California waterL.A. water supply vulnerable to disruption by earthquakes

Eighty-eight percent of Los Angeles’s water comes from the Colorado River, Owens Valley, and the Sacramento-San Joaquin River Delta, passing through three major aqueducts and into the region. The aqueducts cross the San Andreas Fault a total of thirty-two times, making them vulnerable to the much anticipated Big One, a hypothetical earthquake of magnitude 8 or greater which is expected to happen along the fault. A large temblor on the fault could destroy sections of the aqueducts, cutting off the water supply for more than twenty-two million people in Southern California.

If local officials fail to act on retrofitting the aqueducts, the region could be left with less than six months of stored water, and it could take more than a year to get all three aqueducts operating again after a major earthquake.

Los Angeles mayor Eric Garcetti has asked for proposals better to protect the current water flow and develop alternatives in case an earthquake blocks the aqueducts. “This is a regional issue, with significant infrastructure costs,” Garcetti said. “We all know how precious water is these days with our historic drought…. Water is also one of L.A.’s greatest earthquake vulnerabilities, too.”

According to the Los Angeles Times, a first step in ensuring the city’s water supply would be for the agencies that manage the Los Angeles, California, and Colorado River aqueducts collaboratively to develop an earthquake retrofit plan. The Los Angeles Aqueduct crosses the San Andreas fault through the five-mile Elizabeth Tunnel under the mountains north of Santa Clarita. During a large earthquake, the fault can move as much as thirty-three feet and could split the tunnel, “dam it up and collapse some of its concrete sections,” the Times notes. Solutions for this aqueduct include building a wider stronger tunnel, or using electricity to pump water over the mountains toward Los Angeles.

Craig Davis, an earthquake engineering expert for the Department of Water and Power (DWP) said that during a large earthquake, the California Aqueduct would be pulled apart by the San Andreas fault in the Palmdale area, allowing large volumes of water to spill. The Colorado River Aqueduct is vulnerable at a particular section that could be lifted thirteen feet during an earthquake, stopping the flow of water.

“There should be a serious dialogue among the agencies that are responsible for the three sources of water to Southern California,” said Thomas O’Rourke, a Cornell University engineering professor and longtime seismic consultant for the DWP. “Sometimes it’s very difficult to go beyond those institutional barriers…. Somebody just has to take it up.”

Unlike other large cities, Los Angeles is mainly dependent on water sources far from the city center, saidLucy Jones, U.S. Geological Survey seismologist and the mayor’s science advisor on earthquake safety. “We’re the first city that’s really bet its life on outside water,” Jones said. “We have to cross the faults. There’s no way to not go over the fault.” It was a 2008 study conducted by Jones and fellow researchers that raised the alarm on the vulnerability of the three aqueducts during a large earthquake.

Garcetti acknowledges the high cost of retrofitting the area’s water supply, but warns that failure to do so could result in more lasting damage. Water is “one of L.A.’s greatest earthquake vulnerabilities,” Garcetti said. “If it were to take six months to get our water system back … residents and businesses would be forced to relocate for so long that they might never come back.”