Quantifying Benefits of Green Stormwater Infrastructure in Philadelphia

Philadelphia’s Green City Clean Waters program is an innovative plan to reduce the frequency and environmental impact of combined sewer overflows through massive, citywide implementation of green infrastructure practices. The program has been approved by regulatory agencies based on the assumption that a variety of direct benefits and co-benefits will be realized over a 25-year period. We report research on methodology for developing green stormwater infrastructure (GSI) benefit functions that express direct runoff reduction benefits and ancillary co-benefits of GSI as functions of investment levels. Functions for direct benefits are generated by coupling a multiobjective evolutionary optimization algorithm (MOEA) to a hydrologic simulation model. Functions for co-benefits are developed through community-based participatory research enabling prioritization of benefits and GSI implementation strategies that reflect the values of the communities that are served. Benefit functions are used in the StormWISE multiobjective decision support framework to optimize GSI investments at the subwatershed level.