Green Infrastructure Design Principles and Considerations

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Green InfrastructureDesign Principles and Considerations

November 5, 2009 Toledo, OHDaniel P. Christian, PE, D.WRETetra [email protected]

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AgendaIntroductionTypes of Practices and What They DoPlantsSoilsOutletsExample ApproachStrategies for Design/ImplementationImplementation ExamplesSummary

Source: FISRWG 2001 3

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Large Storm Small Storm

Higher Baseflow

Higher and More Rapid Peak Discharge

More Runoff Volume

Lower and Less Rapid Peak

GradualRecession

Pre-developmentPost-development

Large Storm Small Storm

Higher Baseflow

Higher and More Rapid Peak Discharge

More Runoff VolumeLower and Less Rapid Peak

GradualRecession

Pre-development-Post-development

Consequences of Development to Urban Streams

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Green InfrastructureGreen Infrastructure management approaches and technologies infiltrate, evapotranspire, capture and reuse stormwater to maintain or restore natural hydrologiesBenefits

Reduced and delayed stormwater runoff volumeEnhanced groundwater rechargeReduced stormwater pollutantsIncreased carbon sequestrationUrban heat island mitigation and reduced energy demandsImproved air qualityAdditional wildlife habitat and recreational spaceImproved human healthIncreased land values

Source: USEPA Green Infrastructure website

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Water Storage - Surface

Traditional Retention•Poor infiltration•Good evaporation•Poor plant uptake and transpiration

Bioretention (rain garden)•Good infiltration•Poor evaporation•Good plant uptake and transpiration

Traditional Detention•No infiltration•Poor evaporation•Poor plant uptake and transpiration

Green Roof•No infiltration•Good evaporation•Good plant uptake and transpiration

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Water Storage - Underground

CultecEnv21 Cultec

StormChamber

Xerxes

Rotondo

EcoRain

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Rainwater Harvesting and Conservation

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Permeable Pavements

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Other Stormwater BMPsTypes

Sand filtersHydrodynamic devicesInlet TrapsGross Solids Removal Devices

PurposeTarget floatable trash and suspended solidsMay be tailored to other pollutants (e.g. hydrocarbons)

What they don’t doIncrease evapotranspiration and infiltration

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Plants

RoleWater UptakeStabilizationImpeding FlowFiltrationInfiltrationNutrient UptakeToxin UptakePollutant Breakdown

Example ApplicationsNurse crop/cover cropBuffer stripsVegetated trenchesBiofiltration/rain gardensVegetated swales and ditchesStormwater ponds/wetlandsGreen roofsNative plant reconstruction

R. Domm

Source: FISRWG 2001

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Plant Selection and Installation Considerations

Site Conditions to InvestigateTexture, organic content and pHWater levels, soil moistureAdjacent plant communitiesSlopesAmount of sun/shade

Environmental ThreatsFlood depth, duration and frequencyLow water levelsSediment loadsPollutants and toxinsNutrientsSaltTurbidityErosionInvasive plantsHerbivores

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Transpiration Rates of Various Plants

200-800 gpd/treeTree (mature)Weeping Willow

50-350 gpd/treeTree (mature)Cottonwood

20-40 gpd/treeTree (5 year old)Hybrid poplar

2-3.75 gpd/treeTree (2 year old)Cottonwood

0.48 in/dayPrairie speciesPrairie cordgrass

1.9 in/dayWetland/prairie speciesSedge

0.86 in/dayWetland speciesGreat bulrush

0.44 in/dayWetland speciesCommon reed

0.41 in/dayAgriculture cropAlfalfa

0.27 in/dayLawn grassPerennial rye

Transpiration RatePlant TypePlant Name

Source: Plants for Stormwater Design Volume II by D. Shaw and R. Schmidt (ITRC 2001)

