Millennium Ark: Hot News

May 14, 2006
By Lisa M. Krieger
KNIGHT RIDDER

Even a moderate earthquake could cause California's aging levee system to collapse, flooding 400,000 houses and sending brine into the drinking water of homes across Northern California.

According to a computer-generated study presented this week at Stanford University, a 6.5 magnitude quake in the area of Antioch and Rio Vista could trigger the breaching of as many as 50 levees in the southwestern regions of the Sacramento Delta.

"Your levees are not seismically safe. They're just piles of dirt," said retired Brig. Gen. Gerald Galloway of the U.S. Army Corps of Engineers.

Drinking water and farm water exports to Santa Clara County and the San Joaquin Valley from the Delta would halt immediately. Damage could cause the aqueducts that carry water to the Bay Area from the Sierra Nevada to fail.

Two-thirds of Californians depend on the Delta for at least some of their drinking water. And for the 500,000 customers of the Contra Costa Water District, the effects could be particularly devastating. The district manages the largest urban water delivery system that relies entirely on Delta supplies.

If the Delta's waters become undrinkable, the district would have to rely on a six-month supply of water stored in the Los Vaqueros Reservoir, said spokeswoman Patty Friesen.

While Santa Clara County could rely on its reservoirs for a while, they are insufficient to serve the entire population indefinitely, said Martin McCann Jr., a consulting professor of civil and environmental engineering at Stanford.

McCann helped lead the study, which the California Department of Water Resources launched after Hurricane Katrina. The goal was to help the state calculate the effect of a major earthquake or winter flooding in the Delta region.

In the hypothetical disaster scenario presented Wednesday, seismic waves would trigger the collapse of the earthen levees, causing waves of salt water from San Pablo Bay to rush into the Delta.

An earthquake this size has a relatively low probability of occurrence -- a 6.8 percent chance in 50 years. "That seems remote, but not given the size of events that would transpire," Galloway said at a news conference.

"A realistic look at the Sacramento Delta will make us wise and more aware," McCann said. "Once we understand the risk, we can decide how to design, build and operate a levee system. The public can decide what the investment should be."

The study uses a mathematical modeling system of the San Francisco Bay and Sacramento-San Joaquin Delta to identify which regions would be breached and flooded. The model takes into account the Delta region's normal flows, barrier operations, control gates and other structures.

There are 1,100 to 1,600 miles of levees in the Delta and Suisun marshes.

While winter flooding is an ongoing concern, an earthquake would be far more catastrophic, according to scientists.

Even a quake more than 50 miles away in the Bay Area could threaten the levees if it is big enough, according to recent research at Lawrence Livermore Laboratory.

Seismologists Shawn Larsen and Arthur Rodgers used lab supercomputers to simulate the Northern California shaking during the 7.8 magnitude 1906 quake in San Francisco. They found moderate to significant damage would occur to Delta structures during a similar future quake, jeopardizing the levees and the state's water supply.

The foundations of the state's levees, old and poorly maintained, are built on sandy and silty soil, scientists said. In an earthquake, the soil could liquefy and collapse.

And large waves could form in the flooded Delta, eroding more levees, the study released this week predicts.

The most immediate danger would be to the 400,000 people who live in the greater Delta region, McCann said.

"There is no warning for the people who live in the region, no opportunity for evaluation. There are just moments to get out," he said.

It would also affect businesses and an estimated 85,000 acres of farmlands. About $400 billion of the state's annual economy is dependent, either directly or indirectly, on the Delta, McCann said.

Galloway urged the state to invest in levee improvements. "You can't not do it and think you're protected," he said.

Said McCann: "It is a wake-up call for California and the nation about the level of protection provided by levees, and the exposure we have in the event of a failure."
Times staff writers Kiley Russell, Betsy Mason and Mike Taugher contributed to this report.

http://www.contracostatimes.com/mld/cctimes/news/14561883.htm