michael brock, p.e. · 2015. 1. 5. · sheet flow special considerations •application of runoff...

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.


SelectionofEffectiveGIPs


ApplicationtoSiteDesign• Duringthedesignprocess,intrinsicGIPsareappliedtothesitefirstandthen,ifrequired,structuralGIPsareapplied.

• RunoffReductionCredit(RRCredit),Level1(L1)andLevel2(L2),areappliedbasedonthephysicaldesignoftheGIP.

GOALWeightedRv <0.20

Intrinsic GIPs Overview

GeneralConsiderations• Takeadvantageofand/orenhancetheabilityofexistingpervious,naturalorlandscape,surfacestoreduceandtreatstormwater run‐off.

GIPsDisconnectedDownspouts

SheetFlowReforestation

(less design, more landscaping)

Downspout Disconnection

Source: www.lowimpactdevelopment.org


Roofdownspoutsaredisconnectedfromdirectflowintosewerinletsorimperviousareas(driveways,parkinglots,roads)leadingdirectlyintoapublicstormwater system.

RunoffisredirectedtoadownstreamperviousareasorotherGIPs.


Methods• Simple– disconnectandroutetoperviousarea• Series– leadstoadownstreamGIP

Source:VADCR,2011


Performance• Runoffisslowedandgivenmoreopportunitytoforinfiltration,evapotranspiration andrainwaterharvesting/reuse.

• RRCredit:Level1=25%;Level2=50%(usedwithotherGIPs).

SpecialConsiderations• TypicallyrequiresperviousareaequaltoorgreaterthantheimperviousCDA.

• Usuallyinvolvesperiodiclawnorlandscapingmaintenanceinthefilterpath,unlessdirectedtorainbarreloranatural,undisturbedsetting.


RooftopDisconnection– SectionView:SimpleDisconnectiontodownstreamBioretention (Source:VADCR,2011)


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

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

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

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

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

Module Topic Summary

GeneralOverviewIntrinsicGreenInfrastructurePractices

• Key:Takingadvantageofexistingnaturallandscape.StructuralGreenInfrastructurePractices

• Key:

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michael brock, p.e. · 2015. 1. 5. · sheet flow special considerations •application of runoff...

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