Old River Control Structure - Purpose

Purpose

Before Shreve's Cut, the Red River was a tributary of the Mississippi River and the Atchafalaya River a distributary of the Mississippi. Now all of the water from the Red River flows into the Atchafalaya along with about 30% of the Mississippi's water. However, in the 15th century CE, the Red River and Mississippi River were entirely separate rivers and more or less parallel to one another.

Beginning in the 15th century, though, the Mississippi River created a small westward loop, later renamed Turnbull’s Bend, near present-day Angola, La. This loop intercepted the Red River, and the Atchafalaya River was formed as a distributary.

In the heyday of steamboats along the Mississippi River, it took a boat several hours to travel the bend’s 20 miles, and only then it had progressed a mile or so. To reduce travel time, Captain Henry M. Shreve, a river engineer and founder of Shreveport, La., dug a canal in 1831 through the neck of Turnbull’s Bend. At the next high water, the Mississippi roared through this channel.

With the Mississippi River taking a new course, the Red River began emptying into the smaller Atchafalaya River. And the Atchafalaya River was force-fed by the Mississippi River at the abandoned Turnbull’s Bend, which had come to be known as "Old River.” With this extra intake of water, the Atchafalaya River wore deeper and wider throughout the 1800s and early 1900s.

The U.S. Army Corps of Engineers measured the amount of water flowing through the Mississippi River and compared it to the amount entering the Atchafalaya Basin by monitoring “latitude flow” at the latitude of the Red River Landing, located five miles downstream of Old River. In this case, latitude flow is a combination of the flows of the Mississippi and Atchafalaya rivers as they cross an imaginary line at that latitude.

Between 1850 and 1950, the percentage of latitude flow entering the Atchafalaya River had increased from less than 10 percent to about 30 percent. By 1953, the U.S. Army Corps of Engineers concluded that the Mississippi River could change its course to the Atchafalaya River by 1990 if it were not controlled, since this alternative path to the Gulf of Mexico through the Atchafalaya River is much shorter and steeper.

The Corps completed construction on the Old River Control Structure in 1964 to prevent the main channel flow of the Mississippi River from altering its current course to the Gulf of Mexico through the natural geologic process of avulsion. Historically, this natural process has occurred about every 1,000 years, and is overdue. Some researchers believe the likelihood of this event increases each year, despite artificial control efforts.

If the Mississippi diverts its main channel to the Atchafalaya Basin and the Atchafalaya River, it would develop a new delta south of Morgan City in southern Louisiana, greatly reducing water flow to its present channel through Baton Rouge and New Orleans. The Mississippi Flood of 1973 almost caused the control structure to fail. Integrity of the Old River Control Structure, the nearby Morganza Spillway, and other levees in the area is essential to prevent such a diversion; see "Mississippi River: Future course changes" for further discussion. Jeff Masters of Weather Underground noted that failure of that complex "would be a serious blow to the U.S. economy."