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Outline Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates are fully considered. and may require additionalinformation to ensure that allaspectsofthedesign Outline Designbridgesthegapbetween Concept DesignandDetailed Concept Designto meettherequirements oftheLPA andLLFA. Outline Designstage isanopportunityfor theSuDS designerto develop the 8.0 ■ scenarios. flexible to cater for different development The approach to OutlineDesigncanbe planning 8.1 ■ ■ ■ ■ ■ changes. Outline Designconfirming agreed recommendations incorporated into on theConcept Design,with expect apre-application discussion, based development isproposed theLPA would Where alarge orcomplicated must bedemonstrated. combined butthesame designprocess Concept andOutlinedesignmay be For smallerandsimpler developments acceptable outlet. effectively onsite anddischarged to an demonstrate runoffcanbemanaged be presented with flow route analysis to detailed desktop survey ofthesite must access to the site isnotpossible, a On speculative submissions, where full OutlineDesignfor Outline Design Design andPlanningStage 2– ■ ■ ■ ■ ■ ■ The outlinedesign hasdeveloped theconcept additional treatment. manage additionalvolumes andprovide there willusuallybeasecond feature to provides high water qualitytreatment, collect runoff, where thepavement Unless permeablepavement isusedto the managementtrain. hydrocarbon pollutionat thebeginningof control to remove silt,heavy metalsand All sites shoulddemonstrate source ‘treatment stage’ isacceptable. approach’ isappropriate, thenthe demonstrates that the‘simple index the riskscreening (SuDS Manualp571) on low andmedium riskdevelopment. If ‘treatment stage’ approach isacceptable A simpleassessment of riskusingthe proposals to demonstrate how thescheme works andwhat itwilllooklike whenbuilt. Extract from OutlineDesignfor Holyoaks school, Robert Bray Associates. Facing: Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ ■ process. gathered aspartoftheOutlineDesign revisions to layout andadditionalinformation Concept Designstage, withany subsequent aspects oftheSuDS designintroduced at The SuDS OutlineDesignwillconfirm key 8.3 What OutlineDesignshoulddemonstrate of theOutlineDesignprocess to confirm with and additionalinformation gathered aspart account comments at pre-application stage introduced inConcept Designtakinginto SuDS OutlineDesignbuildsontheideas Outline Design 8.2 Objectives ofSuDS ■ ■ ■ the site andhow thesite willfunction the designwillshow theappearance of Route analysis the layout reflects theModifiedFlow SuDS constraints andopportunitiesrelating to appropriate response to site conditions, ■ ■ ■ ■

practically andat reasonable cost. that confirms itcanbe constructed the designwillbedeveloped to astage management train into site layout control andtheintegration of how runoffiscollected, theuseofsource

the LPA andLLFA. the SuDS schemeislikely to beapproved by of anoutlineplanningapplication to confirm An OutlineDesignmay besubmitted aspart detailed design. development priorto investment infull successfully integrated into thewider more certainty how theSuDS willbe demonstrating thefollowing: well asthepracticality ofthedesignby appearance andcharacter oftheSuDS as function, thescale, depth,relative levels, Outline Designwillconfirm how theSuDS will

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Outline Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ design: to evaluate site constraints andinform SuDS The following information shouldbecollated the site at OutlineDesign. augmented to provide afullunderstanding of Concept DesignStage andmust be Limited information may beavailable at ■ ■ 8.3.1 ■ ■ ■ and placement ofSuDS features. depth. These caninfluence layout, depth Existing services, includinglocation and of materials. choice ofSuDS components andtheuse ‘conservation areas’, whichmay influence Planning conditions, for example SuDS in and especiallyHighways Departments. typically adoptionby Local Authorities SuDS willinfluence component selection, Ownership andfuture managementof Information to supportOutlineDesign condition. arrangements would besubjectto aplanning Confirmation of ownership andmaintenance ■ ■ ■ ■ the site. sewer andimpactofrunoffvolumes on infiltration orrunoff to a watercourse or Confirmation ofthemethoddischarge: elements oftheSuDS. Consents affecting off-site andon-site A biodiversity raingarden at Renfrew Close, Newham withcornfield annualsalongside meadow flora for thefuture. The designer shoulddemonstrate Amenity The designershoulddemonstrate Quality The designershouldconfirm Quantity 8.4 Designcriteria considerations Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ and safe ‘by design’ the site isgenerally accessible to people – legibility using thesite andmaintenance personnel the SuDS isunderstandable to people pollution riskalongthemanagementtrain sufficient treatment is available to manage interception losses requirements there are sufficientSuDS surfaces to meet flow control locations sub-catchment design surface contributing area ofimpermeablehard being usedto managevolumes whether Approach 1orApproach 2is runoff site orwhetherrainfall willbemanagedas whether infiltration isappropriate for the ■ ■ ■ ■ ■ ■ ■ ■

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construction. how runoffcould bemanagedduring how spillagecould bemanaged creep. allowances for climate changeandurban outside thesite are exceeded orflows are generated from exceedance routing whendesignvolumes location overflow arrangements from each storage volumes to appropriate flow rates storage locations andapproximate management. providing aSuDS functionfor rainfall functional andcanbe usedwhennot spaces andconnecting routes are multi- enhance thedevelopment the visualcharacter oftheSuDS will

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Outline Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates 8.5.1 8.5 HealthandSafety by design a way that isacceptable to thecommunity. whilst managingany real orperceived riskin a designapproach that celebrates water not oneofriskelimination butofdeveloping The issue ofHealthandSafety istherefore water inthelandscape. and most peoplelike to seeandexperience for itsvisual,recreational andwildlife value Water hasincreasingly become appreciated importance. occupies inoureveryday lives anditscultural It isimportantto consider theplace water presence ofopenwater that isaconcern. with any landscapedesign,itisusuallythe associated withSuDS features, asthere are Although there are anumberofrisks ■ The designershoulddemonstrate Biodiversity ■ ■ ■ using theprincipleofsource control possible alongthemanagementtrain confirm that water iscleanassoon to ensure habitat connectivity and thenonwards to thewiderlandscape, the endofSuDS managementtrain surface asitflows from thebeginning to demonstrate water iskept at ornearthe The place ofwater inthelandscape ■ ■ ■ ■ maintenance. enhance habitat development during confirm ‘managementpractices’ to corridor creation ofhabitats withintheSuDS demonstrate ecological designandthe strikes), highways, sewers etc. 5. 4. 3. 2. 1. theriskofdrowning be identified: A numberofrisksassociated withSuDS can 8.5.2 AspectsofHealthandSafety inSuDS Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates infrastructure issues –aircraft (bird risk oftoxicity risk ofdisease slip andtriphazard

underwater level benchbefore deeperwater. gentle slopeinto thewater andanother wet benchat permanentwater level: another a gentleslope, max1:3down to thewater: a A flat drybench at theedgeof structure: sequence; and outofthefeature safely inthedesign where thedesignallows apersonto walk into wetlands andbasinsisagoodexample of The designofthewater edgeto ponds, safety perspective. the designconsidered from thehealthand accessible to people, witheachelementof that allpartsofaSuDS designshouldbefully approach to ‘HealthandSafety by Design’is the DetailDesignsectionbutgeneral This issue isconsidered ingreater detailin

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Outline Design 8.7 8.6 Affordability recreational space. space e.g. courtyards, play basinsand can beincorporated into multifunctional e.g. apondorwetland, many SuDS features dedicated SuDS components are appropriate Although there willbesituations where everyday management. with SuDS components integrated into the ‘passive maintenance’ shouldbeconsidered by design.Wherever possible theideaof The future maintenance ofSuDS isinfluenced Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates cost oftheprofile construction ismarginally a replacement for impermeablesurfaces. The design istheuseofpermeablepavement as A goodexample ofcost effective SuDS design. savings are onlyrealised through goodSuDS compared to conventional drainage butcost SuDS components are cost effective when suburban layout. quality thanasimpleSuDS designfor a require adifferent approach to thevisual An urbanrenewal project inthecitywill functionality ofthescheme. component isto theappearance and of development andhow importanteach The designofSuDS isinfluenced by thetype Well designedSuDS are not ‘land hungry’inthat they can beintegrated into bothhard and soft landspace spaces whichare available withindevelopment. Making SuDS cost effective Management oftheSuDS resource reinforces therequirement to consider SuDS layout at Concept Designstage. Design Note : structures. checking inlets,outletsandcontrol obligation cansometimesbereduced to just This reduced dedicated maintenance management. allocated to site care rather thanSuDS Wherever possible maintenance shouldbe design. the ‘rain garden’ or‘bioretention’ elementin contribute to landscapeinfrastructure e.g. In otherlocations aSuDS feature can considered. engineering profiles that have to be considerations ofdrainage, surfacing and pavement demonstrates thewider Completing acost comparison for permeable of maintenance into thefuture. confirmed by aflow control anda low level provides 30%void storage whichis interceptors. The opengraded sub-base storage andinsomesituations oil work, gullies,manhole, dedicated SuDS more expensive butavoids extensive pipe susdrain.org/resources/evidence.html SuDS canbefound here: http://www. Evidence for thecost effectiveness of Additional information to inform evaluation ofthescheme: ■ ■ ■ ■ ■ ■ ■ ■ Authority SuDS Officer Organisation) Practical Guidance Information recommended intheLASOO (Local 8.8.2 OutlineDesign–information checklist cannot beconveyed onplan. Statement presenting allinformation that infrastructure together withaSuDS Design plan form, confirming site layout andSuDS The designinformation shouldbeprovided in information includedat that stage. Design hasbeenprovided andthelevel of stage willdependonwhetheraConcept The information required at OutlineDesign 8.8.1 8.8 Outlineinformation required for SuDS evaluation Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ ■ ■ ■ ■ ■ ■ watercourses orsewer locations existing utilities planconfirming existing appropriate infiltration investigation results where via infiltration orrunoff destination anddischarge route ofrainfall analysis topographical information andflow route landscape proposals the planwillincorporate preliminary Outline DesignPlan–layout Outline DesignStrategy Statement of criticalelements Flood RiskAssessment (FRA)–areview ■ ■ ■ ■ ■ ■ since Concept DesignStage. confirm any additionalinformation provided scheme willlooklike, how itwillfunctionand The OutlineSuDS Designwillshow what the

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requirements for potential replacement. design life ofany products usedand general maintenance principles offsite works that may berequired appropriate e.g. SSSIs sensitive receptors for runoff where principle. consent to discharge oragreement in evidence ofthird partyagreement for ground investigation review

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Outline Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates 8.8.3 Designchecklist ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ is at ornearthesurface type ofrunoffcollection to ensure runoff source control typeandlocation series –extent andexpected criticallevels management train –SuDS components in control locations sub-catchment boundarieswithflow storage locations, extent andcriticallevels An earlyexample (2004)of integrated SuDS designwithpermeablepavement collecting, cleaningandstoring rainfall intheupperSuDS sub-catchment. Springhill Cohousing Stroud, RobertBray Associates. ■ ■ ■ ■ ■ ■ ■ ■ manageability –maintenance by design. design clean water, connectivity andhabitat biodiversity –opportunitiesfor wildlife, into site design development andhow SuDS isintegrated landscape character –thenature ofthe surface conveyance –ideally at ornearthe Facing: Australia Road,by theauthors. 67

Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates requirements oftheLPA. to discharge planningconditions, orreverved matters, dependinguponthe upon andwillbepresented witheitherthedetailedplanningapplication or Design stage willdemonstrate that theproject objectives canbedelivered The development andrefinement ofConcept andOutlinedesignsat Detailed runoff willhave beenevaluated anddefinedat earlierdesignstages. management train, selectionofSuDS features andgeneral meansofstoring The SuDS strategy willbereasonably fixed by DetailedDesignstage. The 9.0 ■ can: Failure ofindividualelementsthedesign benefits. effective mannerthat provides wider controlled anddischarged from site inan is collected, conveyed, cleaned,stored, Competent design detailsensure that runoff ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Groundbreaking project integrating SuDS into roadway withexciting planting,to asequence Grey to Green project, Sheffield City Council. flow rates invalidate expected storage volumes and prevent adequate treatment contribute to amenityuse negatively impactormiss opportunitiesto opportunities to supportbiodiversity create hazards to wildlife ormiss inconvenience to thepublic cause localponding,floodingand increase maintenance difficultyand cost. of landscape cells leadingto theRiver Don. the heartof Sheffield, replacing redundant Detailed Design Design andEvaluation Stage 3– 9.2 What Detailed Designshoulddemonstrate 9.1 Objectives ofDetailedDesign ■ ■ ■ ■ over-arching requirements asfollows: all theinfluencing factors ontheschemewith The SuDS DetailedDesignconsiders indetail ■ detailed designshould: and Outlinedesignstages. Outputsfrom the the agreed SuDS strategy from theConcept Detailed Designshoulddevelop andrefine Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ ■ ■ ■ confirm nomaterial changes to drainage strategy from that agreed withLPA at the Concept Schemes invariably evolve andchangefrom concept stage. The designershould therefore or Outlinedesignstages. Any materials changes shouldbediscussed andagreed withthe criteria components meetrespective design demonstrate that individualSuDS conditions in ‘day to day’ andalsoextreme that thesystem willfunctionasintended carefully consider allsite levels to ensure biodiversity through thesite where possible connectivity corridors for route(s) provides for extreme flows and demonstrate that themodifiedflow through thesite provides acontrolled flow ofclean water the useofSource Control techniques the schemewillappearandoperate LPA andLLFA afullunderstanding ofhow provide sufficientinformation to give the LPA prior to detaileddesignsubmission. Design Note :

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the adoptingbody. adoption meettherelevant standards of that SuDS whichare beingoffered for operatives andgeneral usersofthesite demonstrate safe designfor contractors, accord withlocallandscapecharacter materials andplantvarieties specified catchment andfinalsite discharge rates controlled flow rates for eachsub- climate changeandurbancreep, and attenuation volumes withallowances for proportionate analysis to confirm function passively. deliver schemeswhichare legibleand opportunities for amenityandbiodiversity confirm how theSuDS schememaximises and SuDS related planningpolicies NSTS alongwithLocal SuDS Standards meet therequirements for NPPFand 68 Design Detailed 69

