michael brock, p.e. 6 - gips.pdfgreen infrastructure practices (gips) intended to mimic the natural...
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6 ‐ Introduction to Green Infrastructure Practices
Michael Brock, P.E.
Module Content
GeneralOverviewIntrinsicGreenInfrastructurePracticesStructuralGreenInfrastructurePractices
Introduction
GreenInfrastructurePracticesEcosystem‐basedapproachesthatstrategicallyintegratesstormwater controlsthroughouttheurban/rurallandscapetoachievethedesired site
runoffquantityandquality.
(GIPs)
Green Infrastructure Practices (GIPs)
Intendedtomimicthenaturalhydrologicconditionandallowstormwater toinfiltrateintotheground,evaporateintotheair,evapotranspirate byplantuptakeorcapturedforreuse.
Designedtomeetmultiplestormwater managementobjectives,includingreductionsinrunoffvolume,peakflowratereductions,andwaterqualityprotection.
Decentralizedstormwater managementstrategiesofmultiplesmall,localizedcontrolsthatmaybecombinedintoa“treatmenttrain”toprovidecomprehensivestormwater treatment.
Constructedindividually,oraspartoflargerconstructionprojects.
Green Infrastructure Practices (GIPs)
SelectionofEffectiveGIPs
Green Infrastructure Practices (GIPs)
Green Infrastructure Practices (GIPs)
ApplicationtoSiteDesign• Duringthedesignprocess,intrinsicGIPsareappliedtothesitefirstandthen,ifrequired,structuralGIPsareapplied.
• RunoffReductionCredit(RRCredit),Level1(L1)andLevel2(L2),areappliedbasedonthephysicaldesignoftheGIP.
GOALWeightedRv <0.20
Green Infrastructure Practices (GIPs)
Intrinsic GIPs Overview
GeneralConsiderations• Takeadvantageofand/orenhancetheabilityofexistingpervious,naturalorlandscape,surfacestoreduceandtreatstormwater run‐off.
GIPsDisconnectedDownspouts
SheetFlowReforestation
(less design, more landscaping)
Downspout Disconnection
Source: www.lowimpactdevelopment.org
Downspout Disconnection
Roofdownspoutsaredisconnectedfromdirectflowintosewerinletsorimperviousareas(driveways,parkinglots,roads)leadingdirectlyintoapublicstormwater system.
RunoffisredirectedtoadownstreamperviousareasorotherGIPs.
Downspout Disconnection
Methods• Simple– disconnectandroutetoperviousarea• Series– leadstoadownstreamGIP
Source:VADCR,2011
Downspout Disconnection
Performance• Runoffisslowedandgivenmoreopportunitytoforinfiltration,evapotranspiration andrainwaterharvesting/reuse.
• RRCredit:Level1=25%;Level2=50%(usedwithotherGIPs).
SpecialConsiderations• TypicallyrequiresperviousareaequaltoorgreaterthantheimperviousCDA.
• Usuallyinvolvesperiodiclawnorlandscapingmaintenanceinthefilterpath,unlessdirectedtorainbarreloranatural,undisturbedsetting.
Downspout Disconnection
RooftopDisconnection– SectionView:SimpleDisconnectiontodownstreamBioretention (Source:VADCR,2011)
Downspout Disconnection
AmendedFilterPathtoDownstreamGrassChannel,orothertreatment(Source:VADCR,2011)
Sheet Flow
Sheet Flow
Imperviousareasaredisconnectedandrunoffisdirectedthroughalevelspreadercreatingsheetflowontoanadjacentperviousarea.
Twobasicvariations:• Conservedopenspace• Vegetatedfilterstrip
Sheet Flow
Conservedopenspace
Sheet Flow
Vegetatedfilterstrip
Sheet Flow
Performance• Soilbasedsystem• Imperviouscontributative drainagearea~5,000sf(maximum)
• Runofftobeslowed,redirectedandtogivemoreopportunitytoforinfiltration,andsedimentremovalofrunoff.
• Varydependingontheunderlyingsoilpermeability.• RRCredit:Level1– 50%;Level2– 75%(Soildependant)
Sheet Flow
SpecialConsiderations• Applicationofrunoffreductioncreditdependantonmeetingappropriateminimumdesigncriteria.
