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Wednesday, August 10, 2011

LEVEES THAT LIE DOWN: A SOLUTION FOR EARTHQUAKES IN THE DELTA?

By Patricia McBroom

      Levees in California’s Delta have a bad image problem. For several years now, they’ve been called “fragile,” “decrepit,” “crumbling,” and “doomed.” One news story after another warns of a catastrophic collapse from a future earthquake, alongside scenarios showing half the delta under water – quite possibly undrinkable salt water.
When levees fail, an inland sea prevails.
Credit: Patricia McBroom
            The cost of retrofitting these critical structures, meanwhile, is expressed in extravagant terms.  “Astronomical,” said Phil Isenberg, chair of the Delta Stewardship Council, about the cost of making the levees earthquake safe.  Isenberg made the comment most recently during a televised debate on delta dilemmas, but he’s said it before, as have others. The accepted wisdom among water wonks in California is that the levees cannot all be repaired sufficiently to save the state from disaster in the event of a “big one.” Some openly recommend that the state allow major portions of the delta to go underwater, to the consternation of delta residents who live and farm there.
“Why would anyone want to save them,” a state water official was heard to say the other day about the delta levees.  “Everyone knows they’re doomed.”
But what if this public narrative is wrong – or substantially wrong? What if the levees are in better shape than described and – most importantly – can be retrofitted to withstand a big shake?
            If this is the case – if most or all of the levees can be built up to withstand an earthquake, magnitude 7 on the Hayward Fault, for a reasonable amount of money – it would change fundamentally the calculus now driving decisions about major new water infrastructure in California.
Dr. Robert Pyke: Levees can resist earthquakes and
accommodate to sea level rise.
Credit: Patricia McBroom
            The time for that kind of reassessment has arrived with publication of the second draft of an economic sustainability plan for the delta, prepared by a team headed by Dr. Jeffrey Michael at the University of the Pacific.  Little attention has so far been paid to the draft plan’s new information on levees.
            That is a mistake.
            On page 64, in a chapter devoted to delta levees, the report states unequivocally, “This study concludes that the core Delta levees can be made robust under seismic loadings for a total of $1–2 billion.”  
           Written primarily by a civil engineer, Dr. Robert Pyke, who is an expert on earthquake preparedness for dams and levees, working under contract here with Sapper West Inc. in Sacramento, the levee analysis focuses in on 460 miles of agricultural levees that need upgrades, out of a total of some 1,000 delta levee miles.
            The cost of making them seismically resistant is cheap, compared to that of building a tunnel around the Delta ($12–20 billion), or elevating the highways and railways ($10 billion) or even retrofitting San Francisco’s water delivery system from the Hetch Hetchy reservoir ($4.6 billion), the report explains.
            Not only is retrofitting the levees less expensive than other alternatives, but a good bit of the money has already been allocated in bond issues passed by voters in prior years.  California’s Department of Water Resources (DWR) has been dragging its heels in releasing the bond money, slowing the repair process in an unconscionable way, considering the risks.  Officials should have even less of an excuse now, in the light of this new information.
            The key to this claim is an enlarged levee that has such a thick landside shoulder that it looks almost flat from the field.  It’s crest is very wide – 50 feet compared to 16 feet now on some levees – and it has three feet of freeboard on the waterside at the high water mark of a 100-year flood.  It's wide crest means that it can easily be built higher to accommodate sea level rise.  On most days, the proposed levee would stand 10-15 feet above the water.  It’s landside berm would extend for some 140 feet from the crest.
Design of proposed earthquake resistant levee for Webb Tract, by Hultgren-Tillis Engineers, similar to that
proposed by Robert Pyke, in the Economic Sustainability Plan for the Delta
            “Making a levee robust enough to withstand earthquake shaking is a lot simpler than retrofitting or even seismically designing a new building or bridge,” said Pyke. “Basically it just takes a wider cross-section and more dirt.”
            He explained that in an earthquake, the big fat levee would deform a bit, but “it’s unlikely that even with high water that you would have a breach.” Asked in an interview how he can be sure without data that this kind of construction would resist a breach, Pyke replied, “The earthquake behavior of dams and levees is central to my education and experience.  I’ve been an expert witness in about 20 cases in California and as far as I know, I’ve never been on the losing side, because I don’t make things up.  I don’t overstate things.”
