Well crap!
Here is a map showing probable inundation area if the Morganza Spillway is operated at 25%. They opened it yesterday.
http://www.flickr.com/photos/3767199...7626528621473/
Here is a map showing travel times for the flood wave. Notice that once past I-10 there is a valley to the west in which the flood wave will travel north - against the land slope.
http://www.flickr.com/photos/3767199...7626528621473/