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Was flooding worsened by New Orleans levees?

Ronald Dufrene surveys waterlogged furniture outside his flooded home in Jean Lafitte, La., a week after Hurricane Isaac. The community is outside New Orleans' post-Katrina hurricane protections.
(Molly Hennessy-Fiske, Los Angeles Times)

Many residents of areas outside the improved New Orleans levee system blame it for the flooding they experienced during Hurricane Isaac. They say the system sent water to the north in Slidell, to the west in LaPlace and to the south in Braithwaite and Jean Lafitte.

Officials at the U.S. Army Corps of Engineers say this is unlikely, but they have contracted with researchers at the University of North Carolina to help determine whether the new levee system redirected floodwater into certain areas during Isaac or whether the flooding would have occurred during previous storms, such as 1985’s Hurricane Juan, which followed a path similar to that of Isaac.

The corps will be relying on the university’s Advanced Circulation, or ADCIRC, coastal circulation and storm surge computer model to conduct its analysis.

The model incorporates data from about 230 storm surge sensors along the Gulf Coast, and takes into account how the storm interacted with the levee system, officials said. It also takes into account elevation and ground surface cover, both of which can influence flooding.

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Real-time storm surge readings from the model were provided to officials during Hurricane Isaac to help them make decisions such as when to close floodgates and order evacuations.

Experts at the U.S. Geological Survey and National Weather Service say the levee system most likely did not contribute to flooding, or if it did, the amount of water was negligible compared with storm surge and rain already inundating those communities.

“There could be a little of that going on, but I would be surprised if that bears out,” said Louisiana State Climatologist Barry Keim. “It was more just the vectors of wind and how they were blowing that led to that flooding.”

Dave Ramirez, lead hydraulic engineer with the corps in New Orleans, said that when the system was improved after Hurricane Katrina, “it was looked at and determined the impacts would be negligible.”

Still, said Ramirez, who is studying possible storm effects on those outside the system, corps officials are approaching the question with an open mind.

“We’ve got to make sure we won’t hurt anyone else,” he said.

molly.hennessy-fiske@latimes.com


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