New Orleans sits on a deep layer of mud and river silt. There is no bedrock for a hundred feet down in some places. If the water pressure on the water side of the levee gets high enough, the water will just flow UNDER the levee until it undermines it
Rebuilt the city on a slurry wall like the bathtub surrouding the World Trade Center.
Liquefaction in NOLA could kill a lot of people.
American Heritage Science Dictionary: The process by which sediment that is very wet starts to behave like a liquid. Liquefaction occurs because of the increased pore pressure and reduced effective stress between solid particles generated by the presence of liquid. It is often caused by severe shaking, especially that associated with earthquakes.