The Atchafalaya: The River the Army Corps Is Holding Back

There is a structure near Simmesport, Louisiana, that most Americans have never heard of, and the fate of New Orleans and Baton Rouge depends on it continuing to function.

The Old River Control Structure sits at the point where the Mississippi River, the Red River, and the Atchafalaya River intersect. The Atchafalaya is a distributary of the Mississippi: it branches off to the south and runs through the largest river swamp in North America before reaching the Gulf of Mexico near Morgan City. The Atchafalaya is also, by hydraulic calculation, the more efficient path for the Mississippi's water to reach the sea. It is steeper. It is shorter. It is, from the river's perspective, the better option.

The Mississippi has been trying to take the Atchafalaya route for decades. By the nineteen fifties, the Atchafalaya was already capturing more and more of the Mississippi's flow each year. If the process had continued unchecked, hydrologists calculated that by roughly nineteen ninety the Mississippi would have permanently shifted its main channel. New Orleans and Baton Rouge, two of the largest port cities in the country, would have been left on a sluggish backwater with insufficient draft for ocean-going vessels. The port economy would have collapsed.

The Army Corps of Engineers completed the Old River Control Structure in nineteen sixty-three to prevent this. The structure is an enormous set of hydraulic gates that controls exactly how much of the Mississippi's water is allowed into the Atchafalaya: no more, no less, year-round, indefinitely. In nineteen seventy-three, record flooding nearly destroyed the structure. Engineers worked around the clock for weeks to stabilize it. If it had failed, the river would have shifted that year.

The writer John McPhee devoted a section of his book "The Control of Nature" to this structure and the engineers who operate it. His central question, which the structure has not answered, is whether this is a permanent arrangement or a long-term delay.