From a mile up in the thick Louisiana summertime air, the structure looks so fragile, just a spidery wisp of a pale-colored highway bridge crossing an expanse of flat-brown river, the waters of the Mississippi brimming on one side and the outflow like slashing white brushstrokes running down on the other. Even closer, from as close as it is safe to go, it still doesn’t look like much, not too different from a thousand other dams.
But this construction, improvidently christened half a century ago as the Old River Control Structure, is distinctly different, and tasked with the near impossible: controlling the course of America’s biggest and most important waterway. And yet the Mississippi, with its amply deserved reputation for wayward behavior, is with every new day resisting being controlled. The natural world in these parts has been altered greatly in recent decades. The Mississippi is no longer the river it was when engineers first set out, with the construction of these iron and concrete behemoths, to truss and guide it. Back then, in the 1950s, there was no talk of climate change or the effects of El Niño or the frequency of giant storms or the deepening of the isobaric gradients of cyclones—all proximate causes of a crisis that is now threatening these vital structures.
Yet what was already clear back then was that the Mississippi was steadily gaining in strength and that the slender connecting channel between the Mississippi and the Atchafalaya River—the hitherto barely-regarded parallel river into which it has long been tempted to flow—had somehow to be forcibly wrestled into submission. If not, if such a channel switch were permitted to occur, it would signal a death knell for the great cities downstream, Baton Rouge and New Orleans especially; it would ruin refineries, sever pipelines, bring down railroad bridges, cut off drinking water supplies, affect electrical distribution. It would have an immediate and crushing effect on the economies of the United States and, inevitably, of the world.
It’s little wonder, then, that it has been for five decades the stated policy of the United States government to prevent this from happening.
Since the behavior of an alluvial river can change by the minute, the mathematics involved in making any kind of prediction of its future behavior is formidable, the task Sisyphean. Constructing a barrier that would keep the Mississippi from changing its course required the greatest minds of the time to solve the essence of the problem at hand, the compromise that would avert disaster. Hydrologists had calculated that by maintaining a split of the downrushing waters—with 70 percent of the flow going down the Mississippi and 30 allowed to cannonade down into the Atchafalaya—it might just be possible to keep from a wholesale channel switch. To achieve such a split is where Albert Einstein’s son—of all people—comes into the story.
Hans Albert Einstein’s entire academic career, from his graduation from engineering college in Switzerland to his migration to America at the start of the war, had involved hydraulics and sediment transport. He had achieved great fame and distinction in the field, and he knew the Mississippi well from previous assignments upriver. The Old River Control Structure, when eventually built, was the creation of many, but, primus inter pares, Hans Albert Einstein was the man who decided where it should go and what it should look like and how exactly it needed to be made.
A team of engineers, spearheaded by Einstein, who had been summoned across from his laboratory in California, began their work in September 1955. There were to be initially three quite separate constructions, each fashioned from millions of tons of the strongest materials known. At the most southerly point on this section of the Mississippi, on the entrance to the Old River itself, they built a set of lock gates and a sluice that would enable shipping to pass into the Atchafalaya. Further north, on a floodplain that became inundated at every high water, they built what they called the Overbank Structure, a 3,000-foot-long confection of steel and concrete with more than 70 bays and gates made of creosoted needle logs, each 18 feet long, which would be pulled up and out by mobile cranes when the water, and the need, arose.
And in between these two, crucial above all else, they built the all too casually named Low Sill at the head of an entirely newly cut outflow channel, which took the now regulated Mississippi water, the aforementioned 30 percent share, and allowed it, and it alone, to thrust itself down into the Atchafalaya. The Low Sill was designed to be mightily strong: Einstein and his fast-swelling corps of designers calculated that there could be headwaters piling up as much as 37 feet behind it and still it would stand firm. (Beyond that—the figure was inconceivable. So inconceivable, in fact, that it was scarcely worth contemplating. And yet, unrealized by all back then, it needed to be imagined. For the world—and its climate—was about to change.)
The Low Sill that resulted is an understated monstrosity, 500 feet long, 70 high, anchored invisibly deep in the red-dirt earth. It is solid and square and colored a military gray-brown. It sports two identical battleship-gray cranes, each tall and resembling H. G. Wells’s creatures from War of the Worlds, all spindly legs and enormous chamfered heads. They can be manned to lift the triple-sectioned foot-thick iron doors up from the 11 gates, each of them 44 feet wide. Curved arcs of concrete wing walls rise from the riverbed a few feet upstream, gathering the water in toward the barriers and the gates. On the downriver side, too, there are structures that keep the outrushing water from doing great damage to the channel banks.
