The headquarters of some of Silicon Valley’s best-known companies hug the edge of San Francisco Bay, but only upper-floor offices have water views. That’s because the buildings sit on subsided earth that lies several feet below sea level.
Google, Yahoo, and Cisco Systems are just a few of the Silicon Valley companies that lie only a levee or two away from the Bay, and some of their offices risk being inundated when sea level rises by the expected two or so feet in the next half century. Facebook’s headquarters is separated from Bay water by only a skinny bike path on a low levee — even companies with buildings several miles from shore, such as Cisco, are in zones that will get flooded by high tides within fifty years if levees aren’t raised. If protection isn’t increased, by 2067 there’s a one percent chance each year that bay water will overtop levees and flow into some of the office parks south of Highway 237, which lies about 4 miles away from the open waters of the Bay. If the crude dirt levees actually gave way, programmers and social media managers could have wet feet far sooner.
“Many of the levees around the South Bay were not built to provide flood protection. They were built for salt production ponds,” says Caleb Conn of the U.S. Army Corps of Engineers.
Now, engineers and biologists are working together to protect urban areas with both soft, marshes and hard levees. Part one of the protection is the South Bay Salt Ponds Restoration project, now celebrating a decade of work completed. That project is designed to restore wetland habitat, but it’s also providing a buffer against storms and sea level rise for urban areas. “It’s the idea of using our natural infrastructure to enhance our built infrastructure,” says Amy Hutzel of the Coastal Conservancy, which is in charge of the project.
Part two of the protection is a parallel project now undergoing a feasibility analysis known as the South Bay Shoreline Study. The Corps of Engineers is working with the Coastal Conservancy and the Santa Clara Valley Water District, which is responsible for flood control and stream stewardship, to put together a plan for the first of several sections of improved levees by the end of this year. Construction is expected to cost between $80 and $130 million, with the Corps picking up 65 percent of the bill and state and local agencies the rest.
“We want to see additional wetland restoration move forward and we can’t do that without flood protection,” says Hutzel.
Before restoration, the levees encircling each salt pond provided several lines of protection for the urban areas inland of the ponds. But the restoration project is poking lots of holes in the Bay side of the levees to let the tides in and re-establish natural marsh function. With that border breached, the landside levees that separate the city from the marsh need to be strengthened.
The re-engineered levees will protect not just corporate headquarters, but hundreds of homes in the Alviso district of San Jose, as well as the all-important San Jose/Santa Clara Water Pollution Control Plant, which treats sewage for 1.4 million people.
Early versions of the study call for superwide levees 400 feet across that on the Bay side slope so gently that they will create many acres of new transitional habitat between the marsh and upland areas (see opposite). Acquiring soil to create these huge, broad levees — about 2 to 3 million cubic yards, enough to cover 400 to 500 football fields thigh-deep — is a major challenge. The Conservancy is now banking clean, free dirt from urban construction projects to use for future new marsh plain and levees. Construction will likely start in 2017, following Congressional authorization of the plan recommended by the Corps.