Concrete flood walls that were supposed to protect New Orleans were not overwhelmed by high waters during Hurricane Katrina as federal officials have claimed, but ruptured because they were structurally flawed, according to Louisiana scientists.

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From the mud splattered on buildings still standing near to the flood walls and the results of a computer simulation of the storm – known as a “hindcast” – a team from the Hurricane Center at Louisiana State University in Baton Rouge claims it has pieced together how the walls, mounted on small earthen levees, must have broken.

“Either there was a design problem or a construction problem,” says Paul Kemp, an oceanographer at the centre. “They were not supposed to break.”

The US Army Corps of Engineers, responsible for building and maintaining the levees, still claims that the 4-metre walls were simply overtopped by the storm surge – the wall of water that is dragged by a rotating hurricane as it hits a coastline. “We are working from the preliminary theory that the levees were overtopped,” says spokesperson Paul Johnston in Washington DC.

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