The Army Corps of Engineers will conduct a $3 million experiment in New Orleans this week to simulate the conditions that caused critical levee failures and thus severe flooding during Hurricane Katrina.
The test will have engineers pumping water gradually into a section of the London Avenue Canal, one of two canals whose flood walls toppled in the storm two years ago, allowing in most the flood waters in the main part of the city.
As canal waters rise, the engineers will monitor the amount of seepage beneath the flood wall and how much the structure tilts. The measurements will allow crews to determine how much rising water the canal can withstand, and the Army Corps has promised nervous neighbors that the testing will not result in another breach.
"Some computations show the wall is going to fail at certain water levels; some show it won't," said Ray Martin, a geotechnical engineer consulting with the Army Corps on this project. "This experiment will let us know."
Despite three flood defense investigations, key questions and uncertainty remain. The Army Corps of Engineers sponsored a $25 million effort that was reviewed by the American Society of Civil Engineers. A second study was commissioned by the state of Louisiana, and a University of California at Berkeley team conducted a third, which was partially sponsored by the National Science Foundation. The reports generally agree that the post-Katrina disaster was at least partially an engineering failure.
"The bottom line is that the city was destroyed, and the public doesn't yet have an undisputed explanation," said levees.org director Sandy Rosenthal. "There are a lot of questions that have yet to be answered."
Levees.org, a local advocacy group, has been pushing for improved flood defenses and urging politicans to establish a "8/29 commission" modeled after the Sept. 11 commission.
"There have been numerous studies about Katrina, without any clear direction of how to prevent a flood-control-system failure in the future," said Louisiana Sen. Mary Landrieu, a Democratic representative who has embraced the proposal and sought to introduce it into legislation.
The National Research Council, having reviewed reports from the major investigations, noted that the differing views of the "primary failure mechanism[s]" in the canal walls and warned that "the proposal of a single failure mechanism could lead future designers to focus on narrowly drawn conclusions, leading to neglect of other, equally plausible failure modes."
One of the Berkeley team leaders, Robert G. Bea, has called for an 8/29 commission "to truly understand why these failures developed" because "the Corps is still not designing things safely enough."
But University of Maryland's Ed Link, who directed the Corps-sponsored report, said that while "there's lots more to learn and lots more analysis to be done, I don't see a lot of benefit in rehashing what's already been done. Fundamentally, there's a lot of agreement" about what happened during Katrina.
The canal walls that are the subject of the upcoming test are fairly simple; it is the part marsh, part clay, part sand soils beneath them that make the walls' strength unclear.
"This is the Mississippi Delta, built up by hundreds upon thousands of years of sediments and the like being deposited," said Col. Jeff Bedey of the Army Corps, who is overseeing the canal experiment. "It's not simple." Bedey also added that this time around, canal walls are a second line of defense, not a first. New floodgates are now in place, and they should block storm surges from entering the canals
Source: Washington Post
