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A long-term look at levees

Engineers: Breaks should prompt total review of infrastructure

By Marsha Walton
CNN

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New Orleans (Louisiana)
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(CNN) -- The levee system in New Orleans is getting global attention because of the breaks caused by Hurricane Katrina, and now Hurricane Rita. And some engineers say those two disasters should prompt a new look at critical infrastructure.

"New Orleans is a vital port and my guess is that the will of the American people will be not to eliminate the city," said Bill Marcuson, the incoming president of the American Society of Civil Engineers.

"But I think it is an opportunity to look at land-use planning and zoning and perhaps encourage some people that live in those low lying areas to move and live elsewhere," he said.

The levees in New Orleans are just a small part of thousands of miles of levees in coastal areas and along rivers all over the United States. And, disaster or not, time can take a toll on these structures.

The levee system in New Orleans was begun in the 1700's when the city was first being settled. And the basic construction has not changed dramatically over the years: Most levees are made primarily of soil. They often have a core of clay, and can also be reinforced with waterproof cement or compacted clay to block underground seepage.

"They have been extended and rebuilt a number of times, and with a system like that, not a uniform system, it's possible that the add-ons are not as robust as new construction," said John Schuring, a geotechnical engineer and professor at New Jersey Institute of Technology.

The U.S. Army Corps of Engineers patched the levees after the disastrous breaks following Hurricane Katrina, and is in the process of fixing them again after Hurricane Rita.

"A repaired levy like this is not exactly an engineered levee," said Marcuson. "They've dropped rock and sandbags into the breach so they are, to a certain extent, weakened," he said.

Schuring also says that time and sinking soil are factors in the condition of a levee.

"In some areas the city is sinking as much as five millimeters a year, which is about two inches in 10 years," he said.

Another scientific event that must be factored in to the reconstruction of the New Orleans levee system is the rise in global sea levels, at a rate of two to four millimeters per year.

Schuring said in the short term there is a need to patch and repair the levees to protect the city and avoid further damage. But in the long term, he says there has to be a more comprehensive examination of land use.

"After this tragedy and loss of life, the best that could happen is we learn a lesson," Schuring said.

"Infrastructure is taken for granted, but it is the fabric of our civilization. Not only in New Orleans, but throughout the country where there are hurricanes and natural disasters, we have to be proactive, and create a robust infrastructure capable of resisting as much as possible," he said.

Schuring said a careful examination of the levees in Louisiana must include a look at the entire structure: areas that may not have collapsed may still have been weakened by the storms, and could be vulnerable.

"The most insidious damage, that we must be most careful with, is internal seepage, when a levee starts to erode from the inside out," he said.

On Friday an eight-foot storm surge broke through one of the New Orleans levees just repaired by the Army Corps of Engineers after Hurricane Katrina. The water overtopped a section of the Industrial Canal levee, and is flooding the 9th Ward neighborhood.

That low-lying section of town is the area that was overwhelmed when it was originally breached August 29, causing Lake Pontchartrain to flood the city and send hundreds of residents to their roofs for safety. The area is now largely deserted, with only emergency workers left there.

Experts had expected the area to flood again, but did not expect it to happen more than 12 hours before Hurricane Rita's landfall.

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