Detailed Design 9.3 Typical DetailedDesignpackage Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ along withaddressing thefollowing: provided by thesite have beenmaximised and biodiversity andhow opportunities SuDS provisions onquantity, quality, amenity The SuDS DesignStatement shouldcover 9.3.1 SuDS DesignStatement assessment willalsoberequired. calculations, maintenance planandrisk drawings. Supportinginformation including design statement withaccompanying development andwillgenerally encompass a proportionate to thescaleof The DetailedDesignpackage shouldbe ■ ■ ■ loading requirements etc periods, discharge allowance, traffic with LPA. For example, rainfall return confirm drainage designcriteria agreed constraints highlight any othersignificantsite summarise thefindingsofFRAand ■ ■ ■ ■ ■ ■ consents. required, togetherwithanynecessary outline detailsofanyoffsiteworks in terms oftreatment andmanagement explain how SuDS willfunctionpassively climate resilience are dealtwith local objectives for sustainability including multi-functional useofSuDS space and local SuDS policies,requirements for outline how requirements ofNPPF, NSTS,

9.3.2 Drawing package the following: The SuDS drawing package shouldinclude Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates slowly to theRiver Moselle. infiltration basinsthat discharge clean water runoff through silt forebays andunderdrained A smallpublicparkthat collects polluted road Hornsey.Rectory Rainpark, Gardens Facing: drawings Design drawings information Design

Critical designlevels shouldbeidentifiedonall relevant drawings. included onotherdrawings. Planting arrangement andsurface treatment /materials drawings where detailednot drains; details to receiving watercourse /sewers /publicsurface water sewers /highway Construction Details–inlets,outlets,flow controls, storage, edgedetails, connection surrounding site level andproposed finishedfloor levels (where appropriate) Long sectionsandcross sectionsfor theproposed drainage system, including scale agreed) including aNorthdirection arrow. Detailed site layout at anidentifiedscale(1:200or1:500asappropriate orany other within definedsubcatcatchments. Drawing ofsite drainage catchment areas showing permeableandimpermeableareas and phasingwhere appropriate; boundaries, flow control locations, storage locations, contributing impermeablearea, Plan ofsite detailingflow routes including exceedance flow routes, subcatchment infrastructure andownership established Existing utilityservices drawing. Detailsofexisting site surface water drainage root protection zones (RPZ). [note :list isnotexhaustive] presence ofinvasive species,protected habitats, tree Protection Orders (TPO) and archaeological significance, poorground conditions, unexploded ordnance (UXO), areas offloodrisk(fluvial,pluvialand ground water), contaminated land, Coordinated constraints mapidentifyingallpotential designconstraints including Topographical survey ofthesite

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Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates The detaildesign stage confirms thelayout, character andfunction of Plan excerpt: proposed new Holyoaks PrimarySchool,Redditch. the SuDS, Includingdetailedlevels, volumes, flow controls and component design. ■ ■ ■ ■ ■ obtaining necessary consents: may needto beperformed alongwith various investigations, tests andcalculations Depending onthenature ofthescheme 9.3.3 Supportinginformation Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ ■ ■ ■ be required for works in,under, over or Agency) -anEnvironmental Permit may Environmental Permit (Environment in place (or canbeobtained): Confirmation that discharge consents are place (or canbeobtained). together withany necessary consents in Details ofany offsite works required, the LPA. information forms asmay beprovided by Completion ofstandard design appropriate. and underground storage structures as calculations for permeablepavements site includingallhydraulic andstructural compliance withthedesigncriteria for the Design calculations whichdemonstrate monitoring asappropriate. test results, soiltesting andgroundwater Ground investigation, includinginfiltration ■ ■ ■

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proposed for SuDS. Details ofany informative signage site useby public. operation by personnelandday to day consider construction, maintenance and Designers hazard andriskassessment- to or highway) land. private (curtilage) andpublic (open space proposed splitof theSuDS between all nonadopted drainage. Identifyany confirmed managementarrangements for Proposed maintenance scheduleand constraints. Board byelaws, comments and Local Authority andInlandDrainage Protection Zone areas orhigherrisksites; with EAfor Infiltration withinSource public sewer. Discussions shouldbeheld Undertaker for any connections to the (Highways Authority); orwithSewerage in anordinary watercourse; highway drain structure withthepotential to affect flows Watercourse Consent (LLFA) for any plain ofamainriver; Ordinary flood defence or for works intheflood river isinaculvert), works onorneara near amainriver (includingwhere the 72 Design Detailed

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Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates considerations for designandevaluation. The following tableprovides alist ofkey 9.3.4 DetailedDesignEvaluation Checklist details Drainage design levels drainage of site and consideration Detailed calculations Hydraulic discharge locations of method & Confirm standards Design Deliverable Key designpoints the site showing detailedlevels across Designer to present drawing points mightcompromise design. there are nolocations where low Levels are crucial–checkthat Section 9.5.10. Detailed checklist iscontained compaction during construction. will beprotected from Infiltration –outlinehow ground sewer /watercourse. on storage from thereceiving consider likelihood ofsurcharge made to awatercourse /sewer, Where positive discharge is biodiversity. for quantity, quality, amenityand standards have beenachieved Designers shouldconfirm how all flow controls designing protected outletsand Minimise riskofblockage by Key evaluation points areas. and lowest level ofcontributing comparing top level ofstorage, for eachsubcatchment, Sensibilty checkto beperformed complexity ofdrainage. scale ofdevelopment and should reflect theriskof failure, The level ofanalysis required assessed. brownfield sites hasbeen Review how infiltration on of infiltrating close to buildings. during construction. Review risk be protected from compaction confirmed andhow ground will groundwater table level hasbeen Infiltration – review how flood plainlevels/sewer invert. is stored relative to receiving Review thelevel at whichwater biodiversity requirements. rates. Confirm amenityand Confirm allowable attenuation watercourse /sewers connection detailsto receiving controls, storage, edgedetails, Review ofinlets,outlets,flow incorporated onacaseby casebasis. other aspectsfor checkingwhichmay be The CIRIASuDS ManualTable B.3provides to check LLFA LLFA LLFA LPA Responsibility LLFA

Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates arrangements Adoption Maintenance permits Consents & drawings design Landscape schedule design & Planting sections and cross Long sections assessment. hazard &risk Designers match volumes drawing calulations & hydraulic Deliverable Key designpoints which are notbeingadopted. all partsoftheSuDS scheme maintenance responsibilities for Confirmation of ownership and being offered for adoption. adopt aspectsofthescheme Confirmation of commitment to flow control locations. locations suchasoutletsand identifying key maintenance the maintenance regime and Key plan(1sideofA4)detailing defined at pre-app discussion. required consents may beinitially party access consent. The list of consents; offsite works &3rd Vary andcaninclude:discharge landscape design Integrate SuDS withinthewider planting requirements. Outline any SuDS specific how schemewillactuallylook allow proper understanding of exaggerated vertical scalesto Cross sectionsshouldnotuse use by public. personnel andday to day site maintenance /operation by To consider construction, clearly relate to calculations. references /annotations should requirements. Drawings to hydraulic analysis volumes provided andrefer back Drawings shouldconfirm Key evaluation points of propriety products. potential impactofreplacement the drainage. Consider the maintenance andoperation of are inplace for thelongterm Review that sufficientsafeguards maintenance where possible. Design achieves passive features are easilyaccessible. appropriate &proportionate and Maintenance type&cost is principle. in place orcanbeobtainedin Check that relevant consents are landscape quality. contributes to theoverall accessible, multifunctionaland Check that theSuDS network is invasive species. source to minimiseriskof Ensure plantsfrom accredited and depthsshown. Review ingeneral, sideslopes scheme. users andoperatives ofthe Demonstrate safe designfor meet hydraulic calculations. sufficient storage isprovided to performed to ensure that Sensibility checkto be to check Responsibility & WASC Highways &IDB WaSC & LPA, LLFA, LPA &LLFA WASC EA &IDB LPA &LLFA & LPA &LLFA LPA &LLFA LPA &LLFA LPA &LLFA LLFA

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Detailed Design 76 elegantly here. elegantly here. Note : Note Grey to Green project, Sheffield. project, Green to Grey and exceedance are demonstrated demonstrated are and exceedance of levels only - Liability for design is design only - Liability for of levels retained by the designer in all cases. by retained Areas contributing to a storage storage a to contributing Areas below not be situated should component flood may as they of storage level the top being filled. the storage prior to sloping, are that components storage For or linear pavements such as permeable should be storage basins, the ‘effective’ volume entire than the rather determined of the structure. should not identify levels of site A review along obstructions obvious any paths. flow exceedance The 3 flow control criteria: low flow, overflow overflow flow, low criteria: control 3 flow The The LLFA will carry out a high-level review review will carry out a high-level LLFA The ■ ■ ■ ■ ■ ■ The flow control invert level relative to relative level invert control flow The be should not control - the flow storage of the the base level above situated is a there unless component storage permanent or semi- for requirement permanent water. should demonstrate level overflow The is of storage volume the required that invert control the flow between contained level. and the overflow level ■ ■ Oxford City Council SuDS D & E Guide © 2018 McCloy Consulting & Robert Bray Associates Bray & Robert Consulting McCloy © 2018 D & E Guide SuDS City Council Oxford 9.4 Critical levels Critical 9.4 system drainage in any important are Levels SuDS. based surface so for and especially with should align levels surface proposed The providing in analysis route flow the modified storage and the site across path a flow by affected can be significantly volumes levels. inaccurate evaluated should be levels following The a design: or reviewing when developing ■ ■ Facing: Accurate levels were critical at Bewdley Bewdley critical at were levels Accurate Facing: Block. School Science 77 Detailed Design ■ Hydraulic calculations can: flow is controlled to leaving thesite. rainfall characteristics andtherate at which estimated usinginformation suchasthe local The storage volume required canbe sewer. into theground orinto awatercourse or stored itallows for acontrolled release either and elsewhere. Where runoffistemporarily which increases theriskoffloodingonsite Development causesanincrease inrunoff ■ 9.5.1 Objectives ofhydraulic calculations 9.5 Designingfor hydraulic requirements ■ calculation process: Designers shoulddemonstrate through the ■ Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates 9.5.2 What calculations shoulddemonstrate ■ ■ ■ ■ inform andvalidate theSuDS design design standards generated by thedevelopment to desired capacity to cater for theadditionalrunoff provide confidence that there issufficient elsewhere pose afloodriskwithinsite boundaryor generated from development willnot how therates andvolumes ofrunoff accounted for climate changeand urbancreep are that future impactsto runoffsuchas ■ ■ ■ ■ as transparency for evaluation. application withinthe designprocess aswell understandable format allows for easy Expressing calculation outputsinan ■ ■ ■ ■ prone to erosion. function hydraulically andwillnotbe provide confidence that SuDS will as potential for runofffrom off-site make allowance for unknown factors such development. causing unreasonable riskto humansor be managedwithinflow routes without blockage, orflows from offsite, they can such as;designexceedance, instances of where exceptional flows are experienced, processes have beenused that thecorrect calculation inputsand 9.5.3 Calculation processes ■ ■ assess: The calculations for SuDS designare usedto selected andthecalculation process used. will vary dependinguponhow inputsare experienced inreality. Calculation outputs always beviewed asestimates ofwhat is Calculations usedinSuDS designshould Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Calculation process Flow velocity check estimate Long term storage estimate. or infiltration storage Attenuation storage estimate brownfield sites greenfield and Runoff rates from ■ ■ controlled discharge rates (see 9.6) to allow infiltration or attenuation to the volume ofrunoffthat requires storage watercourse orsewer or controlled discharge rates to a appropriate discharge rates viainfiltration Purpose ofcalculationPurpose rainfall to allow settlementof silt. Low flow velocities for 1in year channels donotcauseerosion; Conveyance alongvegetated Flow velocity calculated to ensure: scenarios development andpost development volume ofrunoffbetween pre- Determining thedifference inthe of outflow. balanced against thecontrolled rate The runoffgenerated by thesite is Used to defineflow control rate following table: Calculation processes are summarisedinthe software packages. tools andavariety ofhydraulic modelling manual calculations, spreadsheets, online used to carryoutthecalculations including There are anumberofmethodsthat canbe ■ ■ ■ ■ flow velocities. to bemanaged(see 8.4.7) the long-term storage volume that needs

Main calculation inputs flow rates. surface type(roughness); proposed component gradient; component Component sectionalgeometry; proposed discharge rate(s). volume, losses provide by SuDS, soil characteristics; rain harvest impermeable area; infiltration rates; site impermeablearea; proposed site Local rainfall data; site area; existing discharge rate(s). infiltration rates; soilcharacteristics; climate andcreep adjustments; proposed site impermeablearea; Local rainfall data; site area; characteristics. Local rainfall data; site area; soil 78 Design Detailed

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Detailed Design 9.5.4 Calculation inputs values are consistent withFEH2013 data. designer must demonstrate that rainfall Where FSRrainfall values are usedthe recommended for use. up-to-date data availabale andtherefore FEH 2013 rainfall data isconsidered themost calculated. significant effect onthe volume of storage The choice ofrainfall data canhave a the key calculation inputs. return periodsandstorm durations isoneof Rainfall depthsandintensities for arange of 9.5.4.1 Rainfall data selection Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Company (WaSC). not beingadopted by aWater andSewerage acceptable by the LLFA where drainage is for paved areas would beconsidered Runoff coefficients of 0.95 for roofs and 0.9 1.0. impermeable areas whichequates to aCv of recommends assuming 100%runofffrom Sewers for adoption(SectionC5.1) contributing runoff to thestorage location. coefficient (Cv) for thetypesofsurfaces The designermust evaluate therunoff to beminimal. such asroofs orpaved areas are anticipated anticipated from hard development surfaces In extreme rainfall conditions thelosses 9.5.4.2 Definingrunoff coefficients (Cv) contribution withinattenuation calculations. to allow inputfor permeablesurface runoff The ‘UKSuDS’ website was recently updated this shouldbeconsidered withincalculations. surface contribution to SuDS storage, then Where areasonable amountofpermeable than 0.9 isusedfor calculations. The designermust justify where aCv ofless storage estimation calculations. These default values shouldnotbeusedfor surfaces. summer and16%winter losses from hard Winter) whichassume that there willbe25% ‘Default’ Cv values (0.75 Summer, 0.84 Some modellingsoftware packages contain online at fehweb.ceh.ac.uk FEH 2013 rainfall data canbesourced 9.5.4.3 Makingallowances for interception losses system. the attributes oftheproposed infiltration below ground level shouldseek to replicate The depthofwater anddepthoftest trench design. should berepresentative oftheproposed The specifiedinfiltration test methodology 9.5.4.4 Defininginfiltration rates by 5mm. calculations by reducing therainfall depths This loss canbeappliedwithinstorage make anallowance for interception losses. and hard surfaces) thenitisacceptable to 25% ofthedevelopment area (allbuildings area ofSuDS components equates to at least As aruleofthumb, where thetotal wetted Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Permeable blockandslabpaving withacentral grass detention basin provide afullyintegrated infiltrating SuDS scheme. be located closeto ground surface. pavement, rain gardens orbasinswhichwill infiltration isproposed from permeable 1.5m below ground level when shallow For example, tests shouldnotbeundertaken see SuDS ManualSection24.8 For more detailedanalysis methods

