Los Angeles – This city gets 88 percent of its water from three major aqueducts, flowing from the Colorado River, Owens Valley and the Sacramento-San Joaquin River Delta. But as they make their way into the region, the aqueducts cross the San Andreas fault 32 times.
Officials have long warned that a big earthquake on the San Andreas could destroy key sections of the aqueducts, cutting off the water supply for more than 22 million people in Southern California.
L.A. officials are for the first time taking concrete steps to address the problem. Making the water supply less vulnerable to a huge quake will probably cost billions of dollars, and it is unclear where that money would come from.
Mayor Eric Garcetti has asked for proposals aimed at protecting the water supply and developing alternatives in case a quake blocks the aqueducts. Ideas include strengthening waterways and developing an emergency supply for firefighters using ocean water and reclaimed water.
Los Angeles is behind the San Francisco Bay Area in this effort. The East Bay Municipal Utility District has built backup tunnels, stronger pipes and new waterways to ensure that water continues flowing from the Sierra Nevada even if one of its three main aqueducts is blocked. The efforts have cost more than $350 million, paid by water customers, bonds and government grants.
Flexible pipe
The San Francisco Public Utilities Commission built a new water tunnel under San Francisco Bay and installed a pipe that crosses the Hayward fault. The pipe is connected by accordionlike joints that allow it to flex and swing. The projects are part of a $4.8-billion effort funded by a surcharge on water bills.
Compared with other large cities, Los Angeles is critically dependent on water sources far from the city center, said U.S. Geological Survey seismologist Lucy Jones, the mayor's science adviser.
"We're the first city that's really bet its life on outside water," Jones said. "We have to cross the faults."
A first step would be for the agencies that manage the Los Angeles, California and Colorado River aqueducts to come up with a quake retrofit plan.
After the 1994 Northridge quake, hydrants ran dry in large parts of the San Fernando Valley, forcing firefighters to switch to water-dropping helicopters using swimming pool water to fight blazes.
The Los Angeles Aqueduct, built a century ago by William Mulholland, crosses the San Andreas fault through the 5-mile-long Elizabeth Tunnel under the mountains north of Santa Clarita. Experts said the San Andreas fault can move as much as 33 feet in a big earthquake and could slice the tunnel, dam it up and collapse some of its concrete sections.
The most expensive solutions include building a wider, stronger tunnel; another is to use electricity to pump water over the mountains toward L.A. But the Department of Water and Power hasn't had the resources to study various retrofit options until now, said Craig Davis, the utility's water system and earthquake engineering expert.
Interim solution
The department has already begun sketching out an interim solution — placing a 3-foot-wide strong plastic pipe through the tunnel. Even if the tunnel collapses, it's hoped the plastic pipe might keep enough of the passageway intact to keep some water flowing through, Davis said.
Davis warned that the Edmund G. Brown California Aqueduct could be pulled apart by the San Andreas fault in Palmdale, allowing large volumes of water to escape.
The 1940s-era Colorado River Aqueduct has a different problem. A section of the aqueduct in the mountain pass west of Palm Springs could be lifted 13 feet in a San Andreas quake, stopping the water flow. There are no backup pumps to keep water moving, Davis said.
