New Orleans' Rebuilt Levees "Riddled With Flaws"
Joel K. Bourne, Senior EditorEnvironment, National Geographic Magazine
for National Geographic News
|May 6, 2007|
Almost a year ago the U.S. Army Corps of Engineers declared that it had restored New Orleans' levees and floodwalls to pre-Hurricane Katrina strength.
But the system is actually riddled with flaws, and a storm even weaker than Katrina could breach the levees if it hit this year, say leading experts who have investigated the system.
The unwelcome news comes as residents gird for what is predicted to be a "very active" Atlantic hurricane season, and as residents are still slowly rebuilding their homes and lives after Katrina.
During a recent inspection of the levee system with National Geographic magazine, engineering professor Bob Bea of the University of California, Berkeley, found multiple weak spots.
(See an interactive map of the weak spots).
The most serious flaws turned up in the rebuilt levees along the Mississippi River Gulf Outlet ship channel.
The channel's levees had failed in more than 20 places when Katrina's storm surge pounded them, leading to devastating flooding in the Louisiana city's Lower Ninth Ward and in St. Bernard Parish, which borders the city to the southeast.
Bea found several areas where rainstorms have already eroded the newly rebuilt levees, particularly where they consist of a core of sandy and muddy soils topped with a cap of Mississippi clay.
"It's like icing on the top of angel food cake," Bea said. "These levees will not be here if you put a Katrina surge against them."
(Watch aerial video of "angel food cake" levees.)
Bea also found that decade-old gaps remain in the floodwalls lining the Orleans Avenue Canal. And hurricane-damaged sections of the walls along the London Avenue and 17th Street Canals have not been repaired or replaced.
Even more troubling, water appears to be seeping under the stout new floodwall erected along the Industrial Canal to protect the Lower Ninth Ward.
The new wall sits atop steel sheet piles driven 20 feet (6 meters) into the ground. The piles are long interlocking wall sections that retain water and transfer pressure deeper into the ground, where the soil is more stable.
But water from holes in the canal bed, excavated before Katrina or scoured by the storm, may be seeping under the barrier through permeable layers of sand and silt.
The Army Corps counters that the source of the puddles behind the wall is likely a broken water main.
But Bea, who actually tasted the seepage to make sure it was slightly salty—a sign that it was coming from the canal—said the wall could fail in the next hurricane.
(Watch video of Bea tasting the leaking canal water and addressing the issue of seepage.)
Co-leader of a Berkeley team that investigated the Katrina levee failures, Bea is now serving as an expert witness in a multibillion-dollar class action lawsuit against the Army Corps of Engineers.
Doomed to Fail?
Bea is not alone in his criticisms.
A Dutch engineer recently visited some of the new floodgates and pumps installed at the mouths of the city's three main drainage canals. His verdict: They may be "doomed to fail" in the next big storm.
The engineer, who asked not to be named because he sometimes collaborates with the corps, noted that the gates have no mechanism to remove sediment and other debris that might keep them from closing as a storm approaches. Instead, the corps says it will rely on divers to check for obstructions and clear them away.
The Dutch engineer also pointed out that the pumps installed last year to pump rainwater out of the city when the gates are closed vibrated excessively and had to be repaired. The corps says the pumps are working well now, but some other experts say they have not been fully tested.
Ivor van Heerden is deputy director of Louisiana State University's Hurricane Center and leader of a team of state experts that examined the levee failures.
He concurred with Bea's list of weak spots and said they are representative of others throughout the system.
Van Heerden, who will also testify as an expert witness in the lawsuit, adds that a section of I-shaped floodwall along the Duncan Canal in Jefferson Parish—the city's western defense—is another weak link.
"There is 1,900 feet [580 meters] of I-wall that actually dips—sinking from its own weight," he said.
To shore up the weak wall, the corps has installed sheet piles. But they may be inadequate, van Heerden said.
"A Massive Accomplishment"
The corps says that New Orleans' flood defenses are a work in progress.
"After Katrina we achieved a massive accomplishment, repairing the damage that occurred," said John Meador, deputy director of Task Force Hope, the Army Corps group rebuilding the hurricane-protection system.
"We believe we are putting the system back better than it was before Katrina, but we're not at an end point yet. Any time we're made aware of such situations, we address them immediately."
Bea, of the University of California, isn't satisfied. "The corps's motto is 'Let Us Try,' " he said. "We've been trying long enough. Now it's time to actually do something."
The August 2007 issue of National Geographic magazine will include a full report on the challenges facing New Orleans.
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