The Mighty Atchafalissippi River?

A war is raging in Morganza in Pointe Coupee Parish, north of Baton Rouge.  As with most wars, it began quietly, during the 15th century, when a few renegade battalions of the army of Mother Nature began to undermine the stability of the Mississippi River.  An oxbow of that river intersected the Red River and adopted it as a tributary.  It intersected a small stream known as the Atchafalaya as well, utilizing it as a distributary.

Time passed, and the Atchafalaya River grew and siphoned off more of the Mississippi’s flow.  About three hundred years after this war began, Captain Henry Shreve, navigator of the Red River and founder of Shreveport, led a charge to unintentionally aid and abet the army of Nature by cutting a navigable shortcut between the entrance and exit of that oxbow.  Two days after he completed his canal, it had doubled in width due to the rushing waters of the Mississippi taking advantage of his shortcut, which quickly became the main channel of the river.  The upper leg of the oxbow silted up, the Red merged with the Atchafalaya, and the lower leg became what is now known as Old River, a distributary of the Mississippi, a tributary of the Atchafalaya, and a new battalion in Nature’s mission to divert the Mississippi River to Morgan City.

The Atchafalaya route offers a much more attractive path to the Gulf of Mexico from Pointe Coupee Parish.  It is significantly shorter, about 145 miles compared to the approximately 345 mile path the Mississippi follows through Baton Rouge and New Orleans today.  It is also more efficient, as the soil conditions of the Atchafalaya Basin are much more conducive to river channel formation.  Finally, because the elevation change between Pointe Coupee and the Gulf occurs over that significantly shorter distance, it encourages faster, more violent, and more erosive flow rates.

If Nature were to win that war, we’d find ourselves with a deep, fast, violent Atchafalippi River storming to the Gulf near Morgan City, while Baton Rouge and New Orleans, and their economies dependent in so many ways on the Mississippi, would be left sitting beside a massive lake, watching life as south Louisiana has traditionally known it slip away.

In the mid-1950’s, the Congress of the United States declared war on Mother Nature to prevent that from happening, and commissioned the US Army Corps of Engineers to lead the charge.  Invoking the belief that the rate of diversion from the Mississippi to the Atchafalaya, 30% of the Mississippi’s flow at that time, was somehow ideal, Congress ordered the Corps of Engineers to construct whatever devices were necessary to assure it didn’t escalate.  They built the Old River Control Structure at Morganza, which is basically a control valve allowing 30% of the Mississippi’s discharge to pass through Old River into the Atchafalaya, a series of locks to permit ongoing navigation between the two, and an “oh, my God!” series of relief valves that can be thrown open to relieve the Mississippi during occasions of extreme high water such as we’re experiencing today and thus protect the levee system, another of the Corp’s battlefronts to prevent Nature from allowing the Mississippi River to do whatever she pleases.

Opening those “relief valves” causes about 3000 square miles of land to be inundated with up to 25 feet of water.  That land has been acquired by farmers and sportsmen fully knowledgeable of the likelihood of its being flooded should the Mississippi River receive more influent than it can handle.  Opening the Old River Control Structure into the Morganza Spillway floods that land, while protecting Baton Rouge and New Orleans from devastation that would make the aftermath of Hurricane Katrina seem benign.  After the excitement subsides, the farmers are left with land newly enriched by a fresh deposit of river silt.  While the willful destruction of anyone’s property cannot be taken lightly, the decision seems clear.

But it’s only been made once before.  The Corps opened the Old River Control Structure and flooded the spillway in 1973.  Raising a white flag to half mast, they somewhat surrendered to Mother Nature and diverted much of the Mississippi River’s excess waters down the Atchafalaya.

Mother Nature proved to be a more formidable foe than the Corps had anticipated, however.  The Old River Control Structure is a massive behemoth of concrete and steel, supported on pilings driven deep below the floor of the river, and during the time between its completion in the 1960’s and it’s first test in 1973, the armies of Mother Nature had been utilizing the forces of her river to deteriorate the concrete and to undercut the foundations of the structure, weakening it to the extent that the Corps almost couldn’t get it closed when they lowered the flag of surrender to resume the war.  Mother Nature almost won the battle and the war and we almost had an Atchafalissippi River coming into being.

The Corps resumed the war effort with a vengeance, restoring the structure, improving its foundations, and providing additional measures of protection to prevent Nature from resuming her methods of destruction.  Yet on several occasions in the ‘90’s and early 2000’s, they deliberated over utilizing the Spillway to relieve the Mississippi and chose not to for fear they might lose the war.

The flood of 2011 has left them with no choice.  The Mississippi was forecast to crest in Baton Rouge at levels three to four feet above levees in that area.  The natural flood plain in south Baton Rouge, where plantations once thrived and relished the seasonal deposit of fresh river silt, is now occupied by hundreds of homes, chemical plants, refineries, and Louisiana State University.

The Old River Control Structure was opened on Saturday, May 14, and the Morganza Spillway is slowly filling with water.  Did the Corps lose the war?  Will the structure hold?  Can they get it closed when the waters subside?  While the Corps has expressed no doubts in the integrity of the structure, doomsday prophets throughout south Louisiana are wailing and gnashing their teeth, predicting that the Atchafalissippi and Mother Nature have won.  Predictions of a silted shipping channel closing the ports of Baton Rouge and New Orleans, of saltwater migrating inland and destroying drinking water and plant process water sources, would have one believe that this result is inevitable, and that it will happen before Memorial Day!

Such is not the case.  In the highly unlikely event that the Old River Control Structure fails, the Atchafalissippi River would indeed form quickly, but the present day Mississippi River will continue to exist and thrive for a time.  The doomsday processes would take decades to fully materialize.  During those decades, 21st century engineering skills encompassing a growing knowledge of computational structural analysis, computational fluid flow analysis, and subterranean soil mechanics will create a new arsenal with which to tackle and harness Mother Nature.

She may appear to be winning the battle, but Mother Nature has not won the war.  Ole Man River has not surrendered.  He’s just teasing her while continuing to play hard to get.



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