More on the Morganza Spillway

The Morganza Spillway, shown while open during the 1973 flood. 

From Wikipedia:

The Morganza Spillway is a flood-control structure in Louisiana along the western bank of the Mississippi River at river mile 280, about three miles northeast of Morganza in Pointe Coupee Parish. The spillway stands between the Mississippi and the Morganza Floodway, which leads to the Atchafalaya Basin and the Atchafalaya River in south-central Louisiana. Its purpose is to divert water from the Mississippi River during major flood events by flooding the Atchafalaya Basin, including the Atchafalaya River and the Atchafalaya Swamp. The spillway and adjacent levees also help prevent the Mississippi from changing its present course through the major port cities of Baton Rouge and New Orleans, Louisiana, to a new course directly down the Atchafalaya to the Gulf of Mexico. The Morganza Spillway is operated by the U.S. Army Corps of Engineers. Its gates have been opened only twice, during major Mississippi River floods in 1973 and 2011.

I think it is very important to note the part about how the Morganza Spillway prevents the Mississippi River from changing course, running through the Atchafalaya Basin and leaving New Orleans and Baton Rouge on a back channel.  Also, as is noted at Wikipedia, all of the levees and structures used to relieve levees along the river were put in place after the 1927 flood:

The Great Mississippi Flood of 1927 was the most destructive river flood in the history of the United States,^[6] in large part due to the Mississippi River swelling to 80 miles wide in spots.^[7] To provide protection against river flood and prevent a repeat of the Great Flood of 1927, Congress passed the Flood Control Act of 1928 to authorize the United States Army Corps of Engineers to build the Bonnet Carre Spillway (located 33 miles above New Orleans and completed in 1931^[8]), the Birds Point floodway in Missouri, and the the Morganza Floodway as part of the 1928 Mississippi River and Tributaries Project.^[7] The Morganza control structure portion of the project was completed in 1954^[7] and subsequently became incorporated into the Mississippi River Commission's 1956 Project Design Flood,^[9] which added the Old River Control Structure in 1963 to the protections used to prevent Mississippi River flood.^[10] The Flood Control Act of 1965 provided further regulation over the Morganza Spillway's role in Mississippi River flood prevention. A concrete pit called a stilling basin was added at the Morganza Spillway in 1977 "to provide erosion protection after the velocity of water pouring through the open bays during a 1973 flood caused severe scouring, or gouging out, of the land behind the bays."^[11]

The blowing of the Birds Point levee, while dramatic, has been part of established plan since 1928.  The landowners in the area, while obviously dejected, knew that this is a possibility every year.  As for the Atchafalaya, it is very interesting that without the Corps, the Mississippi River would shift and flow through that basin.