A lot of the current problem in New Orleans is that it's built on deep layers of silt which are slowly compacting. And channelizing the Mississippi has resulted in loss of protective barriers offshore because the silt now goes right out the end of the channel into deep water. Bonus the bedrock itself is slowly tilting sinking towards the gulf.

What the place needs is about three meters of compacted fill under the whole city. ALA Galveston TX and Downtown Chicago.