As a city with a combined sewer system—meaning that stormwater enters the wastewater treatment system—the San Francisco Public Utilities Commission (SFPUC) is undertaking projects around the city to divert stormwater into landscaping, in order to reduce demand on the aging sewer system. One of the eight green infrastructure projects in the SFPUC’s 20 year, multi-billion dollar Sewer System Improvement Program is the Sunset Boulevard Greenway, which could reduce the frequency of combined sewer discharges into the Pacific Ocean along Ocean Beach.
According to the SFPUC, the sewer system treats about 80 million gallons per day during dry weather, a number that swells to 500 million during rainy weather. When the Oceanside Treatment Plant and nearby storage structures—which serve the city’s western watersheds—exceed capacity, combined sewer discharges are released directly onto Ocean Beach after receiving only primary treatment.
San Francisco's watersheds, with the red line representing the dividing point between the western and eastern watersheds. Image Courtesy of San Francisco Public Utilities Commission
Combined sewer systems are predominantly found in older communities in the Midwest and Northeast United States, with the only other combined sewer system in California being found in an older portion of Sacramento. For coastal communities without combined sewer systems, stormwater flows directly into creeks and rivers, reaching the ocean after traveling through catch basins that remove trash—but not chemical pollutants, like paint or motor oil—and require frequent cleanings. Although combined sewers can result wet weather overflows, they are preferable to year-round untreated stormwater.
Low-impact design (LID) strategies like those recommended in the SFPUC Sunset Boulevard Greenway Project represent one solution, allowing for water to soak into the ground, thus removing pollutants through a natural filtration system and mimicking pre-development conditions. According to SFPUC estimates, the Sunset Boulevard Greenway Project would improve stormwater management for over 20 acres of paved surfaces, capturing more than 10 million gallons of runoff annually. In turn, this would lead to an estimated annual reduction of 5 million gallons of combined sewer discharges into the Pacific Ocean.
Many low-impact designs add greenery to streetscapes, providing additional environmental and recreational benefits. Image courtesy of City of Kirkland
In addition to reducing the detrimental urbanizing impacts that cities have on water systems, LID projects can bring much-needed greenery and natural landscapes into cities, often doubling as beautifying measures. LID is achieved through rain gardens, sidewalk gardens and trees—a single street tree removes about 1,000 gallons of stormwater from the sewer annually—and creeks, bioswales, ponds, or restored wetlands (see more about these, and other forms of green infrastructure in a recent blog post by Laura Tam, SPUR’s Sustainable Development Policy Director.
Although specific plans for the Sunset Boulevard Greenway Project will not be released until the planning phase, which is projected to take place between Winter 2013 and Spring 2014, the SFPUC is emphasizing a number of improvements spanning beyond stormwater management, including beautification, revitalized pedestrian and cyclist space and trail use, habitat enhancement, community recreation space, and educational benefits.
The influence that low-impact design projects have on streetscape improvements make them an attractive option for interagency collaboration. San Francisco’s Department of Public Works is incorporating LID strategies within many of its projects as part of the Great Streets Program, including its Taraval Streetscape Improvements Project. LID features are also included in San Francisco Municipal Transportation Agency’s Livable Streets projects (for traffic calming, among other purposes) and Planning Department’s Pavement to Parks Program.
Paved-over front yards and sparse sidewalk vegetation are commonplace in the Sunset District, increasing the amount of stormwater that the city's combined sewer system must treat during wet weather. Image courtesy of Bjorn Griepenburg
The Ocean Beach Master Plan (OBMP) includes a recommendation to employ LID throughout adjacent neighborhoods and along the Great Highway to address stormwater management. Much of the Sunset District lends itself well to potential future LID projects because of its wide, hilly streets, many of which are sparsely vegetated and contain paved-over front yards.
To help plan the Sunset Boulevard Greenway, take the SFPUC’s survey.