• Sheetflowandhydraulicconnectivitymustbemaintained.
• Levelspreader(vegetated,graveldiaphragm,permeableberm,engineeredstructure)isanintegralpartoftheGIPfunction.
• Usuallyinvolvesperiodicmaintenanceoflevelspreaderandlandscapingmaintenanceofvegetatedfilterstriporconservedopenspace.
Sheet Flow
LevelSpreader
Sheet Flow
LevelSpreader
Reforestation
Reforestation
Reforestationrefersto(primarily)treesplantedingroupsinurbanareassuchas:parkinglots,rightofways(ROW),parks,schools,publiclands,vacantland,andneighborhoodopenspaces.
Providesshade,stormwater retentionandaddsthesitesaestheticvalue.
Theexplicitgoalistoestablishamatureforestcanopythatwillinterceptrainfall,increaseevapotranspiration,andenhancesoilinfiltrationrates.
Reforestation
Performance• Soilbasedsystem.•Minimumareasize~5,000sf (contiguous)• ReforestedareaRv basedonHSGsoiltypeandamendment.
• Additionalrunoffreductioncreditavailableifusedasvegetatedfilterstripforsheetflow.
• RRCredit:(Soildependant) Level1;90%‐ 96%(noamendedsoils) Level2;95%‐ 98%(withamendedsoils)
Reforestation
SpecialConsiderations• Usuallyrequireslargededicatedareatoprovidefortreegrowthandforsignificantreductioninstormwaterrunoff.
• Vegetation(tree)selection.
Structural GIPs Overview
Engineeredpracticesthataredesigned,constructedandmaintainedtofacilitateinfiltration,evaporation,evapotranspiration ofstormwaterrunoffandrainwaterharvestingforreuse.GeneralConsiderations
• Soils(HSG/Infiltrationrates/Plantingrequirements).
• ImperviousContributingDrainageArea.• Depthtowatertableorbedrock.• Existingpollution
Structural GIPs Overview
GIPsBioretention Urban
BioretentionWaterQuality
SwaleGreenRoof
GrassChannel Cistern
PermeablePavements
InfiltrationTrench
ExtendedDetention(more design, less landscaping)
Bioretention
Bioretention
Vegetated,shallowdepressions.Capturedrunoffistreatedbyfiltrationthroughanengineeredsoilmedium,andistheneitherinfiltratedintothesubsoilorexfiltrated throughanunderdrain.Primarycomponentisthefilterbed,whichhasamixtureofsand,soilandorganicmaterial(filteringmedia)withasurfacemulchlayer.Onasmallerscalethesearepopularlyknowas“RainGardens”.Variations
• Withoutunderdrains,subsoils withinfiltrationrategreaterthan½”perhour
• Withunderdrains,subsoils withinfiltrationratelessthan½”perhour
Bioretention
Performance• Soilfiltration/gravelbasedstorage/infiltrationsystem.
• ImperviousCDA~2.5acres,multiplecellscanservelargerareas.
• Goodenvironmentforrunoffreduction,filtration,biologicaluptake,andmicrobialactivity,andprovideshighpollutantremoval.
• Canbecomeanattractivelandscapingfeaturewithhighamenityvalueandcommunityacceptance.
• Performancelevelsbasedonfiltermediadepth.• RRCredit:Level1– 60%;Level2– 80%
Bioretention
SpecialConsiderations• Pre‐treatmentrequiredtoremovecoursesediments.• Canbeinstalled: Online,mustprovideforoverflow Offline,alternateflowwhenfull
• Ingeneral,vegetativegoalistoachievesurfaceareacoverageofatleast75%.
• Forabioretention areatoqualifyforL2design,aminimumofonetreemustbeplantedforevery400squarefeet.
• Onceestablished,typicalonlyspringcleanupmaintenance.
Bioretention
Source:VADCR,2010
Bioretention
Source:VADCR,2011
Bioretention
Source:VA‐DCR,2013
Bioretention
Source:VA‐DCR,2013
Bioretention
Source:VA‐DCR,2013
Urban Bioretention
Urban Bioretention
UrbanBioretention issimilartotraditionalbioretentionpractices,butisfitintohard‐sidedcontainerswithinurbanlandscapessuchasplanterboxesortreeplanters.
