Monitoring Performance of Green Infrastructure Source Controls in New York City

New York City Environmental Protection (DEP) is piloting green infrastructure source control retrofits throughout New York City in order to examine the functionality of these systems and the suitability of expanding their use to alleviate combined sewer overflow (CSO) and sewer capacity limitations. A comprehensive monitoring program serves as a key element of this pilot effort, providing valuable information on the challenges these systems present, and benefits they can provide within the unique, ultra-urban environment of New York City. Specifically, the monitoring program seeks to examine the effect of these systems on runoff rates and volumes, and issues associated with water quality, maintenance, longevity and general system functionality.The pilot monitoring program encompasses more than twenty source controls distributed throughout New York City, including bioretention, enhanced tree pits, street-side infiltration swales, constructed wetlands, blue roofs, green roofs, permeable pavement, and subsurface detention and infiltration systems. These source controls were implemented across a range of public properties including street-side sidewalks, medians, parking lots, public housing facilities, and on rooftops. Remote monitoring equipment at each site is being used to assess quantitative aspects of performance such as inflow and outflow rates and volumes, storage within the systems, and drawdown rates. A basic water quality study has been incorporated to identify potential maintenance concerns and provide a basis for comparison with similar studies in other urban areas. Qualitative assessments address implementation issues such as maintenance requirements, aesthetic components, and community perception. In total, these evaluations are expected to better inform future green infrastructure implementation initiatives, supporting stormwater management and CSO reduction efforts throughout the City.