nys stormwater design manual updates
TRANSCRIPT
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Damianos Skaros, EITNYSDEC Region 9270 Michigan AveBuffalo, New York 14203(716)851‐7070
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GP‐0‐10‐001Post Construction Controls
Officially Updated August 2010Design Manual Updates
Chapter 3 – Stormwater Management PlanningChapter 4 – Sizing CriteriaChapter 5 – Green Infrastructure (GI)Other…
Projects designed according to Manual updatesNOI’s submitted after February 28, 2011
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Design Manual StandardsRunoff Reduction Volume (RRv)Green Infrastructure Principles
PlanningDesign Techniques
Water Quality Treatment & Quantity Controls
Change in traditional Stormwater ParadigmTreat rainfall as a resourceInfiltration as a more natural means to handle runoffAvoid curb to gutter design approach
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Conventional Site DesignCollect Concentrate Convey Centralized Control
Credit: HWG
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Rain Garden
Treatment Train Approach
Bioretention CellStorm Drain System
Bioretention Cell
Grass Filter Strip
Credit: HWG
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Holistic Approach for resource protectionNatural infiltration, evapotranspiration, capture/reuse…Maintains/restores natural hydrology and ecological functions
Includes a variety of practices to manage and treat a site’s stormwater
Practices selected according to site specific conditionsPlanning & Design Techniques necessary in incorporation
Promotes RedevelopmentGI not required but encouraged for redevelopment sites
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Maintenance Issues
Traditional methods vs. GI designs/techniquiesPlanningComputationsDesign
Building Codes
Public Acceptance
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Step 1: Site PlanningPreserve natural resources to reduce additional imperviousness
Step 2: Water Quality Volume CalculationsWQv
Step 3: Runoff ReductionCombination of GI & SMPs with RRv capacity
Infiltration practices, bioretention, open channel systems, exc…Table 3.2
Step 4: Apply Standard practices for remaining WQvStep 5: Apply Volume and Peak Rate Control Practices
SMPs to address CPv, Qp, Qf
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Complete list of devices located on websiteBased on technical standards of similar regulatory
agencies
Standard practice for Redevelopment & PretreatmentDeviation from standards with new construction projects
Requires full description to justify deviation in project designEquivalency of performance and sizing capabilities
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Sizing Criteria & Alternative Method
Justifications
Stream Order5th order or Larger
Precipitation Data
Hotspots
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Chapter 4: Unified Stormwater Sizing Criteria
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Objective – replicate predevelopment hydrology conditions using Green Infrastructure techniques
Achieved by maintaining pre‐construction infiltration, controlling peak runoff flow and discharge volume and minimizing concentrated flow
Requires the reduction of the total WQv by means of GI & SMPs
Infiltration, groundwater recharge, reuse, recycle, exc…
RRv > = WQv
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Specified Reduction Factor (S)At a minimum, must reduce a percentage of runoff from
impervious areas to be constructed onsiteBased on Hydrologic Soil Group(s) (HSG)Provide objective technical justification for not achieving full
RRv
Specific Reduction Factor (S)HSG A = 0.55HSG B = 0.40HSG C = 0.30HSG D = 0.20
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RRv calculations:
RRv (acre‐ft of storage) = [(P)(Rv*)(Ai)] / 12
Where:Ai = (S) x (Aic)Ai = impervious cover targeted for runoff reductionS = Hydrologic Soil Group (HSG) Specific Reduction FactorAic = Total area of new impervious coverRv* = 0.05 + 0.009(I) where I is 100% impervious
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Projects which cannot reach 100% of WQvProvide justification which evaluates each of the GI
planning and reduction techniques (Chapter 5)Identify site specific limitationsMeet Minimum RRv
Unacceptable justificationCost of implementation measuresLack of space for required practice
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RRv calculation ResultsIs the RRv > = WQv?