Bromsgrove CivicCentre re-development. 80 Design Detailed 81 Detailed Design ■ follows (see Section6.4.3.5): primary methodsfor controlling rates as equivalent greenfield runoff rates. There are 2 all sites (Greenfield andBrownfield) to LPAs require that SuDS attenuate runofffrom the FEHmethods. The IoH124 method hasbeensupersededby localised catchment isselected. define descriptors to ensure that asmall be taken whenselectingthecatchment to estimating Greenfield runoff rates. Care must FEH methodsare now preferred for and soilcharacteristics. hectare (l/s/ha) depending onlocalrainfall the region of2-7 litres persecond per Qmed /Qbarrates are anticipated to bein ■ 9.5.4.5 Defining attenuation flow control rates Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ NSTS S2,S3andS6 Regional mapsmay notberepresentative ofsite soilconditions andcalculation inputsmay year greenfield runoff rate. controlled to the1inyear and1in100 is controlled, therate ofoutflow is Approach 1-where thevolume ofrunoff rainfall events iscontrolled to Qbar/Qmed. is notcontrolled therate ofoutflow for all Approach 2-where thevolume ofrunoff have to beadjusted accordingly. Design Note: ■ ■ ■ different methodsare listed below: Further notes ontheapplication ofthe become more commonplace. accepted by theLLFA untilFEHmethods its common usageIoH124 values willbe method issimilarto FEHmethodsanddueto In most casesthevalue derived from IoH124 ■ ■ ■ (SuDS ManualTable 24.2) the Qbarrate usinggrowth curve factors. rates shouldbecalculated by factoring 1 inand100year Greenfield runoff of thesite. Where Approach 1isused, the input andthenfactored down to thesize Manual EQ.24.3) isbasedon50haarea Establishing QbarusingIoH124 (SuDS year flow rates are required. analysis to derive flow rates if1and100 descriptors andthenundertake apooling EQ.24.2) usingFEHcatchment designer to establish Qmed(SuDS Manual FEH statistical methodrequires the for thesite. site size to establish thegreenfield runoff catchment runoffisfactored backto the ReFHv2 software. The peakrate of return periodcan bederived usingthe the runoffestimate. The flow rate for any there isnourbanisedcomponent within FEH ReFHv2 –analysis shouldensure that 9.5.4.6 Accounting for Climate Change test indicates potential for flows across the modified flow routes. Whenthesensitivity SuDS components shouldbedirected along Flows inexcess ofthestorage capacityof Change Allowance. to factor uprainfall intensities for Climate calculations thecurrent industry approach is To make allowance for thiswithinSuDS regularity. extreme rainfall events willoccur withgreater Future predictions suggest that more Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates allowing for UpperEndProjections. flood risksare introduced by not demonstrate that nounacceptable be adopted where sensitivitytests climate changeallowances that can These represent theMinimum Central Projection danger to people) during thisevent could present a significant flooddepthsonsite incorporated into design(i.e End Projection allowances must be adjacent sites isidentifiedUpper unacceptable floodrisk to site or Carry outsensitivitytest. Where Upper EndProjection Climate Changeshould beconsidered for bothattenuation storage andconveyance Design Note: 2015-2039 Design life calculations. 10% 5% central projections shouldbeapplied: advisory notes onhow theupperendand change isreplicated below withadditional Table 2from theDEFRAGuidance onclimate velocities whichmay beunsuitable. steep partsofsites may generate high less than0.25m willnotpresent arisk,but development orpeople. Generally, depths ensure there isnosignificantrisk to flood volumes, depthsand velocities to surface, thedesignershouldevaluate likely 2040-2069 Design life 20% 10% Design life 2070-2115

40% 20% 82 Design Detailed 83 Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates with theLLFA at pre-application stage. developments andschoolsshould beagreed Urban creep allowance for commercial roofs, pathways anddriveways. non-adopted impermeableareas, for example hectare andapplythepercentage increase to calculate thenumberofproperties per For housingdevelopments designersshould impermeable area: anticipated percentage increase to Guidance documentanddefinesthe The following tableistaken from LASOO commercial development andschools. residential development butcanalsoapplyto development rightsgenerally appliesto gardens to create driveways. Permitted development suchaspaving over front on thedrainage system from permitted Urban Creep considers thepotential impact 9.5.4.7 Accounting for UrbanCreep lands. within curtilageofprivate proposed impermeablearea applied aspercentage of Percentage area increase ≤ 25 10% 8% 30 Residential development density (dwellings perhectare) could easilyhave beenpermeableblockpaved. surfaces isincreasingly common. This example 6% 35 Paving over front gardens withimpervious 4% 45 ≥ 50 2% flats &apartments 0% during theconstruction phase. draining canquicklybecome compacted straight-forward andsites whichare free However, infiltration schemes are not permeable pavement are resilient to siltation. It isnoted that various systems suchas base istheequivalent ofthefactor ofsafety. assumption ofnoinfiltration through the calculated through thevertical sides.The will siltupandtherefore infiltration isonly of thesystem, suchastraditional soakaway, The BRE365methodassumes that thebase over time. to account for potentially reduced infiltration structure (see C753 Table 25.2),are allocated and thearea draining to theinfiltration depending ontheconsequence offailure, of safety ranging between 1.5and10 of thestructure onanongoingbasis.Factors will beinfiltration through thebaseandsides The CIRIA156methodassumes that there temporary storage for infiltration. There are two methodsfor calculating 9.5.5.1 Infiltration storage withinthedevelopment to hold Both infiltration and attenuation require would beappropriate. and volumes to controlled discharge rates not enableinfiltration, then attenuating flows Where soil,geologyorground conditions do underlying geologyisthefirst preference. Infiltrating runoffthrough thesoilinto by eitherinfiltration or controlled discharge. Runoff rates andvolumes canbemanaged Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates 9.5.5 Calculating storage requirements detail. calculation inputsare considered inmore progressing withthissectionwhere calculation andshould bereferred to priorto of infiltration and attenuation storage Sections 6.4.3.1 and6.4.3.5cover thebasics discharge to awatercourse orsewer. into theground orthrough flow-controlled water longenoughto bedischarged either CIRIA 156method BRE 365method Assume noinfiltration through thebase

Factor of safety applied 84 Design Detailed 85 Detailed Design ■ ■ In otherlocations suchasraingardens and utilised for storage. point at whichtheseareas would befirst The 1in30year event issuggested asthe not to beinundated onaregular basis. purposes suchascarparksorplaying fields It isprudentfor areas whichserve other ■ 9.5.5.2 Attenuation andlong term storage Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates development asfollows: manage thevolume ofrunoffgenerated by There are anumberofways to reduce and the development. (NSTS S4) for theincreased runoffvolume generated by attenuation storage hasemptiedto mitigate retained onsite for alongerperiodafter For Approach 1,somerunoffmust be Approach 1 ■ ■ ■ Infiltration tests where low rates ofinfiltration are anticipated may have tobespecified overa offset against thelong-term storage volume requirements. (BS8515:2009) the majorityoftimeanddemandexceeds supply, 50%oftherain harvesting volume canbe Rain harvesting -Where itcanbedemonstrated that theharvesting system willbeinusefor storage volume requirements. occur even ifrates are very low. These additionallosses canbeoffsetagainst thelong-term considered acceptable by LPAs. Where SuDS components are unlined,someinfiltration may sufficient interception losses, a ratio of‘SuDS space’ to ‘developed area’ of1:4 would be be appliedto rainfall depthsto account for interception losses. To demonstrate potential for Natural Losses –For SuDS components whichprovide natural losses a5mmreduction can procedures onhow frequently longterm storage isutilised. Separate area ofstorage -Aseparate area ofstorage canbeprovided. There are noset period greater than 24 hours Design Note: rate of2l/s/ha. be viainfiltration or a controlled discharge Outflow from Long Term storage area should rainfall events less than1in30year. more regular -i.e. they willbeinundated for complexes thefrequency offillmay bemuch long term storage basinswithinpond rates. (NSTS S6) requirement dueto more restricted outflow analysis, butcanresult inagreater storage by industry at present dueto simplicityof This istheapproach most commonly utilised rainfall event plusclimate changeallowance. rainfall return periodsupto the1in100year Qmed whichisusedby FEHmethods) for all rate (whichisequivalent to a1in2year or should becontrolled to amaximumofQbar predevelopment status, thenoutflow rate Where volumes cannotbemanagedto Approach 2 Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Permeable pavement delivers acontrolled flow of clean water to landscape canalandrillfeatures andto theRiver Welland.

Riverside Court, Stamford. 86 Design Detailed 87

Detailed Design Brownfield sites 9.5.6 Managingrunoff rates from Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates terms ofcalculations anddrainage strategy. development shouldbetreated separately in and theparcel oflandproposed for The existing development remaining intact storage calculations. of thesite whenthedesignerisundertaking impermeable runoffrate from theremainder for thedevelopment parcel with theexisting the combining ofthegreenfield runoff rate In thesecircumstances LLFA willnotaccept runoff status. development to bereturned to greenfield occasions LLFA willnotexpect theentire planned for re-development. Onsuch a smallparcel oftheoverall site may be complete redevelopment ofthesite, andonly Not allplanningapplications comprise a (NSTS S3andS6.) appropriately designedunderground storage. permeable pavements, andtheuseof storage onroofs (e.g. blue-green roofs), options for storage includingtheuseof demonstrate that they have explored all achievable. The designerwillberequired to demonstrate why reduction inrate isnot rates cannotbeachieved, thedesignermust greenfield runoff rates. Where greenfield rate ofdischarge shouldbereduced to in 100year rainfall event isnotpossible, the Developed LandorPDL),ifinfiltration ofthe1 On Brownfield sites (alsoknown asPreviously year return period rainfall event. tube andoverflow that canmanagethe1in100 A raingarden for asingleproperty with control Facing: The Islington, Ashby Grove Raingarden. Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ ■ Designers shouldprovide thefollowing:

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development parcel. controlled to greenfield rates for the impermeable area based onoutflow storage requirements for additional parcel andnotthewiderdevelopment based onthearea oftheredevelopment greenfield runoff rates are calculated the netincrease inimpermeablearea 88 Design Detailed 89

Detailed Design

developers are notrequired to attenuate specifically required by LPA /LLFA or increasing flood riskelsewhere. Unless the site withoutcausingfloodrisk to thesite flows are intercepted andmanagedthrough SuDS designshoulddemonstrate how offsite identified by Surface Water floodmaps. runoff from offsite withindicative flow routes 9.5.7 Designingfor exceedance Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates be adopted for SuDS calculations. the manning’s roughness values whichshould channel. The SuDS ManualFigure 17.7 details how much‘roughness’ isappliedby the flow velocities. The depthofflow willaffect EQ.24.12) isusedto estimate openchannel The Manning’s Equation (SuDS Manual Management Train. encourage siltsto drop outofflow alongthe Where velocities are less than0.3m/s this will vegetated surfaces suchasswale channels. 1m/s velocity to avoid riskoferosion of Peak flows shouldbe retained to less than 9.5.9 Flow velocities 9.5.8 Managingoff-site management train/conveyance route. location to thenext alongadefined exceedance flows to flow from one storage Site levels shouldbedesignedto allow managed inasafe andpredictable manner. flows, beyond designparameters, canbe The designermust demonstrate that extreme Many sites are at riskofsignificantsurface

flows case-by-case basis. circumstances whichwillbedetermined ona advice may berevised inexceptional flows whichare generated from offsite. This flood-risk/ information.service.gov.uk/long-term- EA Floodmaps-www.flood-warning- reduce erosion. requiring rock reinforcement of theswale to been managedwithintheconveyance system, Facing: At thisdevelopment flow rates have not component to thenext intheevent of exceedance orinletblockage. Levels of pathways androads canbeadapted to allow for asimplecascadeof flow from oneSuDS Lamb Drove, Cambourne, Cambridgeshire. Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Below: The amenity planbasinandlow flow channel have aflow control before water

