With hurricane season less than a month away, experts from the United States and the Netherlands say flaws in New Orleans' repaired levee system could leave the region vulnerable to another disastrous breach like the one that occurred after Hurricane Katrina, which was the largest civil engineering disaster in U.S. history.

So warns a special report from National Geographic, which had Robert Bea, a University of California at Berkeley engineering professor and former chief engineer for Shell Oil Co., inspect the protective barriers. Bea found multiple weak spots in critical areas, according to the magazine:

The most serious flaws turned up in the rebuilt levees along the Mississippi River Gulf Outlet 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 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 into the ground, 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. Bea, who actually tasted the seepage to make sure it was brackish -- a sign that it was coming from the canal -- says the wall could fail in the next hurricane.

Bea helped lead a team of Berkeley experts that investigated the Katrina levee failures, and he's currently serving as an expert witness in a class-action lawsuit against the Army Corps of Engineers. But he's not the only engineer who sees problems in the repaired structures. National Geographic also spoke with a Dutch engineer who recently inspected some of the city's new floodgates and pumps. The engineer, who asked to remain anonymous since he sometimes works with the corps, says that in the next big storm the structures may be "doomed to fail" as the gates lack any mechanism to remove debris that could keep them from closing in advance of a storm. The corps is currently depending on divers to clear obstructions.

Another problem plaguing the protective system are the pumps that the corps installed to carry rainwater out of the city; they vibrated excessively and had to be repaired. While the corps claims they're now working fine, other experts charge that they haven't been fully tested. Also casting a shadow of doubt over the pumps is the fact that the deal to provide them went to Moving Water Industries, a politically connected Florida firm that's currently the target of a Department of Justice lawsuit over corruption allegations. As we reported last week, both the corps itself and the Government Accountability Office began investigating whether there were any improprieties in the awarding of that contract after it was discovered that the corps lifted the specs for the job directly from MWI's catalog.

Another expert pointing to flaws in New Orleans' levees is Ivor van Heerden of Louisiana State University's Hurricane Center; he led a team of state experts that probed the levee failures and is another expert witness in the class-action lawsuit against the corps. Van Heerden agrees with Bea's evaluation of weak spots and also notes that a section of floodwall along the Duncan Canal in Jefferson Parish on the city's west side is in trouble, telling National Geographic:

"There is 1,900 feet of I-wall that actually dips -- sinking from its own weight," he says. Sheet pilings installed by the corps to shore up the weak wall may not be adequate, he says.

The New York Times reports that U.S. Sen. Mary Landrieu (D-La.) has been informed of the apparent problems with the levees and floodwalls and plans to send a letter to the corps commander, Lt. Gen. Carl Strock, asking whether his agency's repair work was adequate.

Ensuring that the system protecting New Orleans from deadly flooding is especially critical now, with a more-intense-than-usual storm season anticipated. The hurricane prediction experts at Colorado State University last month said they expect a "very active" tropical storm season for 2007, with about nine hurricanes and 17 named storms. They estimate the probability of a major hurricane hitting the Gulf Coast at 49 percent, compared to last century's average of 30 percent.