The Lower Mississippi River Water Trail

Natchez to St. Francisville

The Atchafalaya

One would be hard pressed to find a river in North America that actually gets cleaner as it flows downstream, as all rivers used to do.  But welcome to the Atchafalaya, the prime example of the healthy river.   The Atchafalaya River is a distributary of the Mississippi River; it flows approximately 150 miles through Louisiana before reaching the Gulf of Mexico.  The wetlands of the Atchafalaya ranks alongside the Everglades and the Okefenokee in size, but it has a big river traveling through the middle of it, something the others lack.  As the Atchafalaya travels downstream, it flows through North America’s largest river swamp, breathing in and out as it flows along, filling the wetlands and marshes on the way in, the water returning to the main channel refreshed, and in the process rids itself of pollutants brought downstream from the Mississippi. It stands as a model of how the persistence and natural function of a river can improve water quality conditions if given the chance. Restoration of the Gulf Coast is also occurring at the Atchafalaya River Delta due to natural sedimentation; it is one of the few areas on the Gulf Coast that is gaining ground.

 

316.3 RBD Hydro Intake -- Old River Control Structure

Maybe you’ve read about it, or heard frightening tales about it.  It’s as legendary as the Chain of Rocks of St. Louis, and as little understood, and as many tall tales told about.  No, you won’t be inexplicably sucked into and flushed down the canal.  Keep several hundred yards off the right bank descending as you approach mile 316, and watch carefully how the water is flowing.  At higher water stay further out, at lower water staying out several hundred yards is enough.  Do not make landings anywhere near the mouth.  This is the first of three openings sucking water out of the Mississippi for destination down the Atchafalaya.  The hydro canal feeds the hydroelectric power plant and is always open with water flowing in.  At low water only the hydro intake will be open.  At medium water the auxiliary opens.  At high water levels all three will be open and flowing strong.  So dismiss fears of being snagged out of the main channel by unavoidable currents.  Keep your distance and carry on downstream paddling for the beautiful bluffs rising in front of you, the Tunica Hills at Fort Adams.

Short History of the Old River Control Structure

Before the 15th century, the Red River and Mississippi River were entirely separate and more or less parallel to one another.  Beginning in the 15th century, the Mississippi River created a small westward loop, later called Turnbull’s Bend, near present-day Angola, La. This loop eventually intersected the Red River, making the downstream part of the Red River a distributary of the Mississippi; this distributary came to be called the “Atchafalaya River.”

 

In the heyday of steamboats along the Mississippi River, it would take a boat several hours to travel the 20 miles of Turnbull’s Bend, after which it would have progressed only a mile or so from the entrance to the bend. To reduce travel time,Capt. Henry Shreve, a river engineer who opened up the famous Red River Snag, also founded his namesake Shreveport, LA, dug a canal in 1831 through the neck of Turnbull’s Bend.  This canal became known as Shreve's Cut.  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. As well as this, the Atchafalaya River drained additional water from the Mississippi River through the abandoned Turnbull’s Bend, which had come to be known as Old River”. With this extra intake of water, the channel of the Atchafalaya River was worn 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 (Knox 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 river delta south of Morgan City in southern Louisiana, greatly reducing water flow to its present channel through Baton Rouge and New Orleans.  The 1973 Mississippi Flood 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. Jeff Masters of Weather Underground noted that failure of that complex would be a serious blow to the U.S. economy.

 

(adopted from Wikipedia)