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Native Vegetation Sources

Natural Resources Conservation Service (NRCS)US Forest ServiceState and Local Stormwater ManualsState Environmental and Natural Resource AgenciesUniversity Extension ServicesFHWA Roadside Use of Native Plants www.fhwa.dot.gov/environment/rdsduse/wv.htmFind a local native plant nursery www.plantnative.org

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Soil CharacteristicsPorosity: void space of soil (space for water)Infiltration: movement of water through soilField Capacity: proportion of void space that stays wet due to surface tension (i.e. after water drains by gravity)Wilting Point: point at which plants can no longer withdraw water fast enough to keep up with transpiration

Source: FISRWG 22

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Consider this . . .

Consider a tree box sized for a 16” caliper tree (1,000 cf of soil)Fine sandy loam soil with 25% unfilled void space (0.45 porosity– 0.2 field capacity)Volume = 250 cf (1,000 cf * 0.25)Area of impervious surface needed to generate 250 cf of stormwater from a 1-inch of runoff = 3,000 sfAssuming drainage from ½ a 66-ft ROW equates to one tree box every 91-ftIgnored evaporation, infiltration, water uptake by plants, and depression storage

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Infiltration CapacityDry Soils, Little or No Vegetation

Sandy soils: 5 in/hrLoam soils: 3 in/hrClay soils: 1 in/hr

Dry soils with Dense VegetationMultiply by 2

Saturated SoilsSandy soils: 1 to 4 in/hrLoam soils: 0.25 to 0.50 in/hrClay soils: 0.01 to 0.06 in/hr

Source: Rawls, W.J., D.L. Brakensiek, and N. Miller, “Green-Ampt Infiltration Parameters from Soil Data” J. Hydr Engr. 109:62, 1983), EPA SWMM 5 Users Manual, and FISRWG 24

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What if you combineda basina water loving tree, andan engineered soil mix?

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Effects of Compaction on Infiltration Rates

Decreased infiltrationDecreased root growthIncreased runoff

Source: Pitt R., S.E. Chen, S. Clark

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2.40.260All other clayey soils (compacted and dry, plus all wetter conditions)

1.59.818Noncompacted and dry clayey soils1.31.439Compacted sandy soils0.41336Noncompacted sandy soils

COVAvg Infil(in/hr)

Number of tests

Source: R. Pitt, S.E. Chen, S. Clark

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KarstBackground

Karst refers to set of physical conditions, landforms and bedrock attributesSoluble carbonate rocks underlie the surface

Most common limestone, dolostone (dolomite) and marbleWeakly acidic rainwater seeps into joints and fractures and gradually enlarges themSinkholes are common, formed by dissolution of near-surface rocks or collapse of underground channels/caves

American Geologic Institute (www.agiweb.org/)

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Karst FeaturesLow density of surface water drainagewaysClosed depressions with internal drainageSinkholesGround water levels that may vary appreciably over relatively short distancesThin soilsHigh flow rate springsHard groundwater and bicarbonate chemistry in streamsUndeveloped state, karst terrain produces less runoff

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Karst Concerns

Highly variable subsurface conditions and often poorly understoodIncreased risk of groundwater contaminationIncreased risk of sinkhole formationPlugged sinkholes may increase the risk of flooding

intentionally through construction and land disturbance or,unintentionally through runoff and sedimentation

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Karst StormwaterDesign PrinciplesDetailed site investigations to fully understand subsurface conditions, karst vulnerability and drainage patternsMinimize site disturbance and changes to soil profileTreat sheetflow runoff before it becomes concentratedLots of small scale practicesDiscourage centralized stormwater practices with large drainage areasMaintain quality and quantity of runoff to predevelopment levelsMinimize rerouting of stormwater from existing drainage

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Stormwater Practice Selection in Karst

