Intended to operate during emergency flooding, the purpose of the Morganza Floodway is to divert excess floodwater from the Mississippi River into the Atchafalaya Basin. The floodway consists of two structures – the Morganza Control Structure and the Morganza Floodway – which are designed to pass up to 600,000 cubic feet per second (cfs) of water to the Gulf of Mexico, alleviating stress for mainline levees downstream along the Mississippi River.
Located at river mile 280 in central Louisiana, the Morganza Floodway begins at the Mississippi River, extends southward to the East Atchafalaya River levee, and eventually joins the Atchafalaya River Basin Floodway near Krotz Springs, Louisiana. Seven design plans were originally proposed, and a two-structure design was selected. Construction of both structures was completed in 1954. The first component at Morganza is the floodway. At twenty miles long and five miles wide, it consists of a stilling basin, an approach and outlet channel, and two guide levees. The second element is a control structure containing a concrete weir, two sluice gates, seventeen scour indicators, and 125 gated openings.
The decision to open the Morganza Floodway relies on current and projected river flows and levee conditions, river currents and 
potential effects on navigation and revetments, extended rain and stage forecasts, and the duration of high river stages. When river flows at the Red River Landing are predicted to reach 1.5 million cfs and rising, the Corps considers opening the Morganza Floodway.
Every year, written notices are issued to all interests reminding them of the possibility of operation of the floodway. In the event that Morganza needs to be opened, the USACE project managers, along with news media and civil officials, will help notify all interested parties as soon as possible. On receipt of such notice, expeditious action must be taken as soon as possible to protect life and property. If the Morganza Floodway is operated, there is a possibility that personal property will be flooded. In the event of an opening, all water and/or gas wells must be sealed and capped to prevent contamination from floodwaters.
The Morganza Floodway was partially operated during the 1973 high water event to relieve pressure on Old River’s Low Sill Structure. Overall, the spillway structure fared well with minor scouring and slight damage to the stilling basin. Repairs have since taken place and the structure has been restored to its original state. Inspections are ongoing to ensure that the structure operates correctly in the event of an opening