San Francisco is a city that loves its nature — most of the time. While some neighborhoods have hills and some neighborhoods have feral green birds, the Mission floods. In heavy rains, like the November and December storms, homeowners and business owners know to break out the sump pumps. Mere water damage is a best-case scenario: A lighter rain in April sent backed-up sewage through homes and businesses.
These woes were the focus of a recent Chronicle column, which identified the epicenter of the Mission's flooding problem at 17th and Folsom streets. That is also where the city is replacing a parking lot with affordable housing — and, sometime this year, where the city will replace asphalt with a new playground and park.
The flooding problem in the area is mostly geographic. The Mission is almost flat, and the 17th and Folsom site is a valley. The land rises by about 5 feet three blocks west toward Mission Street, and by almost 30 feet three blocks east. The result is that the park is a bowl, where most water in the area will naturally flow.
Earlier designs of the park dealt in part with the flooding problem. A 2010 plan for what was to be called "Mission Creek Commons" included an underground cistern at the center of the park — the deepest part of the bowl — which would help feed the park's community gardens. The park's current design still includes the cistern, though not in the central location. And the cistern is not currently designed to handle rainwater runoff, according to Recreation and Park Department spokeswoman Connie Chan.
Another reason why the area at 17th and Folsom floods so regularly is the overtaxed storm sewer system. Minor clogs in the city's 100-year-old sewers can lead to big-time backups, like the sewage messes mentioned above. So Rec and Park's plan is to direct water at the park not to the drains in the street, but to drain through the ground, Chan said.
This might work, except for all the water around the area flowing to the same spot. This is land that wants to be wet: It's part of the Mission Creek watershed, and some cartographers believe this area was a lagoon or at least a marshland when the Spanish settled San Francisco in the 18th century.
It may want to be wet, but it'll be housing and a park in the future. Both affordable housing and open space are key needs for the Mission District, and the site is one of the few spaces in the Mission open to development.
How will the water affect the gardens and play equipment in storms? Gotta learn to swim sometime.