The Rain in SF is Mainly in the Drain


Islais Creek is San Francisco's equivalent of the L.A. River--it's currently hidden underground. Courtesy Rosey Jencks/San Francisco Public Utilities Commission

The winter rains in the Bay Area, as usual, seem to be too much of a good thing. There’s a fair number of flooded streets and general consternation about this stuff falling from the sky. But if we thought about it differently, it might seem more like manna from heaven. I did a little calculation this morning to see what was going down the drain.

San Francisco is roughly 49 square miles and gets an average rainfall of 21 inches of rain per year, so if my math works out, that means about 18 billion gallons a year are largely thrown out as garbage (SF, like a lot of major cities,  has a combined sewer system that processes rainwater as sewage.) The US consumed 8.6 billion gallons of bottled water in 2008, making it a multibillion-dollar industry. If SF harvested half of its rainwater, we could corner the US bottled water market!

Amusing speculations aside,  the concept of saving our wastewater is starting to catch on.  Last Thursday, at a salon organized by Re: Vision and architect Michelle Kaufmann, Rosey Jencks of the SF Public Utilities Commission talked how to re-engineer the cityscape to keep as much as 30 percent of the rainwater out of the sewers.

Here in SF, recent legislation requires all construction projects with a footprint greater than 5,000 square feet to have onsite stormwater management–which could take on the form of green roofs, cisterns, permeable paving, and other features, according to the city’s Stormwater Design Guidelines.  (An aside: Chicago appears to have beaten other cities to the punch in paving city streets with permeable concrete.)

Meanwhile, the PUC has also come up with a whole series of projects, many which bring a sense of romance to the mission. We don’t have a river here, as in L.A., but there are a couple of creeks that are good candidates for daylighting.  Revealed instead of snaking underground through pipes, Islais Creek–which runs through the neighborhoods of Glen Park and Mission Bay (as shown in Jencks’ slide above)–could be the grand public stroke, the visible symbol of the city connecting to its watershed. Like the other PUC projects, it’s a question of getting the money to do it. Maybe the city could raise funds by selling its own overpriced bottled water ?

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