New York City intends to capture and retain more stormwater falling on rooftops, through a new plan unveiled by Mayor Michael Bloomberg.
New York City, like other older urban centers, is largely serviced by a combined sewer system where stormwater and wastewater are carried through one system. During heavy storms, the system often reaches capacity and must discharge a mix of stormwater and wastewater–called a combined sewer overflow–into New York Harbor.
The new plan, called NYC Green Infrastructure, will replace the existing approach for sewer overflow control, which relies solely on traditional investments like holding tanks and tunnels, with a mix of green infrastructure and traditional infrastructure that is expected to reduce sewer overflows into waterways by 40% by 2030 by capturing more stormwater.
The plan will reduce the City’s long-term sewer management costs by $2.4 billion over the next 20 years, according to the Mayor’s office.
The NYC Green Infrastructure plan will make more of the City’s waterways available for recreational use, a key goal of PlaNYC–the long-term vision for a green New York–and of the Waterfront Vision and Enhancement Strategy–the City’s initiative to revitalize more than 500 miles of waterfront.
“Our green infrastructure plan is bringing a new approach to an old problem by using natural means to capture the stormwater that too frequently overloads the system. The plan will help clean our waterways, green the city and reduce the costs for residents and business owners, who pay the bills for maintaining the City’s water and sewer systems,” Mayor Bloomberg said.
Green infrastructure installs natural features on buildings, roads and other locations to absorb and retain stormwater.
Examples of green infrastructure projects include: blue roofs and green roofs, which use mechanical devices or vegetation to slow roof water from draining too quickly and overwhelming storm sewers; porous pavement for parking lots that allows water to seep through it and be absorbed into the ground rather than running-off into the sewer system; tree pits and streetside swales for roadways that allow water to pool in underground holding areas until it can dissipate in the ground or transpire through plants; wetlands and swales for parks; and rain barrels in some residential areas.
Under the plan, the first inch of rainfall on 10% of the impervious areas in combined sewer areas of the city will be captured and will not enter the sewer system. Green infrastructure investments will be installed throughout the City’s combined sewer drainage areas, including the South Bronx, Flushing and northeastern and southeastern Queens, and the area around the Gowanus Canal.
Under the existing "grey infrastructure" plan currently required, the City would invest $6.8 billion in traditional sewer infrastructure, paid for with New York City Municipal Water Finance Authority Bonds, which are repaid through residential and commercial water bills. As an alternative the NYC Green Infrastructure Plan will invest $2.9 billion in grey infrastructure and $2.4 billion in green infrastructure–a total of $5.3 billion. The funding for the green infrastructure plan includes $900 million of funding from new development, bringing the total savings for the City’s water customers to $2.4 billion. The funding will be generated through enhanced regulations and standards for onsite stormwater detention and infiltration to be incorporated into the design of new construction projects.
The City already has more than 30 green infrastructure demonstration projects that have been built, are under construction, or are in design, to test the performance and costs of green infrastructure over time. A robust monitoring program measures and analyzes the effectiveness of each of these demonstration projects.