continues alongaconveyance swale. 90 Design Detailed 91 Detailed Design 9.5.10 Calculation checklist Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates checklist identifiesusefulcalculation checks: checklist’ (see appendix).The following presented inthe‘Flows andVolumes Key calculation inputsandoutputsshouldbe Parameter volume runoff Control of duration Critical losses interception Initial Urban creep allowance change Climate rate flow control Maximum runoff generating Areas data. Rainfall Guidance ondesign/calculation input for the control offlow beingdischarge from thesite. ‘lost’ orstored separately Approach 1can beapplied Where thedesignerdemonstrates that water canbe calculating attenuation storage. A range ofrainfall durations must beconsidered when each m allowance may bemadefor interception losses for no greater than4timestheSuDS wetted area, a5mm As aruleofthumb, where thearea ofdevelopment is development islikely to occur. impermeable areas ondevelopments where permitted Urban creep allowance appliedto non-adoptable assessment. design life ofdevelopment andany appliedsensitivity CCA hasbeenappliedwithincalculations based on infrastructure. rates basedontheavailable capacityofreceiving IDB orEA,mightplace restrictions ontheoutfall flow Statutory authoritiese.g. LLFA, sewerage undertaker, for impermeablearea isusedfor calculations. The designermust justify where aCv ofless than0.9 within thestorage calculation. All area ofcontributing runoffshould berepresented bring inlinewithFEHrainfall data. data isused,conversion factors shouldbeappliedto FEH 2013 rainfall data preferred. Where FSRrainfall 2 ofdevelopment. assessment Information for technical controlled. volume ofrunoffhasbeen Designer to confirm how worst casescenario. been considered to achieve sufficient rainfall durations have Designer to demonstrate that been appliedincalculation. 5mm interception losses have Designer to confirm whether Urban Creep percentage Designer to justify selectionof type anddesignlife. CCA basedondevelopment Designer to justify selectionof method for definingthe rate. identified alongwiththe The flow control rate shouldbe justify useofCv less than0.9. Designer to state Cvs usedand subcatchment. runoff contribution withineach identifying theareas ofsurface Provide adrawing clearly data. any conversions appliedto Confirm the rainfall source and Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Parameter and design. calculations of Consistency off site. flows from Managing exceedance for Designing check Erosion section Long design Outfall layout. of theSuDS Modelling Guidance ondesign/calculation input calculations. flow control sizingand storage provision isasper The LLFA willconsider designdrawings to ensure that account slopes andlow lyinglevels. hydraulic calculations /hydraulic models,takinginto Detailed designofSuDS components shouldreflect may berequired onacase by casebasis). anticipated would notbe considered compulsory (but Detailed modellingto establish therates offlow should notincrease floodriskelsewhere. to quantify. Managementofflows through thesite offsite. These flows canbeunpredictable anddifficult The FRAshouldidentifythepotential for flows from exceedance events. should identifytheanticipated flow route for deal withanticipated flow rates. SuDS layout drawing demonstrate that overflows have sufficientcapacity to SuDS component. Hydraulic calculations should The designshouldincorporate overflows at each Concentrated inletpointsare alsoprone to erosion. less than1-2l/s. at riskfrom erosion. Peak flow velocities shouldbe Flows alongswales (or othervegetated surfaces) are levels across thesite. Long sectionswillallow detailedconsideration of and accounted for withincalculations asappropriate. assumed. The riskofsurcharge shouldbeassessed storage beingrequired. Free discharge shouldnotbe elevated water levels. This canresult inadditional at riskofsurcharge andlackoffree discharge dueto Outfalls into receiving sewers orwatercourses canbe numbering convention usedby models. drawings shouldbeclearlylabelledwiththe accepted inlieuofahydraulic model.Layout hydraulically complex standard calculations willbe instances where theschemeisrelatively smallandnot modelling ofextensive pipedsystems. Insome It isnotanticipated that SuDS designwillrequire

assessment Information for technical calculated volumes. confirm that drawings deliver design statement should sections andlongsections. The flow controls withcross site levels, storage locations and Drawings shouldclearlyidentify statement. the layout drawing anddesign managed through thesite using flows from offsite willbe demonstrate how anticipated The designershould exceedance flow route. drawing alongwithproposed be identifiedonthelayout Locations ofoverflows should provided asappropriate. velocity calculations to be safeguard scheme. Peak flow erosion andtaken measures to they have considered riskof Designer to demonstrate that water levels. Long sectionshowing peak discharge. water levels at thepointof likely to beinfluenced by high SuDS storage calculation is Designer isto indicate whether proforma support theFlows andVolumes outputs shouldbeprovided to undertaken. Calculations/model no hydraulic modellingis The designeristo justify where 92 Design Detailed

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Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates These features visiblyfillwhenever it rains. Bewdley SchoolScience Block. green space for creative water managementat andrillexploitingRaingarden smallpockets of component. stored andcontrolled withineachSuDS space canbeinfluenced by how flows are Appearance, functionalityandcharacter ofa flexible. for storage across thesite are diverse and storage location. However, theopportunities to tryandaccommodate allflow at asingle it istheintuitive response ofmost designers Where asinglestorage volume ispresented, 9.6 Controlling flows between standard slabsat Abbey Park Campus areas, includingthepedestrian entrance plaza Plastic spacers are usedto form openjoints Leicester College, where allhard landscape to thebuilding,are usedfor storage. Single, tiered storage components ■ Single, uniform storage components Distributed storage components summarised asfollows: discharge from thesite. They canbe underground storage structure priorto development rather thandefaulting to an integrating storage aspartofthe about thepossibilities that exist for are intended to inspire thedesignerto think are explored by thisguide. These approaches deliver variable outflow rates (Approach 1) A framework ofthree approaches which 9.6.1 Designflexibility ■ ■ Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■

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to achieve thevariable outflow rates. extreme rainfall events andopeningssized within amore extensive basin for more a smallerbasinusedonregular basis single, tiered storage component, suchas store upto the1in100year rainfall ina variable outflow rates. with openingssized to achieve the permeable pavement orblue-green roof, single storage component, suchas a store upto the1in100year rainfall ina depths beingstored at eachlocation. with thepotential for different rainfall swales, basinsandpermeablepavement storage components suchasraingardens, distributed storage volumes into discreet 94 Design Detailed 95

Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates runoff rates. respective 1in and1in100year greenfield depth ofstored flow discharged at the control would bedesignedto ensure that the their footprint. Inthis scenario theflow all rainfall events upto the1in 100year within which have relatively flat formations can store Permeable pavements andblue-green roofs components 9.6.3 95% ofrainfall events would bemanagedby components from regular wetting asaround This approach keeps subsequentstorage management train to site control. rainfall volumes conveyed alongthe 1 year and1in10year rainfall, withexcess features are usuallysized for between the1in located closeto buildings.These small rain gardens andsmallbasinswhichcanbe development andresults infeatures, suchas parcels ofavailable space withinthe This approach isusefulfor exploiting small 9.6.2 Distributed storage components Single, uniform storage Raingardens, suchasthiswildflowerRaingardens, raingarden at St Paters School,Gloucestershire, are anexcellent further storage. components withouttherequirement for passively move through subsequent storage outflows from one storage component will component canbeeasilycalculated and The flow control opening for each downstream components asamenityspaces. This canprotect thefunctionalityof the first component. distributing storage throughout adevelopment. Permeable forming aplazaoutsideBewdley example of theopportunitiespresented by School Science Block. outflows at various depthsof storage. be designedto managethedesired variable with otherapproaches theflow control can volumes ofrunoffupto the1in100event. As basin whichcanaccommodate further smaller basinlocated withinamore expansive component by accommodating themina prevented from covering thewholestorage less runoffsuchasthe1inevent, are More frequent rainfall events whichproduced desired habitat. basin by creating wetland orany other Biodiversity canbeintroduced inthesmaller features for general amenity, play orsports. useful inorder to maximize theusabilityof this scenario, atiered approach to storage is flows are taken to anamenityplay basin.In Source control shouldbeinplace where components 9.6.4 Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Single, tiered storage berm ontheleftof thephoto -canstore upto tiered basinwithtwo levels (B&C)at anew Below: Excerpt of adetailedplanshowing a This wetland basinat Fort Royal Schoolcan larger basininwhichitsits-defined by the warehouse inEvesham. This example also demonstrates theprincipleof distributed store day-to-day rainfall whilst themuch storage components with a planted raingarden (A)accommodating up to the1in10rainfall event.

the 1in100volume. 96 Design Detailed 97

Detailed Design 9.6.5 Flow controls for SuDS Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates exceedance ofthedesignstorm. arrangement to dealwithblockage or control. There shouldalways beanoverflow ‘greenfield rates’ ofrunoffthrough eachflow components isslow asitisrestricted to The rate offlow of water through SuDS unless theopeningisprotected. of flow controls canbeprone to blockage V-notch weirs andvortex controls. Any type many forms includingorifice plates, slotor several flow controls. Flow controls come in and alongthemanagementtrain canrequire Attenuation storage withinsub-catchments Hollington Schoolare very easy to unblock. to blockage, features suchasthisslot weir at how thesystem works. Althoughmore prone interesting features andhelptell thestory of Flow controls inthelandscapecanmake cost-effective andeasy to maintain. by Controflow are simple, reliable, Orifice flow control chamberssuchasthisone the storage structure fills. can direct floating debrispast theoutletas design features suchasslopingheadwalls the casewithconventional drainage. Simple outlets isnotdriven against openings;asis throughout, floating debristhat easilyblocks Where slow movement offlow ismaintained and settlesoutalongthemanagementtrain. Silt istrapped at source inSuDS components ■ ■ protected openings: Key pointsto beconsidered whendesigning migrating through thepipe. opening hasameshguard to stop stone protection for pipeopenings.Note thepipe 150mm aggregate forms aneffective A stainless steel meshbasket filledwith80- diameter) withshallow depthofstorage. – 2l/s usingsmallopenings(15-20mm rates. Flows canbecontrolled down to 0.5 sites may needto meetminimaloutflow flow Small sites andsub-catchments oflarger protected openings. flow rate controls andthedesignof take into account theneedinSuDS for low a minimumflow rate of5l/s butthisdoesnot Previously thedrainage industry hasapplied attenuated flow rates inSuDS design. There are nominimumthresholds for Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates 9.6.6 The importance ofprotected openings ■ ■ located onaslopeto encourage debristo Outlets inopenstructures shouldbe across thesurface oftheprotection. accumulation oflitter andvegetation reasonable surface area to allow for Protection to theopeningshouldbeofa control. to prevent floating debris reaching theflow connecting pipeopeningsetwithinthestone filled with80-150mm stone withthe protection isto useastainless steel basket protection. Oneway to provide this ponds andbasins,require additional Open SuDS components suchasswales, opening requires littleadditionalprotection. perforated pipesorsimilar, theflow control pre-filtered, andassuming collection through pavements, bioretention orfilter drains are SuDS components suchaspermeable ■

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orifice opening. protective screen willpass through the thus any residual siltpassing through be smallerthantheorifice openingsize, Openings intheprotective screen should SuDS component. pass over the outletaswater rises inthe 98 Design Detailed 99 Detailed Design 9.6.8 Sizingflow control openings Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates full andthedesignheadreached. only reached when theSuDS component is It isnoted that themaximum Qbarrate is reasonable drain down times. of 2l/sec/ha isacceptable to enable development. Alower flow control threshold maximum Qbarrate (or equivalent) for the including CCA should bedischarged at a runoff from thesite for the1in100year event control (S3)cannotbeachieved thenall Where thedesign requirements for volume Approach 2-Qbarmethod the respective rainfall events. and 1in100year greenfield runoff rates for for varying theoutflow rate for the1in year Non Statutory Technical Standard S2allows Approach 1–Variable control the control offlow, summarisedas follows: Section 6.4.3.6outlinestwo approaches for selection ofequations andcoefficients. consideration shouldalways begiven to the knowledge ofhydraulic calculations. Careful controls are intended for useby thosewith The following methodologiesfor sizingflow Graph comparing required flow rates and thevariable flow rate through a simple orifice as head increases. 3. 2. 1. control to meettherequirements ofNSTS S2: calculating theopening size ofanorifice flow The following steps outlinetheprocess of as the‘driving head’ofwater stored. through theopening-sometimesreferred to gravitational pressure forces more flow As thedepthofstored water increases the increases, producing andstoring more runoff. outflow rates astheseverity of rainfall An orifice openingwilldeliver variable 9.6.8.1 Approach 1methodology Head catchment, for the1in100year event and your SuDS component, basedonits Calculate themaximumstorage depthfor base) ofstorage. invert at thebase(or slightlybelow the reasonable starting pointisto setthe Define thefirst, lower orifice invert. A and 1in100year rainfall event. Greenfieldrates runoff) for the1in year Establish thecontrolled outflow (or relationship between drivingheadand flow through anorifice flow control required 1inflow rate

Flow Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates 7. 6. 5. 4.

have to be reconsidered. Amendthe mindful that the1in100year scenario will recalculate basedonthe1inevent being rate thenreduce theopeningsize and 1 event islarger thanthe1inyear control If thecalculated maximum flow for the1in opening doesnotneedchanging. that the1inyear control rate thenthe If thecalculated maximum flow isless lower. through theorifice willbesignificantly rainfall event andtherefore theflow rate be significantlysmaller for the1in year the volume andtherefore drivingheadwill depth andmaximumflow rate. Note that – make anote ofthemaximumstorage how a1inyear rainfall event willbehave design andflow control opening,calculate Based onthesamestorage component this storage depth. size to achieve the1in100flow rate at Make anote ofthecalculated opening pavement orupto 600mmfor basins. may be350mm for apermeable the 1in100flow rate - for example this and respective growth curve flow rates derived by area drained required 1in100flow rate 8. ■ ■ year flows: rates for both the1inyear and1in100 there isdifficultyinmatching outflow Other optionscanbeexplored where ■ ■ combination ofthefollowing: rates canbeachieved by any Both the1inand100discharge ■ ■ ■ ■ for the1in100event. achieved at the maximumstorage depth storage depthuntilthe1in100flow rate is opening size andheightabove the1in100 behavior ina1100event. Adjust the storage depthandrecalculate thestorage point (invert) isat orabove the1in second openingsothat it’s lower most storage depthnoted instep 7. Add a opening may beplaced above the1in necessary. To overcome this,asecond resulting inmore storage thanis be below theallowable discharge rate opening. The maximumflow rate willnow year event basedonthechanged Re-run thecalculations for the1in100 storage depth. make anote oftheresulting maximum attenuated to the1indischarge rate and opening size untilthe1inyear event is NSTS. the site must meetrequirements of catchment. The finaldischarge from 100 year return periodinevery sub- is notnecessary to store for the1in Store for adifferent return period–it as rectangular andv-notch weirs. Try different typesofopeningssuch openings Incorporating oneormore additional therefore volume ofeachtier storage tierby adjusting thearea and Adjusting thedepthofeachdefined

Design Notes:

