New Public Domain Technologies for Stormwater Quality Benefits: Structural Stormwater BMP Prioritization and Analysis Tool

The City of Los Angeles, in partnership with the County of Los Angeles Department of Public Works, and Heal the Bay developed a new, GIS-based, public domain technology for water quality planning. Numerous efforts to improve storm water quality on a watershed-wide basis have lacked a reproducible, transparent, methodical approach to optimize the selection and implementation of Best Management Practices (BMPs) to meet receiving water quality goals. Structural BMPs had, at times, not been selected based on water quality need (i.e., priority areas) and potential benefit. Projects were identified in an opportunistic, site-specific fashion, focusing on one or a few pollutants, stakeholder inputs, or local funding availability. As geographical information systems (GIS) technologies improved, agencies developed land use datasets, pollutant loading and treatment efficiency datasets become more robust, and computing power increases, this effort presented a significant opportunity to improve watershed-based implementation planning efforts. This new technology, a Structural BMP Prioritization and Analysis Tool (SBPAT) makes watershed-wide planning possible without knowing a priori the locations of potential projects.This paper presents methods to prioritize water quality improvement needs and identify structural BMP opportunities, increasing the water quality return on investment. Opportunities are screened and evaluated initially based on property ownership and the potential for retrofitting to achieve multiple benefits, such as water quality, aesthetics, recreation, and habitat. It is recognized that different types of land parcels typically have different types of opportunities and constraints. Structural BMP opportunities can be regional or distributed in nature depending on the land use, size, and location of the public parcel, among other things. By utilizing GIS-based parcel and land use information in the context of water quality need, potential opportunities, and constraints, watershed-wide benefits of BMP implementation can be assessed.SBPAT was developed in the ArcGIS™ environment and automates many of these spatial prioritization and identification processes, while maintaining transparency for stakeholders and decisions-makers to provide meaningful input that supports BMP implementation decisions. Once candidate BMPs have been identified for a high priority area, the tool estimates the potential pollutant load reductions and planning level costs associated with site-specific implementation, based on actual BMP performance data, hydrologic modeling, and site-specific constraints.The City has used this tool as a key element for TMDL Implementation Planning, and has made the tool readily available for public use and download, with open source code architecture, to facilitate additional users.