re: February 1987 New Yorker article on ORCS and the Miss/Atch Rivers

quote:

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Calculating maximum storms, frequency of storms, maximum snowmelts, sustained saturation of the upper valley, coincident storms in scattered parts of the watershed, the Corps reached for the figure that would float Noah. The round number was three million—that is, three million cubic feet per second coming past Old River. This was twenty-five per cent above the 1927 high. The expanded control system, with its variety of devices, would have to be designed to process that. Various names were given to this blue-moon superflow, this concatenation of recorded moments written in the future unknown. It was called the Design Flood. Alternatively, it was called the Project Flood.
Bonnet Carre was the first spillway—completed in 1931, roughly thirty miles upriver from New Orleans. The water was meant to Spill into Lake Pontchartrain and go on into the Gulf, dispersing eight and a half per cent of the Project Flood. Bonnet Carre (locally pronounced “Bonny Carey”) would replace dynamite in the defense of New Orleans. When the great crest of 1937 came down the river—setting an all-time record at Natchez—enough of the new improvements were in place to see it through in relative safety, with the final and supreme test presented at Bonnet Carre, where the gates were opened for the first time. At the high point, more than two hundred thousand feet per second were diverted into Lake Pontchartrain, and the flow that went on by New Orleans left the city low and dry.


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The Atchafalaya, continuing to grow, had become, by volume of discharge, the second-largest river in the United States. Compared with the Mississippi, it had a three-to-one advantage in slope. Around 1950, geologists predicted that by 1975 the shift would be unstoppable. The Mississippi River and Tributaries Project would be in large part invalidated, the entire levee system of southern Louisiana would have to be rebuilt, communities like Morgan City in the Atchafalaya Basin would be a good deal less preserved than Pompeii, and the new mouth of the Mississippi would be a hundred and twenty miles from the old. Old River Control was authorized in 1954.
The levees were raised again. What had been adequate in 1937 was problematical in the nineteen-fifties. New grades were set. New dollars were spent to meet the grades. So often compared with the Great Wall of China, the levees had more in common with the Maginot Line. Taken together, they were a retroactive redoubt, more than adequate to wage a bygone war but below the requirements of the war to come. The levee grades of the nineteen-fifties would prove inadequate in the nineteen-seventies. Every shopping center, every drainage improvement, every square foot of new pavement in nearly half the United States was accelerating runoff toward Louisiana. Streams were being channelized to drain swamps. Meanders were cut off to speed up flow. The valley’s natural storage capacities were everywhere reduced. As contributing factors grew, the river delivered more flood for less rain. The precipitation that produced the great flood of 1973 was only about twenty per cent above normal. Yet the crest at St. Louis was the highest ever recorded there. The flood proved that control of the Mississippi was as much a hope for the future as control of the Mississippi had ever been. The 1973 high water did not come close to being a Project Flood. It merely came close to wiping out the project.

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