Opening the Morganza Spillway

The Morganza Spillway in 1973 

           The Mississippi River has been above flood stage for four months. Continuous rain in the Midwest has sent torrents of water down the Mississippi towards the Gulf of Mexico. With no let-up on the way and the increasing threat of the Mississippi overflowing its banks at Baton Rouge and New Orleans, the Army Corps of Engineers is preparing to open the Morganza Spillway to alleviate the problem. The opening of the Spillway will divert the excess water into the Atchafalaya Basin, relieving the flood threat. It will also destroy wildlife, ruin crops, and devastate the crawfish, oyster, and other aquatic life. 

            Since the opening of the Morganza in 1954, the Corps of Engineers has only opened it twice—for 56 days in 1973 and 55 days in 2011. The opening of the Spillway is generally considered as a last resort to protect populated areas from flooding. As the Corps of Engineers prepares to open the Spillway, let’s take a look at the point of the Spillway, its history, and what happens next. 

The Spillway in action 

            In 1927, heavy rainfall that began the previous year swelled the banks of the Mississippi causing the river to overflow its banks. The resulting flood left 700,000 people homeless and put over 27,000 square miles of land under water. In a desperate attempt to save the city of New Orleans, city and government authorities blew up the levee 13 miles south of the city at Caernarvon. By blowing up the levee, they hoped to divert the floodwaters into the lowlands south of the city. Ultimately, however, the detonation was unnecessary. Other levees had already broken upstream that lessened the flow of water towards the city. 

            The following year, Congress passed the Flood Control Act of 1928 to try and prevent future disasters. The law authorized the Army Corps of Engineers to design a system of levees and spillways to divert water away from populated areas during floods, but also keep the Mississippi on its current course through Baton Rouge and New Orleans before reaching the Gulf of Mexico. The Corps of Engineers eventually constructed multiple spillways along the Mississippi River including the Bonnet Carre Spillway outside of New Orleans that directs floodwaters into Lake Pontchartrain. Work on the Morganza Spillway’s levees began in the late 1930s, but was not completed until 1954. 

Graphic from The Advocate 

            The land around the Morganza is well above the normal river level, so for most of the year, the land is dry. Water only reaches the Spillway when the Mississippi rises above flood stage. When the water level is normal, the Old River Control Structure (ORCS) and Old River Control Auxiliary Structure (ORCAS) control the flow of water before it ever reaches the Morganza. ORCS and ORCAS divert excess water from the Mississippi River into the adjacent Atchafalaya River. By sending about 70% of the water to the Mississippi and 30% to the Atchafalaya, ORCS and ORCAS have kept the Mississippi River on its current path. If left to its own devices, the river would have shifted to the west down the Atchafalaya, which is now the shortest distance to the Gulf. 

When the ORCS and ORCAS systems can no longer direct the course of the water, the Corps of Engineers considers opening up the Morganza. The structure itself has 125 gates that can be opened or closed to allow more water to flow from the Mississippi. To open the gates, the Corps of Engineers employs 25 foot cranes to open and close the gates as needed. As the flood waters rise higher, the Corps of Engineers needs to open the spillway before the water rises over it and ruining any chance of lessening the flood levels. 

            As a result, the Morganza has only been opened twice in its history—in 1973 and 2011—and the Corps has never opened all 125 gates. In 1973, they opened 42 and in 2011 only 21. Considering the large amount of water being diverted, the Corps prefers to release the water gradually. 

Flood damage from 2011 

            The opening of the Morganza will cause immense damage to the Atchafalaya basin, which is filled with a diverse range of wildlife, farms, and seafood. Over the years, people—especially the poor—have taken to living in the basin because they cannot afford to live elsewhere. The water will damage their homes and livelihoods. The influx of water will also drive animals of all kinds—deer, bears, turkeys, hogs, rabbits—from their homes, forcing them to seek higher ground that could include roads and residents’ homes. With a lack of available high ground, most will die. The water will also be devastating to fisheries the influx of warm fresh water will kill crawfish and oysters, which thrive in salty, cold water. This river water, which has largely been accumulating near the Spillway, is stagnant and will kill fish or other aquatic life. Birds may be better off, but ground birds and birds in the midst of nesting will likely drown. 

            All of this will be the result of nearly a hundred years of flood control where the Corps of Engineers decided to try and assert its authority over the Mississippi River itself.