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Giant sandbags plug largest levee breach

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ENGINEERS WERE still fighting to plug breaches in New Orleans' flood protection levees as NCE went to press.

On Monday night the largest breach, a 100m section of the city's 17th Street Canal, was finally closed, six days after it gave way.

Giant m 3 sand bags were carried by helicopter to plug the gap. In all, 10,000m 3 of material was needed, said John Hall, a liaison officer with the US Army Corps of Engineers, which is carrying out the work.

The US Army Corps has also installed a temporary sheetpiled retaining wall across the canal to stem water flow into the canal from Lake Pontchartrain, Hall said.

But access for construction plant and materials to the failed structures had been blocked by the trail of wreckage left by Hurricane Katrina, Hall added.

'Accessibility is proving difficult - helicopters don't provide the necessary capacity.' The 17th Street Canal levee failure was the most devastating, but two other levee breaches on the London Avenue Canal and the Industrial Canal were also serious, Hall said.

There were five breaches in all.

The three biggest breaches were of sheet piled and concrete 'combi' wall structures erected on top of earth embankments, with a combined height of approximately 4m.

It is thought that the steel piles were driven between 9m and 10m into the ground, Hall said. Failure occurred when the walls were overtopped by rising water levels.

Cascading water eroded soil on the land side of the defences to the point where there was not enough restraint at the toe, leading to catastrophic failure.

'The water level was exceptionally high and was exerting a powerful force, ' Hall said.

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