"I don't think anybody could have predicted that Gretna would shut down the bridge and keep these people from leaving"
Leaving to go where? You don't explain yet where they would go to. From the waters edge in Orleans Parish to the waters edge in Jefferson Parish?
Well, the places they could have gone include the Cajundome in Lafayette, the Maravich Center in Baton Rouge, the Downtown Convention Center in Baton Rouge, and countless little private shelters all over the place.
Exactly where they wound up, but they could have gotten that much closer that much sooner, instead of hanging around being robbed and raped in the New Orleans Convention Center and the Superdome.