The big stink in the media right now is that it appears that the
levees will be rebuilt more or less the way they were before Katrina.

What I don't get this. The canals are long and thin. It's very
expensive to construct levee walls that will stay up during high water
/ high wind events. Why not build a gate system at both ends of these
canals to basically shut them during a hurricane? With the canals
blocked off, even if the levee walls fail, the damage would be limited
to the (relatively small?) amount of water in the canals.