State water supply vulnerable to quakes, floods ENVIRONMENT: The Sacramento-San Joaquin River Delta

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Earthquakes and severe storms could destroy hundreds of miles of mostly earthen levees in the Sacramento-San Joaquin River Delta in coming decades, according to a state report that provides the most detail yet on the vulnerabilities of the hub of California's water system.

Among the findings in the 1,000-page report released Friday by the Department of Water Resources: There is a 40 percent chance that a major earthquake will flood 27 delta islands between now and 2030, costing billions in repairs and knocking out the water source for 25 million Californians for more than a year.

"There are some risks (to the levees) that can be mitigated pretty well by existing programs," said Dave Mraz, head of the department's Delta-Suisun Marsh Office, "But there is one risk that's very difficult to deal with - seismic."

The report, the first of a two-part analysis of the risks facing the delta, found that the 1,100 miles of levees that protect 60 or so islands at the confluence of the Sacramento and San Joaquin rivers are growing more susceptible to breaches due to age, storms, rising sea levels and subsidence of some land by 25 feet or more.

Without intervention, researchers predicted, about 140 levees could fail in the next century due to storms or rising seas. An earthquake of magnitude 6.7 or greater could result in fatalities, flooding of islands and costs of $15 billion. Levees have failed about 160 times in the past 109 years.

The second part of the report, to be released this fall, will focus on ways to head off those worst-case scenarios, including raising the height of levees throughout the estuary or building a so-called peripheral canal that would route water from the Sacramento River to large pumps in the southern delta. The delta acts as a giant funnel, channeling meltwaters from the Sierra Nevada to long pipelines that deliver water to two-thirds of the state - mostly the Central Valley and Southern California, but some to the Bay Area.

Critics argue the report overstates the dangers posed by earthquakes and might simply bolster the state administration's push to build a peripheral canal. A peripheral canal proposal was defeated in 1982, but the idea has gained new momentum as the delta deteriorates and demands on the water supply grow greater. Some worry a canal will simply distribute more water to Southern California and push out farmers who have been growing crops in the delta for generations.

"They keep painting a picture that the levees are doomed, the levees are doomed - and that's a reason to build a peripheral canal," said Barbara Barrigan-Parrilla, director of Restore the Delta, a group of residents, businesses, farmers that oppose the canal. "If we know the seismic threat, we should be in there now doing levee fortification."

State officials say they have increased the amount of money for reinforcing and repairing the levees - some of which date back to the Gold Rush era - from $12 million in the 1990s to $50 million last year. Still, that may not be enough to protect key islands from floods.

In addition to supporting thousands of residents, some delta islands have important highways, rail lines, power lines and natural gas facilities that could be wiped out by raging waters. Levees are also important to water quality. If multiple islands are submerged, salt water could push farther east, diluting freshwater and increasing costs to purify it.

Because different islands within the delta have different values - economic, residential, environmental - Mraz said his agency is attempting to make sure all of the levees receive a certain amount of funding. But he did acknowledge that in the face of a catastrophic event, the agency would have to prioritize which islands to save.

Steve Mello, who farms 2,500 acres on Tyler Island, worries that under either situation - floods or a peripheral canal - his family business could collapse.

Tyler Island "is on the bubble in terms of whether it would be reclaimed" in a flood, Mello said. "What I worry about more, though, is a peripheral canal ... and arguments that say 25 million people in (Los Angeles) need this water more than you."