            In any case, he added with a smile, “It’s hard to see how the levee can fall over when it’s already lying down.”
            Pyke’s claim to expertise is backed up by other civil engineers he’s worked with on multiple projects in the state.  “He’s very, very good – one of the best,” said Ed Idriss, retired UC Davis civil engineering professor who worked with Pyke on a four-man team to evaluate potential ground motion from an earthquake for the new East Bay Bridge.
            “In terms of knowledge, I’d put Bob Pyke way up there.  He’s one of the most qualified to look at the effects of earthquakes on levees."  Idriss served on the Seismic Safety Peer Review Panel for the new bridge.
            If the new report is true, however, it raises a sticky question:  How did so many other experts on the delta get it wrong for so long?  The answer appears to lie in a controversial, but nonetheless influential, report put out in 2005 by the DWR.  Titled “Delta Risk Management Strategy,” , phase 1, the DRMS report made highly sophisticated calculations of levee failure in the event of an earthquake, estimating that up to 50 breaches could occur, flooding 20 islands and disrupting the state’s water supply to 23 million people.  Such estimates were not based on new data on actual levees, and little has been collected since.  In fact, there are gaping holes in bare facts, such as how much loose sand lies under existing structures.  No one knows.
            According to Pyke, lack of basic facts leads to inaccurate predictions. “The data was just not there to do such advanced calculations,” he said. “If you lack adequate data in a study like that, it leads to greater uncertainty.  Greater uncertainty pushes up the mean results.  It’s inescapable and very common.  I caution people not to rush into risk and probability analysis unless you have enough data to do it accurately.”
            Nevertheless, the DRMS study became the basis of more calculations and more analysis by scientists at UC Davis and UC Berkeley who expanded the earthquake predictions into a full-fledged story of levee collapse – still with no new information on how the levees are actually constructed.
            To make matters more complicated, there’s every reason to be concerned.  The hundreds of miles of levees that surround about 70 islands are highly variable, ranging from good to very poor.  They’ve been unevenly maintained; they are made from different materials; some would probably breach in an earthquake if not improved as soon as possible.       
Low freeboard; easily overtopped Delta levee
            “These levees are the poor stepchild – the one critical feature in California that is still being neglected (for seismic upgrades)” said Pyke, noting that Cal Trans and public utilities in the East Bay and San Francisco have spent billions to upgrade their infrastructure.  But levee repair is lagging, even though voters have twice voted for money to fix them.
            Many would argue that the delay can be traced to the state’s preoccupation with building a multi-billion dollar “isolated conveyance” (aka, peripheral canal). If the levees can be retrofitted for earthquakes, one good reason for building the canal would be lost, and wealthy interests in the state want the conveyance – actually a tunnel under the delta.
            Conspiracy or not, it’s clear there is a powerful constituency, highly influenced  by work done by UC Davis scientists at the Public Policy Institute of California, to write the levees off – or many of them.
            Based on this new report, ordered by the Delta Protection Commission, there should be a powerful constituency now to build them up.  At the very least, state planners need to reverse gears and not let them waste away.

3 comments:

  1. Pat, Thanks so much for these updates and for keeping track of important water issues in Calif.

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  2. This is interesting. It is nice to see the assertions of Delta levee redemption finally developed and presented in more technical form. This should improve the quality of the discussion.

    Much of this conflict is more contrived than real. The UC Davis and PPIC folks have always said that many (but not nearly all) Delta levees are worth repairing, and that significant levee repairs will be needed until more permanent Delta solutions are in place. In the long run, even if levee retrofitting was free and perfect, sea level rise, increasing drinking water standards, and endangered species problems will continue to drive urban and agricultural water users from direct Delta supplies.

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  3. Interest to read. Thanks For Update. Pls Update More news Letterhead Design with Wholesale Printing

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