A natural disaster could cause widespread levee failure in Northern California, flooding cropland and disrupting the water supply.

Date:   9/2/2005 5:15:13 PM ( 19 y ago)

September 1, 2005 Los Angeles Times, California

Delta Is at Risk, Geologist Warns
By Bettina Boxall, Times Staff Writer


When UC Davis geology professor Jeffrey Mount looks at the images of broken levees and surging floodwaters in New Orleans, he sees the future of the Sacramento-San Joaquin Delta.

"There is a natural tendency of Californians to look at what is going on in the Gulf Coast as as foreign to us as the tsunami in Indonesia — 'That's not something that could ever happen to us.' — Oh, they couldn't be more wrong," Mount said Wednesday.

In a study published in a Bay Area scientific journal last March, Mount and another scientist concluded that over the next 50 years, there is a 2-in-3 chance that a major storm or earthquake will cause widespread levee failure in the Northern California delta, part of the West Coast's largest estuary and the source of drinking water for more than 22 million Californians. Such a catastrophe would flood reclaimed marshlands that are sprouting housing developments and send seawater rushing into the delta, forcing a shutdown of the enormous pumps that send water south to Central Valley agriculture and Southern California cities.

"The water supply to a major portion of the state is at risk from this kind of event," Mount said. "The odds are quite high that the unexpected will arrive, and like New Orleans, we'll be dealing with a very interesting disaster."

Once a vast marsh rich with wildlife, the delta is the meeting point for the ocean waters of San Francisco Bay and the fresh waters of the Sacramento and San Joaquin rivers. Its rich, peaty soils were drained more than a century ago for cropland. Earthen levees, some of them built by hand by Chinese laborers and resting on unstable soil, hold back the water. Cultivation has promoted the breakdown of the peat so that land that was at sea level 100 years ago is now 20 feet below that.

Add a big earthquake or waves driven by a mighty winter storm and you have a recipe for extensive levee breaks. An earthquake of the magnitude that struck Northridge in 1994 in the delta could split open 30 levees, some experts believe.

Mount, director of the Center for Watershed Sciences at UC Davis' John Muir Institute of the Environment, was up before dawn Wednesday jotting down the similarities between California's delta and the Mississippi's.

There are many. Both are at the bottom of a large, flood-prone river system. They have been reclaimed with a vast system of levees. The land is subsiding below sea level. They have lost much of the wetlands that could absorb storm waves and floods. And they are both vulnerable to rising sea levels tied to global warming.

The only major difference Mount noted is that the Mississippi Delta is occupied by a major city, whereas the drained land in California's delta is mostly farmed. But that is changing as growth pushes outward from Stockton and other delta communities.

"There are proposals for upwards of 100,000 new homes in our delta and most of these are on lands that are subsided below sea level," Mount said.

His study, which Mount conducted with Robert Twiss of UC Berkeley, builds on earlier work done by the state Department of Water Resources and CalFed, a wide-ranging government program focused on the delta.

"I think what [Mount] has come up with is reasonable and is not out of the question," said Les Harder, the Water Resources Department's acting deputy director, who was involved in some of the earlier studies.

Harder too has been watching the watery disaster unfold in New Orleans. "For those of us involved in levees and flood control, it is a very sobering experience to see those images. And so yes, it does give all of us pause."

The levee system is in need of $1 billion worth of work just to bring it to basic standards, Mount said. Trying to protect the levees from a major natural disaster would require much more money. "It's just incredibly expensive."

California got a reminder of the weaknesses of the delta's 1,000-plus miles of levees last year when one was breached at the Jones Tract, flooding 12,000 acres of cropland west of Stockton. When repairs, property and crop damage are added up, the cost of that failure approaches $100 million.

After the Jones break, which occurred spontaneously without a storm or other nudge from nature, the state launched a two-year study of levee failure risk. What are the chances it will happen? What would the impacts be on water supply, wildlife, agriculture and other delta uses? What might be done to reduce the risk?

In 1972, Harder said, the failure of one levee stopped delta water exports for a month. Depending on how many levee breaks there were and where they occurred, a major disaster in the delta could stop water deliveries for months or even a year, he said.

On average, the delta supplies 20% to 30% of the water consumed in Southern California. "We've long known about the levee situation and it's been part of our discussions for some time," said Bob Muir, a spokesman for the Metropolitan Water District of Southern California, the region's major water wholesaler. "The Jones Tract certainly opened our eyes and now with [New Orleans], it crystallizes our vision even more."

Metropolitan's delta deliveries, which come from the State Water Project, can vary substantially according to how wet or dry the year is. But they can make up as much as 60% of the agency's supplies.

To guard against a major earthquake that could shut down not only delta deliveries but also the Colorado River Aqueduct, Metropolitan maintains a six-month emergency water supply in Southern California reservoirs. "That was one of the major reasons why we went ahead with Diamond Lake," said Debra Man, Metropolitan's chief operating officer, referring to a large reservoir recently constructed in Riverside County.


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