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Detailed Design Approach 1-worked example discharge at Qbarrate. calculating theopeningsize ofanorifice to The following steps outlinetheprocess of volumes. it may alsoresult inincreased storage only onetarget flow to besized for, however, simpler to applythanApproach 1asthere is design headisreached. This methodologyis whenever the storage volume isfullandthe The Qbar(or Qmed) flow rate willoccur is heldbackonsite for longer. considered to demonstrate S6asmore flow requirements ofNSTS S2butcanbe rainfall event. This doesnotmeetthe discharge at Qbarfor the1in100year +CCA A singleopeningcanalsobesized to 9.6.8.2 Approach 2methodology Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates l/s outflow 150mm above baseinvert ofstorage provides 4.2 Using anadditional55mmopeningwithinvert utilised. will onlyoperate once the1inyear storage is will beprovided by anadditionalopeningwhich Therefore 11.1 –6.9=4.2l/s. The additionalflow discharge is11.1l/s. provides outflow rate of6.9l/s. Allowable 65mm openingfor 600mmdepthofstorage 1 in100year in 1year, whichprovides 3.5l/s outflow . 65mm openingwith150mmdepthofstorage for 1 1 inyear periods respectively. 600mm for 1inyear and1in100year return Depths ofstorage are assumed as150mmand • • rates are assumed: For thepurposeofexample thefollowing 1 in100year 11.1 l/s 1 inyear 3.5l/s 4. 3. 2. 1. above theorifice). defined 1in100 year head (depth of water convey therequired QBar flow rate at the establish theopening size whichwill Using theappropriate orifice equation storage. base (or slightlybelow thebase) of starting pointisto settheinvert at the Define theorifice invert. A reasonable Define themaximum storage depth. the 1in100year +CCA rainfall event. example 600mmcould beadopted for Define themaximum storage depth. For catchment. proportional to thecontributing control location. The Qbarrate shouldbe Establish theQbarrate for theflow 600mm – total depth of storage 1 in 100 year rainfall + CCA

150mm 1in1 450mm additional storage - storage 422mm head for 2nd orifice opening 65mm dia. opening 55mm dia. ■ ■ water NPPF by providing acontrolled flow ofclean train, SuDS delivers therequirements of Using source control andthemanagement within development. creation, notjust inthewiderlandscape, but opportunities for biodiversity andhabitat the environment andencourages provisioning development to have nonegative impacton The NPPFsetsanobligation onproposed pollution over time. no builduporneedfor removal ofthis down organic pollution,meaningthat there is processes inmany SuDS components break bioremediation. Naturally occurring through sedimentation, filtration and SuDS components most pollutionisremoved surfaces. Asrunoffmoves slowly through Rainfall picksuppollutionfrom development 9.7 Water quality Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates 9.7.1 The objectives ofdesigningfor water quality ■ ■ held andtreated on site. polluted partofrunoffismore effectively most smallrainfall events sothat themost Design for interception losses to occur for wider landscape. watercourses andwater bodieswithinthe biodiversity aswell asreceiving to thedevelopment’s landscapeand Treat runoffto prevent negative impacts through thedevelopment. series. number ofcomponents already limited in normally achieved by default, due to the this document,water qualityobjectives are management train approach, asoutlinedin Where water quantitydesignadoptsaSuDS ■ management train. pollutants removed at source andalongthe and wetlands should beprotected with The amenityandbiodiversity value ofponds ■ ■ treatment. directly from development withoutsufficient Open water features shouldnotreceive flows

■ ■ ■ NPPF Paragraphs 109, 117and118

system. and maximisetreatment through the where possible to begintreatment quickly to source and at ornearthesurface Manage surface water runoffat orclose up oftoxic sediments. maintenance problems dueto thebuild- the aquatic environment andaddto Silts whichcarryheavy metalsimpacton for extended periods. Hydrocarbons remain inpondsediments

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Detailed Design identified as follows: The varying levels ofassessment are with thelevel ofrisk. the extent ofanalysis required associated ‘Source-Pathway-Receptor’ approach, with 2015 CIRIASuDS Manualwhichadoptsa applied correctly, buthasbeenrefined by the discharge. This methodremains robust if suitable SuDS components priorto allowing run-offto pass through aseriesof inferred that treatment was provided by adopted the‘treatment train’ approach. This Prior to 2015, SuDS water qualitydesign 9.7.3 Hazard andmitigation riskassessment Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ should bedesignedto: For effective treatment ofrunoffSuDS ■ ■ ■ 9.7.2 What water qualitydesignshoulddemonstrate ■ ■ ■ ■ incorporating interception losses reduce thefrequency ofrunoffby management train maximise travel timealongthe trap arange ofcontaminates minimise impactsfrom accidental spillage. Table 26.15 of the2015 SuDS Manualdenotes that conventional gully andpipedrainage provide zero treatment. Design Note: ■ ■ ■ management train. provision ofsource controls anda Effective treatment isprovided through ■ ■ ■ quality parameter compliance limits. assessment required anddischarge water Environment Agency willoutline level of requirement for adischarge licence. The For HighRisksites, there islikely to bea (CIRIA SuDS ManualSection26.7.2). components required priorto infiltration to identifythenumberofSuDS permitted andapplytheIndices approach establish whetherinfiltration willbe via infiltration, undertake riskscreening to For mediumrisksites where discharge is Section 26.7.1). components required (CIRIA SuDS Manual to identifythenumberofSuDS ‘Hazard andMitigation’ Indices approach discharge isto surface water –apply On low to mediumrisksites where brownfield sites. where contamination isidentifiedon site overlies Source Protection Zones 1or2 Discussion willberequired withEAwhere the infiltration. of treatment required priorto thepointof indices approach isappliedto definethelevel it willbepermissible to infiltrate andthe screening assessment willdetermine whether the infiltration riskscreening assessment. The underlying geologyisrequired to undertake A level ofunderstanding ofthesite’s soiland reasonably simplistic to apply. approach for discharge to surface waters is For low to mediumrisksites, theindices Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates On freely draining sites where insufficient treatment isprovided at thefirst stage of treatment On low to mediumrisksites permeable pavement willprovide sufficient treatment prior to source control, initialSuDS components may require liningto prevent direct infiltration infiltration into theground viathepavement subbase. carrying pollutantsinto underlyinggeology. Design Notes:

wiyby/37833.aspx http://apps.environment-agency.gov.uk/ SPZ areas identifiedontheEAwebsite:

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Detailed Design 9.7.4 Dealingwithspillage Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Designing for spillageshoulddemonstrate: left insituto breakdown naturally. take uptheexcess andtheresidual pollutants organic basedpollutantaspillkitisusedto SuDS components. Where thespillageisan treatment processes whichoccur within spillage occurs thiscanoverload the dealing with‘day to day’ pollution.Whena SuDS components are very effective at Milk spillageswillbypass conventional drainage methodsof spillcontainment https://naturalresources.wales/about-us/news-and-events/news/nrw- respond-to-milk-spillage-in-llantrisant/?lang=en. ■ ■ ■ ■ ■ ■ provide simpleandrobust containment. visible andcanbeeasilysealedoffwill awareness ofoutletlocations whichare locatable at thetimeofspillage. An inherent riskoftheessential keys notbe valves shouldbeavoided dueto the mechanical mechanismssuchasshutoff and initialcleanupto take place management train allows timefor reaction slow travel timethrough aSuDS so that itisvisibleand accessible. spillage iscontained at ornearthesurface 9.7.5 Water qualitydesignchecklist Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Item plan maintenance Operation and phase Construction Infiltration Treatment discharge Method of What isbeingchecked minor /majorspillage Contingency measures intheevent ofa to breakdown organic pollutantspassively. should deploy natural treatment process implement. Where available, SuDS design simple to understand andeasy to Operation andmaintenance shouldbe runoff. environment dueto siltyconstruction the riskofpollutionto thewider managed duringconstruction to minimise Demonstration ofhow site runoffcould be depth to seasonalhighgroundwater table. Presence ofSPZ’s, contaminated land, and managementtrain. Evidence ofsource control, subcatchments the widerenvironment. site biodiversity andamenityassets and Sufficient treatment inplace protecting treatment required Sensitivity ofreceptor andlevel of

assessment Information presented for appropriate) and positioningofspillkits(as Plan indicating potential for containment part ofSuDS treatment process). not beenfullybroken down passively as pollutants (i.e. organic pollutantshave site to remove hydrocarbon based of where personnelare required to visit plan. Descriptionoftasksanddetailing Concise operation andmaintenance uptake. Contractors willberesponsible for for construction runoffmanagement. statement outliningapotential approach Section ofthedrainage design of discussion withEAwhere appropriate Coordinated constraints plan.Evidence appropriate). infiltration screening assessment (as Details ofIndices approach and components andmanagementtrain. Layout drawing clearlyindicating SuDS discharge andsensitivityofreceptor. Design statement to specifymethodof

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Detailed Design 9.8 Amenity Confirming integrated SuDS design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ Considerations willinclude: should highlightany problems withlegibility. how theschemepresents itselfto thevisitor train from source to outfall andimagining An exercise infollowing eachmanagement after it. of theSuDS environment andthosewholook functions isimportantbothto everyday users Understanding how theSuDS design 9.8.1 Legibility Concept Design. amenity usesthedesigncriteria setoutin An evaluation ofthesuccessful integration of will beenhanced by detaildesignat stage. design stages but some finer aspects of value considered at bothConcept andOutline The amenityvalue ofSuDS willhave been functionality andvisualquality. surface’, andconsiders bothmulti- associated withfeatures ‘at ornearthe aesthetic elementsofSuDS design Amenity focuses ontheusefulness and interpretation andjudgement. design andperhapsopento themost Amenity isoneofthefour pillarsofSuDS ■ ■ ■ How israinfall collected? and maintained? been usedandhow they canbeaccessed What ‘source control’ techniques have ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ understandable? Is theoutfall obvious, accessible and and understandable? Are overflow and exceedance routes clear Where are flow controls are located? occur withinpermeable construction? recognising that thesefunctionsmay the managementtrain in‘site controls’ Where isrunoffstored andcleaned along site. This isconveyance? control’ components to eachpartofthe been collected onwards through ‘source How doesrunoff travel from where ithas Informal play, through integrated design. landscape. designed to bemanaged elsewhere in the rainfall (1-2year return period events) canbe time butnotwheninundated. Everyday sports andothersocialactivitymost ofthe Reasonably level green space canbeusedfor pedestrian use. also allows vehicle access, parkingand always available for managing rainfall and multi-functionality inthat thesurface is Permeable pavement isanexample offull rainfall. useful inways not associated withmanaging Many partsoftheSuDS landscapecanbe 9.8.3 Multifunctionality ■ ■ ■ ■ ■ every elementofdesignincluding: Full accessibility requires safety by designfor managers. accessible to botheveryday usersandsite All partsoftheSuDS landscapeshouldbe 9.8.2 Accessibility Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ ■ ■ ■ changes andopenwater. understanding ofthelimitations oflevel physical accessibility to allwithan clear visibilityofthesystem outlets design detailingeg.headwalls, inletsand changes oflevel open water valuable for play. within housingwhere grass surfaces are surfaces drymost ofthetime. For instance, trenches below theground to keep grass enhanced by under-draining into filter Usability ofswales andbasinscanbe ■ ■ ■ ■ ■ Other functionalitycaninclude: balastrade withwet benchandplanted aquatic ■ ■ ■ ■ ■ Hopwood Park MSA M42.Wooden terrace and education. wildlife habitat etc community activities suchasgardening dog-walking etc informal leisure like jogging,picnics, landscape play opportunitythroughout theSuDS

bench protection to openwater.

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Detailed Design 9.8.4 Visual quality Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates people. management withtheuseofdevelopment by integrate therequirements ofrainfall integrated SuDS design.SuDS designshould important to understand theprincipleof In order to maximize thevalue ofSuDS itis additional site maintenance. land hungry, expensive andrequired fenced. They were therefore thoughtto be In many caseswetland features would be separate from thedevelopment they served. basins, swales andwetlands that were dedicated SuDS corridors withaseriesof Early SuDS designinBritaintended to create and SuDS 9.8.5 The integration ofamenity Design Stage. profiles remain to be confirmed duringDetail channels andbasinswiththeiredges particularly inlets,outlets,control structures, Design detailingofSuDS components, Design stages. considered duringConcept andOutline and surrounding areas willhave been The overall character oftheSuDS landscape Mini-courtyard withrainchain, rain slide, Fort Royal PrimarySchool,Worcester. raised pool andrill. combined. conveyance ofwater andbiodiversity canbe and publicpedestrian routes where occasional heavy storms canbemanaged, space, where botheveryday rainfall and integrate withbothdesignated publicopen compatible withSuDS design.SuDS should Community useandwildlife interest are both management train. flow reduction at thebeginningof and basinscanallprovide earlycleaningand roofs, bioretention andinsomecasesswales permeable surfaces, filter strips, green/blue Source control components suchas pollution. of theSuDS to remove siltandgross This requires ‘source control’ at thebeginning for bothAmenityandBiodiversity benefits. through development isascleanpossible soon aspossible sothat water that flows Secondly itisimportantto cleanrunoffas the landscapecharacter ofadevelopment. for instance, shouldbeconsidered aspartof development, spouts,rillssurface channels, runoff canaddvisualinterest to Firstly thecollection andconveyance of Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Springhill, Stroud poolandsocialspace. -Raised ■ ■ ■ additional benefitsincluding: Biodiversity andsite layout provides The integration ofSuDS withAmenity, ■ ■ ■ integrated site design. visual andbiodiversity interest aspartof landscape space usability through integrated useof multi-functionality efficient useofspace through Tile hungcascadeconveys water through terracotta T-piece to lower level.

