Almost one-third third of Southern California's drinking water comes from 300 miles away in an area between San Francisco and Sacramento known as the delta and travels through a century-old system of levees that could easily be destroyed in an earthquake, according to experts.
The delta is where the San Joaquin and Sacramento rivers meet and fill hundreds of miles of streams with freshwater. Most of the delta, a system of dirt mounds and channels that protect property from flooding in the Central Valley, is below sea level.
The man-made barriers around the hub of California's water system are more than 100 years old and 55 percent of the most critical levees statewide are considered "high hazard," according to a December 2011 report issued by California’s Department of Water Resources. State engineers studied approximately 2,100 miles of these critical levees for the report.
"The most vulnerable spot in our water system is the Delta area," said Jeff Kightlinger, general manager of the Southern California Metropolitan Water District.
A team of UCLA engineers has been studying the delta and the soil used to build the levee system, first built in the 1880s using peat that was fertile for agriculture, but not the strongest choice for levee foundations.
His team has created simulations of an earthquake's impact on delta soil and found the earth under the levees could become unstable through a process known as "liquefaction" -- the strength of soil is reduced by shaking.
"The kind of earthquake we worry about would be similar to the earthquake that happened in Napa Valley, maybe a little bigger than that," Brandenberg said. "That would certainly result in strong enough shaking that would result in levee failures."
The magnitude-6.0 Napa Valley quake in August was centered just 35 miles from the delta. It shook a widespread part of the region and damaged older commercial buildings in downtown Napa.
"We dodged a bullet," said Kightlinger.
Levee failures consistent with Brandenberg's models could result in flooding and the mixing of salt and freshwater. Significant damage to the aqueducts that usher that freshwater to Southern California could take years to repair.
"It could be anywhere from three to five years until that's rebuilt," Kightlinger said. "So that would be severe rationing, crimps on business, basically a pretty dire situation.
"It would mean a loss of about a third of our water supply. There is no doubt that we would have very strict rationing after an earthquake."
There is a 66-percent chance of a magnitude-6.7 quake or greater in the delta region within the next 30 years, according to experts.
"You need to understand that issues in the California Delta that's 300 miles away from here, that you may never have heard of, have a real impact on our lives so they are worth paying attention to," said Brandenberg.
Steps are being taken to address the problem. In the 1990s, a $2 billion reservoir considered the jewel of the water system opened 90 miles south of Los Angeles. Diamond Valley Lake reservoir provides water to communities from San Diego to Ventura County.
Kightlinger calls the reservoir the region's insurance policy because it is designed to provide six months of emergency water in case of a damaging earthquake.
Gov. Jerry Brown has campaigned for a tunnel designed to carry freshwater under the delta. That expensive project would require years to build.
Brown's California Water Action Plan just made $150 million available to improve urban levees in the Central Valley. The funding comes from the 2006 Disaster Preparedness and Flood Protection Bond Act or Proposition 1-E.
To date, nearly 300 levee repair sites have been identified, and more than 100 of the most critical sites have already been completed with AB142 funds.