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San Francisco Embraces the Beauty of Bioswales

Disrupting drainage.

The bioswale

The bioswale 

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Of San Francisco’s many peculiarities, its oft-flooded sewage system is one of the least attractive—and most consequential. San Francisco is the only coastal city in California with a combined sewer and storm water network, which sends both sewage and rainwater through the same pipes to treatment plants. The Public Utilities Commission (PUC) has embarked on a multibillion-dollar effort to upgrade the 100-year-old system by piloting projects in each of the city’s eight watersheds to simultaneously prevent floods and make the city greener.

Most impressive has been the introduction of bioswales: special flood-diverting plots, also known as rain gardens, placed near parking lots and roads to channel water away from impermeable asphalt. To an untrained eye, they’re almost indistinguishable from standard landscaping, as most of their functional parts—water pipes, a gravel bed for filtration—are buried beneath an assortment of water-absorbing plants.

UCSF’s new Mission Bay campus has bioswales surrounding its parking lots (thanks to a city ordinance requiring large developments to manage their own runoff), and dozens more are planned for Sunset Boulevard. But building them has involved a steep learning curve: A relatively small one at Sunset Circle near Lake Merced cost $200,000 and took over four months to construct. And because they contain living things, bioswales require more maintenance than conventional drainage systems. But PUC vice president Francesca Vietor sees green infrastructure as a solution to more than one problem: She hopes that besides helping developers handle water more intelligently, bioswales will generate new jobs. “We’re creating apprentice programs and retraining engineers,” she says. “It’s an educational opportunity, and a whole new language that needs to be learned.”


Originally published in the June issue of San Francisco

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