State Route 15 passes on top of the barricade, and the few cars and trucks that run along the levees today pass by at great speed. Seldom does anyone stop, but there are fences to keep the curious out—although, considering how critical are the national security implications of this structure’s possible failure, and that “acts of sabotage or war” remain listed in the pantheon of risks attendant on the structures, the fences look all too penetrable.
I did once stop, some years ago. I pulled over to the shoulder, left my car, and strolled down the slope to watch the spectacle of the downstream flood, roaring in through the open gates and enveloped in great clouds of spray below the dam. I clambered up onto one of the piles of riprap barrier stones to gaze, enthralled, at the millions of tons of wild water churning out from the Mississippi. But someone had been watching from the office, and within moments a white Ford truck sped down and I was asked—for my own safety, the driver said—to move away. If I stepped carelessly off the bank and the water ever got hold of me, he said, I’d be on my way to the Atchafalaya and Morgan City in a trice—and as a corpse, broken to pieces.
More recently—this time with the full permission of senior figures at the River Commission—I was back again. This time I was allowed through the security fence and escorted along the inspection path on the upstream side of the Low Sill. The river was high—not high enough to cover the Overbank, which I could see half a mile away, but likely to become so in another day or so, said the two Corps women who were running the structure that day.
To keep the outflow at the 30 percent mandated by the US Congress, three of the gates were open; from the path above one of the open gates, I leaned—too precariously, I thought—over the railing, looking down, half-paralyzed with fear, into a maelstrom of water pressing up against the iron walls and being sucked beneath them, hurtling down as if in some Mississippi version of the Corryvreckan whirlpool, with a thunder of roaring suction. A sentry boat was barely visible on the eastern horizon, watching for any passing barge traffic. That was always the risk in times like this: that a chain of barges would get sucked in, sweeping the barges themselves to probable destruction, sure, but, rather more important, damaging with the collision the fragile integrity of these all too critical iron gates.
It is possible to walk on an iron grid around to the downstream side of the gates, and at a stroke to appreciate for once the difference in height—17 feet or so; it varies by season and by whim—between the Mississippi and the stream that so dearly wants to capture it, and which is the reason for the existence of all these Einstein-designed monster creations. On the downstream side it is warmer, less windy; and below my feet, through the grid, the water thrusts its way out of the gates at first smoothly, like molten copper, until it breaks into huge, white, airy billows as it smashes against invisible underwater cement speed-breaking baffles, which force it up into the air, slow its velocity, and help break and mitigate its destructive force as it barrels—millions of tons of high-speed water—down the outflow channel and on its way down the sluiceway.
The forces at work are formidable, breathtaking, dizzying to see. And yet in 1963, with completion of both the Low Sill and the Overbank, the Corps of Engineers breathed a collective sigh of relief. Their job was done. Mission accomplished. The river was saved. “A threat of catastrophic proportions has been ended forever,” chorused a Corps colonel in a triumphal essay the following year.
In just under a decade, however, the colonel would be compelled to eat his words. The river, it turned out, had other plans. This was most amply demonstrated when, in the fall of 1972, the weather in the Midwest suddenly turned bad—and when the consequent spring flood of 1973 turned out to be exceptionally and unexpectedly ominous.
At the height of the crisis, and on a springtime Saturday evening when the rest of America was glued to the national coverage of the Watergate crisis—how appropriate the word!—the Low Sill very nearly gave way. The river pressed so hard against it, whirlpools were born beneath it, protective walls beside it were utterly wrecked, and the dam’s foundations were scoured to the thinness of tissue paper. The structure managed to hold through that terrible night—but only just.
The Corps of Engineers promptly decided that to keep the ever-angrier river in check yet another structure, this time even bigger and still more costly, needed urgently to be built close by. It was called the Auxiliary Structure and it was completed and its lock gates firmly closed in 1986. It has been successfully operational now for 35 years.
But the Mississippi is rising still. Climate changes are rendering the storms upriver ever worse and the floods ever higher, longer-lasting, and more dangerous. Can this latest marvel of civil engineering continue to hold in the face of rapidly accelerating hydraulic challenges? “We can continue to throw iron and concrete at the river to keep it where we want it,” a Corps of Engineers hydraulics specialist told me. But what if it fails? What next for America’s iconic river, and for the cities that lie, quite careless of disaster, in the miles below?
The dam, so fragile-looking from the air, is all that protects them now. It is said by some who fear for its future to be America’s Achilles heel. As climate changes force the weather upstream to worsen and the rains to fall ever more violently and the Ol’ Man River’s waters to rise up to its fearful but once-inconceivable levels, it is becoming abundantly clear just why.
Adapted from The End of the River by Simon Winchester, published by Scribd Originals.
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