As residents of New Orleans slowly rebuild their homes and lives after Hurricane Katrina, they are relying on the city's cordon of levees and floodwalls to protect them from the next big storm. The U.S. Army Corps of Engineers declared almost a year ago that it had restored the barriers to pre-Katrina strength. But leading experts from the U.S. and the Netherlands say the system is riddled with flaws. They say that even a weaker storm than Katrina could breach the levees if it hit this season.

During an inspection of the levee system with National Geographic magazine, engineering professor Bob Bea of the University of California, Berkeley found multiple weak spots. The most serious flaws turned up in the rebuilt levees along the Mississippi River Gulf Outlet (MRGO) ship channel, which broke in more than 20 places when Katrina's storm surge pounded it, leading to devastating flooding in the Lower Ninth Ward and St. Bernard Parish. 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 says. "These levees will not be here if you put a Katrina surge against them."

Bea, who is serving as an expert witness in a multi-billion-dollar class-action lawsuit against the corps, is not alone in his concerns. J. David Rogers, a geological engineer from the University of Missouri-Rolla who investigated the levee failures with Bea, concurs with his assessment of the system's weak spots, particularly the eroded levees that are the primary hurricane protection for St. Bernard Parish and the Lower Ninth Ward. Both engineers say a more detailed study of the levee soils is necessary to determine just how weak the MRGO levees are, but Rogers says the image of the eroded structure "certainly doesn't give me any confidence that it would survive eight hours of overtopping—what you would need for a Category 3 storm. It might survive an hour. They've obviously got a problem there. The veneer is not thick enough, and the core of the levee is cohesiveless material—organic muck and silt."

Other weak spots in the system noted by Bea include decade-old gaps in the floodwalls lining the Orleans Avenue Canal and hurricane-damaged sections of the walls along the London Avenue and 17th Street Canals that have not been repaired or replaced. Bea also believes water could seep 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, but Bea says water from holes in the canal bed, excavated before Katrina or scoured by the storm, could make its way under the barrier through permeable layers of old marsh soils. The marshy soils were identified during the corps's own investigation of the floodwall failure during Katrina, as well as by Bea's colleagues from Berkeley and other independent investigators from Louisiana State University. Bea says such seepage could lead to a blowout beneath the wall during a hurricane.

Bea raised the possibility of seepage after spotting puddles along the floodwall and finding that the water tasted salty, a sign, he said, that it originated in the canal. But after this report was first posted, the corps hired Paul Lo, an environmental health specialist from Tulane University, to test several puddles. The salt levels turned out to be far below that of the Industrial Canal—evidence, says the corps, that the water is actually seeping from broken municipal water pipes. Moreover, the corps says the soils beneath the floodwall are predominantly clays with very low permeability, although Bea says the soil tests so far don't dispel his doubts.