Development and Implementation of Innovative Urban Watershed Planning for San Francisco

San Francisco Water Power and Sewer is the agency in San Francisco responsible for providing water, wastewater, stormwater and energy utility services to the City and County of San Francisco. Within the agency, the Urban Watershed Management Program has been leading efforts for several years to find ways to encourage, require or incentivize the diversion of stormwater from the San Francisco sewer system through Low Impact Design (LID).Cities around the world are taking advantage of green stormwater management technologies, often called Low Impact Design approaches (often referred to as “green infrastructure”), which can help mitigate the effects of urbanization on stormwater. These technologies and designs mimic natural watershed processes by replicating pre-existing hydrologic site conditions. LID directs runoff to natural vegetated systems, such as landscaped planters, swales and gardens that reduce, filter or slow stormwater runoff. LID can also lead to the use of rainwater as a resource and can even help reduce pollutants from stormwater run off. Strategic placement of these vegetated systems helps mitigate the impacts of impervious surfaces and, in some cases, increases the level of service provided by traditional sewer pipes (“grey infrastructure”). San Francisco is served primary by a combined sewer system, thus LID can also help reduce excessive stormwater entering the system during peak flow periods.This paper presents the overall approach taken by San Francisco to address the challenge of integrating LID approaches throughout the City in order to maximize the benefits they can bring both to the sewer system and to enhancing and greening neighborhoods. This approach is one which acknowledges that various entities must be targeted because of their individual contribution of storm water into the collection system. These include private developers and residents, as well as City departments (because of the many projects in the public right-of-way or in relation to large capital improvement projects). By targeting these various entities, the Urban Watershed Management Program has developed an innovative and effective strategy that acknowledges that various parties control the urban landscape and must be addressed if stormwater flows are to be captured, diverted and or slowed down. Recently, an Urban Watershed Framework (UWF) has been developed to enable the agency to determine the preferred balance of “grey” infrastructure and “green” infrastructure for each watershed basin in the City. The UWF uses a triple bottom line (TBL) approach and will be a transparent screening tool.