Capturedrunoffistreatedbyfiltrationthroughanengineeredsoilmedium,andistheneitherinfiltratedintothesubsoilorexfiltrated throughanunderdrain.
Primaryuseisforsmallfragmenteddrainageareasandfeature“hardedges”.
Variations:• Stormwater planters– betweenbuildings,sidewalksandroadways• GreenStreets– roadsidesandmedians
Urban Bioretention
Performance• Soilfiltration/gravelbasedstorage/infiltrationsystem• ImperviousCDA~2,500sf (maximum)• UrbanBioretention createsagoodenvironmentforrunoffreduction,filtration,biologicaluptake,andmicrobialactivity,andprovideshighpollutantremoval.UrbanBioretention canbecomeanattractivelandscapingfeaturewithhighamenityvalueandcommunityacceptance.
• RRCredit:Level1– 60%
Urban Bioretention
SpecialConsiderations• SmallimperviousCDA.• Usuallyrequiresflowdiversionandunderdrain withconnectionstolocalstormwater system.
• Protectionofadjacentbuildingfoundationsandlocationofoverheadandundergroundutilities.
• Considervisualobstructions,utilitiesandmaintenanceforplantingschosen.
•Maintenance Landscapeandtrashremoval. Mayrequireirrigationduringperiodsofdrought.
Urban Bioretention
Water Quality Swale
Water Quality Swale
Vegetatedopenchannelsdesignedtocaptureandinfiltratestormwater runoffwithinadrystoragelayerbeneaththebaseofthechannel.Swalesareessentiallybioretention cellsthatareshallower,configuredaslinearchannels.Canbeplantedwithturfgrass,tallmeadowgrasses,decorativeherbaceouscoverortrees.Swaleisasoilfiltersystemthattemporarilystoresandthenfiltersthedesiredtreatmentvolume.ConveyancechanneltodownstreamGIP.Variations:
• Withoutunderdrains,subsoils withinfiltrationrategreaterthan½”perhour
• Withunderdrains,subsoils withinfiltrationratelessthan½”perhour
Water Quality Swale
Performance• Soilfiltration/gravelbasedstorage/infiltrationsystem.
• ImperviousCDA~2.5acres• Primarypollutantremovalmechanismsoperatinginswalesaresettling,filteringinfiltrationandplantuptake.
• RRCredit:Level1– 40%;Level2– 60%
Water Quality Swale
SpecialConsiderations• Runoffacceptancecanbeeitherlongitudinalorlateral.• Slopeslessthan2%orprovidecheckdamstoslowchannelvelocities.
• Underdrains mayberequiredwithHSGC&HSGDsoils.•Multiplevariationsingeometrytofitexistingsitetopography
•Maintenance Landscapeandtrashremoval. Onceestablished,typicalonlyspringcleanup.
Water Quality Swale
Water Quality Swale
Storage/ Infiltration without Underdrain
Storage/ Infiltration with Underdrain
With Underdrain
Source:VADCR,2011
Grass Channel
Grass Channel
Conveyancechannelsthataredesignedtoprovidesometreatmentofrunoff,aswellastoslowdownrunoffvelocitiesfortreatmentbyotherdownstreamGIPs.
Appropriateforanumberofapplicationsincludingtreatingrunofffrompavedroadsandotherimperviousareas.
Limitedapplicationstructuralcontrolintendedforsmalldrainageareas.
Apreferablealternativetobothcurbandgutterstormwater conveyance,wheredevelopmentdensity,topographyandsoilspermit.
Grass Channel
Performance• Soilbasedsystem.• ImperviousCDA~5acres• Channelsthatarevegetatedandaredesignedtofilterstormwater runoffthroughsettlingandbiologicaluptakemechanisms,aswellastoslowwaterfortreatmentbyanotherstructuralcontrol.
