Going Green with the NYS Stormwater Design Standards Shohreh Karimipour, P.E. NYSDEC
History of Stormwater Management Ancient Greek Cisterns Water Cistern Systems in Greece from Minoan to Hellenistic Period, Figure 3, Page 4
Ancient Romans: The sewers carried off sewage, urban runoff, and drainage water together efficiently (based on Macaulay).
Pre-1990 s Local Flood Management Detention ponds for peak rate control
1990 s SPDES required pollutant removal on > 5acre sites Best Management Practices (BMPs) that capture and treat First Flush
New York State Stormwater Management Design Manual First Release 2001 Volumetric Control of 90% Storm Performance Criteria 40% Phosphorus Removal 80% TSS Removal Accepted Treatment Practices Channel Protection, Flood Control Updates: 2003, 2007, 2008 2010: Green Infrastructure
Back to Cisterns Brooklyn Bears Carlton
Changing Stormwater Strategy 2008 NRC Findings: regulate stormwater by flow or by impervious cover 2008 2009 State public meeting process: integration of green infrastructure and runoff reduction
Updates to the Design Manual Green Infrastructure Definition In the context of stormwater management, the term green infrastructure includes a wide array of practices at multiple scales to manage and treat stormwater, maintain and restore natural hydrology and ecological function by infiltration, evapotranspiration, capture and reuse of stormwater, and establishment of natural vegetative features.
Chapter 3 - New Stormwater Steps Site planning to preserve natural areas and reduce impervious cover to MEP Calculate Water Quality Volume (WQv) Apply GI practices to meet the Runoff Reduction Volume (RRv) Apply standard practices to treat remaining WQv Apply Volume and Rate controls for 1, 10 and 100 year storm events
Chapter 4 Sizing Criteria Sizing Criteria & Alternative Method Water Quality Volume (WQv) Runoff Reduction Volume (RRv) (total WQv) Alternative method (WQv): Channel Protection Flood Control
Water Quality Volume (WQv) Runoff Reduction Volume(RRv) Alternative method (WQv): 90% Rule: WQ v (acre-feet) = [(P)(Rv)(A)] /12 Rv = 0.05+0.009(I) I = Impervious Cover (Percent) P(inch) = 90% Rainfall Event Number A = drainage area in acres RRv (acre-feet) = Reduction of the total WQv by application of green infrastructure techniques and SMPs to replicate predevelopment hydrology. The minimum required RRv defined as the Specified Reduction Factor provided objective technical justification is documented. Credit for storage (ponding, void space) or area reduction. Design, construct, and maintain systems sized to capture, reduce, reuse, treat, and manage rainfall on-site, and prevent the off-site discharge of the precipitation from all rainfall events less than or equal to the 95th percentile rainfall event, computed by an acceptable continuous simulation model. Redevelopment Projects (%25 Reduction/treatment)
Runoff Reduction Design GI practices to treat the full WQv If 100% reduction is not achievable, at minimum reduce to the following level, given objective and quantitative justification is provided: 55% on A soils 40% on B soils 30% on C soils 20% on D soils * Use a weighted average of mixed soil types Treat the remaining WQv prior to discharge.
Chapter 5-5.1 Avoid Impact Preserve Natural Resources 5.2 Reduce Impact Impervious Cover 5.3 Manage Impact GI Techniques
Preserve Natural Features Preservation of Undisturbed Areas Preservation of Buffers Reduction of Clearing & Grading Locate Sites in Less Sensitive Areas Soil Restoration Updates: Avoid the Impacts
Soil Compaction
The Integral Component of Retention: Hydrology - storage /evaporation /recharge/detention De-compaction Storing Cycling Nutrients (bacteria / fungi) Plant Productivity (vigor) Soil Restoration Water Quality infiltrate, filter, immobilize & detoxify organic and inorganic materials REQUIRED De-compaction ( mechanical, soil enhancement) Increase CN if restoration is not applied.
Updates: Reduce the Impact Reduce Impervious Cover Design to traffic density Minimize roadway lengths & Widths Reduce Sidewalk width Cul-de-sac Parking area Footprint Shared driveway
Updates: Manage the Impact Slow it down, Spread it out, Soak it in Runoff Reduction (RR) Techniques: Conservation of natural areas Sheetflow to riparian buffers or filter strips Vegetated open swale Tree planting / tree box Rooftop Runoff disconnection Stream daylighting Rain garden Green roof Stormwater planter Rain tank/cistern Permeable paving
Runoff Reduction Technique: Conservation of Natural Areas
Runoff Reduction Technique: Vegetated Buffer/Filter Strips Treat & control runoff with: Forested areas Stream buffers Vegetated filter strips Width, slope, density
Runoff Reduction Technique: Rooftop Runoff Disconnection
Runoff Reduction Technique: Grass Swale and BioSwale
Convey & treat runoff with: Natural drainage paths Properly designed & constructed channels On right-of-way Slopes, velocity, depth, travel time Runoff Reduction Technique: Open Vegetated Channels
Stream Daylighting for Redevelopment Increases aesthetics Improves water quality Prevents flooding increased storage Improves in-stream habitat Increases public use Increases property values Sunlight
Tree Planting In stormwater management practices (where appropriate) In landscape plans Revegetate buffer areas Storage / area sizing
Rain Gardens, Bio-retention
Rain Gardens Rain Garden Applications treating small volumes of runoff with made soil and plants WQ V < V SM + V DL +(D P x A RG ) Limitations Steep slopes, Compacted and clay soils Sheet / shallow concentrated flow; roof drain downspout < 1,000 sf Design controls (ponding, soil and plant specifications, overflow)
Cisterns & Rain Barrels Applications Capture and store stormwater runoff for reuse or irrigation Limitations Maintenance Water use Cold Climate Community Acceptance
Cisterns & Rain Barrels Sizing based on the contributing area: Vol = WQv * 7.5 gals/ft 3 Credits: NYC community gardens
Green Roofs
Extensive Green Roof Intensive Green Roof Applications Limitations, benefits Sizing (storage) Design (media, plant, drainage, water proofing) Maintenance
Stormwater Planters Applications On-site soils, high GW table not suitable for infiltration Reduction of discharge volume, velocity from impervious areas Design Flow through, contained, infiltration Sizing WQv based on surface area, depth of soil & hydraulic conductivity A f = WQ v x (d f )/ [k x (h f + d f )(t f )]
Applications low-traffic areas overflow parking Residential single family home GW recharge Limitations suitability of the site grades Subsoils Drainage characteristics Groundwater conditions Sizing based on surface area Permeable Paving
http://www.wbdg.org/design/lidtech.php Porous Pavement Sizing A p = WQv/n x d t Ap = Porous Pavement Surface Area WQv = Design Volume (cubic feet) n = porosity of gravel bed/reservoir (0.4) dt = depth of gravel bed (maximum 4 feet)
Challenges and Opportunities Challenges: Maintenance Access Cold Climate Soils Water table Easement Local Laws Opportunities: Green initiatives across the State New York State smart growth bill Governor's Cleaner Greener NY - 2010
Questions? Shohreh Karimipour, P.E. sxkarimi@gw.dec.state.ny.us (518) 402-8115