[StBernard] Corps making minor changes to Chalmette Loop hurricane levee to ease future maintenance

[Westley Annis]

Corps making minor changes to Chalmette Loop hurricane levee to ease future
maintenance
 By Mark Schleifstein, NOLA.com | The Times-Picayune 
on January 23, 2013 at 6:10 PM, updated January 23, 2013 at 6:17 PM Print

The Army Corps of Engineers is making minor changes to parts of the
Chalmette Loop hurricane levee system that protects St. Bernard Parish. The
improvements include building a 15-foot-wide road for maintenance vehicles
and a swing gate across Bayou Bienvenue to give crews access to a six-mile
stretch of the levee between Bayou Bienvenue and Bayou Dupre.

A third project will increase the height of a small segment of floodwall and
levee to 26 feet above sea level where the existing wall meets the
Mississippi River levee adjacent to the Caernarvon Freshwater Diversion
Project.

The levee already provided protection from storm surges moving north from
the Gulf of Mexico during a hurricane with a 1 percent chance of occurring
in any year, the so-called 100-year storm.

But the connection area was found to be too low to provide a second required
factor of safety that the corps labels as "resiliency." That measures the
ability of the levee and wall combination to withstand the forces from
surges created by a storm with a 0.2 percent chance of occurring, a
so-called 500-year storm, without failing.

Such a storm would likely cause overtopping, but the additional height would
both limit the overtopping and assure that the levee section didn't fail.

Even without the improvements, all of the St. Bernard levee loop meets the
100-year surge protection standard today, said Chris Gilmore, the corps
senior project manager. The system protects both St. Bernard Parish and
parts of New Orleans, including the Lower 9th Ward.

Each of the three projects will cost between $5 million and $15 million,
Gilmore said.

The projects are described in a recently released draft supplemental
Individual Environmental Report. The public has until Feb. 15 to review and
comment on the report.

Comments can be sent to mvnenvironmental at usace.army.mil .

The new road will replace a an 85-foot-wide dirt path that was used by
trucks and other equipment when the earthen levee was rebuilt and a T-wall
was placed on top in the aftermath of Hurricane Katrina. The upgrade will
reduce the chance that traffic on the dirt road could cause ruts or other
erosion problems that would weaken the levee.

As part of a separate effort, the corps also is conducting tests of levee
soils in several locations in the loop to assure subsiding soils haven't
created cavities beneath the new T-wall.

The swing bridge would be tethered on the southern shore of Bayou Bienvenue,
to assure that it can't be harmed by members of the public. It will be
operated by officials with the Lake Borgne Basin Levee District or the
Southeast Louisiana Flood Protection Authority-East, who will reach it by a
walkway that stretches over a new floodgate in the rebuilt levee where Bayou
Bienvenue enters the Mississippi River-Gulf Outlet.

Local levee officials, who will be required to maintain the new levee system
when it is certified and turned over to them -- probably later this year --
requested the bridge be added to assure the safety of employees who will
have to close three wildlife access floodgates in the wall that are between
the two bayous.

Without the bridge, officials would have to use boats to reach three flood
gates that need to be closed. In 2012, the levee authority insisted on the
gates being closed from August to the end of October, the height of the
hurricane season.

But that poses an environmental problem, because the gates are required as a
passageway for wildlife. The gates are used by a variety of animals,
including coyotes, alligators and small mammals. There are six more wildlife
gates along the rest of the loop's floodwall.