• Varydependingontheunderlyingsoilpermeability.• RRCredit:Level1– 10%,20%;Level2– 20%,30%(Soildependant)
Grass Channel
SpecialConsiderations• Slopeslessthan2%orprovidecheckdamstoslowchannelvelocities.
• HSGC&HSGDsoilsshouldbeamendedtoimproveperformance.
• Grassesshouldbeseeded(notsodded)toprovide90%turf(thick,dense)coverage.
• Grassesshouldbefloodanddroughttolerant.Maintenance
• Maintaingrassheightof3to4inches.• Removalofsedimentbuildupinchannelbottomwhenitaccumulatesto25%oforiginaltotalchannelvolume.
• Ensurethatrillsandgullieshavenotformedonsideslopes.• Removetrashanddebrisbuildup.• Replantareaswherevegetationhasnotbeensuccessfullyestablished.
• Onceestablished,springcleanup.
Grass Channel
Grass Channel
Grass Channel
Permeable Pavements
Permeable Pavements
Allowstormwater runofftofilterthroughvoidsinthepavementsurfaceintoanunderlyingstonereservoir,whereitistemporarilystoredand/orinfiltrated.Severaldesignvariants,butallhaveasimilarstructure,consistingofasurfacepavementlayer,anunderlyingstoneaggregatereservoirlayerandafilterlayerorfabricinstalledonthebottom.MajorCategories:
• Modularblocksystems• Perviousconcrete• PorousAsphalt• Grassandgravel
Permeable Pavements
Performance• Gravelbasedstorage/infiltrationsystem.• Designgoalistomaximizerunoffreduction(Tv capture).• RRCredit: Level1;45%(allowedtohandleuptotwiceimperviousCDA) Level2;75%(onlyallowedhandlingrainfallonitssurface)
SpecialConsiderations• Underdrain requiredifsubsoilinfiltrationratelessthan½”perhour.
• PrimelocationsonHSGAandHSGBsoils.• Sensitivetohighsedimentanddebris(trashloading).• Sensitivetotrafficloads(shearstresses).
Maintenance• Usuallyinvolvesvacuumsweepingofpavementsurfaces.
Permeable Pavements
Infiltration Trench
Infiltration Trench
Trenchesareexcavationstypicallyfilledwithstone(#57)tocreateanundergroundreservoirforstormwater runoff.
Runoffvolumegraduallyexfiltrates throughthebottomandsidesofthetrenchintothesubsoils andoveraperiodoftimeeventualreachingthewatertable.
Bydivertingrunoffintothesoil,thetrenchnotonlytreatsthewaterqualityvolume,butalsohelpstopreservethenaturalwaterbalanceonasiteandcanrechargegroundwater,preservingthebaseflow.
Limitedtoareaswithhighlyporoussoilswherethewatertableand/orbedrockarelocatedwellbelowthebottomofthetrench.
Infiltration Trench
Performance• Gravelbasestorage,soilbasedinfiltration.• ImperviousCDA~2.5acres•Widevarietyofpollutantsfromstormwater throughabsorption,precipitation,filtering,andbacterialandchemicaldegradation.
• RRCredit:Level1– 50%;Level2– 90%SpecialConsiderations
• Sedimentloadandothersuspendedsolidsshouldberemovedfromrunoffbypretreatmentmeasures.
• On‐lineandoff‐lineapplications.• Requiresinfiltrationratesgreaterthan½”perhour.• Notapplicableforrunofffrompollutionhotspots.
Infiltration Trench
Maintenance• Ensurethatcontributingareaandinletsareclearofdebris.• Removesedimentandoil/greasefrompretreatmentandoverflowdevices.
• Checkobservationwellsfollowing3daysofdryweather.Failuretopercolateindicatesclogging.
• Removetreesthatstarttogrowinthevicinityofthetrench.
• Replacepeagravel/topsoilandtopsurfacefilterfabric(whenclogged).
