Urban stormwater runoff is the leading contributor of pollutants to Puget Sound, degrading water quality and aquatic habitat to inland and coastal waterways. To prevent further degradation and to restore damaged ecological function, municipalities have increasingly employed green stormwater infrastructure (GSI) and other stormwater best management practices (BMPs) to reduce pollutants and runoff volumes. Historically, stormwater managers have made decisions on GSI/BMP investments based on general guidance documents and/or evaluations of the direct tributary areas to the GSI/BMP without as much consideration of the watershed-wide implications, cumulative effects, other environmental outcomes or environmental justice issues.
We are developing a GSI/BMP decision support/prioritization support tool, that includes pollutant loads and GSI/BMP performance modeling as well as assesses other social-ecological factors, to assist decision makers on making better informed decisions on GSI/BMP investments. We intend for it to be used by a variety of audiences including the public, stormwater managers, municipal decision makers, and industry. Wide scale adoption and geographic expansion of tools such as this one can allow better prioritization of stormwater investments and lead to quicker recovery of the Puget Sound ecosystem.
Results/Conclusions
This tool utilizes pollutant loading information from local urban runoff and BMP monitoring programs, the International BMP Database, and peer-reviewed literature along with customized GIS layers and local precipitation data. It assigns loading information to parcels based on landuse and imperviousness to calculate average annual pollutant loadings for a variety of urban stormwater pollutants. From this, the tool can produce 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 combined with other data and a decision support framework to make optimal decisions for GSI/BMP investments. Initial heat-map analysis indicates that high-volume roadways, developments on steep slopes, and commercial areas with high impervious surface cover are major contributors of stormwater volume and pollutants.
Heat-map analysis will be coupled with other environmental information, using a powerful multi-criteria decision analysis module to identify potentially optimal locations and GSI/BMP types for investments. Additional information includes locations of/proximity to fish bearing streams, 303d listings, critical marine nursery areas, and environmental social justice (ESJ) indices. Preliminary data indicates that pairing ecological and ESJ index information with pollution heatmaps can shift priority areas for green stormwater infrastructure, allowing decision-makers to prioritize actions in basins with greater ecological and social need.