The Morganza Control Structure is another central feature in flood control efforts for the Mississippi River. Located approximately 30 miles downriver from the Old River Control Complex in Pointe Coupee Parish, this 4,159 foot controlled spillway was designed for emergency use to divert water from the Mississippi River. Following the Great Mississippi River Flood of 1927, the most destructive river flood in the history of the United States, Congress passed the Flood Control Act of 1928. The Flood Control Act authorized the U.S. Army Corps of Engineers to construct the Morganza Floodway, which is composed of the Morganza Control Structure and adjacent levees which funnel Mississippi River water into the Atchafalaya Basin Floodway. Construction began on the Morganza Floodway in 1938 and was completed in 1954. Since that time, the Morganza Control Structure has only been opened twice–once in 1973 and again in 2011.
The Morganza Control Structure, composed of 125 gates, each 21 feet wide, was designed to divert up to 600,000 cubic feet per second of flow from the Mississippi River during major flood events. Guided by levees, this water then flows into the Atchafalaya Basin Floodway on its way to the Gulf of Mexico. The resultant flooding can inundate not only the Atchafalaya Basin Floodway but also extensive additional areas of south central Louisiana and can affect people living in communities along the way. Residents of these areas receive an annual written notice from the USACE to remind all parties that there is a possibility of flooding due to opening the Morganza Control Structure.