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Neighborhood Demonstration Area Projects

While DEP’s Pilot Monitoring Program provided performance data for individual green infrastructure practices, DEP scaled up its monitoring efforts by implementing Neighborhood Demonstration Area Projects (Demonstration Projects). DEP identified three neighborhoods in priority combined sewer tributary areas: Hutchinson River in the Bronx and Newtown Creek and Jamaica Bay in Brooklyn, to test the effectiveness of green infrastructure (GI) systems on a multi-block scale.

Starting in 2011, DEP installed flow monitoring equipment within the combined sewers of these three areas to collect up to 16 months of wet weather flow data. This allowed DEP to document existing baseline conditions for stormwater runoff flow rates. DEP then constructed multiple green infrastructure practices such as bioswales and stormwater greenstreets within each area in addition to on-site GI practices in Newtown Creek and Jamaica tributary areas. After construction was complete, DEP continued flow monitoring for an additional 12 months to determine the changes in wet weather flows. DEP has produced a comprehensive Post-construction Monitoring Report, which describes in detail this monitoring program and provides a summary of the analyses and results for each Demonstration Project.

The data collected shows that the green infrastructure practices were able to manage the first inch of rain that fell on over 14 percent of the impervious surfaces across all three demonstration areas. This exceeded the design goal to manage one inch of rain on 10 percent of the impervious surfaces. On average, across all three demonstration areas, the green infrastructure reduced the stormwater runoff entering the combined sewer system by at least 20 percent during a typical New York City rainstorm.

Hutchinson River Demonstration Project

GI Constructed: 22 bioswales
Tributary Area: 24 Acres
Design & Construction Costs: $545,000
Map available here

Jamaica Bay Demonstration Project

GI Constructed: 29 bioswales, 2 stormwater greenstreets, and 2 permeable pavement retrofits at NYCHA’s Seth Low Houses
Tributary Area: 23 Acres
Design & Construction Costs: $1.3 million
Map available here

Newtown Creek Demonstration Project

GI Constructed: 19 bioswales, and 3 biortention areas and 1 subsurface retention system at NYCHA’s Hope Gardens Houses
Tributary Area: 20 Acres
Design & Construction Costs: $1.4 million
Map available here

Summary of Results

 Hutchinson River Demonstration ProjectJamaica Bay Demonstration ProjectNewtown Creek Demonstration Project
Total Tributary Drainage Area 24.1 ac 22.7 ac 19.3 ac
Impervious Cover* 81% 92% 92%
Design Managed Area for 1-inch Rainfall (% of Impervious Tributary Drainage Area*) 1.2 ac (6.1%) 2.5 ac (12.0%)** 0.9 ac (5.1%)***
Measured Managed Area for 1-inch Rainfall (% of Impervious Tributary Drainage Area*) 3.5 ac (17.9%) 3.9 ac (18.7%) 0.9 ac (5.1%)
Average Reduction in Stormwater Runoff Coefficient for 1-inch Rainfall or less **** 20% 21% 23%
Measured Managed Volume for 1 inch Rainfall 12,700 ft3 14,300 ft3 3,200 ft3
% Managed Area for 1 inch Runoff from Impervious Area* across all three Demo Areas 14.3%

* Based on impervious coverage as measured by analysis of multi-spectral infrared satellite imagery.
** Excludes on-site GI. Including on-site would increase design managed area to 3.0 acres.
*** Excludes on-site GI. Including on-site would increase design managed area to 1.6 acres.
**** The proportion of rainfall leaving each Demonstration Area as stormwater runoff into the combined sewer system.

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