Yes: Move to next design step No: Adjust or incorporate additional practices in design
Or provide assessment and justification
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Alternative to single theoretical design storm
Continuous simulation modeling of designed systemUtilizes historical precipitation dataEstimates runoff volumes, duration, and pollutant loadingExamines watershed parameters vs. single designed storm
event
Specific modeling standards still being developed
Refer to Section 4.7 of Design Manual
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Basic minimum Guidelines:Include rainfall events less than or equal to 95th
percentileMinimum 20 year timeline of dataPerform an analysis that shows post construction flowduration, shape of hydrograph, and downstreamhydrology results
Continuous simulation modeling tools:SWMM WinSLAMMHSPF
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Land use or activity that generates higher concentrations of hydrocarbons, trace metals, and other contaminants
Salvage yards, fueling stations, industrial sites, exc…Refer to Table 4.3 of Design Manual
Stormwater from HotspotsCannot be allowed to infiltrate untreated into groundwaterSeries of additional treatment practices necessary for adequate
treatment
Not normally considered HotspotsResidential streets/development, rural highways, office
developments, exc…
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5th Order StreamsAre exempt from performing Quantity Controls
No Longer 4th Order (previous version of Design Manual)
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Preservation of Natural Features and Conservation DesignPlanning for Green InfrastructureHelps in reduction of RRv for site
Reduction of Impervious CoverPlanning for Green InfrastructureReduces impervious covering
Green Infrastructure TechniquesDesign of GI practicesSite specific details in design of practices
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Preservation of Undisturbed AreasDelineate and create permanent conservation sections
Preservation of BuffersDefine, delineate, and preserve naturally vegetated buffers
Reduction of Clearing and GradingLimit clearing in development
Locating Sites in Less Sensitive AreasFloodplains, steep slopes, erodible soils
Open Space DesignClustering to reduce impervious cover
Soil Restoration
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RoadwaySidewalkDrivewayCul‐de‐sac
Vegetative CenterBuilding Footprint
Single vs. Two storyParking Area
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Runoff reduction by GI techniques, fall under two general methods:
Subtracting conserved areas from total site areaResults in a reduced WQv & CPv
Storage of runoff volumeBased on selected practice’s capabilitiesComputed accordingly
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Runoff Reduction by Area:Conservation of Natural AreasSheetflow to Riperian Buffers or filter stripsVegetated SwaleTree Planting/Tree PitRooftop Runoff
DisconnectionStream Daylighting
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Delineate areas on project plans and marked in fieldPlaced in permanent conservation easement
Helps retain the pre‐development characteristics of undisturbed areas
Forest areas, wetland buffers, stream corridors
Size by deduction of area from WQvReduces runoff treatment volume
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Runoff Reduction by VolumeRain GardensGreen RoofsStormwater plantersRain Barrels/CisternsPorous Pavement
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Treats small volumes of runoff using a conditioned planting soil and materials.
Filter runoff stored within a depression
LimitationsSteep slopesUnsuitable soilsHeavy tree/root cover
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Reduce runoff volumesInsulation from the heat and coldEnergy conservationPervious area for RRv
Limitations:MaintenanceVegetative survivalWaterproofing damage
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Small landscaped stormwater treatment devicesAbove or below ground levelContained, flow through, infiltration
Useful if soils and/or groundwater table not suitable for infiltration
Reduction of discharge volumefrom impervious areas
Aesthetics
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Capture and store stormwater runoff from entering drainage system
Recycles / reusesrainwater
Limitations:MaintenanceCold climateCommunity acceptance
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Helps in recharge of groundwater Runoff reductionAestheticsTreatment of pollutants
Limitations:Maintenance (clogging)Requires highly permeable soils
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Conserved Natural Resources
Open Drainage
Rain Gardens
Amended Soils
Rain Barrel
Porous Pavement
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Chapters 9 & 10Redevelopment ProjectsEnhanced Phosphorus Removal
Future UpdatesBioretention mixHotspot treatmentSchematicsRural projectsMaintenance guidanceInfiltration testing
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Damianos Skaros, EITNYSDEC Region 9(716)851‐7070
NYS DEC Stormwater Page:http://www.dec.ny.gov/chemical/8468.html
NYS DEC Design Manual link:http://www.dec.ny.gov/chemical/29072.html
NYS DEC Verified Proprietary Stormwater Devices Link:http://www.dec.ny.gov/chemical/29089.html