Integrating Green and Gray Infrastructure for Stormwater Management

Authors:

  • Jim Garin and Dana Gumb - NYCDEP
  • Sandeep Mehrotra and Jamie Ong - Hazen and Sawyer

Green infrastructure includes low impact development (LID) source controls, such as bioretention areas.

Stormwater best management practices (BMPs), which include extended detention wetlands designed for flood storage and conveyance, are another type of green infrastructure approach.

The Staten Island Bluebelt program focuses on addressing areas of poor drainage, which are a result of natural landscape, tidal factors and overdevelopment. Using Best Management Practices (BMPs), the New York City Department of Environmental Protection (DEP) seeks to mitigate stormwater flooding and improve water quality in a cost-effective manner. BMPs such as detention ponds, outlet stilling basins, and restored stream channels connect storm sewers with existing waterways and wetlands. In addition, DEP employs Low Impact Development (LID) strategies, including pervious pavement, infiltration swales, and bioretention areas, to provide a comprehensive, watershed-level approach to stormwater management.

Beginning in 1997, the Bluebelt program evaluated many options to mitigate stormwater impacts and decrease flooding. Previous drainage plans suggested implementing an all-pipe network. However, this solution would have eliminated the only remaining, contiguous freshwater wetland network in New York City. Bluebelt drainage plans were designed to augment the idea of the typical pipe-and-pond solution. With a combination of sewers, BMPs and waterways, these innovative plans uniquely integrate green and gray infrastructure for sustainable, long-term management of stormwater runoff.

BMPs are effective, practical methods which delay and attenuate peak flows during storm events, and reduce the movement of sediment, nutrients, pesticides and other pollutants to surface or ground water. They use various natural processes, including detention, infiltration, evapotranspiration, and biological uptake, to improve water quality and provide positive benefits for the time of concentration, volume, and flow rate of stormwater runoff.

As the Bluebelt program developed, it adopted LID strategies, which are designed to maintain and enhance the pre-development hydrologic regime of urban and developed watersheds, into its drainage planning methodology. LID achieves runoff control at its source by locating small, cost-effective landscape features that store, infiltrate, evaporate, and detain runoff throughout the watershed. Currently, DEP is examining its drainage planning criteria to identify LID opportunities and analyze and account for the effect of these practices on overall storm hydrology and hydraulics.

LID techniques successfully incorporated into the Bluebelt program more closely mimic the watershed’s natural hydrologic function and the water balance between runoff, infiltration, storage, groundwater recharge and evapotranspiration. Combined with stormwater BMPs that connect sewer networks with existing waterways, the program further integrates green infrastructure, conventional piped systems, and natural area and stream corridor restoration to provide sustainable flood-control solutions. Through this endeavor, DEP is adapting current policies and utilizing the latest tools to enhance our ability to protect surface and groundwater quality, preserve the physical integrity of receiving streams, and enhance the environmental value of aquatic ecosystems and local communities.

To request a copy of the full paper, please contact the author at jong@hazenandsawyer.com.

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