Q&A: Repairing New Orleans' Levees

Workers construct L-walls for a levee that was breached in New Orleans East

Workers construct L-walls for a levee that was breached in New Orleans East. Army Corps of Engineers hide caption

itoggle caption Army Corps of Engineers
floodgate diagram

The Army Corps is adding floodgates to canals that can be closed in case of a storm to keep water from coming into the city's canals from Lake Pontchartrain. Temporary pumps would remove water from the canals when the gates are closed. Army Corps of Engineers hide caption

itoggle caption Army Corps of Engineers

With the start of hurricane season about three months away, many people are asking whether repairs to New Orleans' flood-protection system will be ready in time. NPR Science Correspondent David Kestenbaum provides an update on efforts to restore the city's levees.

How far along are efforts to rebuild New Orleans' levees?

The U.S. Army Corps of Engineers has pledged to rebuild the area's flood-protection system to the level that was in place prior to Katrina. The Corps says it will have the work completed by June 1, the beginning of hurricane season. A spokesman for the Corps says the project is now about 40-percent complete.

What changes are being made?

The major change is the construction of three new floodgates that can be closed in case of a storm and keep water from coming into the city's canals from Lake Pontchartrain. Normally, these canals are used to pump rainwater out of town and into the lake. But during Katrina, storm surge from the lake rushed into the canals and the canal walls failed, flooding downtown. The idea now is to close off the canals from the lake if the storm surge gets high.

The Corps is also building some tougher walls to replace the ones that gave way. The new stretches of canal wall will be a stronger "T-wall" or "L-wall" design, which have more support at the base. And the metal support for the wall (known as sheet pile) will be driven down to greater depths than before (in some cases, 40 feet below sea level) to increase strength and prevent water from seeping underneath. The Corps is not rebuilding all of the canals this way — only the sections that broke.

I've heard that levee repairs may not be finished in time for the start of the 2006 hurricane season. Is that true?

Some engineers outside the Corps are skeptical that the repairs can be done by the promised date, and worry about the quality of the work. For instance, Robert Bea and Ray Seed, who are both engineering professors at the University of California, Berkeley, say they saw poor, easily erodible materials being used to rebuild an earthen levee near St. Bernard Parish. Walter Baumy, deputy chief of the Army Corps' project to rebuild the levees, tells NPR that he knows of a couple isolated incidents where substandard materials were provided or used, but he says the problems have been fixed. Baumy says repairs are on track to be completed by June 1, but the flood protection will only be as good as it was before Katrina. If another Katrina-like storm comes, there could be massive flooding again in some areas of New Orleans.

What's the cost estimate for levee rebuilding?

The Corps has committed to some $495 million in contracts for repair work so far. The total cost is expected to be $770 million.

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BEFORE AND AFTER

Diagrams from the Army Corps of Engineers show planned repairs for a levee in New Orleans East.

Levee -- BEFORE

 

Levee - after

Key:

1 - Concrete armoring — to prevent erosion

2 - Splash pad — to prevent scour caused by water overtopping levee walls

3 - Sheet pile — will be 34 feet longer and 32.5 feet deeper to provide more stability and better seepage control

4 - An H-pile — for enhanced stability

5 - L-Wall — 1.5 feet higher in elevation

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