Department of Water Resources
A daily compilation for DWR personnel of significant news articles and comment
March 23, 2009
Top Items–
State water supply vulnerable to quakes, floods
San Francisco Chronicle
Report says quakes pose big risk to Calif. Levees
Associated Press
A 6.7 or larger quake could flood islands in the delta, cost billions and take years to fix, a new report says.
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State water supply vulnerable to quakes, floods
San Francisco Chronicle – 3/21/09
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
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
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
"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
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2009/03/21/MN2416KD35.DTL
Report says quakes pose big risk to Calif. Levees
Associated Press – 3/20/09
By SAMANTHA YOUNG
The California Department of Water Resources says there is a 50 percent chance that 20 islands in the Sacramento-San Joaquin Delta would flood after a 6.7-magnitude earthquake. Repairs could cost up to $2.3 billion and take three years to complete.
In the meantime, water exports to 25 million residents in Southern California and the
The U.S. Geological Survey has estimated a 62 percent chance that a quake with a magnitude of 6.7 or greater will strike in the vicinity of the delta region by 2032. The San Andreas,
The delta stretches from the state capital to
State water officials have known that earthquakes and flooding pose risks to the delta, but they said Friday's report offers the most comprehensive look yet at the risks and costs associated with levee failures.
"The report is really focused on quantifying risks," said Dave Mraz, chief of the Delta-Suisun Marsh office in the Department of Water Resources. "It's these faults that give us probably the greatest risk for delta assets and those assets that come through the delta."
The delta's 1,330 miles of levees are unstable for a variety of reasons. Most were built with peat soil and sand by landowners in the late 1800s and early 1900s.
Meanwhile, the islands that sit behind those levees have sunk as low as 25 feet below sea level, adding pressure to the already fragile barriers.
Experts say the energy of a major earthquake along any of the three faults threatens to liquefy the peat soils.
Deaths from earthquake-related flooding would likely occur because quakes come with no warning and flooding would be rapid. The report found a 40 percent probability of 90 or more deaths.
Flooding also poses risks to the delta, although not as severe as an earthquake. The report said flooding could cause an estimated 140 levee breaches over the next 100 years.
There is a 40 percent chance that 20 islands would flood at the same time, causing roughly $8 billion in economic costs, partly from lost farm production.
In 2006,
It also is completing a second phase of the report that is examining how the state could spend money to minimize the risks from earthquakes and flooding. That report is expected to be released later this year.
The Department of Water Resources has paid consulting firms URS Corp. and Jack R. Benjamin & Associates $13 million over the past three years to develop the report. #
http://www.sacbee.com/state_wire/story/1716606.html
A 6.7 or larger quake could flood islands in the delta, cost billions and take years to fix, a new report says.
By Jia-Rui Chong
A major earthquake in the Bay Area could flood numerous islands in the Sacramento-San Joaquin River Delta, cripple the state's water system and cost billions of dollars, according to a state report released Friday.
The report, from the Department of Water Resources, found there is a 40% probability of an earthquake of magnitude 6.7 or higher causing 27 or more islands to flood at the same time in the next 25 years.
· Study finds troubling pattern of Southern California quakes
If 20 islands were flooded, the flow of fresh water through the delta could be interrupted for a year and a half, the report found. Emergency repairs on 20 islands could cost up to $2.3 billion and take about three years.
"Not everybody agreed an earthquake in the delta would be a problem, so we had to have a good team of well-respected scientists and engineers take a look at it," said Dave Mraz, chief of the department's Delta-Suisun Marsh office, which oversaw the report. "As it turns out, it's a very significant one."
U.S. Geological Survey seismologist Lucy Jones said she was very happy the state has taken the step of trying to quantify the scope of the problem. "This is the type of thing needed by decision makers to act," she said.
Former state Assemblyman John Laird began asking for a study of the effect of natural disasters on the levees in early 2005. The disastrous consequences of levee breaks during Hurricane Katrina later that year added urgency.
Mraz said his office worked with consulting groups URS Corp. and Jack R. Benjamin and Associates on the assessment as quickly as possible to synthesize data from earthquake scientists, engineers and economists. The report released Friday about the scope of the risk was the first phase. A second report will look at ways to address the risks.
Friday's report cited U.S. Geological Survey research finding that there is a 67% probability of an earthquake registering magnitude 6.7 or greater in the Bay Area in the next 25 years.
An earthquake of that size in a delta would probably cause liquefaction, in which shaking causes loose, water-soaked soil to turn into quicksand, Mraz said. The earthen levees that help channel water would sink, leading to flooding on the islands and salt water intrusion into the freshwater delivery system.
The ground movements "required to cause the delta to liquefy are very low," Mraz said. "That's kind of an Achilles heel in the delta."#
http://www.latimes.com/news/local/la-me-quake21-2009mar21,0,2527038.story
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