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.
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