Last week the SFPUC partnered with Earthwatch and HSBC Holdings volunteers to conduct some citizen science out in the field on the oldest rain gardens in San Francisco.

Rain gardens are also known as “green infrastructure,” a stormwater management technology that uses the natural power of plants and soils to slow down, clean and re-route stormwater to help reduce the burden of stormwater on the City’s sewer system during rain storms.

Rain gardens and bioswales at the Sunset Circle on the northern terminus of Lake Merced were installed in 2009 and treat stormwater running off the Sunset Circle parking lot before entering Lake Merced. Prior installing the rain gardens and bioswales, stormwater flowed untreated into Lake Merced carrying along with it pollutants, such as suspended sediment and car oil.

Volunteers measured the infiltration rate of the rain garden soils to learn how fast water currently soaks into the ground and also collected soil samples to measure the content of the soil. They also conducted vegetation mapping analysis to determine the density of vegetation in the rain gardens and swales. This valuable data will be used to inform the existing SFPUC green infrastructure monitoring program research, which kicked off at this site back in 2012. 

From 2012-2014 the SFPUC and San Francisco Estuary Institute monitored the Sunset Circle project to determine how much stormwater it was treating. However, it is difficult to fund long-term research efforts to see how green infrastructure technologies like rain gardens perform over time. Citizen science opportunities like this not only provide valuable data to inform future SFPUC green infrastructure projects, but also engages San Franciscans in scientific field research and educational opportunities to promote the understanding and action necessary for a sustainable San Francisco.

The SFPUC is installing rain gardens across the city as part of the Sewer System Improvement Program (SSIP), a multibillion dollar project to improve, upgrade and replace the City’s 100-year-old underground sewer system. To date, the SFPUC has constructed 60 rain gardens across the city that help manage more than 10 million gallons of stormwater per year.