Morganza Spillway enters the Morganza Floodway, which extends from the spillway at the Mississippi River south to the East Atchafalaya River levee. The floodway, long and wide, includes a stilling basin, an approach channel, an outlet channel, and two guide levees. From there, diverted water enters the Atchafalaya River Basin Floodway near Krotz Springs, Louisiana, and continues to the Gulf of Mexico. In an extreme flood event, a major release of water from the Morganza Spillway into the Morganza Floodway and Atchafalaya Basin inundates not only the floodways themselves (between their levees), but extensive additional areas of southern Louisiana throughout the Atchafalaya
2011 Mississippi River floods to open more gates on the spillway, the Corps studied four flooding scenarios, all of which assumed the Bonnet Carré Spillway near New Orleans would be concurrently operating at full capacity (100%). Following this analysis, which showed that extensive flooding was expected in the Atchafalaya Basin regardless of the choice made regarding the Morganza Spillway, the Corps decided to start the 2011 diversion by opening the spillway a bit less than described in scenario 1a (21%, not 25%) The Corps of Engineers subsequently released a map showing the estimated times it would take the flood waters to reach the various