The mayor and to a lesser extent the governor dropped the ball here.
The thing is to help people, not apportion blame. That being said, they clearly did not rise to the occasion.
Regarding all the talk about engineering and the superdome - My guess is in a case like this someone (Engineer big wigs) convinced the Gov and then from there the President that the superdome would be a safe place for those people. Otherwise if there was no 'safe' place the C-130s would have been sent in.