New York City Green Infrastructure Demonstration Projects
New York City’s Green Infrastructure Program utilizes an adaptive management approach based on pilot project monitoring results and information collected and assessed from green infrastructure demonstration projects. Neighborhood Demonstration Areas were established in New York City pursuant to a March 2012 Modified Consent Order with the New York State Department of Environmental Conservation. This Order formalized the City’s inclusion of green infrastructure as an important component of its plan to reduce combined sewer overflows (CSOs) into local waterways, and improve the ecological health and quality of New York City harbor water. The Order contains design, construction, and monitoring milestones for three Demonstration Projects.
DEP has built and monitored the Demonstration Projects within a total of 63 acres in the Newtown Creek, Hutchinson River and Jamaica Bay CSO tributary areas. The development and monitoring of these projects began in 2012 and culminated in the submission of a post-construction monitoring report in August 2014. These pilot systems have already provided information that has influenced the designs and locations of other NYC green infrastructure projects.
#1: Construction of Right of Way Bioswales* as part of the Hutchinson River Green Infrastructure Demonstration Project started in September 2012 and was completed in April 2013. There were 22 Right-of-way Bioswales installed within the 24-acre tributary area, and the design and construction costs were approximately $545,000. The installation of green infrastructure in this section of the Bronx prevents nearly 2 million gallons of stormwater from reaching the combined sewer system each year and in turn greatly improves the health and cleanliness of the Hutchinson River and New York Harbor.
(*As described in NYC’s Green Infrastructure Plan, Right of Way Bioswales are similar to existing tree pits and are built within sidewalks up-stream of existing catch basins to capture runoff from the street and sidewalk.)
#2: In December 2012, DEP completed the Jamaica Bay Green Infrastructure Demonstration Project in the 26th Ward Tributary Area. The project includes 29 bioswales and two Greenstreets within a 23-acre tributary area. Additional permeable pavement retrofit projects were implemented at NYC Housing Authority’s Seth Low Houses in 2013. The total design and construction costs were approximately $1.3 million.
#3: Finally, in the 16-acre Newtown Creek Green Infrastructure Demonstration Project, DEP constructed 19 Right of Way Bioswales, two rain gardens, and a subsurface storm chamber system on the site of NYC Housing Authority’s Hope Gardens Houses. These projects were completed in 2013, and costs were approximately $1.4 million for design and construction.
In addition to the massive volume of water quality improvements, the data from the Demonstration Projects allows for progressive analysis and green infrastructure program development:
The Neighborhood Demonstration Areas provide the City data on actual combined sewer flow measurements before and after the green infrastructure projects were installed, and on other associated benefits of the installations on a multi-block scale.
The information collected from the projects is used to develop green infrastructure performance metrics to relate the benefits of CSO reduction to the amount of constructed green infrastructure.
The data collected from each of the three Demonstration Areas has subsequently been extrapolated for calculating and modeling green infrastructure water quality and cost-benefit data on a waterbody and citywide basis.
The 2014 Post-Construction Monitoring Report results showed a decrease in stormwater runoff entering the combined sewers in all three areas after the construction of the green infrastructure practices. For storms less than or equal to one inch, the runoff entering the combined sewers at the manhole where the flow meters were installed decreased by 20 to 23 percent across all three areas.
In terms of impervious surfaces managed, Demonstration Areas 1 and 2 managed 17.9 and 18.7 percent, respectively, almost doubling the NYS Order goal of 10 percent.
According to NYC, green infrastructure investments will eliminate 1.5 billion gallons of sewer overflow annually by 2030, while 12 billion gallons will be kept out of New York’s waterways through combined green and grey infrastructure systems.
Publication Date: 2014
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