Low Impact Development/Better Site Design Roundtable

Transcription

1 Low Impact Development/Better Site Design Roundtable Pros, Cons and Planning Considerations January Prepared by: Shannon Rooney, P.E. SR-Engineers

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3 Planning & Non Traditional Approaches - Preservation of Natural Features & Conservation Design - Reduction of Impervious Cover - Use of Natural Features and Source Controls for Stormwater Management

4 18 Better Site Design Practices Residential Streets & Parking Lots 1. Roadway 2. Cul-de-Sacs 3. Parking 4. Open Vegetated Channels 5. Vegetated Buffer/Filter Strips Lot Development 6. Building Footprint 7. Sidewalk 8. Driveways 9. Tree Planting 10. Rooftop Runoff 11. Bioretention & Rain Gardens 12. Infiltration Conservation of Natural Areas 13. Undisturbed 14. Aquatic Buffers 15. Clearing and Grading 16. Sensitive Resource Areas 17. Open Space/Clustering Design 18. Stream Daylighting (for Redevelopment) Source: Source: NY DEC. April Better Site Design, Horsley Witten Group.

5 Source: NY DEC. April Better Site Design, Horsley Witten Group.

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7 Vegetated Filter Strip Mass DEP. February Massachusetts Stormwater Handbook. CONS: Variability in removal efficiencies Improper grading/construction can diminish pollutant removal. PROS: Ideal for residential settings, small parking lots and roads Effective pretreatment for bioretention Can mimic natural hydrology Can be used in combination with other BMPs Low maintenance Little or no entrapment hazard for amphibians or other small creatures

8 Vegetated Filter Strip - Planning Considerations Best for smaller drainage areas of less than 1-acre with gentle slopes (2% to 6%) Not for use in highly clay soils, limited infiltration or soils that cannot sustain grass cover Not appropriate in areas of higher pollutant loading because of direct infiltration (unless infiltration prevented) May be used as a stand-alone practice for redevelopments Can fit within the open space and rights-of-way along roads

9 Vegetated Open Channel PROS: Reduces cost of storm sewer construction Provides some treatment, runoff storage & infiltration Stormwater design credit taken if allowed by local review authority Increases travel times and lowers peak discharges Accents natural landscape Mass DEP. February Massachusetts Stormwater Handbook. Reduces driving hazards by CONS: keeping stomrwater away from street surfaces Local codes may not allow it Negative perception that requires more maintenance Lack of curbing may increase pavement failure at interface Subject to erosion during large storms

10 Vegetated Open Channel - Planning Considerations Impractical in areas with very flat grades, steep topography or poorly drained soil Preserve natural flow paths Direct runoff to natural drainage ways, ensuring that peak flows and velocities will not cause channel erosion (Source: MA EOEA, 2005)

11 Bioretention & Rain Garden CONS: Requires careful landscaping and maintenance Not suitable for large drainage areas PROS: Provides recharge, preserves the natural water balance Supplies shade, absorbs noise, and provides windbreaks Removes TSS, P, N and metals Good retrofit and residential option Good for small lots with space constraints Little or no hazard for amphibians or other small animals Promotes watershed education & stewardship

12 Bioretention & Rain Garden -Planning Considerations Integrate into parking lots or roadway design Integrate into residential designs If potential for oil and grease, other types of pretreatment required Do not locate on slopes greater than 20% Don t excavate an extensive rain garden under large trees and disturb shallow root system, existing adjacent trees must be water tolerant Location must allow for overflow to formal drainage system Soil media must be 24- to 30-inches deep to achieve removal of nitrogen Depth of soil media depends on type of vegetation Never store snow in Bioretention area

13 PROS: Ideal in ultra-urban environment and large commercial Conserves space UV protection Aesthetic benefit Improves air quality Tax incentive Green Roof CONS: Precipitation is not recharged Irrigation may reduce available water volume Capital costs Possible heat sink in certain winter conditions Liability/safety concerns, increased cost of insurance Additional structural strengthening if retrofit Void of roof warranty O&M costs Green Roof Garden Shed, Raleigh, NC

14 Green Roof - Planning Considerations Do not use where recharge is a priority (aquifers) Nutrient-rich fertilizers must not be used where the runoff may be discharged to nutrient impaired surface waters Costs vary widely, $5 to $70 per square foot (PlanNYC 2008) Can be installed on roofs with slope up to 30% Consider State Building Codes Consider State Plumbing Code for overflow design Runoff Curve Number = 86 versus 98 impervious

15 Permeable Pavements PROS: Consists of Permeable Pavers, Porous Asphalt, or Porous Concrete Can last for decades in cold climates if properly sited, designed, installed, and maintained Can be used for a retrofit Improved site landscaping benefits (grass pavers) Reduces need for other BMPs resulting in cost savings Reduces amount of land required for stormwater management May infiltrate as much as % annual rainfall Structural soils may meet tree requirements for root growth meable_pavement_ri.jpg

16 Permeable Pavements CONS: Clogging of pore spaces may inhibit performance over time Requires aggressive maintenance No winter sanding Underlying soils have to have high permeability rate Special care during construction to prevent compaction of underlying soils Mass DEP. February Massachusetts Stormwater Handbook.

