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Author: Michael Drennan, Carl Blum (Am. Society of Civil Engineers), Andy Lipkis (TreePeople), Vik Bapna (LA County Dept. of Public Works), Susan Burke, (MWH)
Date: 7/104
From WEF's Watershed Conference 2004

The traditional approach to solving 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 have reduced indirect impacts, and 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 a flooding problem. Human development of the Sun Valley Watershed has resulted in a heavily urbanized area of approximately 2700 acres located entirely within the City and County of Los Angeles, and tributary to the Los Angeles River. Land use in the area is a mixture of industrial, commercial and residential, with few parks or recreational open space. Flooding of city streets routinely occurs during moderate rainfall events, due to heavy development and absence of underground storm drains. The cost of constructing a traditional storm drain to eliminate the problem has been estimated to be $75 million. Rather than authorizing the traditional single-purpose storm drain solution, the County is exploring the possibility of alternative solutions in the watershed that would address the primary flooding problem, as well as other objectives such as increased recreation and aesthetics in the local neighborhoods, flow reduction to the Los Angeles River, water conservation, reduced stormwater pollution, habitat enhancement, and energy conservation. Alternative solutions will offer the same level of flood protection that would be provided through traditional solutions. As one example, the County has envisioned that these alternative projects will be a series of detention basins and infiltration facilities throughout the watershed which will also serve as community parks and open space. These basins will be strategically located such that they accomplish the primary objective of reducing local flooding, as well as other desirable objectives such as conserving water through increased groundwater recharge, reducing the amount of trash, bacteria, and other pollutants in neighborhood stormwater as well as stormwater discharged to the Los Angeles River, increasing the amount of recreational opportunities in this park-poor community, and increasing wildlife habitat in the watershed. Additionally, this project could serve as a model for future flood control projects in other parts of the region. This paper will describe the results of a detailed hydrologic analysis and a benefit-cost analysis (BCA) which were performed as 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, and potential funding partners.