Published: August 2007

A City’s Faulty Armor

Duncan Wall

A City’s Faulty Armor

Experts question repairs to New Orleans levees
(Originally published online in April 2007)

By Joel K. Bourne, Jr., Senior Editor - Environment
National Geographic staff
Photograph by Tyrone Turner

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.

Other levee experts outside the Corps of Engineers are equally concerned about the repaired system. 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, notes 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 engineer also points 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, deputy director of Louisiana State University’s Hurricane Center and leader of a team of state experts that examined the levee failures, concurs with Bea’s list of weak spots and says 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 says. Sheet pilings installed by the corps to shore up the weak wall, he continues, may not be adequate.

The corps says the city’s flood defenses are a work in progress. “After Katrina we achieved a massive accomplishment, repairing the damage that occurred,” says 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.”

This summer, the corps released two reports offering its perspective on the past and future. The first is a detailed flood-risk assessment of the city—a long-delayed section of the corps’s $25-million analysis of the levee failures during Hurricane Katrina. Web-based flood maps created from 152 different supercomputer-generated storm scenarios allow homeowners to type in their street address and compare their annual risk of flooding before Katrina hit and with the levees in their current state of repair. The maps show that, compared with the risk before Katrina struck, the flood risk has dropped substantially for some neighborhoods, like Lakeview, but has changed little for many others, such as New Orleans East, the West Bank, and St. Bernard Parish.

Additional maps due out later this summer will show flood risks after the levees are raised further to protect the city against a 1-in-100-year storm. The corps estimates that those improvements will be completed by 2011. “Our number one goal was to inform the public of what the risk is,” says Ed Link, an engineering professor at the University of Maryland whose team created the risk-mapping tool. Even when 100-year protection is in place, “some of these areas will still be vulnerable. Then you’ll have to ask, can you really protect it at a higher level?”

The second report is a detailed chronology of the decisions and events that shaped New Orleans’ hurricane protection system from when it was first conceived in the 1950s until Katrina hit. The draft report reveals how legal, technical, political, and funding issues beset the massive project virtually throughout its construction, as the corps and local interests struggled to control both costs and storm surge in a changing political and coastal environment. The report details the battle between the corps and the city over whether to erect floodgates at the mouths of the three major drainage canals or rely on floodwalls along the canals, and it explains the corps’s decision to shorten the sheet-pile foundations beneath the floodwalls to shave millions from the cost.

“My view is the corps is a crippled organization,” says Leonard Shabman, a national water policy expert who coauthored the chronology. According to Shabman, Congress and the Reagan Administration did most of the gutting in the 1980s, under the presumption that the corps had outlived its usefulness. “So we starved the beast, for good environmental reasons and good economic reasons. What happened in New Orleans are the consequences.”

Shabman believes, however, that in time the corps, the city, and the nation can learn from the Katrina disaster, once everyone understands the future risks and the cost of reducing them. “We haven’t had an intelligent conversation over this yet, but we have to have it,” he says. “How do we have an honest debate on what that city should look like? If you put it back exactly like it was, you haven’t learned anything.”

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