Post on 17-Apr-2018
LLowow IImpactmpact DDevelopmentevelopment
At At
WWetlandetland SStudiestudies andand SSolutions,olutions, IInc.nc.
Wetland
WSSI’s building is serviced by an existing regional pond –NO ON-SITE STORMWATER MANAGEMENT IS REQUIRED.
So, why implement LID?
To mimic the predevelopment hydrology, thereby minimizing stream degradation, because we believe it’s the right thing to do.
To satisfy our curiosity:To see how different types of pervious pavement systems perform relative to
their costTo determine the actual maintenance requirements of an LID projectTo determine the real cost of an LID projectTo determine the barriers to LID implementation
To provide a laboratory for the study of LID performance
To create an integrated LID plan, rather than using a slapdash approach to LID
WWhyhy ddidid wwetlandetland sstudiestudies
iimplementmplement lid?lid?
Wetland
To reduce the post-development curve number to the pre-development curve number by using permeable paving surfaces.
To minimize the effect of increased runoff volume on downstream waters by reducing the post-developed runoff rate below the pre-developed, forested rate through increased storage and time of concentration.
To demonstrate compliance with Chesapeake Bay Preservation Ordinance and stormwater management ordinance regulations without a conventional stormwater management/BMP facility.
WWhathat wwere the ere the TTechnical echnical ggoalsoals
ofof thethe pprojectroject??
Wetland
Conservation and protection of natural features that provide stormwater control.
Minimization of impervious areas and impacts to natural areas.
Direction of runoff to natural areas to slow down and capture water so it can infiltrate natural areas, evaporate, or be reused.
Use of multiple small-scale controls that work to reproduce natural processes with rainfall, including infiltration, detention, retention, evaporation, and groundwater recharge.
Pollution prevention through erosion and sediment control and prevention of soil compaction during site preparation and construction.
Education regarding the practice of LID techniques and maintenance of stormwater infiltration facilities.
WWhathat aarere thethe bbasicsasics ofof lid?lid?
Wetland
HHowow isis lid ilid implementedmplemented
atat thethe wssi bwssi buildinguilding??
Gravel DetentionGravel Detention
Native VegetationNative Vegetation
CisternCistern
BioBio--swaleswale
Wetland
Green RoofGreen Roof Pervious ParkingPervious Parking
Rain GardenRain Garden
TThehe ggreenreen rroofoof
1
2
3
1. Steel joist
2. Metal roof deck
3. 5” R-30 foam insulation
4. ½” gypsum protection board
5. 75 mil ethylene propylene diene monomer (EPDM) membrane
6. ½” foam protection board
7. 40 mil high-density polyethylene (HDPE) root barrier
8. Protection fabric
9. 1” drainage layer
10. Filter fabric
11. 3-9” lightweight growing medium
12. Stone features, sedum, and native perennials and shrubs
4
1112
56
78
910
Wetland
Green Roof Cross Section
TThehe ggreenreen rroofoofCombination of extensive (3-4” soil) and intensive (4-9” soil) planting areasReduces impervious area by 3,626 sfReduces roof runoffEngineered to support 62 lbs/sfIncreases green area and provides amenityCost: $31.80/sf installed
Wetland
8,000 g8,000 gallonallon ccisternisternCollects the “first flush” of roof runoff (1/2”)Provides irrigation waterOverflows to rain garden and gravel bed detentionCost: $3.88/gal installed
$1.23/ sf impervious area treated(Cistern material only cost: $2.88/gal)
Wetland
TThehe rrainain ggardenarden
Treats 34,660 sf of impervious roof and parking lot area1,536 sf bed; 11,693 sf grassed bufferDrains to gravel bed detentionCost: $2.60 /sf impervious area treated
Wetland
Pervious Concrete 3,342 sf
GravelPave2 19,862 sf
Gravel Paving 1,273 sf
Concrete Pavers 5,502 sf
Asphalt 55,896 sf
PPerviouservious PParkingarkingWetland
PPerviouservious CConcreteoncreteReduce impervious area by 3,342 sf. (3.9% of total parking area)Drains to gravel bed detentionApproximate cost: $6.00/sf installed(Asphalt cost: $2.56/sf)
Wetland
GGravelravelPPaveave2 2 andand GGravelravel PPavingavingReduce impervious area by 21,135 sf (24.6% of total parking area)Drains to gravel bed detentionGravelPave2 cost: $6.00/sf installed Gravel paving cost: $4.32/sf installed (Asphalt cost: $2.56/sf)(GravelPave2 materials only cost: $3.20/sf)
Wetland
CConcreteoncrete PPaversaversReduce impervious area by 5,502 sf. (6.4% of total parking area)Drains to existing vegetated floodplainCost: $7.10/sf installed + $0.80/sf header curb (Asphalt cost: $2.56/sf)(Paver material only cost: $2.55/sf)
Wetland
GGravelravel BBeded DDetentionetentionOrifice controlled- drains to existing stream systemDetains the 1-yr storm over 24 hours.Cost: $2.28/cf treatment volume installed$0.32/sf impervious area treated
1.6251.625”” OutflowOutflow
Wetland
WWaterater qqualityuality sswalewale
Collects runoff from 12,650 sf of impervious parking surfacesSlows runoffWater quality volume filters through check damsCost: $3.68/sf impervious area treated
Wetland
nnative ative vvegetationegetationMaintains habitatDecreases water consumptionUses a drip irrigation system and captured rainwater Landscape and drip irrigation cost: $125,864 (Typical landscape and irrigation cost: $80,000)
Wetland
DDidid wwetlandetland sstudiestudies mmeeteet itsits
ttechnicalechnical ggoalsoals??
