And the story gets more interesting:
Louisiana’s top hurricane experts have rejected the official explanations for the floodwall collapses that inundated much of New Orleans, concluding that Hurricane Katrina’s storm surges were much smaller than authorities have suggested and that the city’s flood- protection system should have kept most of the city dry…
In the weeks since Katrina drowned this low-lying city, there has been an intense focus on the chaotic government response to the flood. But Ivor van Heerden, the Hurricane Center’s deputy director, said the real scandal of Katrina is the “catastrophic structural failure” of barriers that should have handled the hurricane with relative ease…
The center’s researchers said it is too early to say whether the breaches were caused by poor design, faulty construction or some combination. But van Heerden said the floodwalls at issue — massive concrete slabs mounted on steel sheet pilings — looked more like the sound barriers found on major highways. He also suggested that the slabs should have been interlocked, and that the canals they were supposed to protect should have had floodgates to keep out water from the lake.
Former representative Bob Livingston (R-La.), who helped lead the charge for Corps projects in Louisiana when he chaired the House Appropriations Committee, noted that the earthen levees along Lake Pontchartrain had all held, while the concrete floodwalls had failed. He was especially concerned about the 17th Street barrier, saying it “shouldn’t have broken.”
“I don’t know if it’s bad construction or bad design, but whoever the contractor is has a problem,” said Livingston, now a lobbyist on Capitol Hill.
Former senator J. Bennett Johnston (D-La.) said he remembers numerous briefings from Corps officials about the danger of a hurricane overtopping the New Orleans levees. But he said he never envisioned a scenario like this one. “This came as a surprise,” he said.
The Corps has not identified the contractors who built the floodgates that failed; Paul Johnston said there will be a full investigation into the breaches.
If this is faulty construction or design flaws, there is going to be hell to pay.
The NY Times has more:
Along the Mississippi River and Lake Pontchartrain, great earthen levees were ample to hold off much of the surging water propelled by Hurricane Katrina.
But concrete flood walls installed over the last several decades along the drainage and barge canals cutting into New Orleans were built in a way that by Army Corps of Engineers standards left them potentially unstable in a flood, according to government documents and interviews. The walls collapsed in several places during the storm.
A corps engineering manual cautions that such flood walls “rarely exceed” seven feet because they can lose stability as waters rise. But some of the New Orleans canal walls rose as high as 11 feet above dirt berms in which they were anchored…
Hassan S. Mashriqui, an engineering professor at Louisiana State University and an expert on storm surges, said the segmented nature of the walls could be an additional problem, since any weak point could cause a catastrophic failure.
“Since they’re not tied together you get a little bit of a gap and that’s what water needs to make it fail,” Dr. Mashriqui said.
Other questions surround the walls’ design, known as an “I-wall” for its slim cross section that fits easily into densely developed areas.
The corps manual for flood control construction suggests a different design for walls higher than seven feet – walls shaped like an inverted T, with the horizontal section buried in the dirt for extra stability.
They better get this right when they rebuild.
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