Springhill Cohousing, Stroud. 110 Design Detailed 111 Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ecological character ofsurrounding natural The widerhost landscapeshouldreflect the close to buildings. ornamental planting,particularly where itis include natural habitat orreflect more This surrounding ‘host landscape’may management. features andtheimpactofrainfall landscape notdirectly affected by SuDS ‘management train’. This term describesthe provides an enclosing envelope to theSuDS There isusuallyahost landscapethat can beinfluenced by SuDS design. biodiversity inadeveloped landscapeand design andhabitat managementallaffect Local topography, aspect,soils,landscape types likely to evolve over time. landscape anddetermine thebasichabitat influences onthenatural character ofthe Geology andclimate are fundamental 9.9 Biodiversity 9.9.2 Biodiversity at development scale 9.9.1 Principlesofdesignfor biodiversity otherwise hostile environment. birds, insectsandotherwildlife inan and feeding sites for mobilespecieslike ‘service stations’, that actasstaging posts biodiverse islands,sometimes likened to development, thenSuDS spaces canactas for instance inurban retrofit and re- Where SuDS installations are more isolated, guidance. ornamental plantingby following specific design canstill enhance wildlife value in habitat wherever thisispossible butcareful linkages withinandaround development. scale to provide habitat andconnectivity green /blueinfrastructure andalsoat alocal catchment scaleto create asympathetic Biodiversity must beconsidered at thelarger A biodiversity micro-pool setwithinameadow raingarden at St Peters SchoolGloucester, wetlands to feed. from oneplace to thenext anduseSuDS individual trees andwoodland edgesto travel the ground butanimalslike bats use are particularlyimportantbothfor animalson development landscape. These connections colonisation into andthroughout the both withinandoutsidethesite encourages Connectivity between wetland habitat areas 9.9.3.3 Connectivity cover. structure oftrees, shrubsandherbaceous vegetation by developing acomplex vertical Ornamental plantingshouldmimicnatural easily beenhanced for habitat creation. swales, basins,wetlands andpondsthat can inherent inmany SuDS features particularly variety for wildlife. Structural diversity is and invegetation generally provides habitat vertically withinwater features, thelandscape Structural diversity bothhorizontally and 9.9.3.2 Structural diversity management train. features andfurthersite controls alongthe contaminants reaching water, source control prevention measures to prevent Clean water isdelivered usinginitialpollution all openwater features inthelandscape. Clean water iscriticalassoonpossible for 9.9.3.1 Cleanwater Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates 9.9.3 Key designcriteria for biodiversity inthedeveloped landscape

landscape character. ensure acceptance ofamore natural the aspirations ofthe localcommunity to biodiversity butshouldbecompatible with Sympathetic maintenance enhances 9.9.3.5 Maintenance for wildlife fertilizer, pesticides andherbicides. should bedesignedto avoid theuseof surfaces to prevent siltrunoffandplanting Permanent vegetation shouldcover allsoil 9.9.3.4 Prevent pollutionto habitat flow ofclean fromwater’ thedevelopment. infrastructure that receives the‘controlled the SuDS landscapeandtheblue/green There shouldbeadirect connection between wildlife links. inspection chambers,ishelpfulinretaining with aminimumuseofpipework and Surface conveyance andoverflow routes, carefully where onefeature linksto thenext. train principlebutmust beconsidered Connectivity isinherent inthemanagement 112 Design Detailed 113 Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates environment from chemicalcontamination. conditions andto protect thewider SuDS functionality, different ground conventional landscapedesignfor reasons of The SuDS plantpalette willoften vary from contribution to amenityandbiodiversity. control functionalityaswell asthe significantly affect hydraulic andpollution Vegetation typeandspeciesselectioncan aesthetics, usabilityandwildlife benefits. SuDS feature aswell asbeingabout inherent functional part of any soft-landscape SuDS systems andfeatures. Vegetation isan species isanimportantaspectofdesigning The choice ofvegetation cover andplant 9.10 9.10.1 Objectives ofplantingdesignfor SuDS ■ fulfill specificSuDS functions, suchas: requirements. Inaddition,plantingshould awareness ofthelandscapemaintenance planting designcriteria and relies onan SuDS plantingdesignshouldsatisfy general ■ ■ ■ ■ ■ ■ ■ collecting roof runoff andaccess road runoff. Contemporary ‘prarie’ plantinginraingarden preventing soilerosion trapping siltandpollutionfrom runoff infiltration andtranspiration) encouraging interception (evaporation, soil profiles through the root growth cycle enabling longterm infiltration by opening Planting designfor SuDS Strutts Centre, Belper. ■ ■ ■ ■ ■ ■ fertilizer treatment. the needfor herbicides, pesticides or protection oftheenvironment by avoiding community amenity creating attractive surroundings and (refer to theBiodiversity section9.9) species richness andcareful management augmenting biodiversity by structure, ■ ■ ■ ■ ■ achieve thefollowing: SuDS vegetation choice anddesignshould Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates 9.10.2 The PrinciplesofSuDS plantingselection&design ■ ■ ■ ■ ■ weed growth andimprove soilfertility. compost’ asanalternative to suppress conditioner suchas ‘green waste careful plantselectionandasoil SuDS andgroundwater. They shoulduse to avoid leachingofchemicalsinto the pesticides orherbicideswherever possible Planting designshouldavoid fertilizer, the ground throughout rainfall events. root mat, encourages natural losses into particularly whenforming anextensive A vigorous growth ofvegetation, swales andbasins. settle outincomponents like filter strips, filtering water andencouraging silt to vegetation slows theflow ofrunoff, The matrix ofroots, stems andleaves of prevent erosion ofthesoilsurface. ground, bothinsummer andwinter, to Vegetation shouldpermanentlycover the appropriate. (9.9) shouldbefollowed where criteria setoutintheBiodiversity section benefit andbiodiversity. The design planting creating linkages for visual grassland, woodland orornamental with theSuDS landscape, ideallywith General plantingdesignshouldconnect Brick channelscollect roofwater for linear raingarden withgarden style planting. Strutts Centre, Belper.

a SuDS function. integrity ofvegetation surfaces that perform for additionalorremedial works to ensure the Contract arrangements shouldalways allow expensive. and managementcanbemore difficultand wildlife asnative plantingbutthecapitalcost hemisphere canprovide similarbenefits to to thewildtype, especiallyfrom thenorthern demonstrated that ornamentalplants,close Royal Horticultural Society(RHS)has / blueroof surfaces. Recent research by the raingardens, bio-retention features andgreen ornamental designstyle may berequired for In builtupareas amore formal and maintenance requirements. most likely to have modest longterm well asbeingcost effective, resilient and providing maximumbiodiversity benefitsas planting isusuallythemost appropriate, applied to agreenfield site. Naturalistic character, particularly where SuDS are being SuDS plantingisoften naturalistic in 114 Design Detailed 115 Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates appropriate topsoil depth isnecessary. repair themselves ifdamaged.For this,an Grass swards must bevigorous andableto benefits. and canprovide biodiversity andamenity important requirements inmanagingrunoff establish, simpleto maintain,meetthemost Grass surfaces are reasonably easy to host landscape. often merge seamlessly withthesurrounding of wetlands andponds.Grass surfaces will like filter strips, swales, basinsandtheedges familiar surface for vegetated SuDS features Grass isthemost cost effective, flexible and 9.10.3.1 Grass surfaces ■ commonly usedinSuDS: There are anumberofvegetation types ■ ■ ■ These are covered inthe following sections. ■ 9.10.3 SuDS vegetation types ■ ■ ■ ■ ■ cover grass surfaces –acommon SuDS ground raingardens andbioretention herbaceous planting-typicallyusedin based onnative wetland habitats wetland andpondplanting–usually interception losses enhance thelandscapeandaid trees andshrubplanting–usedto for shallow growing mediaonroofs. green /blueroofs –resilient low planting ■ ■ ■ used inSuDS landscapes: There are 3general typesofgrass surfaces ■ ■ ■ Forebays, swales andunderdrained basinsuse year. with anannualcuttowards theend ofthe of grasses andflowering plantsleftlong Meadow Grassland -containing a mixture temporary storage where water may flow orbe contained in SuDS Grass –alongeramenitygrass used use andto give acared for appearance Amenity Grass -for everyday community SuDS turf(100-150mm) to filter runoff, with Rectory Gardens Rainpark, Hornsey.Rectory Rainpark, Gardens amenity grass for publicuse. ■ ■ ■ ■ space for thecommunity. edge to longergrass andasamenitygreen useful for providing a1mwidecosmetic neat designed to bedrymost ofthetime. Itis well asbasesofSuDS features that are on thedryshouldersofswales andbasinsas laid onground that isnottoo wet. Itwillgrow of thetimeitwillestablish quicklyifproperly availability aspurposegrown turfandmost The great advantage ofamenitygrass isits in SuDS features allowing regular publicuse. An everyday grass surface that canbeused Amenity grass Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates microplastics to theenvironment. Photo-degradable isnotthesameasbio-degradable asthe ■ ■ ■ ■ Avoid turf products withplastic mesh(unless they are bio-degradable) astheseintroduce required inSuDS. provide the flow reduction andfiltering susceptible to drought anddoesnot to thepublic.This shortgrass is preferred by many Councils andisfamiliar 50mm asthisistheshort-mown grass Amenity grass isusuallymown at 35- give amaintainedappearance. that thelongergrass isdeliberate andto meadow grass isusedto make it clear important where SuDS grass andlonger A mown edgeof amenity grass isoften erosion protection. practical way to provide temporary conditions. Coir orjute matting isa option butcanfail easilyinadverse Seeding isacheaperandmore flexible loam to aidsurface drainage. Amenity turfshouldbegrown onasandy plastic breaks down into microplastics. Design Note: integrated into site design,managesoccasional Amenity grass shallow detention basinfeature, Parkside, Bromsgrove.

extreme rainfall. 116 Design Detailed 117 Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ the growing season. there isaleadintime of10ormore weeks in specific mixes canbepurposegrown where offer standard speciesmixes although flows across thesurface. Suppliers tend to surface ofSuDS components before water often usedasseedingorturfto cover the the first instance anamenitygrass mixis wildflowers adapted to regular cuttingbutin Eventually thisturfcanbecolonized by flow areas. It isidealfor theimmediate protection ofany or flow, even minimally. grass usedwherever water islikely to move SuDS grass describesthelongeramenity SuDS grass ■ ■ ■ ■ ■ 150mm inheight. must bemaintainedbetween 75mm and (lying flat underflow conditions) andso but shortenoughto prevent ‘lodging’ The grass islongenoughto actasafilter turves. pegs, to prevent water flow liftingthe be necessary, withfullybiodegradable weather insummer. Pegging theturfmay instance inmildspells inwinter orwet when weather conditions are suitable, for Turf canbelaidinspringandautumnor patches to repair intheautumn. establish grass butthere may bebare covering a seededsurface canbeusedto In dryweather acoir orjute mesh This isbest specifiedasturfitisfunctional assoonitislaid. Design Note: paved surfaces andaraingarden. Longer SuDS grass asafilter strip between raingarden’ at Renfrew CloseCommunity Facing: Aseededmeadow ina‘playful Raingardens, Newham.Raingardens, ■ grass profile. of theflow of water asitpasses through the provides very effective filtering andslowing infiltration and evaporation losses. It greater root andleafmass that assist both The grass andherbspeciesdevelop amuch interest. including habitat connectivity andvisual and offers amenityandbiodiversity benefits dry conditions withless likelihood oflodging Meadow vegetation hasgreater resilience to Meadow vegetation Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ all meadow grass habitat canrequire time in winter andsummerdrought butaswith mixture istolerant ofbothwet conditions community (NVC classification). This expected isbasedontheMG5grassland where regular oroccasional inundation is The meadow mixture that ismost useful ■ ■ ■ ■

■ ■ ■ ■

break dormancy (cold stratification). meadow plantsneed cold weather to Autumn isthebest time to seedassome management. year for specificvisualorspecies can becarriedoutat othertimesofthe sward visuallyacceptable. Further cuts or earlyOctober issufficient to keep the of cuttingstowards theendofSeptember Usually asinglecut,rake offandremoval native UKprovenance seed. Meadow vegetation shouldcomprise can give afloral impactin year one. The additionofanannualcornflower mix might beexpected. available where adrierorwetter grassland and care to establish. Othermixtures are 118 Design Detailed 119 Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates the growing season. strim inFebruary andsomeweeding during planting usuallyneedsaminimumofone as grasses like MiscanthusandStipa. This ‘deamii’) orwithwinter-present foliage such Alchemilla mollisandRudbeckiafulgida plants that shrinkbackto avisibleclump(e.g. macrorhizum and Phlomisrusseliana) or Plants canbeevergreen (e.g. Geranium feature. other erosion controls where water enters the This ishelpedifthere are inletaprons or an ornamentalplantingapproach to betaken. structures withless dramatic flows that allow bioretention are examples ofsmallerbasin planting ofSuDS features. Raingardens and Flowing water canbeaconstraint to the appropriate to aformal landscapecontext. ornamental appearance orplantingthat is sometimes low shrubsto create an particular, useherbaceous plantsand Raingardens andbioretention features, in 9.10.3.2 Herbaceous planting ■ ■ ■ ■ ■ criteria: the SuDS network, by meansofthefollowing general softlandscapedesign,must protect functional andaesthetic criteria ofmore Herbaceous planting,aswell asfulfillingthe ■ ■ ■ ■ ■ protect receiving watercourses. on herbicides,pesticides andfertilisers to Planting choice shouldavoid thereliance together. with afibrous root system to holdthesoil Herbaceous plantsshouldbeselected empty withinaround 24 hours. most rainfall events willusually return to time andalthoughitwillbeinundated in that theraingarden willbedrymost ofthe Plant selectionmust take into account a presence at ground level year-round. planting must beeitherevergreen orhave Unlike general amenityplanting,the collectively beattractive allyear. the trapping ofsiltandpollutionaswell as The plantingmust resist flow, encourage Park. to dramatic effect at Australia RoadSuDS Facing: Herbaceous andgrass plantingused ■ ■ ■ ■ requirements exist: environment for plantingandsofurther permeable soils.This canbeatesting aggregate filtration below specialist highly Bioretention features are defined by Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ ■ ■ and thesurface ofthesoilopen. is alsoimportantto keep thesoilhealthy A regular mulchof coarse organic matter Select drought tolerant species. fall. species that donotgenerate heavy leaf If tree planting,consider fineleaved maintenance. occasional damageandrequire simple shrubs andornamentalgrasses canresist and neglect.Certain evergreen suckering open space, must beresistant to damage Bioretention planting,located inpublic Attractive andwildlife friendlyherbaceous planting by SheffieldCity Councilin a crushed stone bioretention substrate.

rather thanadenseplantingmix. large surface area ofvery free draining soil Road runoffislargely managedby the very topped by crushedstone. to themixmay beused.This soillayer isthen organic matter andabout10%ofloamadded based oncrushedstone with15-20% overlain by anopengraded growing medium In thesecases,adeepstone drainage layer sources. free-draining soilprofiles may befrom many Plants chosento withstand dryconditions of features. on green roofs andmodifiedbio retention bioretention structures andare beingtrialled with thefree draining soilsrecommended for palette ofherbaceous plantsandgrasses These new approaches combine anew used inrecent SuDS features. choice ofplantsandthegrowing mediums planting style’, have influenced boththe Recent ideasaboutplanting,including‘prairie

