Gilbert Cosio stands with his feet spread, one foot higher than the other, astride a sloping, 100-year-old levee surrounding Bouldin Island, 40 miles due south of Sacramento, Calif. We’re here to take a look at improvements that Cosio, a civil engineer, has made to this levee, part of a serpentine network of flood control infrastructure that was imposed piecemeal over the course of the 19th and 20th centuries on the largest estuary on the West Coast of the Americas, the Sacramento-San Joaquin River Delta.
The levee was originally made from dirt that Chinese “coolies” dredged from the swamp to carve out cheap farmland for California’s new white settlers. Today, it and the hundreds of Delta levees like it must do more: They must — as they’ve been doing since the 1850s — keep the water out of the farms, many of which have fallen below sea level because of soil subsidence. But they must also keep San Francisco Bay, contiguous to the Delta’s western edge, from flowing into the Delta. The miles of levees surrounding Delta land also confine the estuary itself, creating a quasi-natural reservoir for freshwater that’s pumped to 28 million people and billions of dollars of croplands, from Silicon Valley to San Diego. And the levees don’t just protect farms and the estuary; they keep cities and suburbs and crucial infrastructure dry.