Urban Runoff and Stormwater Quality Management Using the Los Angeles County Flood Control District's Watershed Management Modeling System: A Pilot Application

The Los Angeles County Flood Control District through a joint effort with United States Environmental Protection Agency has been developing the Watershed management Modeling System (WMMS) that would identify cost-effective water quality improvement projects through an integrated, watershed based approach. In WMMS, watershed model closely estimates collective impact of a variety of point and non-point pollutant sources. The results are incorporated into detailed BMP simulation models and combined with locally derived Best Management Practice (BMP) installation and maintenance costs. The WMMS has been applied to a small pilot watershed to demonstrate the watershed modeling and BMP selection methodologies and to improve accuracy prior to a regional application. The best solutions identified by the WMMS for the pilot watershed are composed of centralized BMP sizes, distributed BMP types and sizes, and percent of area treated for each land use within the delineated eight subarea groups. The WMMS made it possible to quantify the BMP implementation details at various watershed conditions to achieve specific management goals such as TMDLs.