Rebuilt New Orleans Levees Pass First Hurricane Test

While the partially revitalized levee system held its ground during Gustav, major work is still required to deliver 100-year-level protection

Beth Stackpole, Contributing Editor -- Design News, September 4, 2008

The U.S. Army Corps of Engineers' ongoing rebuilding effort of New Orleans' levee system passed its first major test this week. The infrastructure held its own during Hurricane Gustav, which thankfully turned out to bruise, not batter the still-recovering city three years after the devastation of Hurricane Katrina.

While Gustav turned out to be far less of a threat than anticipated, officials from the Army Corps of Engineers say the storm was powerful enough to put the partially revitalized levee and pump system to the test. "This was not a trivial storm," says Major Tim Kurgan, public affairs officer for the New Orleans branch of the Army Corps of Engineers. "It drove a 12-foot storm surge into the Industrial Canal ... and the ultimate field test of those [levee] walls is to fill them to the top."

Katrina is typically characterized as a 400-year storm with a 28-ft to 30-ft storm surge that flooded and devastated portions of the city. In comparison, experts are classifying Gustav as somewhere in the vicinity of a 50-year storm. While there was some minor flooding during Gustav, the retooled levees delivered a solid performance. "The same kind of overtopping during Katrina caused a lot of erosion on the back sides of the levee walls, which caused some levees to fail," says Dr. Lewis Link, a professor of civil engineering at the University of Maryland and director of IPET (Interagency Performance Evaluation Task Force), a task force assigned to evaluate what went wrong with the levee system in the aftermath of Katrina.

Since Katrina, the Army Corps of Engineers has made close to $2 billion in improvements to the levee system, including repairs to 220 miles of flood walls along with the addition of new pumping stations and flood gates. Moving forward, there's an ongoing rebuild and redesign effort to shore up the levee system to withstand a 100-year storm. The target goal is to complete the work by 2011.

Using simulation software including finite element analysis tools, the teams were able to model the timing of storm surges and water levels to determine when to close the newly built surge gates and when to activate the pumps. During Gustav, these models were also put to the test and were proven to work, at least with a storm of Gustav's magnitude. "At this point, the structures have performed quite well and that's gratifying, but it also points out big time that there is still work ahead," Link says.

One of the more critical works-in-progress is a surge gate planned for the entrance of the Gulf Intracoastal Waterway, Link says. The proposed gate, slated to be built near the intersection of the Gulf Intracoastal Waterway and the Mississippi River Gulf Outlet, will close during severe storms, essentially blocking the Industrial Canal from hurricane storm surges like those leading to the flooding damage in the Lower Ninth Ward during Katrina. "The biggest vulnerability is the Industrial Canal – it's the Achilles heel," Kurgan says, acknowledging the gate is a linchpin of the Corps' rebuilding effort.

In May, the Army Corps of Engineers awarded a $695 million design-and-build contract for the gate, dubbed the Inner Harbor Navigation Canal Hurricane Protection Project, to Shaw Environmental and Infrastructure Inc. of New Orleans. The contract, the largest design/build civil works project undertaken by the Corps, will result in a concrete pile wall complete with concrete-reinforced steel pilings that will provide 100-year-level protection. While the complete surge gate is slated to be finished by 2011, the contract specifies interim protections to be delivered by next hurricane season. Specifically, Kurgan says the team will break ground this fall on phase one of the project – a 20.5-ft wall to provide the interim protection. The remaining 6 or 7 ft of the surge gate will be completed by 2011, he says.

The Corps opted for a design/build contract rather than going with separate partners for each phase of the surge gate because of the complexity of the project. "This is a very large, very complex project and this arrangement allows our contractors to come up with innovations that will expedite design and give us the best system possible," he says.