Atchafalaya Basin Atchafalaya River has been a backswamp, low area between the paths of the Mississippi River through the process of delta switching, which has built the extensive delta plain of Louisiana. The natural levees of the Mississippi River (on the east) and the levees along its previous course (now Bayou Teche) on the west define the Atchafalaya Basin. The central basin is further bordered by man-made levees designed to contain and funnel floodwaters released from the Mississippi at the Old River Control Structure and the Morganza Spillway south toward Morgan City and eventually to the Gulf of Mexico. Historically there were
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