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The Pumps Of New Orleans
Most of New Orleans is below sea level, and a good rainfall used to submerge it—until A. Baldwin Wood designed and installed a massive system of pumps to drain 20 million gallons a minute
Fall 1992 | Volume 8, Issue 2
From the outside the pumps are simply large metal drums with an axle running through the center. Water passes through metal screens and is pulled up huge intake pipes. Once the water enters the pump, it is screwed forward by the rotating turbine and released on the other side of the pump house. There it courses down cement spillways and continues down the canal toward the outfall stations. The pumps are driven by electric motors powered by a twenty-five-cycle AC system. They are virtually immortal. The original twelve-foot pumps were installed in 1915 and are essentially as good as new. The only time one has ever broken down was during the 1978 flood, when a car tire somehow got into the casing and snapped a blade. The water board has its own steam and gas turbines that generate up to 61,000 kilowatts for its pumping stations; another 18,000 kilowatts can also be converted from the local power company. In addition, some pumping stations have their own emergency generators above flood levels. They would slowly empty the city in the case of a complete inundation.
“To give you an idea of the amount of water moved by Wood’s screw pumps,” says Larry Bodet, a senior civil engineer at the water board, “understand that an average of fifty-eight inches of rain a year falls on the city of New Orleans. With a 35 percent retention rate that’s 8,418,358,475 cubic feet of water. Multiply that by seven and a half, and you get the number of gallons. Every drop of that must be lifted up over the levees and into the lake.”
The reason New Orleans has any flooding at all, he says, is that the city uses a “dry” drainage system. That means that there is nowhere for runoff to be stored temporarily until the pumps can get rid of it. A “wet” system—one with big canals or a swamp, for example—needs fewer pumps because city streets aren’t underwater and there is no urgency to drain the area. The cost of a pumping system that could get rid of water as fast as it fell—or poured through a levee breach —would be too high for New Orleans to afford. A catastrophic storm might cost $100 million in damage. It would be easier to absorb that cost every century or so than to improve a pumping and drainage system that is already worth $1.5 billion.
Down the hall from Bodet is Wesley Busby. Both men are thirty-year veterans of the water board. Busby has a photograph in his office (shown on page 42-43) of the inside of a fourteenfoot screw pump during construction. It looks big enough to gallop horses through four abreast. Secretaries are posed for the photograph inside the pump’s huge iron belly. One of them reaches down to hold the hand of a smiling A. Baldwin Wood.
“If we turned off all the pumps, this city would just go back to the swamps,” says Busby. “In the event the levees were topped during a hurricane, NOPSI [the city’s power company] would be out; even the water-board generators would be out. So we have two stations at flood elevations plus ten [feet] that would have to empty the city. Basically you’re looking at a saucer full of water.”
Fred Chattery has been with the Corps of Engineers since 1946. Photographs of levees and a map of the Mississippi Delta hang on his wall. The river itself, brown and swollen with spring rain, fills the view from his office window. The corps building sits directly on the levee at Carrollton Bend, and the official city flood gauge is visible down below in the muddy water (“our public relations gauge,” Chattery calls it). It has been raining hard since morning, and all over the city Wood’s screw pumps are going full bore.
“Floods are getting worse because the land is subsiding,” says Chattery. “That’s a characteristic of greater development. And there’s more storm run-off because it’s all concrete now. Those are areas where you could’ve hunted rabbits when I was a boy.”
What happened was that development upstream—in other words, development anywhere in the 41 percent of the contiguous United States that makes up the Mississippi River Basin—increased the flow of the river and reduced the amount of silt it carried. Silt builds wetlands, which absorb heavy river flow during times of flood. Today’s increased river flow deepens the channels, which then move water faster and consequently raise flood levels downstream. This process has been going on for the past hundred years.
“We have something called a project flood,” says Chattery. “It’s the largest hypothetical flood the system must be able to pass. That happens to be three million cubic feet per second at the latitude of Old River [the Louisiana-Mississippi line]. The flood of ‘27 was only 27 percent of that. The likelihood of a flood too big to handle is very remote. Besides, it wouldn’t invalidate the whole system; it would just cause some damage.”