NEW YORK — New York City Department of Environmental Protection (DEP) Commissioner Carter Strickland announced that the recently completed installation of green infrastructure in the Edenwald section of the Bronx will prevent nearly 2 million gallons of stormwater from reaching the combined sewer system each year and thereby improve the health and cleanliness of the Hutchinson River and New York Harbor. As part of the $300,000 project, DEP worked with the Department of Parks and Recreation to build 22 bioswales to collect and absorb stormwater, along Schiefflin Avenue between East 226th Drive and East 229th Street.

The cluster was installed in a defined area that drains to a single sewer pipe in which flow meters were installed to measure the amount of stormwater before construction, and after green infrastructure began to manage stormwater runoff from impervious surfaces such as roadways, sidewalks, and rooftops. Preconstruction data was collected for 14 months and post-construction data will be collected for one year.

“In order to improve the health of local waterways we have to better manage the stormwater that falls on city streets, sidewalks, parking lots, and rooftops” said Commissioner Strickland. “This green infrastructure installation will collect and absorb stormwater, which will improve the cleanliness of the Hutchinson River, while also greening the neighborhood, providing shade in the summer months, and cleaning the air. The important data we collect will quantify the reduction in pollution and will support our water quality planning efforts.”

The Neighborhood Demonstration Area is the second of three to be completed pursuant to a March 2012 Modified Consent Order with The New York State Department of Environmental Conservation (DEC), which 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 cleanliness of New York City harbor water. A similar green infrastructure installation in the Jamaica Bay tributary area was completed in December 2012 and a Newtown Creek cluster will be finished in the coming weeks.

“Converting the city’s impervious neighborhoods to a more natural and absorbent landscape integrates water quality and ecological benefits for cleaner waterways and a more sustainable community,” said DEC Commissioner Joe Martens. “NYSDEC continues to enthusiastically support GI demonstration projects, like this one in Edenwald as they provide the City an opportunity to monitor the performance of bioswales and curbside gardens constructed under the 2012 Modified Consent Order to determine their cost effectiveness as adaptable elements of the City’s CSO Long Term Control Plans.”

Bioswales resemble standard street tree pits but they are significantly larger, have curb cuts that allow stormwater to enter and exit, and have been designed in a way that will allow each one to manage approximately 2,244 gallons of street and sidewalk runoff during a storm. During construction they were excavated to a depth of 5 feet and were backfilled with layers of broken stone and engineered soil. These layers contain void spaces which store stormwater and promote infiltration. The addition of hardy plants will further encourage infiltration through root growth and increase the capacity of the bioswale through evapotranspiration. DEP provides funding for Department of Parks and Recreation crews to maintain all bioswales.

View a video of a bioswale absorbing stormwater

The Neighborhood Demonstration Areas, including the one in Edenwald, were developed in order to collect and analyze data on actual combined sewer flow measurements before and after green infrastructure projects were installed in a defined area, and the other associated benefits of the installations on a multi-block scale. The data collected from each of the three Demonstration Areas will then be extrapolated for calculating and modeling green infrastructure water quality and cost-benefit data on a waterbody and citywide basis. DEP also continues to collect data on a project-level basis to quantify the stormwater reduction from individual green roofs, blue roofs, bioswales, and other decentralized stormwater controls.

View the 2012 Green Infrastructure Annual Report

The Edenwald Demonstration Area is located within and adjacent to the Edenwald Houses, the largest New York City Housing Authority development in the Bronx. Approximately 7,750 people living within the Demonstration Area will benefit from a larger tree canopy as well as improved street drainage during rainstorms. The approximately 24-acre drainage area is served by combined sewers which all drain to a single point, located near the intersection of Schieffelin Avenue and East 229th Street, where they connect to a single 36-inch sewer that conveys both sanitary and stormwater flow toward the Hunts Point Wastewater Treatment Plant.

Prior to the installation of the green infrastructure, in March 2012, DEP installed depth and flow meter devices in the sewer pipe where it exits the demonstration area at Schiefflin Avenue and East 229th Street. Normal and peak flow levels have been collected continuously in the sewer pipe over the last 14 months to provide preconstruction, or baseline, flow data. Now that the green infrastructure projects are complete, the preconstruction flow data will be compared with the post-construction flow data. This comparison analysis will allow DEP to determine how much stormwater the green infrastructure is keeping out of the sewer system during wet weather.

Since 2002, DEP has invested more than $10 billion in upgrades to wastewater treatment plants and related efforts to reduce CSOs and the cleanliness and health of New York City harbor water continues to improve to levels not seen in more than a century. However, CSOs remain the city’s major harbor water quality challenge. As further “grey” infrastructure upgrades became increasingly expensive and the resulting level of water quality improvements diminished, in 2010 DEP launched the Green Infrastructure Plan, an alternative approach to improving water quality that combines traditional infrastructure upgrades and the integration of green infrastructure to capture and retain stormwater runoff before it ever enters the sewer system. Over the next 20 years, DEP is planning for $2.4 billion in public and private funding for targeted green infrastructure installations, as well as $2.9 billion in cost-effective grey infrastructure upgrades, to significantly reduce CSOs. Thus far, DEP has installed 119 bioswales city-wide; hundreds more will be completed by the end of the year, and thousands will be added during the next five years.