Infiltration Trench
Green Roof
Green Roof
Arealternativeroofsurfacesthattypicallyconsistofwaterproofinganddrainagematerialandanengineeredgrowingmediathatisdesignedtosupportplantgrowth(alsoknownasvegetatedroofs,livingroofsorecoroofs).Captureandtemporarilystorestormwater runoffinthegrowingmediabeforeitisconveyedintothestormdrainsystem.Aportionofthecapturedstormwater evaporatesoristakenupbyplants(evapotranspiration),reducingrunoffvolumes,peakrunoffandpollutantloads.TwoTypes:
• Extensive• Intensive– deepergrowingmedia
Green Roof
Green Roof
Green Roof
Performance• Capture/engineeredgrowthmediainfiltration.• Roofarea(maximum)withnon‐vegetatedareas<20%.• Primarilyrunoffreductionbyevaporationandplantuptake.
• RRCredit:Level1– 80%;Level2– 90%Maintenance
• Handweedingandfertilizing.• Plantreplacement.• Roofleakrepair.
Green Roof
SpecialConsiderations• AlldesignsmustbeinconformancetoASTM(2005)InternationalGreen(Vegetated)RoofStandards.
• Designsmaybelimitedtoroofstructuralcapacityandaccess.• Plantselectionforvegetatedrooftopsisanintegraldesignconsideration,whichisgovernedbylocalclimateanddesignobjectives.Theprimarygroundcoverformostvegetatedroofinstallationsisahardy,low‐growingsucculentsthatarematchedtothelocalclimateconditionsandcantoleratethedifficultgrowingconditions(sunlight,drought,saturatedsoil).
• Requirementforirrigationduringperiodsofdrought.• Protectionfrombuildingmaintenanceactivities,particularlyinvolvingcleaning(overspray)ofchemicalagents.
Green Roof
Cistern
Cistern
Raintanksandcisternsareusedtointercept,divert,storeandreleaserainfallingonrooftopsforfutureuse.Twomethods:
• Aboveground• Belowground
Cistern
Performance• Captureandnon‐potablewaterreuse.• Capturevolumebasedonstorage(tank)capacity.Capacityisprimarilybasedonanticipateddemand,roofareaandrainfall.
• Primarilybasedondedicatedreusedemand.• RRCredit:Variableupto90%reduction(treatmentvolume).
SpecialConsiderations• SteepterrainapplicationwhereotherGIPsarenotappropriate.
• Varioussystemdesignconfigurations: Yearroundindoorusewithoptionalseasonaloutdooruse. Seasonaloutdooruseandoptionalyear‐roundsecondaryrunoffreductionpractice. Year‐roundindooruse,seasonaloutdoorirrigation,andnon‐seasonaltreatmentinasecondaryrunoffreductionpractice.
Cistern
Maintenance• Inspectedtwiceyearly(spring/fall).• Usuallycleaningoffiltersandsedimentaccumulationinstoragetank(s).
Extended Detention
Extended Detention
Constructedstormwater detentionbasinthathasapermanentpool,ormicropool.Runofffromeachraineventiscapturedandtreatedthroughsettlementofsuspendedsolids.Variations:
•Wetextendeddetention•Micropool extendeddetention.•Multiplepondsystem.
Extended Detention
Performance• Thetemporaryponding enablesparticulatepollutantstosettleoutandreducesthemaximumpeakdischargetothedownstreamchannelreducingtheeffectiveshearstressonthedownstreambanks.
• RRCredit:Level1– 15%Maintenance
• Inspectedannually.• Typicalactivities: Lowfloworificemaintenance(twiceyearly). Removaloftrashandfloatablematerials. Sedimentremoval. Vegetationmaintenance.
Extended Detention
SpecialConsiderations• Designtoachieveaminimumdrawdowntime(24hours),ratherthanpeakflow.
• Accessformaintenanceandinspection.• Emergencyspillwayforlargestormevents.• No‐erosiveinlet/outfallvelocity.• Screeningoflowfloworifices.• Landscapingandplantingplans.•Mosquitoabatement.• TennesseeSafeDamsActmayapplytopondswithstoragevolumesandembankmentheightslargeenoughtofallundertheregulationfordamsafety.
•Multi‐usefunctionality.
Extended Detention
Extended Detention
Module Topic Summary
GeneralOverviewIntrinsicGreenInfrastructurePractices
• Key:Takingadvantageofexistingnaturallandscape.StructuralGreenInfrastructurePractices
• Key:
Questions?