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121 Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ categories: Wetland plants canbedividedinto 3 species. aquatic nurseryisfree from alienandinvasive accredited source withconfirmation that the proposals andshouldbeobtainedfrom an wetland plantsshouldbeusedinplanting are partofanenclosedurbansituation native invasive plantsandtherefore unless theSuDS Wetland habitats are very sensitive to The plantingrequirements are very similar. wetlands around 25%. that pondshave around 75% openwater and but notidentical.Onedefinitionsuggests The biologyofpondsandwetlands issimilar, 9.10.3.3 Wetland &pondplanting ■ slowing asautumnapproaches. spring andthrough thesummerwithgrowth wetlands. Wetland plantsgrow vigorously in plants persquare metre orasalinearedge to These plantsare usuallyplanted at 5or8 ■ This colonizing plantshouldbeconsidered apotentially dominating weed until adiverse plant ■ ■ ■ Reedmace (alsocalledBulrushorTypha latifolia) canseedrapidly onexposed mud edges. water dependingonitsdepth vertically around theedgeandinto the emergent plants that tend to grow water dependingonthedepth horizontally around theedgeandinto the spreading plants that tend to grow floating. column eitheranchored by roots orfree water plantsthat grow inthewater community isestablished. Design Note: ■ ■ Wetland and pondplantingdesigncriteria: planting. of plantsthat addattractiveness to waterside Loosestrife (Lythrum salicaria)are examples Flag iris(Irispseudacorus) andPurple enhance acceptability by thecommunity. attractive native plantscanbeselected to people are often present e.g. housing,visually Where wetland plantsare beingusedwhere in springorearlysummerwherever possible. tend to beuprooted by water orwind.Plant plants often fails to establish well andthey Autumn andwinter plantingofwetland ■ ■ environment. risk ofdirect linksto thenatural may bejustified butnotwhere there isa In urbandesignsomeornamentalplanting and spreading plants. normally benative, andamixofemergent Selection ofaquatic plantsshould maintain healthy plantgrowth. ideally benominally100mmordeeperto absorption ofrainfall. Soildepthshould stronger plantcommunity andgreater conditions. Agreater depthofsoilpermitsa prone to plantfailure dueto drought Shallow soilsof50-80mm depthare also conditions, particularlyonapitched roof. Drainage layers canexacerbate drought source’, ontheroof. used for collecting andstoring rainfall ‘at development ofthegreen roof whereby itis managing rainfall. The blueroof isa Green roofs are now afamiliar technique for 9.10.3.5 Green &blueroof planting 9.10.3.4 Aplace for trees andshrubsintheSuDS landscape ■ ■ Design criteria: great numberofothernatural benefits. to theSuDS landscape, aswell asproviding a Trees provide anumberoffunctionsspecific Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Agreater depth of soilpermitsastronger plantcommunity andgreater absorptionofrainfall. ■ ■ A biodiverse native wildflower mixcanbe combined withplugplanting at between 8-16/m Allow healthy SuDS vegetation below by and root growth. Ensure sufficientspace for crown spread Greenroof withgravel edgeandrainchain. Ruskin MillHorsely, Glos. Design Notes: ■ ■ ■ ■ Design criteria: ■ ■ ■ ■ ■ ■ per square metre. Plug plantingisnormallyat 20-30 plants Plant choice shouldbedrought resistant. proposed useand desired character. Plant choice shouldbeappropriate for the proposed depthof growing medium. Plant choice shouldbeappropriate for the outlets. reduce theriskofblockage to inletsor smothering thevegetation below andto type that willdegrade easily, to avoid Give preference to asmallorpinnate leaf weeping orsuckering varieties. using atree withalightfoliage andavoid

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Detailed Design brick channelinto araingarden. A retrofit downpipe shoeand Strutts Centre, Belper. storage: control where itprovides therequired site considered asbothsource control andsite example apermeablepavement canbe The following classifications are notrigid, for the authors. components garnered over many years by detail solutionsofcommonly usedSuDS considerations, experiences andpractical section isto outlinesomeofthekey 2015 Sections11-23.The purposeofthis design are considered intheSuDS Manual The general principlesofSuDS component discharged from site inaneffective manner. conveyed, cleaned,stored, controlled and components ensures that runoffiscollected, Competent designanddetailingofSuDS Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates 9.11 SuDS Components ■ ■ ■ ■ site assets. basins, wetland andpondsto bedesigned as metals andheavy oilsfrom runoff, allowing Source controls remove most silt,heavy volume andsize ofsite controls. site isexploited, greatly reducing theoverall that every opportunityfor storage across the (distributed storage components), means Providing storage throughout thesite Source Controls providing storage ■ ■ ■ SuDS. can artificiallyincrease thedepthand cost of design. Designdetailssuchasroad gullies is aprimaryconsideration ofany SuDS crossing points such asfootpaths androads How runoffiscollected andconveyed under including spouts,surface channelsandrills. number ofsurface collection methods required. Historic urbandesignshows usa conveyance to theSuDS component may be Where runoffiscollected from roofs, Collection andconnection ■ ■ ■ ■ ■ ■ ■ permeable pavements bioretention raingardens green/ blueroofs pipe connections filter strips channels &rills ■ ■ ■ ■ multi-functional useandbiodiversity. places providing maximumopportunitiesfor with different designvolumes indifferent Careful designcanmaximize opportunities should beexplored. opportunities withinpavements andon roofs Where landscape islimited, storage of water inthelandscape. cost effective way to managelarge volumes the natural landscape, istheeasiest andmost depression intheground, mimicinghollows in Where runoffiscollected at thesurface, a Site Controls ■ ■ of ponding. the hard surface effectively withouttherisk filter strips or swales thenrunoffmust leave runoff flows directly from hard surfaces to as sheetflow from ahard surface. Where from animpermeablesurface isto intercept it The simplest methodofcollection ofrunoff permeable surfaces. structures, oritmust becollected through surface to allow runoffto flow into SuDS Water must eitherbekept at ornearthe conveyance Source Controls providing collection & Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ ■ ■ ■ ■ storage structures ponds wetlands basins filter drains swales Low riskaccess road with1.2mwidefilter strip Swale conveyance into pondsite control for Pershore HighSchool,Worcestershire. Pershore HighSchool,Worcestershire. source control andconveyance swale.

final treatment and storage.

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Detailed Design 1. lack ofdrought resillience. planting onthistypeofgreen roof dueto There are now many examples offailure of cost andtheideaofminimummaintenance. based vegetation. This approach isdriven by Sedum (fleshy leaved, drought tolerant plant) shallow depthofgrowing mediumwitha Recent examples intheUKhave focused ona Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Green &blueroofs natural drygrassland vegetation. this designisparticularlysuitablefor a recommended for drought resilience and A minimum100mmsoildepthis 3 3. 2. would bereferred to asablueroof. footprint may take upallofthesite. This urban redevelopment where thebuilding arrangement isparticularlyimportantfor stored againat orbelow ground level.This meaning that itdoesnothave to be opportunity to retain water ontheroof overflow arrangements provides anideal A simpleorifice control together with 30-40% void ratio. a water storage capacityofbetween Most green andblueroof substrates have 1 2 attractive site features. available to maintainthesepotentially used where community orprivate care is and low riskdrives andpathways, hasbeen manage reasonably cleanwater from roofs Raingardens are designedto collect and larger regional stormwater ponds. proposed for individualhousesto replace 1990 whensmallstormwater basinswere Prince George’s County, Maryland,USA in The raingarden concept was pioneered in Raingardens Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates 1 2 3 4 5. 4. 3. 2. 1. Key aspectsofraingarden designinclude: impeded drainage. an overflow incaseofheavy rain or particularly adapted to dryconditions most garden plantsotherthanthose submersion andwet soil–thisincludes garden plantsthat cantolerate occasional with upto 20%course compost a minimumof450mmimproved topsoil underdrain to avoid permanentwetness a free-draining soil,sometimeswith an the surface gentle sideslopeswithwater collected at

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Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates plant matter arisingfrom maintenance. well composted greenwaste orshredded yearly by theapplication ofamulchlayer of should berelatively highandreplenished the soil.The proportion oforganic matter leads to thewashing away ofnutrientsfrom The free-draining nature ofengineered soils the build-upofinorganic silt. maintenance shouldbeexpected to remove and urbanstreet use. Therefore, some normally carrysiltandpollutionfrom vehicles The runoffentering bioretention features will meet urbandesignstandards. the urbanscene soshouldbedesignedto These features cancontribute significantly to urban runoffinstreet locations andcarparks. top soilandisusedto managepolluted raingarden inthat itemploys anengineered A bioretention structure differs from a Bioretention Raingardens 1 6 2 6. 5. 4. 3. 2. 1. raingardens include; Key designaspectsfor bioretention 4 event ofblockage. a surface overflow for heavy rain orin the that discharges to anoutfall protects theunder-drained drainage layer a transition layer ofgritand/or sand and conveys runoffto adrainage layer with 20-30% organic matter cleans,stores a free draining soil,450-600mmdeep, the soil gravel protects theinfiltration capacityof a surface mulchoforganic matter, gritor through theengineered soil collection andstilling before infiltration space above thesoilprofile for water silt collection inforebays 3 5 3. 2. 1. available. Allshouldhave incommon: There are anumberofpermeablesurfaces infiltration into theground. structure for cleaningandstorage or to direct rainfall straight into aSuDS Permeable surfaces enableSuDS designers Permeable surfaces Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ ■ detailing asfollows: This riskcanbemanagedthrough design can leadto localisedsurface clogging. Silt washed offadjacent landscapeareas available for water storage. pavement withabout30%by volume provides structural strength to the an open-graded sub-baselayer that the pavement surface a pervioussurface to allow water through ■ ■ ■ be min.50mmbelow thepavement soil inadjacent plantingbedsshould adjacent areas use paved orturfed surfaces to slope adjacent landscapeareas away 3 2 1 replacement. and suctionremoval ofgritjointsandjoint 10 and20years ofusecomprising abrush maintenance may berequired after between clogging undernormaluse. Adedicated There are noreported issues withsurface website www.paving.org.uk SuDS Manual(Section20)andtheInterpave pavements are covered by guidance inthe The designandconstruction ofpervious Soft landscapeareas are setbelow kerb level at ■ ■ ■ ■ the pervioussurface. ideally anunderdrain before reaching surfaces shouldhave adepression and slopes runningtoward permeable ground cover to bindthesoilinplace adjacent plantingshouldincludedense edge

this permeablepaving installation. Almac CarPark, Limerick,Ireland.

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Detailed Design 3. 2. 1. store runoff. channels whichcancollect, treat, convey and Swales are shallow, flat bottomed vegetated Swale Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates rooting andassist infiltration. key for thetopsoil, encourage deep establishment oftheswale by providing a or lightharrowing willimprove 150mm cleantopsoil over subsoil.Ripping meandering channelcandevelop. conversely, basewidthwiderthan3ma the riskoferosion andditch forming, Base widthless than1mwidewillincrease 1 in50to prevent erosion. slope to aflat base falling at nomore than The basicprofile isa1in3or4side 1 2 5. 4. 3 erosion apron may beneeded. points through anupstand kerb an Where inletflows are concentrated to rounded to prevent thishappening. The shouldersshouldtherefore be swale canbe‘scalped’ leaving bare soil. 100mm, theshouldersat thetop ofthe Where swale vegetation iskept less than 4 2. 1. open stone filledtrench. after HenryFlaggFrench (1813-1885), isan Filter drains, sometimescalledaFrench drain Filter drains Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates reduce potential for clogging. strip placed infront ofthefilter drain will simple removal. Alternatively, agrass filter at thetop ofthedrain to trap any siltfor A sacrificial top layer may be considered unconsolidated soil. leading edgeto prevent erosion of a temporary level timberboard alongthe of thetrench asasheet.This may require Runoff shouldideallycross thelongedge 1 2 3 around thefilter drain willhave stabilised. biodegrade over timeby thetimesoils alterative lineristheuseofhessian whichwill blinding from finematerials insoils.An lining. Many geotextiles are susceptible to Most filter drains are designedwithgeotextile 3.

design andlocation. may benecessary dependingonthe can actasanoverflow. However, neither discharge andanupperperforated pipe A lower perforated pipewillassist

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131 Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Use ofpipes flush kerb inletor chute gullymay be needed. difficult where there isapath present anda Collecting runofffrom aroad canbemore prone to blockage. should notbetoo smallorthegrating willbe be more appropriate butthemeshsize In someplaces agrated surface channelmay landscape. inconvenience ofdeepstructures inthe reducing cost, triphazards andthe water to flow directly into SuDS features near thesurface. This isimportantasitallows Sett Channelsandrillskeep rainwater at or Channels andrills ■ points to consider are asfollows: footpaths andothercrossing points.Key in providing connections underroads, short lengthsofpipecanstill bevery useful requirement for extensive pipednetworks, Although SuDS are delivered withoutthe ■ ■ ■ ■ ■ ■ ■ chambers. to theotherwithoutneedfor internal direct rodding from oneendofthepipe Short lengthsofpipework shouldallow that they are notprone to blockage. Inlets andoutletsshouldbedesignedso immediately after the crossing. unpredictable flows are directed SuDS above pipework to ensure that integrated into thedevelopment surface An exceedance flow path shouldbe pipework. Different pipematerials or a requirement for structural cover over should notbeartificially increased due to The depthofthedownstream component provide minimalcover for adriveway crossing at A granite settchannelcollecting andconveying Concrete pipesurround hasbeenusedhere to above. crossings at the Devonshire Hillproject minimise cover -asusedfor driveway concrete surround canbeconsidered to runoff at Holland Park, London. Devonshire Hill,Haringey. A planted rillat Bewdley School Science Block. 2. 1. swale after ashortdistance. and willconnect to SuDS feature suchasa strips are effective at removing siltat source strip isgenerally defined by a kerb. Filter The hard edgefrom apavement to afilter Filter strips Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates edge ofthepavement. to ensure goodgrass growth upto the at minimumof100mm below thesurface The concrete haunchshouldbefinished off thepavement. of thekerb allows runoffto move freely Provision ofasmalldrop across theedge 1 2 4. 3.