9.5 (71%)Curve Number Reduction87.5Conventional Postdevelopment Curve Number78.0LID Postdevelopment Curve Number74.1Predevelopment Curve Number
Curve Number Reduction:
Chesapeake Bay Ordinance:
51.3%50.0%
Actual phosphorous removalRequired phosphorous removal
Wetland
DDidid wwetlandetland sstudiestudies mmeeteet itsits
ttechnicalechnical ggoalsoals??
Runoff Rate:
Due to limitations with current modeling methods, the time of concentration (Tc) is assumed to be five minutes in both the pre-developed and post-developed case. In reality, the Tc may be less than five minutes in the pre-developed case and may be greater than five minutes in the post-developed case, potentially lowering the peak runoff from the site further than indicated.
7.94 cfsPostdevelopment runoff rate (1.5-year storm)9.42 cfsPredevelopment runoff rate (1.5-year storm)
12,609 c.f.Actual storage provided3,686 c.f. Required storage per Prince Georges County LID Manual
Wetland
Conservation and protection: WSSI conserved on-site wetlands and hardwood areas through the use of retaining walls.
Minimization: WSSI minimized impervious areas through the use of pervious paving systems.
Education: The WSSI building will be used as a showcase piece and a laboratory for the study and promotion of Low-Impact Development.
DDid id wwetlandetland sstudiestudies
ffulfillulfill thethe bbasicsasics ofof lid?lid?
Wetland
DDid id wwetlandetland sstudiestudies
ffulfillulfill thethe bbasicsasics ofof lid?lid?Direction of runoff: WSSI’s gravel bed detention and water quality swale direct runoff
to an existing stream and wetland system on the site. The pervious pavement underdrains direct water to existing vegetated floodplain.
Wetland
Use of multiple small-scale controls:The WSSI site plan includes a green roof, three different pervious pavements, a cistern, a swale, native landscaping, and underground detention to treat stormwater from 3.89 acres of disturbed land.
Pollution prevention: The WSSI site plan called for extensive erosion and sediment controls to protect downstream resources during construction and meets the “no increase” in post-development non-point source pollutant loads requirement.
HHowow mmuchuch ddidid itit ccostost??Rain Garden
Cistern
Green Roof
Pervious Concrete Pavers
Gravel Pavement
GravelPave2 System
Gravel Bed Detention
Swale
Total
Standard Asphalt / Curb and Gutter Estimate
$90,000
$31,000
$115,316
$39,000
$5,500
$143,500
$24,000
$46,525
$360,115
$620,705
Native Landscaping and Drip Irrigation $125,864
Item $/sf impervious Cost
$2.60
$1.23
$31.80
$7.90
$4.32
$6.00
$0.32
$3.68
Wetland
N/A
Pervious Concrete N/A$6.00
WWherehere is theis the pprojectroject llocatedocated??Rte. 29Rte. 29 II--6666
Rte. 29Rte. 29
NN
NN
Wetland
5300 Wellington Branch Drive, Gainesville
FForor ffurtherurther iinformation nformation
on on tthese hese lid plid practicesracticesPervious Pavement Systems:
http://www.uni-groupusa.org/uni-eco-.htmhttp://www.invisiblestructures.comhttp://www.nrmca.org
Green Roofing:http://manual.fsbp.com/Garden%20Roofing%20Systems%20Design%20Guide.pdfhttp://www.greenroofs.comhttp://www.greenroofs.org
Cistern:http://www.xerxescorp.com/index.shtml
General Links:http://www.wetlandstudies.comhttp://www.epa.gov/owow/nps/lid/lid_hydr.pdfhttp://www.lowimpactdevelopment.org
Wetland
TThankshanks to theto the wssiwssi pprojectroject tteameam
Project Management – The Peterson CompaniesConcept Plan – Wetland Studies and Solutions, Inc.General Contracting – EEReed Construction, LPCivil Engineering – Urban Engineering and Associates, Inc.Site Work – S.W. Rodgers Green Roof Installation – The Furbish CompanyPervious Concrete – Virginia Ready Mixed Concrete Association
Wetland