of application or stagewithin the planning process will vary depending on the size of the development, flood risk, constraints,proposed sustainable drainage system and so on as shown in the table below:333Flood Risk Assessment/Statement (checklist)333Drainage Strategy/Statement & sketchlayout plan (checklist)Document submitted3Preliminary layout drawings3Preliminary “Outline” hydraulic calculations3Preliminary landscape proposals3Ground investigation report (for infiltration)3Evidence of third party agreement for discharge to theirsystem (in principle/ consent to discharge)333Maintenance program and on-goingmaintenance responsibilities33333Detailed flood & drainage design drawings333Full Structural, hydraulic & ground investigations333Geotechnical factual and interpretive reports,including infiltration results333Detailed landscaping details333Discharge agreements (temporary and permanent)333Development Management & ConstructionPhasing PlanDetailed development layoutAdditional information may be required under specific site conditionsor development proposals.Non-Statutory Technical Standards for Sustainable Drainage: Practice Guidance9

2.15. Whether the application is an outline or full application, the surface water drainagefor the application is determined at the time when the application itself is determined.2.16. Following an outline application, reserve matters must be consistent with thedrainage strategy which was approved.2.17. For a full application it would usually be necessary for a fully detailed drainagedesign or strategy to be submitted for consideration by the LPA and to be subject to commentby the statutory consultees or others that the LPA may wish to consult.2.18. The drainage strategy may include a Flood Risk Assessment, but in somecircumstances a fully detailed design does not form part of a flood risk assessment.Statutory Consultations2.19. The Lead local Flood Authority is the statutory consultee for Major development withsurface water drainage. However, local arrangements may exist between the LPA and theLead Local Flood Authority (LLFA) with regard to providing advice/comments on Minor development.2.20. The Environment Agency is the statutory consultee, as stated in the:Development Management Procedure Order 2015 for:Development involving the carrying out of works or operations in thebed of, or within 20 metres of the top of a bank of, a main river whichhas been notified to the local planning authority by the EnvironmentAgency as a main river for the purposes of this provisionDevelopment, other than minor development, which is to be carried out on land:(i) in an area within Flood Zone 2 or Flood Zone 3; or(ii) in an area within Flood Zone 1 which has critical drainage problems andwhich has been notified to the local planning authority by the Environment AgencyNon-Statutory Consultations2.21. It would be normal if discharging to a drainage system maintained/operated by otherauthorities (IDBs, highway authority, sewerage undertaker, or Canals and River Trust) thatevidence of consultation and the acceptability of any discharge to their system is presentedfor consideration by the LLFA and LPA.Non-Statutory Technical Standards for Sustainable Drainage: Practice Guidance10

Conditions and Planning Obligations2.22. The granting of approval for an outline or full application may result in conditionsand/or reserve matters being attached.2.23. These conditions may address the drainage design and its integration withlayout, landscaping, maintenance, compliance with the technical standards, etc.2.24. The statutory consultees may wish to recommend conditions for the LPA to consider,but they will be a matter for the LPA to determine whether they are appropriate.2.25. In some circumstances it may be that planning obligations via a Section 106 agreementmay be used in lieu of conditions. Conditions associated with drainage and flooding cannot be“deemed to be discharged” and must be reviewed and approved prior to discharge.Non-Statutory Technical Standards for Sustainable Drainage: Practice Guidance11

Non-statutory technical standardsIntroduction to delivering sustainable drainage3.1. The layout of the development site and the drainage system should bedesigned to mimic natural drainage flow paths, utilising existing natural lowlyingareas and conveyance pathways where appropriate.3.2. Where development results in changes in natural flow paths and runoffdestinations, the design must account for how the surface flows are managedand demonstrate it does not impact on off-site flood risk.3.3. Exceedance flows that cannot be contained within the drainage system must bemanaged via flood conveyance routes. If the proposed system connects to anexisting drainage system, whether it is a sewer, highway drain, water body orsustainable drainage system, consideration must be given to the operationa

Non-Statutory Technical Standards for Sustainable Drainage: Practice Guidance 2 Introduction 1.1. The Minister announced on 18 December 2014 that sustainable drainage would be delivered through the planning system. This relies on the National Planning Policy Framework, Planning Practice Guidance and Non-statutory

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