liner. infiltration negating the requirement for a surface withlimited potential for Clay soils-runoffwillflow across the groundwater. pollution migrating through subsoilsto offset from thepavement to prevent clean sub-soilfor anagreed distance should besituated at least 300mmbelow Free draining soils-aprotective liner

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Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates and causeanuisance for maintenance teams. control, asloosestones easilymove around Avoid usingriprap asaform oferosion 2. 1. Basins, wetlands andponds gabion basket inlet. concrete headwall orstainless steel neutral headwall, suchasamitred should flow through asafe andvisually Where apipeentryisunavoidable it in achannelorswale. control components at ornearthesurface source control, shouldflow into site Reasonably cleanwater, through useof 1 This basinat SpringhillCohousing inStroud can children are doingadance andmovement class Facing: Anexample of ‘safety bedesign’:these in aSuDS storage area at RedHillSchool. be usedthroughout theyear. 2 135

Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates 2. 1. carefully. and ponddesignshouldbeconsidered The safety considerations inbasin,wetland the basinisfullofwater. the basinasthey willnotbevisiblewhen habitat shouldbeintegrated carefully into dry. Shallow micropools andwetland that most ofthetimebaseisfirmand storage drybasinshouldslopegentlyso in water. The bottom ofthetemporary this depthiscriticalfor afeeling ofsafety should notnormallyexceed 600mmas The overall depthoftemporary storage SuDS basinsandponds. accepted asanappropriate detailingfor series ofslopesandlevel benchesisnow slope shouldbeconsidered. The ideaofa basins access ramps withamore gentle not exceed 1in3or4andlarger maintenance machinery. Slopesshould easy andsafe access for peopleand The profile ofthe structure shouldallow 1 3. 2 account. 1.8m andthedesignmust take thisinto provides atotal potential stored depthof over permanentwater depthof1.2m is desired. Effective storage of600mm benches canbeconsidered ifopenwater the pond,withsurrounding shallower Therefore, andeeperarea inthecentre of beyond 1.2mdepthofpermanentwater. Most wetland edgeplantscannotcolonise vegetation willcover thepondintime. without regular maintenance meansthat activity occurs. However, adepth600mm natural pondsandwhere most biological 600mm asthisisacommon depthof Permanent ponddepth neednotexceed 3 Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates designed. no needfor suchmeasures ifproperly now nopublicaccess allowed. There shouldbe features into aresidential pocket park.There is health andsafety whendesigningattenuation This project failed to adequately consider 6. 5. 4. throughout. varying theprofile ofthepond swimming. This canbeachieved by designed for easeofopenwater Pond depthsandprofiles shouldnotbe accessible for rescue ifthisisrequired. ponds shouldbeeasy to exit and dangerous condition. Well designed out ofpondsandmerely acknowledges a Protective fencing willnotkeep children of concussion. which willprevent drowning intheevent set back1mfrom permanentwater edge, All hard engineered structures shouldbe 9. 8. 7.

catered for by design. imply that riskshave notbeensufficiently and lifebuoys should beavoided, asthey The useof‘danger –deepwater’ signs well designedinformative signage. permanent andtemporary water using messages identifyingthepresence of sensitively communicate healthandsafety landscape character. Itisusefulto community that openwater ispartofa There must beanacceptance by the over thefence for rescue. toddlers andallows adultsto easilystep should beconsidered asthisstops most expected a600-700mm picket fence Where unsupervisedtoddlers may be

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Detailed Design Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ train. they canform partoftheSuDS management confused withafullSuDS approach; however, providing underground tanksshouldnotbe being intheform ofgeocellular tanks.Simply construction industry withmay applications structures iscurrently utilisedthroughout Attenuation storage inunderground 9.11.5 Storage structures ■ ■ ■ catastrophic. consequences of failure canbe noticed, whichmay meanthat the failures andblockages tend notto get Where storage isinanunderground tank, management train. require integration withaSuDS inherent treatment capacity andtherefore Underground storage tanksdonothave ■ ■ manual (Section21.1) clarifiesthat: their useisstill beingunderstood. The SuDS industry andthelongterm implications of still relatively recent intheconstruction The introduction ofgeocellular structures is ■ ■ O’Brien etal,inpress) (see C737) design. (see Mallettetal,2014, and these systems causedby inadequate there have beenanumberof collapses of systems tends to bemore complex and The structural designof geocellular adequate sedimentremoval. upstream treatment isrequired to ensure inspection orcleaning,sovery effective tend notto beeasilyaccessible for Geocellular systems andplastic arches ■ ■ ■ considered: Manual thefollowing shouldalsobe In addition,to thestatements from theSuDS Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ ■ functionality ofthedrainage system andthescheme. Consideration shouldalsobegiven to Where thestated designlife ofthetank doesnotmeetthedesignlife ofthedevelopment, on thesurvival ofproduct manufacturers. Guarantees andwarranties are dependent construction phase. for oneofinferior qualityduringthe that aspecifiedproduct isnot swapped characteristics. Surety must beprovided products eachwithitsown loading There are awiderange ofattenuation not beaware of. design life loadingthat thedesignermay construction loading,whichmay exceed There are risksofstructural failure dueto the designshoulddemonstrate how thestructure willbereplaced whist maintainingthe funding mechanismfor undertakingthesereplacement works. Design Note: ■ ■ that: options thedesignershoulddemonstrate after afullexploration oftheavailable Where underground storage ispreferred

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of designinformation accordingly. followed andpresent theappropriate level the classification system hasbeen 0-3). Designersshoulddemonstrate that classification system (Scored between structural designrequirements usingarisk (Table 21.1) provides asummaryofthe geocellular tanks.The SuDS Manual C737 outlinesthedesignrequirements for receiving vehicular loading.CIRIAreport design consideration even ifthey are not Underground structures require structural 2012). negligible to zero treatment (Ellisetal, suggested by Table 26.15 to provide downsteam. Equally, gullypotsare catchpits canberemobilised andwashed 4.1) clarifiesthat sedimentswithin of siltremoval. The SuDS manual(Section not beaccepted asademonstrable form control SuDS components. Catchpits will permeable pavement) orothersource through meansoffiltration (bioretention, Robust siltremoval hasbeenprovided

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Detailed Design 9.12 management 9.12.1 The principles ofSuDS Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates requirement willbeminimised. through theuseofsource controls this be required for SuDS to remove silt,however redundant. Intervention maintenance canalso completed, rendering thetreatment function which canbecostly andinmany casesnot and gritfrom interceptors andseparators to remove toxic liquorfrom gullysumpsoroil which isrequired for conventional drainage This isdifferent to ‘intervention’ maintenance features oraquatic environments. and therefore form nothreat to amenity within Source controls at low concentrations metals andinorganic pollutantsare trapped term buildupoforganic pollution.Heavy components meaningthat there isnolong (passive treatment), withinmany SuDS surfaces isbroken down by natural processes pollution suchaswhichwash offhard Hydrocarbons andotherorganic based maintenance. management rather thandedicated SuDS much ofthecare for SuDS issite not implynomaintenance butrather that maintenance’ approach for SuDS. This does This documentintroduces a‘passive woodland oranurbanwasteland. carried outdevelopment willevolve towards management. Where maintenance isnot All designedlandscapesrequire somelevel of Management oftheSuDS landscape integrated SuDS design. Passive maintenance istherefore linked to overall management costs. and pipework isnotneededwhichreduces dedicated SuDS care. The cleaningofgullies should beconsidered assite care andnot regardless ofSuDS), thisminimalattention landscape (whichwould bepresent Importantly, where SuDS form partofa vegetation to de-water next to thewetland, A lighttracked excavator removes aquatic before moving to awildlife pile. Hopwood Park MSA M42. ■ ■ ■ of Work covering thefollowing: The managementplanwillincludeaSchedule including anticipated changes over time. SuDS managementwillbeexplained functionality ofSuDS. site operates andthebenefitsof retaining SuDS, how theSuDS infrastructure onthe The planwillprovide abriefexplanation of future expansion orredevelopment. expected changesover timeincludingany aspirations for thedevelopment and landscape maintenance. Itwilldescribethe SuDS inmanagingrainfall andcaninclude describes thedevelopment, theplace of A SuDS ManagementPlanisadocumentthat 9.12.2 The SuDS ManagementPlan Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates ■ ■ ■ Information inthemanagement planshouldbeconveyed inamannerthat isunderstandable exceed a doublesidedA4whichcanbelaminated andretained intheoperatives work van. to Site Operatives. Useoftechnical terms andunnecessary information shouldbeavoided. technical details. specification notes required to explain contractor where appropriate withany a pricingschedulefor themaintenance (including EAexemption) waste managementrequirements of undertaking maintenance tasksidentifyingfrequency The Maintenance Scheduleandkey planidentifyinglocations ofkey features shouldnot Design Note: ■ ■ ■ by theplan. remedial maintenance shouldalsobecovered maintenance. Occasional andpotential which corresponds withmost SuDS of regular site attendance, often monthly, Site managementusuallyrequires anelement

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provisions madeelsewhere. tanks shouldbecovered here or a definedlifespan, suchasgeocellular ground. Replacement ofitems whichhave vehicle access hasoccurred onwet instance, ruttingwhere unexpected design failure. Damagemay include, for cannot beanticipated orisaresult of Remedial maintenance –covers work that accurately orisinfrequent. where thefrequency cannotbepredicted Occasional maintenance –covers tasks everyday site managementvisits. be at amonthlyfrequency to match Regular maintenance –SuDS visitsshould

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Detailed Design 9.12.3 Example ofSuDS andSite Maintenance Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates Type pond Wetland & controls Flow paving Permeable Occasional Tasks paving Permeable outlets inlets & Grass Grass Grass LItter Regular Maintenance Activity removed to wildlife pilesor from site. year rotation or30%eachyear. Allcuttings to be Wetland vegetation to becut at 100mmon3–5 and checkfree flow Annual inspectionofcontrol chambers-remove silt ponding occurs Sweep andsuction brushpermeablepaving when Sweep allpaving regularly to keep surface tidy debris. Strim 1mround for access Inspect monthly, remove siltfrom slabaprons and rotation –30%eachyear –allcuttingsremoved Wildflower areas strimmed to 100mmon3 year Or end ofschoolholidays –allcuttingsremoved Wildflower areas strimmed to 100mminSeptor at collected annually aswildflower areas –1st andlast cuts to be 100mm with150mmmax.Cutwet swales orbasins to low flow channelsandotherSUDS features at Mow alldryswales, drySUDS basinsandmargins 35-50mm with75mm max.Leaving cuttingsinsitu Mow allgrass verges, paths andamenitygrass at with remainder ofthesite –remove from site Pick upalllitter inSUDS Landscapeareas along (SuDS) maintenance SuDS-specific care (Site) or Normal site Site Site Site Site SuDS SuDS Site SuDS Site frequency Suggested required year oras 4-8 visitsper 1 visitmonthly As required or 1 visitmonthly As required 1 visitannually year intervals estimate 10-15 As required - or asrequired 1 visitannually 1 visitmonthly 1 visitannually 1 visitannually Position Statement 055are met. where therequirements ofRegulatory application for anenvironmental permit component profile. The EAwillnotpursuean within thesite butoutsidetheSuDS sites canbede-watered andlandapplied Silt removed from most low to mediumrisk visually andby simplemonitoring. important to monitor siltaccumulation for instance inSuDS retrofit schemes, itis specifically includedasilt collection feature, components downstream orthedesignhas Where silthasaccumulated inSuDS ponds andwetlands. of themanagementtrain, particularlyin becomes more difficultand costly at theend be removed easily. Managementofsilt at thesurface siltaccumulates slowly andcan most caseswhere SuDS features are located a majorelementofSuDS management.In Silt andsedimentremoval isoften considered 9.12.4 Silt andwaste management Oxford City Council SuDS D&EGuide ©2018 McCloy Consulting &Robert Bray Associates SuDS General Remedial Work planting Native Silt Silt Undertake remedial work asrequired. when carryingoutothertasks. Inspect SuDS system to checkfor damageorfailure erosion. good ground cover to protect soilprofile from Remove lower branches where necessary to ensure flows. Spread, rake and overseed. feature, butoutsidethedesignprofile where water Excavate silt,stack anddrywithin10moftheSUDS accumulation Inspect swales, ponds,wetlands annuallyfor silt p709 Manual Chapter 33–Waste management should beevaluated assetoutintheSUDS Any waste considered to be contaminated any otherplanted feature onsite. considered for raingardens, bioretention or chipped woody material shouldbe The useofcomposted green waste or arrangements or taken offsite. waste, eitheronsite inwildlife piles,compost managed inthesameway assite green SuDS vegetation green waste canbe SuDS ManualChapter 32p699 should follow theprotocols setoutinthe Silt managementandremoval from site file/525315/LIT_9936.pdf system/uploads/attachment_data/ www.gov.uk/government/uploads/ EA Regulator Position Statement 055 SuDS SuDS Site &SuDS Site &SuDS

As required Monthly 1 visitannually As required 1 visitannually

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Sheffield Grey to Green : an excellent council- Acronyms used in this guide : led SuDS project with SuDS advice from McCloy Consulting and Robert Bray Associates. AEP Annual Event Probability AONB Area of Outstanding Natural Beauty BGS British Geological Survey BRE Building Research Establishment CCA Climate Change Allowance CDM Construction (Design & Management) Regulations CIRIA Construction Industry Research and Information Association Cv Coefficient of volumetric runoff DEFRA Department for Environment Food & Rural Affairs EA Environment Agency FEH Flood Estimation Handbook GWSPZ Groundwater Source Protection Zone IoH Institute of Hydrology LASOO Local Authority SuDS Officer Organisation

LLFA Lead Local Flood Authority LPA Local Planning Authority NPPF National Planning Policy Framework NSTS Non-Statutory Technical Standards PPG Planning Practice Guidance RefH2 The Revitalised Flood Hydrograph Model SAC Special Area of Conservation SFRA Strategic Flood Risk Assessment SSSI Site of Special Scientific Interest SuDS Sustainable Drainage Systems SWMP Surface Water Management Plan WaSC Water and Sewerage Company WFD Water Framework Directive