Earthquake could threaten California's water supply

Earth Day Special Feature 2011: Two-thirds of Californians get their water from the Delta. A look at Sherman Island and the aging levees in the Delta.
Written by Boonsri Dickinson, Contributing Editor

Water from the Sacramento River is pulled through the Delta to pumps that deliver water to California residents. Most of the water, though, is used to satisfy agricultural needs.

All of this exported water disrupts the natural water flow through the region. However, now with sea level rising and increased and improved seismic risk assessment - the aging infrastructure in the Delta might be putting the water supply of 23 million Californians in jeopardy.

While the Sacramento-San Joaquin Delta has been there for thousands of years, building levees has changed the area’s pristine marshland into farmland.

The Delta is the hub of the water for two-thirds of California's population and supplies water for up to three million acres of farmland. The area is a habitat for 500 species and is home to more than 400,000 people. Highways, pipelines, power distribution, railroads and deep water ports go through the Delta.

To understand what's going on in the region, take a look at Sherman Island.

The man-made island is an infrastructure choke point with six highways, three railroads, major transmission lines and gas lines and telecommunication towers that run through. However, Sherman Island has evolved quite a bit in the past century: In 1869, Chinese laborers built levees that were 4 feet high and 12 feet at the base on Sherman Island. This was the first evidence that large-scale reclamation was underway – forever changing the landscape of the Delta.

It didn’t not take long before the island flooded. By the end of the 1870s, hand labor was replaced by steam-powered dredges. During World War 1, more levees were built.

Today, the Delta takes up more than 700,000 acres, with 1,115 miles of levees to separate the salt water from the fresh water. In June 2004, two Jones Tracts collapsed and nearby farmland was flooded. And in 1980, the tracts flooded again.

The levees are aging - some are now a century old. Robert Bea, a professor at the University of California at Berkeley, heads the Resilient and Sustainable Infrastructure (RESIN), a research center set up to deal with the Delta crisis.

“The situation is extremely serious. All of our analyses, and those done before, clearly indicate the California Delta infrastructure systems do not meet guidelines for acceptable public performance for extreme storm and earthquake conditions,” says Bea.

An earthquake in California could trigger a disaster as big as Hurricane Katrina. “The problems we see in the Delta are the same ones we saw in New Orleans,” Bea previously said in a statement to UC at Berkeley.

The U.S. Geological Survey reported a 99 percent probability that an earthquake with a magnitude of 6.7 would strike the Bay Area in the next 30 years. If a magnitude 7.8 earthquake from the San Andreas Fault hit the region, the disaster could induce liquefaction by turning sand into quicksand and causing the levees to sink. As it turns out, liquefaction occurred during the recent Japan earthquake, which has caused more long-term damage. In the event that levees fail, billions of gallons of salt water would flood the islands and flow into the Delta within days.

“The effect on the water supply is a key consequence of significant failures of the levees - flood protection systems in the California Delta. The studies indicate that the fresh water supplies for the state would be disrupted for a period exceeding five years given a large earthquake in the area,” Bea says. Such a scenario would threaten the supply of California's emergency water storage capacity.

It could have a domino effect on California’s economy. “I truly believe the main issue is the vulnerability of the levees to even a moderate earthquake say 4.5, centered near the Delta. Also, over-pumping of ground water in the San Joaquin Valley is causing the California Aqueduct to sink. An earthquake could cause its catastrophic failure. Either situation would cause southern California to lose 80 percent of its supply,” says John Barbieri, founder of Natural Resources Corporation.

It's not all that rare for levees to fail: 160 Delta levees have failed in the past century, according to the California Department of Water Resources. Seven of those have occurred on Sherman Island.

So, how much water can we take from the delta, and have it still be considered healthy? Farming is the major allocation and urban areas are second. We must ask: What kinds of sustainable water allocations we can have for the Delta? There are a few factors to consider: high water flows, sea level is rising, aging levees and the introduction of non-native plants and animals. And lastly, changing weather patterns: There has been more rain and less snow.

Cliff Dahm, a lead scientist for the Bay-Delta science program, says the delta plan is being written this year and will be released in January of next year. There’s only a finite amount of money. Upgrading thousands of miles of levees will cost billions of dollars.

“We need to figure out where money is best spent. Clearly protecting human life and protecting property is important in that decision making,” Dahm says.

Bea thinks more structurally about the situation. If a storm induced breaching of the levees, the effects will depend on which islands and how many islands are affected.

“If the islands near Suisun Bay were flooded, the saltwater intrusion would affect the water supplies for southern California, until the levees were repaired and the water from the Sacramento and San Joaquin rivers are allowed to re-establish the boundaries between fresh and saline waters,” Bea says.

[via UC Berkeley]

Photo: California Department of Water Resources

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