Tuesday, March 14, 2006

National Science Foundation: Tests predicted levee failure

NEW ORLEANS — The U.S. Army Corps of Engineers did a full-scale test 20 years ago on a floodwall like one that collapsed here during Hurricane Katrina, with results that predicted its failure, scientists working on an independent study of the failure said Monday.

On Friday, the Corps task force set up to investigate the failures reported that the breach at the 17th Street Canal was the result of water working its way in between the floodwall and the earthen levee into which it was set, and of soft subsurface clay. Once the levee split, the force of the high water pushed the floodwall, and the half of the levee behind it, backward on the clay, the corps task force said.

The corps called it an unforeseen combination of events that split the earthen levee and toppled the floodwall.

But Raymond B. Seed and Robert G. Bea, in charge of the National Science Foundation's Independent Levee Investigation Team, said Monday that the results should have been foreseen, given the results of a 1985 test done near Morgan City in south-central Louisiana. The test was done at an Atchafalaya Basin levee and floodwall system built to test whether a design similar to that of the 17th Street Canal levee and floodwall would work.

The test ended when — with water nearly 8 feet high along the test floodwall — sheet piles supporting it inside the levee began tilting backward, "indicating that failure was imminent," the statement said.

"Not only did they have that in their repertoire of information, they failed to use it, as best we can tell," Seed said in a telephone interview from the University of California at Berkeley.

The Corps' Interagency Performance Evaluation Task Force, which issued its report Friday, did know about that test, Corps spokesman Wayne Stroupe said. He said he would forward Seed's and Bea's statement to a Corps scientist for a response.

Seed and Bea said the soft clay behind the levee also should have been known to the corps.

"The U.S. Army Corps of Engineers had a masterful knowledge and understanding of the complex and challenging geology of this region in the 1950s," and a 1958 report by two of its scientists "is a landmark exposition of these challenging foundation conditions," Seed and Bea wrote.

"The Corps should not claim that the weak foundation soil strata at the 17th Street canal breach site were unexpected, and that no prior publications would have disclosed this possibility," their statement said.

The lack of action after the 1985 test apparently "comes down to an internal schism within the Corps," Seed said. "The researchers doing the work were from the Waterways Experiment Station — a think tank within the Corps where experimental research was done.

"Sometimes there's separation between the engineers in the research center and the working Joes in some of the districts. It wasn't all that surprising. It was just disappointing," he said.

Seed also said Monday that two other problems that could have caused the floodwall failure are still being studied by the NSF team, which won't describe those problems until their next report comes out in early May.

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