New rain gardens take load off sewers
in San Francisco’s Ingleside neighborhood.
The gardens are complemented by 16,000 square feet of porous concrete that also allows storm water to seep back into the ground. As a result, storm water that ordinarily would flow back into the sewer system can be slowly filtered by layers of rock and soil before being absorbed back into the landscape, said Sarah Minick, a PUC wastewater program manager.
“The storm water goes into the planter and is absorbed, like a concave sponge in the land, catching the water before it runs off into the sewer,” Minick said. “Anything we can do with green infrastructure will make our system work better overall by slowing down water and keeping it from going into the sewer.”
The locations for the rain gardens and permeable concrete were strategically placed atop the city’s eight urban watersheds. All together, the eight projects come with an anticipated ratepayer-funded price tag of $57 million. Some of that money will come in the form of low-interest loans the PUC has obtained from the state revolving fund. Another rain garden project is wrapping up along Valencia between Mission and Cesar Chavez streets. The next project the PUC will tackle is in Visitacion Valley.
Among coastal cities in California, San Francisco is unique in its use of a combined sewer system — one that collects and treats wastewater and storm water using the same set of pipes. That puts a strain on the city’s water treatment plants, which, during the region’s rainy season, handles about 500 million gallons per day. During drier months, that number hovers around 80 million gallons per day.
The PUC expects the Holloway Avenue rain gardens and porous concrete to siphon off around 950,000 gallons of water annually. The other seven projects are in various stages of construction, planning or design, but once all eight are fully functional, they’ll be swallowing about 17.3 million gallons of storm water each year.
“By implementing green infrastructure, we’re actually increasing the system’s capacity,” said Chris Colwick, a PUC spokesman.
Looking decades down the line, the PUC has set a goal of using a wide array of green infrastructure projects to manage 1 billion gallons of storm water by 2050, Minick said.
The rain gardens and porous concrete projects represent one prong of the city’s 20-year sewer system improvement program, a multiphase, multibillion-dollar program to upgrade San Francisco’s sewer infrastructure.
Raelyn Ruppel is looking forward to watching the Holloway Avenue project in action the next time it rains. She saw crews digging up the street to install them from her home on the corner of Holloway and Jules Avenue, and said she starts to get a bit anxious when the rain starts falling faster than a half-inch per hour.
“I hope it helps. I’ve had problems with my own sewer backing up into my basement, so hopefully these will help to get some of the water off the street,” Ruppel said.
“They’re pretty, too,” she said. “They make the street look better.”
“The storm water goes into the planter and is absorbed, like a concave sponge in the land, catching the water before it runs off into the sewer.” Sarah Minick, PUC wastewater program manager