Mississippi flood of 1973 western tributaries such as the Missouri and Arkansas to form a final catastrophic high in June. The flood resulted in the largest volume of water to flow down the Mississippi since the Great Mississippi Flood of 1927. Both the Bonnet Carre Spillway and the Morganza Spillway were employed. The Bonnet Carre was fully opened between April 7 and June 14 for a record 75 days. The 1973 flood was the first time the Morganza Spillway was opened: from April 19 through June 13. At Memphis, Tennessee, the Mississippi was over flood stage for 63 days, more than that of the
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