Prohibited

Discouraged

Adequate

PreferredSuitability

Use small-scale insteadLarge Scale InfiltrationLined. At least 6-ft of soil over bedrock. <6-ft of ponding depthDry Extended DetentionLined. At least 6-ft of soil over bedrock. <6-ft of ponding depthWet PondsLined and Linear Cells, at least 3-ft of soil over bedrockConstructed WetlandsIf sinkhole formation and groundwater contamination are not a concernPermeable PaversClosed systemsMicro-bioretentionNot at stormwater hotspotsSmall Scale Infiltration

Soil Compost AmendmentCompost amendment, discourage check damsGrass ChannelFlow to karst swalesFilter StripsLinedFiltering PracticesLined with underdrainDry Swale

Green RoofsExtend discharge at least 15-ft from buildingRooftop DisconnectionTanks above ground preferred over below ground installationRain Tank/Cistern

Underdrain if <3-ft of soil. Liner if groundwater contamination concern. Tributary area <20,000 sf. Surface ponding < 9-inches.

BioretentionNotesPractice

CSN 2009

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Karst References

American Rivers. 2007. Using Green Infrastructure in Karst Regions. Washington, D.C. www.americanrivers.orgFennessey, L. 2003. Defining Natural Land Areas Critical to Stormwater Control in Karst Regions. Proceedings of the 2003 Pennsylvania Stormwater Management Symposium. October, 2003. Villanova University. Philadelphia, PA.Karst Working Group, 2009. Stormwater Design Guidelines for Karst Terrain in the Chesapeake Bay Watershed. CSN Technical Bulletin No. 1, Version 2.0. www.chesapeakestormwater.netRalston, M. and I. Oweis. 1999. Geotechnical Engineering Considerations for Stormwater Management in Karst Terrain. Proceedings of the 1999 Southeastern Pennsylvania Stormwater Management Symposium. Villanova University. Philadelphia, PA.

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Engineered Soil Mix Examples

Prince Georges Co. MD: 50-60% sand; 20-30% compost; 20-30% topsoil (Minnesota added <5% clay stipulation)NCSU: 85% sand; 12% fines; 3-5% organicsPortland OR: 60-70% sand; 30-40% compost (35-65% organic); particle gradation specifiedLow Impact Development Center: 50% sand; 30% planting soil (50-85% sand, 0-50% silt, 10-20% clay, 1.5 -10% organic); 20% shredded hardwood mulchTypical infiltration rate of soil mixes is 1 to 8 in/hr

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Soil Strategies

Protect native soil during construction by limiting access, grading/clearingIncrease soil volume by connecting planting areas, thereby sharing rooting spaceAlternative Soil Strategies

Soil TrenchesStructural Soil (use of stone to provide load bearing integrity while preserving void space)Suspended Pavements and Structural Cells

Avoid conflicts between rooting and infrastructure subgrade by using soil free aggregate under hardscape surfaces or use of root barriers

Urban Watershed Forestry Manual Part 3, 2006

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Outlet Controls

UnderdrainsLinersOverflowsDiversionsInjection Wells

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Outlet Controls

Filtration vs Infiltration

Underdrain Overflow/Diversion

Underdrained systems are flow-through systems, and discharge water from even small ‘design storms’.

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Reasons to IncludeUnderdrains and Liners

Protect surrounding infrastructure

BasementsRoads/parking

Isolate contaminated soilsLeaky underground storage tanks

Prevent unwanted flora and fauna

Mosquitoes

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Overflows and Diversions

Think about big stormsInline Systems

Water forced to flow through system

Offline SystemWater diverted after capacity reached

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Class V Injection WellClass V wells are shallow wells used to place a variety of fluids directly below the land surface. An “injection well” is a “well” into which “fluids” are being injected (40 CFR §144.3).Memo & guide issued June 13, 2008 by EPA clarifies which infiltration practices are generally considered class V wells

If stormwater directed into hole that is deeper than it’s widest point orhas a subsurface distribution system

Potential examplesInfiltration trenchesCommercially manufactured stormwater infiltration devicesDry wells and seepage pits

