Reducing New York City s CSOs Using Green Infrastructure Think Blue Maine Conference November 21-22, 2013 Portland, ME Anne Kitchell, LEED AP, Horsley Witten Group John McLaughlin, NYCDEP Matthew Jones, PE, PhD, Hazen and Sawyer William Leo, PE, HDR HydroQual
Today s Discussion Why GI in NYC? Process for implementation Monitoring results to date What s next? Right-of-way Bioswale (ROWB)
Why GI in NYC? Combined sewers 49% of city Impervious cover >70% Typical rainfall 44 in/yr Discharge ~20-30 BGY from ~450 CSO outfalls Consent Order requires use of green infrastructure to manage 1 inch of runoff from 10% of impervious surfaces in the combined sewer areas (CSIA) = 1.5 BGY out of system 3
GI strategy considered more cost-effective than new tanks and tunnels. Plus there are additional benefits of GI (e.g., heat island, aesthetics, air quality). 4
Implementation Process 1. Agency alignment and coordination 5
Implementation Process 2. Targeted GI implementation to priority CSO tributaries
Implementation Process 3. BMP Design and Performance Testing Pilot project monitoring (30+ for 2 years) Various BMPs Publicly-owned land Neighborhood-scale demonstrations(3) Modeling scale-up and additional R&D 4. City-wide implementation ROWBs are meat and potatoes for rapid implementation 1.5% CSIA managed by 2015 10% of CSIA managed by 2030 Grants program New stormwater rules
Bronx River Houses perforated pipe systems North & South Conduit bioretention Metropolitan Avenue blue roof trays 99 th Ave. street-side infiltration swale Pilots to develop designs and measure performance MTA Parking Lot wet meadow PS 118 green roof and blue roof check dams Far Rockaway porous pavement
Neighborhood demonstrations to test implementation 9
Stream-lined ROWBs to meet city-wide implementation milestones 10
Implementation challenges include surviving the siting process. Design variants and other BMPs (public/private) may be also required. 11
Stormwater Pilot Study (2010-2013) Storm characteristics Rainfall, temp, wind Volume retention and peak flow reduction of BMPs Inflow, outflow Storage, infiltration, etc Water quality Maintenance issues Co-benefits
Results graphics Representative hydrograph shows inflow vs outlfow as direct measure at pipe; may also show water level/ponding Performance Charts: Each dot is a single storm >0.1 Volume retained= portion of inflow into BMP that does not discharge into sewer Peak flow reduction= difference between highest measured inflow and outflow rates as a %
Blue-Roof Detention (Peak Shaving) Metropolitan Ave. Blue Roof Modified Inlet 2 Check Dams Trays 2
Example: 1.3 Storm on 6/22/13 Results: Overall, Trays consistently provide 80-100% reduction of peak flow Results: 50-80% retention due to ponding and evap.
Permeable Pavement Far Rockaway Bus Terminal Parking Lot (15,000 sf) Porous Pavement Standard Asphalt FilterPave
Permeable Pavement 17 Results (67 Storms): FilterPave consistently captures 100%, but experiencing wear and tear Standard and Porous Asphalts variable Porous Asphalt generally captures >50%
Subsurface Detention/Infiltration Stormwater Chambers & Perforated Pipes Public Housing Facility Parking Lots Perforated Pipes Chamber System South Parking Lot North Parking Lot
Subsurface Systems Chamber System (North Parking Lot) Perforated Pipe System (South Parking Lot)
Rain Gardens and Bioretention Bronx Public Houses RAIN GARDENS North/South Conduit Bioretention
Rain Garden Performance Example: 1.4 Storm (May 24, 2012)
Rain Gardens: Volume Retained Volume Retained 100% 80% 60% 40% 20% 0% 0.0625 0.25 1 4 Bio 1-7:1 Bio 2-6:1 Volume Retained 100% 80% 60% 40% 20% Effective Storm Depth (in) 0% 0.0625 0.25 1 4 100% 80% 60% 40% 20% Bio 3-9:1 Effective Storm Depth (in) Bio 4-17:1 Volume Retained Volume Retained 100% 0% 0.0625 0.25 1 4 80% 60% 40% 20% Effective Storm Depth (in) 2011 2012 0% 0.0625 0.25 1 4 Effective Storm Depth (in)
Median Bioretention: Volume Retained DA:GI Ratio = 11:1 73 storms
24 Observations Rain gardens Retained 90%+ of runoff up to 1 inch, generally 50%+ even for larger storms Curb cut sumps effective at capturing litter and debris helps with litter-removal maintenance Most plants have performed well (>50% 2-yr survival) Bioretention Effective at retaining most storms System typically drained within 8 hrs Vegetated swales infiltrate substantial runoff volumes Retention improved as vegetation grew Larger areas like this less common in NYC
ROW Bioswales (ROWBs) 25
ROWBs: Volume Retention 26
ROW Bioswales 27 Observations: Performance is dependent on many factors Design modifications have improved performance in many aspects Curb cut design Gravel chimney to ensure flow to storage Ratio DA:GI can limit performance Site conditions can be important (slope, soils, utilities, blocked curb cuts)
28 What s next? Final pilot monitoring results Be on look-out for neighborhood demo monitoring results Maintenance threshold testing Siting feasibility results for 6,000 ROWBs Modeling estimates for citywide implementation
29 Acknowledgements NYCDEP Hazen and Sawyer HDR HydroQual Biohabitats Horsley Witten Group Geosyntec Brooklyn College Questions Akitchell@horsleywitten.com Additional material in: www.nyc.gov/html/dep/pdf/green_infrastructure/2012_green_infrastructure_pilot_monitoring_report.pdf