The Control of Nature

The Control of Nature

If you've never read John McPhee's fine piece on the Atchafalaya River Basin's ambition to capture the Mississippi River, or even if it's just been a while, now is a good time to take advantage of The New Yorker's decision to move it out from behind the paywall:

Southern Louisiana exists in its present form because the Mississippi River has jumped here and there within an arc about two hundred miles wide, like a pianist playing with one hand—frequently and radically changing course, surging over the left or the right bank to go off in utterly new directions. Always it is the river’s purpose to get to the Gulf by the shortest and steepest gradient. As the mouth advances southward and the river lengthens, the gradient declines, the current slows, and sediment builds up the bed. Eventually, it builds up so much that the river spills to one side. Major shifts of that nature have tended to occur roughly once a millennium. . . . By the nineteen-fifties, the Mississippi River had advanced so far past New Orleans and out into the Gulf that it was about to shift again, and its offspring Atchafalaya was ready to receive it. By the route of the Atchafalaya, the distance across the delta plain was a hundred and forty-five miles—well under half the length of the route of the master stream.

For the Mississippi to make such a change was completely natural, but in the interval since the last shift Europeans had settled beside the river, a nation had developed, and the nation could not afford nature. The consequences of the Atchafalaya’s conquest of the Mississippi would include but not be limited to the demise of Baton Rouge and the virtual destruction of New Orleans.

. . .

[Just north of Baton Rouge, on the west bank of the Mississippi, the U.S. Army Corps of Engineers] dug into a piece of dry ground and built what appeared for a time to be an incongruous, waterless bridge. Five hundred and sixty-six feet long, [the Morganza Spillway] stood parallel to the Mississippi and about a thousand yards back from the water. Between its abutments were ten piers, framing eleven gates that could be lifted or dropped, opened or shut, like windows. To this structure, and through it, there soon came a new Old River—an excavated channel leading in from the Mississippi and out seven miles to the Red-Atchafalaya. The Corps was not intending to accommodate nature. Its engineers were intending to control it in space and arrest it in time. In 1950, shortly before the project began, the Atchafalaya was taking thirty per cent of the water that came down from the north to Old River. This water was known as the latitude flow, and it consisted of a little in the Red, a lot in the Mississippi. The United States Congress, in its deliberations, decided that “the distribution of flow and sediment in the Mississippi and Atchafalaya Rivers is now in desirable proportions and should be so maintained.” The Corps was thereby ordered to preserve 1950. In perpetuity, at Old River, thirty per cent of the latitude flow was to pass to the Atchafalaya.

Until it doesn't. During the 1973 flood, the Morganza spillway floodgates had to open wide, sending a good part of the Mississippi floodwaters through the Old River channel across to the Atchafalaya to the west:

In mid-March,Raphael G. Kazmann, author of a book called “Modern Hydrology” and professor of civil engineering at Louisiana State University . . . got into his car, crossed the Mississippi on the high bridge at Baton Rouge, and made his way north to Old River. He parked, got out, and began to walk the [Morganza Spillway] structure. An extremely low percentage of its five hundred and sixty-six feet eradicated his curiosity. “That whole miserable structure was vibrating,” he recalled in 1986, adding that he had felt as if he were standing on a platform at a small rural train station when “a fully loaded freight goes through.” Kazmann opted not to wait for the caboose. “I thought, This thing weighs two hundred thousand tons. When two hundred thousand tons vibrates like this, this is no place for R. G. Kazmann."

It makes you wonder whether the Atchafalaya will win this time. The whole McPhee article, including an account of the levee system beginning in the early 18th century, is worth reading.