Some California cities think they’re safe from sea level rise. They’re not, new data show | Los Angeles Times

Just north of the Golden Gate Bridge, yet a world away from San Francisco, in an unincorporated and oft-overlooked area known as Marin City, sea level rise is rarely the first worry that comes to mind.

Traditional flood maps for this predominantly Black and working-class community suggest that the area is safe until sea level rise reaches 3 feet or more.

But sea level rise is a lot more complicated than just waves breaking over seawalls and beaches disappearing.

Imagine the groundwater beneath your feet. As the ocean moves inland, it will push all this trapped water upward until it breaks the surface. Basements will heave, brackish water could corrode sewer pipes, toxic contaminants buried in the soil could bubble up and spread.

In many areas along San Francisco Bay, this sea beneath us is already leaking out of the ground, said Kristina Hill, whose research at UC Berkeley focuses on this less-talked-about vulnerability. With even 1 foot more of sea rise, an unexpected swath of Marin City could increasingly flood.

Aside from homes and roads, human health is also a huge concern, she said. “Any pollution in the soil, capped from above but lying just below, will be re-mobilized.”

From Northern to Southern California, scientists and planners are waking up to the reality that rising seas will threaten not only California’s precious shoreline but also areas once considered less vulnerable to flooding. In the Bay Area alone, Hill and her team found that more than twice as much land could flood from groundwater as the ocean rises.

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