Are Green Roofs an Answer to New York City's Combined Sewer Overflow Problem?

Impervious surfaces comprise nearly 70% of New York City’s land mass and contribute to runoff, ultimately becoming Combined Sewer Overflow (CSO) that is discharged through hundreds of outfalls to local waterways. This thesis has explored the viability of green infrastructure to manage stormwater runoff in New York City by using stormwater utility fees to incentivize green roofs. This research posits that implementing stormwater utility fees that are based on percentage of impervious cover on a parcel could incentivize the presence of green infrastructure, and specifically green roofs. This study aggregated and expanded upon a report done by The Urban Design Lab in 2012, which provided a baseline for creating a methodology to generate a series of query expressions within available PLUTO data. This formed a foundation on which a matrix was created to determine what this research calls “structurality” of buildings, through conducting a series of calculations to determine which borough(s) had buildings that were most amenable to accommodating green roofs. Using that data as a launching point, research conducted by teams led by Dr. Gaffin and Dr. Rosenzweig at the Earth Institute provided a foundation for exploring the possible rates of retention for green roofs in New York City. Publicly available city and state initiatives, as well as scholarly research and scientific reports were also consulted for this research. Lastly, this thesis was guided by literature published by the U.S. Environmental Protection Agency that focused on different methodologies for implementing stormwater utility fees, and looked at 23 municipalities with such fees. Focusing on Seattle as an example, this study presented two possible recommendations for developing a stormwater utility fee appropriate for New York City.