National Geographic : 1960 Nov
In 1937 the work of the Engineers was put to the acid test. Floodwaters poured down the Mississippi. Authorities were ready to evacuate a million people if the levees broke. Cairo, trapped between the Ohio and the Mis sissippi Rivers, pumped water out of town as fast as it seeped through the levees. The river was three miles wide at Memphis and climbing into town. It was a near thing. In many places the water was levee high. Hodding Carter, editor of the Delta Democrat-Times, looked from his newspaper office window in Greenville to see Coast Guard cutters moored 20 feet above street level. But the levees held. Above New Orleans, the Bonnet Carre Spillway, completed only two years before, was opened, one gate at a time. Through it enough water spilled off to cover 1,250,000 acres 10 feet deep. This lowered the river level for more than a hundred miles, and New Orleans was safe. Engineers Anticipate Superfloods The Engineers were not satisfied. This had been a giant among the big floods. But sup pose there should be one still bigger? Plans were made to cope with it, should it ever come. One of the more ambitious projects was the Morganza Floodway, completed in 1954 to divert floodwaters from the Mississippi down the basin of the Atchafalaya to the Gulf. Today such floodways, reservoirs on tributary streams, cutoffs on the river, bank revetments, strengthened levees-all are insurance against possible superflood. A constant challenge to the Engineers is the maintenance of a channel 9 feet deep all the way to Minneapolis. Eventually they will deepen it to 12 feet. From Baton Rouge down, a channel at least 35 feet deep is main tained for ocean-going vessels. We rode one of the patrol boats, sounding to determine where dredging must be done. No deckhand stood on the bow, dropping a lead line. A Fathometer at the captain's elbow sent an impulse to the bottom, and the time it took to bounce back indicated the depth, which was recorded on a graph. Most modern towboats are equipped with Fathometers in the pilothouse to show the depth at the head of the tow. Otherwise, the captain blows a sounding signal on his whistle, and a deckhand runs out to the end of the tow to heave the lead in the time-honored way. But no longer does the leadsman call out in the colorful manner that gave Sam Clemens his pen name. 704 Lower Mississippi in miniature attracts visitors to the United States Army Engineer Waterways Experiment Station at Vicksburg. The model represents ten million acres. Feed ing controlled amounts of water into it, engi neers can simulate floods and study river im provements. White sticks serve as mileposts to gauge the river's speed. Hardware cloth lining the banks retards the water, as trees and brush do in nature. Largest hydraulic model in the world, near Jackson, Mississippi, experiments with flood control problems throughout the Mississippi's entire drainage basin-40 percent of the 48 States. Here, in a reproduction of the 1950 flood, engineers observe conditions at New Madrid, Missouri. Brass pegs on the river bottom provide resistance to flow, as eddies do. A gauge straddling the stream keeps a continuous record of its depth.