Katrina was much more than just a hurricane. It was also the resulting floods that resulted from levy's breaking. New Orleans sits in a bowl, surrounded by water. First off, it's a crazy, insane place to ever build a city. So, the concrete structures you speak about wouldn't have helped in the case of N.O.

__________________
"This is a time for a national imperative not to fail in Iraq." Condoleeza Rice, January 11, 2007