17 Permeable Pavements - Planning Considerations Installed costs range from $10 to $15 SF, depending on surface type, depth of porous medium or structural soil underneath (PlaNYC 2008) For use on pedestrian surfaces, patios, plazas, recreation spaces and low-speed, low-impact vehicle use such as residential driveways, cul-de-sacs, parking stalls, alleys, and overflow parking areas O&M costs vary and depend on frequency and level of street sweeping, vacuuming, and power washing Must not receive stormwater from other drainage areas especially areas that are not fully stabilized For drainage areas less than 5 acres Generally drains within 24 hours Used on areas with gentle slopes (less than 5%) Can be designed with a perimeter trench to provide some overflow treatment should the surface clog, which may be connected to the stone reservoir

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19 Rain Barrels & Cisterns PROS: Reduces water demand for irrigation Saves money on water bills Reduces stormwater runoff volume for small storms Public water systems may experience lower peak demand Rain barrels cost between $3 to $9 per gallon of capacity (PlaNYC 2008) Cisterns costs range from $0.50 per gallon for plastic tanks to $2 per gallon for large galvanized steel tank (PlaNYC 2008) CONS: Reuse or captured stored water is limited to non-potable uses Must be emptied between storms Good for managing stormwater for only half a year due to freezing in winter

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21 Tree Box Filter, Contained Stormwater Planter & Greenstreets PROS: Perceived as value add Effectively manages runoff at micro scale Community based projects Improves air quality Relatively inexpensive Good for urban retrofit: rooftop, courtyard, plaza runoff CONS: Compacted poorly drained soils limit root growth, encourage root rot, and result in stormwater ponding atop tree pit. Bound roots can split pavement O/M costs Liability issues

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23 Tree Valuation What is a tree worth? Aesthetic Benefit Historic Benefit Social Benefit Reduces Stormwater Runoff and prevents soil erosion Climate Control - absorbs solar radiation Air Pollution - can remove both solid and gaseous particles from the air Noise Pollution Water Quality Monetary Value

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25 How do we incorporate Better Site Design/LID into Local Ordinances? Review and Amend Zoning/Conservation for: Establishing buffer zones/floodplain Management Districts Open space/maximum percent impervious requirements Setbacks Development standards Review and Amend Stormwater Management for: Review thresholds (<1 acre), 15% Impervious or greater? Recharge requirements Design credits/promote use of Better Site Design/LID Sizing criteria Other related ordinances that protect stormwater quality: Landscape Excavation (Cut) and Fill Steep slopes Tree Preservation

26 List of References NYS Department of Environmental Conservation. April Better Site Design, Horsley Witten Group. NYS DEC. April New York State Stormwater Management Design Manual. Mass DEP. February Massachusetts Stormwater Handbook. NYC Soil & Water Conservation District Better Site Development Workshop, Tim Conover White edesign Dynamics. The City of New York Sustainable Stormwater Management Plan. The City of New York Plan NYC Progress Report.

27 Sponsors & Resource Personnel P. Lynn Oliva, River Associate Saw Mill River Coalition/Groundwork Hudson Valley 6 Wells Avenue Yonkers, NY P: lynn@groundworkhv.org Ann-Marie Mitroff, Director of River Programs Saw Mill River Coalition/Groundwork Hudson Valley 6 Wells Avenue Yonkers, NY P: F: annmarie@groundworkhv.org Anne Jaffe Holmes Coordinator of School Programs & Environmental Projects Greenburgh Nature Center 99 Dromore Road Scarsdale, NY P: F: ajaffeholmes@greenburghnaturecenter.org Christie Ferguson Candidate for Master of Landscape Architecture University of British Columbia, Vancouver, BC 3701 Victoria Drive Mount Kisco, NY 1054 P: christief@gmail.com Shannon Rooney, P.E. SR-Engineers 65 Rose Street Hastings-on-Hudson, NY P: Srooney@sr-engineers.com Sandeep Mehrotra, P.E. Hazen and Sawyer 498 Seventh Ave. 11th Fl. New York, NY P: Smehrota@hazenandsawyer.com Paul Petretti, P.E., L.S. 30 Gould Ave. Dobbs Ferry, NY P: pjpcels@aol.com Mark Gilliland Chair of the Irvington Tree Commission Irvington, NY P: mg@markg.org