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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
Wood’s pumps go a long way toward keeping New Orleans dry, but they are inseparable from a levee system that encircles the city. The pumps get rid of rain that falls on the city; the levees keep the river’s waters out. Levees are huge earthen walls that confine a river to its channel and keep it off the settled floodplains on either side; the Mississippi has levees stretching all the way to Cairo, Illinois, where the Ohio joins it. Levees are helpful in controlling routine flooding, but during times of particularly heavy flow they can actually make matters worse. When a river can’t overflow onto its floodplains, it has no choice but to rise higher and move faster, endangering people downstream. That was never so clearly demonstrated as during the spring of 1927, when one of the greatest floods in United States history began making its way down the Mississippi.
Engineers knew it was going to be a bad one that year because the spring rises on the major tributaries—the Missouri, the Ohio, and the Arkansas —had all coincided. River gauges up and down the Mississippi Valley were setting records. On April 15 more than fourteen inches of rain fell on New Orleans, a deluge of almost biblical proportions. Three days later the river gauge in Cairo reached 56.2 feet, the highest reading ever. The levees were sure to break somewhere along the river, but the question was where. Disaster for one town meant lower water levels and less danger elsewhere. Armed guards patrolled the riverbanks to make sure that no one settled the question with a stick of dynamite. Finally, on April 21, crevasses (levee breaches) occurred at Mound Landing, Mississippi, and Pendleton, Arkansas. The next day the main levee failed in Greenville, Mississippi, and a wall of brown water twenty feet high swept through the fields.
Flooding continued for weeks throughout the Mississippi Valley. In the end several hundred people were killed, and almost 700,000 were left homeless. Damage was at least a billion dollars in today’s terms. “The Flood of ‘27 was of such devastation that it awakened the realization local agencies couldn’t handle it,” says Fred Chattery, chief engineer for the New Orleans branch of the U.S. Army Corps of Engineers, which runs the system of levees along the Mississippi. “It cried out for a total solution.”
The solution was the Flood Control Act, which Congress passed the following year. Up until then the belief had been that safety lay in building bigger and bigger earthworks to protect the settled floodplains of the river. That approach traded minor yearly flooding for rare, unpredictable disasters. When a main-line levee breaks, it unleashes a destructive force that a river could never achieve on its own. As Maj. Gen. Lytle Brown wrote at the time of the 1927 flood, “The cost of a levee increases more rapidly than the square of its height, and the destructiveness of the crevasse increases in like proportion.”
The flood-control plan included new levees and similar structures, with measures to make them more effective; cutoffs of several loops in the meandering river to shorten it by 150 miles, making drainage that much faster; and construction of the Bonnet Carré Spillway, which can drain 10 percent of the expected floodwaters away from New Orleans to Lake Pontchartrain. (The Bonnet Carré has since been supplemented upriver by the Morganza, West Atchafalaya, and Bohemia floodways, all of which route floodwaters past major population centers. In all, less than a third of the expected floodwaters now go past New Orleans down the original Mississippi River.)
Because engineers have been so successful in controlling the flow of the Mississippi, pumps are not needed to save the city from river-borne catastrophe. Rather, they are most valuable in the day-to-day task of draining what is in effect a huge catch-basin. Today there are twentyone pumping stations in New Orleans, with a combined pumping capacity of 47,000 cubic feet of water per second. Their combined force would propel a ten-foot column of water a mile and a half in the air. Storm run-off collects in canals under the city streets and is moved by a set of pumping stations to the edges of Lake Pontchartrain and Lake Borgne, to the north of the city. There a different set of pumping stations takes over and lifts the runoff over the twenty-five-foot levees. Both lakes are saltwater and eventually drain into the Gulf of Mexico. The Mississippi runs along the southern edge of the city, but it isn’t practical as a way of getting rid of storm run-off because its flood levels are much higher than those on the lakes.
Station 6 is the biggest pumping station in the city, and until recently it was the biggest in the world. It could fill the Superdome in two and a half hours. It pushes water north along the Métairie Relief Outfall Canal to Station 12, where it is lifted into the lake. Ordinarily Station 6 has a staff of four, but during emergencies up to thirty people may be swarming over the facility. The first-floor windows of the station are bricked in to keep out floodwaters. Inside, everything is big: control dials the size of wall clocks, machine bolts bigger than your fist. At full power the pumps sound like jet airplanes taking off.