I was really thinking more in the lines of a long flat metal beam structure formed with large crossbeams and smaller crossbeams that could stretch from one wall to the other and then place sand bags so that the current doesn't just wash the bags away. Oh well I'm not there just an idea.
I'm sure civil engineers will come up with something. I just wanted to point out (since it may not be obvious to everyone) that repairing a loaded levy is a non-trivial task.
Actually, at this point I suspect there are some real questions as to what the engineers should even try to be doing. At present, there's a really big bowl of rather nasty chemical soup in New Orleans. The pollution is at present somewhat contained; I don't know whether anyone is going to try to mitigate its spread, or if people are just going to hope that diluting it with the ocean will render it harmless.
One thing I've personally wondered about, though this is probably an absurd idea, is whether it would make sense to try to get some river water flowing through New Orleans (without increasing the depth) before the city is drained. I would think that might help clean up the city somewhat, but I have no idea whether it would do more harm than good, or whether any good that it might do would outweigh the extra time the city was under water.