Reducing Flood Risk: San Francisco District Tackles Multiple Bay Area Flood Challenges

Published July 24, 2018
The crumbling San Francisco seawall, a 100 plus year-old structure along the city's Embarcadero that is in danger of failing during a costal surge or a major earthquake.

The crumbling San Francisco seawall, a 100 plus year-old structure along the city's Embarcadero that is in danger of failing during a costal surge or a major earthquake.

The San Francisco Bay Area has not had a major flood since 1997. That situation changed with the 2017 California winter storms which caused millions of dollars in damage, and triggered a renewed sense of urgency about the threats posed by sea level rise.

It’s a risk compounded by the amount of low-lying shoreline around the bay that is dense with expensive real estate including homes, sports stadiums and multi-billion dollar businesses all at risk of flooding by torrential rains and rising seas. Some estimates predict sea levels in the Bay Area could rise by as much as 66 inches over the next century.

To highlight the urgency of the threat, the Corps’ South Pacific Division now considers the San Francisco waterfront, protected by a seawall more than a century old and deemed likely to falter during a major storm surge or earthquake, to be the highest priority for new federal dollars, or what is known as new start investigations. The structure provides flood protection for downtown neighborhoods and if it fails, the city estimates water damage to property and business could run as high as $35 billion.

“The San Francisco seawall is our last defense against the rising sea levels brought on by climate change and if we do not act now, our city will feel the impact for generations to come,” said former Mayor Mark Farrell. City voters will be asked in November to approve a bond measure that would raise hundreds of millions of dollars for the project.

South of the city in Silicon Valley, some of the world’s most expensive real estate and highly valued companies are considered especially vulnerable, so much so that the Corps’ San Francisco District and Santa Clara County are among those conducting a feasibility study to determine the best way to mitigate against the considerable risk of tidal flooding across areas of land protected by little more than non-engineered dikes. Major transportation hubs and highways are among the vital infrastructure considered vulnerable. Runways at San Francisco’s main airport jut out into the Bay with little defense against a sea surge.  Nearby is highway 101, a major artery used by hundreds of thousands of motorists daily that is located just feet from the Bay and would likely be submerged during a major tidal surge if predictions of sea level rise are realized.

“Agencies in the Bay Area recognize that sea level rise will cause coastal flooding in the near future if no action is taken,” said San Francisco District Flood Risk Management Program Manager Craig Conner. “Because of these issues, there has been a renewed interest by local agencies to partner with the Corps on flood risk management projects.”

BART, the Bay Area’s rapid transit system, is also at risk of flooding and the Corps just completed a $27 million project designed in part to protect the system’s Milpitas station which is located on a floodplain. The reinforced levees will also bring flood protection to homes and businesses along several miles of densely populated Upper Berryessa Creek and North San Jose, areas that have experienced three major floods since 1982.

Storm damage last year also triggered the repair of the Pajaro River and Salsipuedes Creek levee systems in nearby Santa Cruz County, a $6 million project expected to be completed in several months.  Not far away, the Corps is working with the Santa Clara Valley Water District and the California Coastal Conservancy to protect low-lying areas of the South Bay from coastal flooding and threatened sea level rise, including the cities of San Jose and Alviso, a region that is home to many multi-billion dollar Silicon Valley companies.  "We are grateful to the Army Corps for this influx of funding which means we can help protect the vulnerable people and businesses of this area," said Richard Santos, chair of the water district's board of directors.