Will California's Levee System Hold up in an Earthquake?

A recent state report calls into question the state levee system’s ability to sustain an earthquake or other natural disaster.The state’s levee system runs 13,000 miles: a distance equivalent to driving from San Francisco to New York City and back, twice. The complex chain of channels and dirt mounds is responsible for delivering more than two-thirds of the clean drinking water to California homes and protects nearly $47 billion of property from flooding in the Central Valley. According to a December 2011 report issued by California’s Department of Water Resources, 55 percent of the most critical levees statewide are considered “high hazard.” According to the state's own definition, “These levees are in the most danger of failure.”

According to experts, if the levees break, the concern is twofold: local businesses and agriculture would experience flooding and Californians living in the Bay Area or Southern California could have their drinking water contaminated. “I’ll tell you, I worry every year when we have high water,” said Mark Morais, a Central Valley restaurant owner. “The levees are only as good as the reclamation districts make them.” Morais is the third generation in his family to own Giusti’s Restaurant, built right next to a levee in the Central Valley. He worries, if some of the nearly 150-year-old levees break, his business would be flooded. Rhea Dearing, owner of Alma’s River Café, has similar concerns: “If the river lost, we’re going to lose our business here,” she said. Her restaurant sits along the levee holding back the Sacramento River in Walnut Grove. “Everything here depends into the levee and the river.”

California’s levee system was first built in the 1880s when farmers in the Sacramento-San Joaquin Delta wanted to prevent flooding on their farmland. While the peat was fertile for agriculture, it was not the strongest choice for levee foundations. It largely remains today. Brandenberg’s team built “mini-levees” on peat and other soils. What they found was that during an earthquake event, the earth under levees could become highly unstable in what they call “liquefaction.” In other locations, the peat can compact, undermining the levees sitting on top of it. That type of levee failure can also lead to salt water mixing with fresh water, contaminating the water supply, or flooding it altogether. If the levees failed in the wrong place, the resulting flood could also damage the aqueducts that carry fresh water to the Bay Area and to Southern California. A serious rupture of any of those aqueduct systems could take years to repair if it were severe.

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*Note: Many levees are beginning to break around Sacramento and other surrounding areas as of late.