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The Joys of Art

Saturday, March 25, 2006

The subject that just won't go away

But then again this tragedy shouldn't have gotten to this point in the first place!!!

All levees should be re-evaluated, report says

By Bob Marshall
and Sheila Grissett
Staff writers

The safety of the New Orleans area hurricane protection system is “open to question” until the Army Corps of Engineers evaluates every levee and floodwall in light of recent findings on how the 17th Street canal failed during Hurricane Katrina, the agency’s own external review panel said Friday.

“We conclude that a determination of the overall safety of the hurricane protection system cannot be made until such time as the remainder of the system can be evaluated with the benefit of this new information,” the American Society of Civil Engineers’ panel said in a letter to Lt. Gen. Carl Strock, the corps’ commander.

The corps has said it is rebuilding the system to “pre-Katrina standards” by the start of hurricane season June 1. But evidence of engineering problems at the 17th Street canal project, including inadequate soil strength analysis and designs “too close to the margins for a critical life-safety structure” raise grave concerns about the methods employed to build the system, according to the panel.

Asked if the critique means that the city’s hurricane protection system is not safe, Lawrence Roth, Society of Civil Engineers deputy executive director said, “That’s what this is all about; it’s certainly suspect. I think the letter speaks for itself.”

A spokesman for the corps’ New Orleans District said the agency agreed with the panel’s concerns in general, and had already begun implementing some of its recommendations.
Of particular concern to the review panel was a recent claim by a corps task force that the forces that caused the floodwall collapse could not have been foreseen by project designers. Those forces included a flexing of the wall under pressure from rising water that allowed a water-filled gap to form between the wall and the canal, and a layer of weak soil at the land-side toe of the levee that went unnoticed by designers and later failed as water pressure from the canal increased, bringing down the levee and the wall.

The failure was related to the “I-wall” design, a vertical concrete barrier anchored by steel sheet pile driven into the levee, a common structure in the New Orleans area system.

Echoing criticism by other groups, the review panel said that type of failure had been studied by corps researchers as early as 1988. Noting that the corps missed the assessment then and has since not required designers to account for it, the panel said “the ability of any I-wall in New Orleans to withstand design flood level loading is unknown.”

Roth did note that the floodgates being installed by the corps at the 17th Street, Orleans Avenue and London Avenue canals should take the pressure off those floodwalls by preventing storm surge from entering the waterways.

That and other vulnerabilities exposed by Katrina prompted the panel to make a list of recommendations it said warrants the corps’ immediate attention, including:
-- Re-evaluating the design of all I-walls to include a water-filled gap on the canal side of he wall. The corps said there are about 38 miles of I-walls in the system: 30 in New Orleans, one mile each in St. Charles and St. Bernard parishes, 2.5 in East Jefferson, and 4 on the West Bank, which includes Algiers, West Jefferson and Plaquemines Parish.
-- Reevaluating the designs for levees taking into account the soil strength at their toes.
-- Identifying and redesigning all sections of the system that were designed with a safety factor considered too close to the acceptable margin for protecting populated areas.
-- Redefining the definition of the hurricane threat using design criteria for other infrequent but potentially catastrophic disasters such as earthquakes and floods.

The review panel also warned that the “standard project hurricanes” on which the levees were designed were inadequate and outdated. The corps based its levee and floodwall designs on assumptions resulting from 1959 and 1979 studies of historical hurricanes that hit New Orleans.

But the panel said the corps should not look only at past storms, but needs to consider the effects of future storms, some of which may be larger than the city has ever experienced.

National Hurricane Center hurricane specialist Jack Beven told corps engineers in December that even based on the last look at historical data, the risk of larger storms hitting the area has risen. He said there’s a chance of a Category 5 hurricane coming within 75 miles of the New Orleans area once every 53 years, and of a Category 4 once every 39 years, which is a much shorter return period than in the older studies. Corps officials said that that still may translate into a smaller risk number for a specific stretch of levee or levee wall.

Ivor van Heerden, assistant director of the LSU Hurricane Center and a member of the Team Louisiana group investigating the levee failures, said all I-walls in the region are of critical importance and should be evaluated as quickly as possible.

In recent weeks, van Heerden has twice taken geotechnical engineers to examine 1,600-feet of skewed and sagging canal floodwall on the Jefferson-St. Charles parish line where the corps used I-walls on either side of the Vintage Drive pedestrian gate. Most of the rest of the West Return Canal floodwall was built of sturdier a T-wall design and doesn’t show disfigurement.

“We have major concerns here, and we will do testing,” van Heerden said Friday. “It looks like the wall is sinking under its own weight and suggests very, very weak soil or too-short sheet pile he said.

“We know that 169 out of 350 miles of the system were compromised, damaged, and destroyed, but I don’t know how many more I-walls like the (Vintage gate) wall there are,” he said. “But all of them must be identified, assessed and fixed.”

The corps has said that it will drive 60-foot-long sheet piling and add another 5 feet of grassy berm — as well as a paved, erosion-resistant apron — to protect the I-wall in Kenner this hurricane season. But van Heerden said independent review teams should evaluate to make certain that’s the best short-term fix.

The corps has already implemented some of the recommendations. Corps officials last week said the agency had begun conducting soil borings at the toe of levees protecting floodwalls to check soil strengths at those critical points. Other engineers were re-evaluating levee stability work done by the original design teams.

But some work suggested by the society of engineers review panel goes to the problem it says was built into the system: a design that wasn’t strong enough considering the risk to human life of failure. For example, armoring the land side of floodwalls and levees could have prevented breaches caused when the structures were overtopped by the storm surge. Choosing a design without such protection “is another indicator of a lack of conservatism,” the panel said.

Concerned that decision was a pattern, the panel “believes that the safety offered by the levees and floodwalls in New Orleans is open to question until it can be established that a sufficiently high degree of conservatism for critical life-safety structures has been incorporated into the designs.”

Bob Bea, an engineering professor who is part of the University of California-Berkeley team that has been highly critical of the corps, said the review team’s findings are “right on” and hoped the corps would follow the recommendations.

“They are throwing some important, additional logs on the fire of understanding this failure ... and when you flood 90 percent of the city, even from many sources, I call it a single failure,” Bea said. “The challenge now is to get the corps there with us. They’ve got to get on that page if there is to be hope for providing sufficient protection to the New Orleans area. “

Bea said the findings should provide New Orleans area residents with hope as well as concern. “They should take hope that there are people who are seriously and deeply concerned about what happened and what should happen going forward to make them safer,” he said.

Van Heerden said Team Louisiana members want to see a sort of “superboard” of forensic engineers and scientists appointed to begin making assessments and recommending changes to the corps’ chosen methods of repair, when investigators think it warranted.

The society of engineer review team’s findings also mean that all independent teams are now on the same page and can move together, and with urgency, to assess the safety of corps repairs and the hurricane system itself, van Heerden said.

“We may disagree on whether or not the slippery surface was in the peat or the clay,” he said. “But that’s academic. What we all agree on is that it was a catastrophic structural failure, and the design was at fault.”

Staff writer Mark Schleifstein contributed to this report.

Bob Marshall can be reached at rmarshall@timespicayune.com or (504) 826-3539. Sheila Grissett can be reached at sgrissett@timespicayune.com or (504)883-7058.


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