Not much is left of the old delta, the ecological equivalent of clear-cut logging. So, there wasn't much to stop Katrina and the next hurricane.
Although the oil companies can be blamed for some things, people have got to realize that it's sinking because they are living there! Although, it's very romantic and such, the delta only got built up by horrible silty flooding! You take that away with flood control, and the whole thing does it's natural consolidation, without build-up. You could simulate the floods by pumping in yucky, smelly organic silt, but you couldn't live there!
The same thing goes for beautiful, treeless, sand bars on the East coast. Everybody wants to build on these things, but they forget the reason why there are no trees! Every hundred years or so, a super hurricane cleans things up!