Reporting requirements40

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Consider a typical development example

Area = 2.98 acBuilding Footprint = 20.9%Parking/sidewalk = 36.5%Turf grass = 42.6%

B/C soilFlatEPA-SWMM V5 model

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No Stormwater Controls

Average Annual (from 50-years)

Natural Hydrology

Post Development

Evaporation 10% 19%

Infiltration 90% 38%

Surface Runoff <1% 43%

■ Traditional development with no stormwater controls

Rainfall

Post Development

Natural Hydrology

10-yr 24-hr SCS Type II

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Traditional Detention


Natural Hydrology

Post Development

Evaporation 10% 19%



■ Traditional drainage system■ Detention sized with 0.15 cfs/acre maximum

release rate■ No change in average annual surface runoff

Time (hr)

Rainfall

Post Development

Natural Hydrology


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Impervious → Pervious


Natural Hydrology

Post Development

Evaporation 10% 20%



■ Impervious surfaces discharge to green areas■ Green areas discharge to drainage system■ Decreased average annual surface runoff from

43% to 9%

Rainfall

Post Development

Natural Hydrology


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Added Storage


Natural Hydrology

Post Development

Evaporation 10% 32%



■ Impervious → Pervious■ 1-inch roof storage (or equiv)■ 1-inch storage on pervious areas

Rainfall

Post Development

Natural Hydrology


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Enhanced Infiltration and Evapotranspiration


Natural Hydrology

Post Development

Evaporation 10% 32%



■ Impervious → Pervious■ 1-inch roof storage (or equivalent)■ 1-inch storage on pervious areas with

enhanced rates

Note peak flow difference

Rainfall

Post Development

Natural Hydrology


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Design StrategiesPreserve natural systemsEngineer systems to mimic natural functions

Evapotranspiration ↑Plants (water uptake and transpiration)Surface water (evaporation)

Infiltration ↓SoilsStorage (provides additional time to infiltrate)

Surface Runoff →Pipes, gutters, swales, ditches, underdrainsTime of concentration (longer is better)

“Treat” raindrop as close as possible to where it fellLots of little BMPs instead of few regional systemsBMPs in series not parallel

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PlanningDuring Design

Design BMPs with maintenance in mindROW, easements, vehicle access, cleanouts, manholesAt what depth should sediment be removed?Involve maintenance staff on BMP selection and design

Prepare a site specific maintenance guideThink about

Staff gauges or offset pointsDewatering pipes and valvesGeese, mosquitoes, rodents, etc.

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Design Details

Test infiltration capacity, don’t assume itObservation ports for water levelsUnderdrains designed to be cleanedPonding depth in bio-systems approximately 6-12 inchExtend time of concentration

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Ideas to ConsiderRoto-till pervious surfaces before topsoil/seedAmend soilsLoosen up compacted soils with a ditchwitch/auger and leaf compostValves on underdrainsIf you need an underdrain, don’t put it at the bottomTake every opportunity to educate the publicAdopt-a-rain gardenTry something. Anything is better than nothing.

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Residential Rain Gardens

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Bioretention Swale

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Bioretention Swale

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Bioretention Swalewith Parking

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Bioretention atOffice Complex

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Bioretention Planter

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Bioretention Planter

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Planter Box Style Bioretention

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Curb Extension

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Green Roof

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Porous Pavement

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Filter Strip

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Rainwater Harvesting

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Interpretive Sign

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Putting it All Together . . . Recreating Natural HydrologyProtect natural featuresLet pervious be perviousMinimize impervious surfacesRoute grey to greenPromote vigorous plant growthSlow the water downDesign for stormwater as an asset and amenity

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Think outside the pipe!

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Dan Christian, Tetra [email protected]

Green Infrastructure Design Principles and Considerations

Documents

plant selection

stormwater pollutants

consequences of development

reduced energy

suspended solids

runoff volumelower

flood depth

organic content