The SD did hold up during the hurricane - but if they had planned on it in advance, why wasn't it stocked? Even if people had only been there a couple of days (normal in a hurricane without flooding), they would have needed water and food and lots of Porta-Potties.
The judge who is running things in Houston was asked today how they had been able to get things set up so quickly, and he said "we had a plan." Obviously, NO didn't.
It appears that they had a plan to shelter people from the wind. It doesn't appear that they had a plan to cope with flooding. They may have recognized that if the levees broke and the city flooded there would not be much that they could do. I think that the death toll assumed in this "worst case" scenario was much higher than we seem to have.
They probably never contemplated that the levees would break the day after the hurricane.
It's not clear how practical their plans were. I think that Entergy was supposed to set up their command post in the Hyatt Regency. But that is clearly a bad idea, compared with setting it up in Baton Rouge or somewhere else well inland.