Salish Sea Ecosystem Conference

Optimizing green stormwater infrastructure for people and nature: advancing urban stormwater planning through design thinking, pollution loading, and social equity metrics

Although urban stormwater pollution is a widely recognized threat to coastal cities and ecosystems, stormwater retrofit planning, especially green stormwater infrastructure (GSI), remains an opportunistic, locally-focused endeavor as opposed to an efficiently optimized planning process. We are developing a decision support/prioritization tool for the Puget Sound region that estimates pollutant loads, GSI performance modeling, and other factors to assist decision makers on making better informed GSI investment decisions. Wide scale adoption and geographic expansion of tools such as this one can allow better prioritization of stormwater investments and lead to more rapid recovery of the Puget Sound ecosystem. We utilized Design Thinking to deepen our understanding of stormwater managers’ current decision-making processes, and to outline a distribution of needs and barriers within the stormwater community of practice for using GSI. We found that GSI/BMP investments are made with little consideration of watershed-wide implications, cumulative effects, pollution loading, or environmental justice issues, leading to continued ecosystem and community degradation. The developing tool utilizes pollutant loading information from local urban runoff and BMP monitoring programs, the International BMP Database, and peer-reviewed literature to develop customized GIS layers via an online interface. It assigns loading information to parcels based on landuse and imperviousness to calculate average annual pollutant loadings for nine common urban stormwater pollutants. From this, the tool produces pollutant loading “heatmaps” that identify the estimated contribution of stormwater pollutants at a sub-neighborhood level. These heatmaps can be used on their own to identify hotspots, or can be utilized by the tool’s decision support framework to decide on infrastructure investments. Other information used to support the decision framework include locations of/proximity to fish bearing streams, 303d listings, and social justice demographics. These data are then coupled with a multi-criteria decision analysis module to identify optimal locations and GSI/BMP types for investments. We intend for the tool to be used by a variety of audiences including the public, stormwater managers, municipal decision makers, and industry.