Tuesday, August 28, 2012

When the Mississippi Changes Course

Reading about Isaac headed up the Mississippi River Valley reminded me of this article: "Mississippi Rising: Apocalypse Now?"
There is an event coming to the Deep South that is as inevitable, and as imminent in geologic time, and as unpredictable in human time, and as dangerous to human life and enterprise, as are the Great California Earthquakes. It is as easy to say as it is hard to imagine: the Mississippi River is going to change course, and when it does will reach the sea 65 miles west of New Orleans, at Morgan City. This meandering of the great river is not at all unusual – it happens frequently in geologic time – and is the process that created the Mississippi River Delta – a 200-mile-wide, three-million-acre arc of coastal wetlands stretching roughly from Lafayette, Louisiana, east to Biloxi, Mississippi. As the river nears the Gulf of Mexico, on the flat coastal plain, the current slows, allowing its massive loads of silt to settle out, creating new wetlands and building up the river bed, which eventually becomes higher than the surrounding area. Eventually the river breaks out, seeks a new and quicker way to the Gulf until the process repeats in about a thousand years.

In the 1950s the Mississippi was ready for another change, exploring in ever greater enthusiasm the Atchafalaya River basin. But this time the river had a new enemy: money. If the river succeeded in doing what it had always done, it would leave high and dry the Port of New Orleans, devastate the city’s economy as well as that of Baton Rouge, cut off nearly 20 per cent of the country’s oil imports and 16 per cent of the nation’s fisheries harvest, and choke off a major outlet for U.S. Agricultural exports. It would leave high and dry a chain of refineries and factories stretching from Baton Rouge to New Orleans that depend for their existence on the barges and the fresh water that the river wants to give to the Atchafalaya. It was, well, unthinkable. The Congress ordered the U.S. Army Corps of Engineers to go to war with the Mississippi. “We are fighting Mother Nature,” the Corps declared in a promotional film, “It’s a battle we have to fight day by day, year by year; the health of our economy depends on victory. Our opponent could cause the United States to lose nearly all her seaborne commerce, to lose her standing as first among trading nations.”

The result of this declaration of war was named, with typical Corps hubris, the Old River Control Structures. The Old River was a natural east-west channel that had opened between the Mississippi and Atchafalaya Rivers about 200 miles above New Orleans. By the 1950s, 30 per cent of the Mississippi’s flow was roaring down the steeper, lower Atchafalaya drainage, scouring it ever deeper, getting ready to switch its course entirely. The Corps’ war on water consisted of throwing a dam across the Old River, then building, 10 miles upstream, a 560-foot-long set of 11 floodgates across an artificial channel that henceforth would bend the Father of Waters to the will of the United States Congress. That body declared it illegal for the Mississippi to yield more than 30 per cent of its flow to the Atchafalaya. That is how much it gave up in 1950, and by law, for the Mississippi, it was to be forever 1950. The implementation of the law began in 1963, when the Control Structures took over. It was all part of the Corps of Engineers’ “Mississippi River and Tributaries Project” — the war to end all floods for all time from Cairo, Illinois, to New Orleans.

Ten quiet years followed, for which the Corps took a great deal of credit. Then came a most unquiet year, when a combination of heavy rains in the fall of 1972, heavy winter snow and repeated deluges in the spring of 1973 brought massive flooding. The Corps ran up the white flag and opened all the floodgates at Old River, and still, day after day, the Father of Waters hammered on the bars of its cell, shook the structure as if it were in a Magnitude 8 earthquake, threw nine-ton boulders at it and ate away at its massive foundations. If you stopped a car on top of the control structure (yes, there’s a road – Route 15 – across what you might call the bridge to San Luis Rey, Louisiana) and opened the car door, the vibration of the structure would slam it shut. One of the massive walls that gathered the flow of the Mississippi in to the floodgates collapsed. When the whole thing was a whisker away from total failure, the waters began to recede.

Afterward, the badly frightened engineers of the Corps wondered how close it had been. As John McPhee described one of the more riveting moments in the long history of man’s war on nature:
“As soon as the water began to recede they set about learning the dimensions of the damage. The structure was obviously undermined, but how much so, and where? What was solid, what was not? What was directly below the gates and the roadway? With a diamond drill, in a central position, they bored the first of many holes in the structure. When they had penetrated to basal levels, they lowered a television camera into the hole. They saw fish.”

The Corps propped the structure up, poured more concrete, set more pilings, built even more floodgates (the so-called auxiliary structure, deployed in 1986) and saw it withstand major flooding in 1983, 1993 and 1997. But the river will win this war, and will go to Morgan City, and bring down the Control Structures and with them the economy of the United States. As a study conducted by the Water Resources Research Institute, at Louisiana State University, concluded: “It could happen next year, during the next decade, or sometime in the next thirty or forty years. But the final outcome is simply a matter of time and it is only prudent to prepare for it.”

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