The traditional approach to addressing stormwater pollution is a combination of program activities and best management practices to reduce pollutants to the maximum extent practicable. As water bodies continue to be identified as impaired throughout the country, increasing numbers of water quality regulations, such as total maximum daily loads (TMDLs), are being implemented which mandate numerical effluent standards for stormwater runoff. Stormwater management agencies are increasingly being asked to develop capital improvement projects which provide pollutant reduction in stormwater runoff to comply with these numerical standards. Understanding the economic benefits of these projects in addition to the costs, is crucial in developing the support of the public and elected officials who must provide the ultimate approval for expenditure of funds. The traditional approach to addressing flood control problems in the Los Angeles region has been to construct underground storm drains which connect to modified natural channels. As more is learned about the indirect negative impacts associated with traditional concrete solutions to local flooding problems (such as the potential for increased flooding downstream, reduced groundwater recharge, and loss of wildlife habitat among others), attention is turning to non-traditional solutions which not only have reduced indirect impacts, but additional local and regional benefits (such as stormwater pollution reduction, increased recreational and aesthetic opportunities, and even energy conservation and improved air quality). In recognition of these issues, the Los Angeles County Department of Public Works with strong support of Supervisor Zev Yaroslavsky of the County Board of Supervisors identified the Sun Valley Watershed as an opportunity to implement a pilot project which tested the validity of alternative approaches to addressing both stormwater pollution and flood control objectives. As one example, the County has envisioned that these alternative projects would be a series of detention basins and infiltration facilities throughout the watershed which would be operated to provide flood control, stormwater pollution reduction, groundwater recharge and would also serve as community parks and open space. This paper will describe the results of a detailed hydrologic analysis and a benefit-cost analysis (BCA) which were performed as a part of the alternatives analysis of potential multipurpose solutions for the Sun Valley Watershed Plan. The results of the BCA indicate that one alternative will yield the same level of flood protection as the traditional single purpose solution, but provide multiple benefits including: approximately $78 million in flood control benefits, $88 million in stormwater quality benefits, and $78 million in water supply benefits, with a cost of approximately $172 million. The benefits of the traditional single purpose solution have been estimated to be $73 million with a cost of $74 million. These quantified benefits will be used as a basis for approaching water supply and water quality agencies, as well as park departments, as potential funding partners.