The Consequences of Controlling a River Course

America’s Rivers Are At Risk

This year’s flooding spotlights some of the challenges that our rivers are facing. On May 17th, we’re announcing the newest America’s Most Endangered Rivers. Sign up to find out how you can get involved.


The threat of flooding on the Mississippi River is so severe that the officials are taking dramatic action all along the river to protect cities and towns.  Earlier this week, the US Army Corps of Engineers (Corps) dynamited a levee and flooded thousands of acres and nearly 100 homes to protect the nearby city of Cairo, Illinois

Downstream, the Corps took additional critical steps earlier this week because the Mississippi River levee through southern Louisiana system is nearing carrying capacity.  First, they announced the plan to open the Bonnet Carre Spillway, which diverts a portion of the Mississippi River into Lake Pontchartrain, the waterbody bordering New Orleans to the north The Bonnet Carre Spillway has only been opened 9 times since its construction in 1931. 

Then the Corps announced that they may open the Morganza Spillway next week, allowing tens of thousands of acres of farmland to flood if necessary to protect New Orleans and Baton Rouge.  The gates of the Morganza Spillway have been closed for over 35 years.  These dramatic actions prompted Louisiana’s Governor Bobby Jindal on Thursday to request a federal Disaster Declaration for his state.

Unlike the Bonne Carre, the Morganza Spillway diverts floodwaters into an adjacent river basin, the Atchafalaya River, which parallels the Mississippi to the west. In 1953 the Corps determined that the Mississippi was slowly migrating through the landscape toward the Atchafalaya.  The Corps estimated that, if left alone, the Mississippi would join the Atchafalaya by 1990, disrupting infrastructure and commerce in southern Louisiana that had built up around the rivers. As a result, the Corps built the “Old River Control Project” (ORC) to control flows between the Mississippi and Atchafalaya and maintain their current locations.  During the floods of 1973 the Mississippi fought these constraints and nearly destroyed ORC, which would have allowed the Mississippi to capture join the Atchafalaya. 

If the Mississippi River were to shift course, the effects would be devastating. Several cities would be inundated and might require relocation. Oil and gas pipelines throughout southern LA would rupture and commerce on the river and in New Orleans would be severely disrupted. 

However, in ecological terms, the Louisiana coast would be revitalized.  The western part of the Mississippi delta would receive the sediment and freshwater it has been deprived of for decades.  Increased sediment distribution would reduce coastal erosion, and provide nutrient-rich sediments for terrestrial and aquatic habitat. Additionally, this would reduce Louisiana coastal wetland loss, which currently occurs at a rate of 1 acre every 38 minutes.  The combined effects of these ecological benefits would ultimately increase the sustainability of Gulf Coast fisheries.

If the Mississippi and Atchafalaya were given the freedom to flow and flood more naturally, initial impacts to adjacent agricultural land and infrastructure would have to be managed, but the risk of catastrophic floods would be permanently reduced.  Additionally, the increase in freshwater and sediment into the western part of the delta would reduce coastal erosion and increase aquatic habitat, thus increasing the ecological and commercial fishery integrity of the system.