Ironically, much of the Atchafalaya Basin would still flood if the spillway is not opened, according to the new map, because the Old River Control Structure will be sending twice as much water from the Mississippi into the basin as it normally does. Meanwhile, the river will still overtop the relatively low Morganza floodway structure even if it's not opened, and several other levee failures could occur between Morganza and Baton Rouge.
Also this is interesting. The most critical time for levees may be after the water goes down.
Even if the river doesn't go much over 17 feet at New Orleans, a level reached at noon Tuesday, levee officials will be keeping careful watch when the river begins to drop, now not expected until mid-June, Turner said.
"If the river begins to fall rapidly, we could have incidents where saturated levees slide into the river," he said.