The bottom line is, Katrina's storm surge did not wash the wall away. As you may remember, water had been seeping under the floodwall at the break location for about a year before Katrina. The ground under the levee was soaked and ready to give at any moment...Read it all.
What I will say next will probably completely throw you. Katrina saved probably over 50,000 lives.
That levee was doomed. If it had failed without notice, the death toll would have been measured in tens of thousands. There would be no evacuation, no preparation, no Feds at all. (such that they were anyway) no Coast Guard in choppers etc. Tens of thousands of people would have been dead in hours and tens of thousands more would have died on 120 degree rooftops waiting for rescue. It would have been unimaginable. - More unimaginable.
"Luckily" -and I groan when I say that- Katrina allowed the city to be evacuated.
The bottom line is, we are arguing over the WRONG thing, apparently. Not Bush, or Nagin, or FEMA, but the incompetence of building the levee. The federal government has dumped so much money into New Orleans and building the levees but they were built wrong from the get-go. Who benefited? Who got all that money?
This is the issue that needs to be resolved.