Rivers Remodeled

They needed a breakwater in Puerto Rico's San Juan harbor: what with the tides, currents and dangerous shoals, the water was so choppy that naval patrol planes could not always alight. The problem was tackled by the U.S. Waterways Experiment Station at Vicksburg, Miss.

Its staff built a small-scale model of San Juan harbor, sloshed & swished its waters until it reproduced the known behavior of the harbor. Then models of a breakwater were installed and maneuvered until they worked most efficiently. Modeled on this model, the actual breakwater is part of the $30,000,000 air and naval base completed this year. This week several other new Caribbean plane and warship bases, together with U.S. harbor and navy-yard improvements, dams and reservoirs for power production-in all, 34 wartime projects-are being analyzed at Vicksburg.

The Waterways Station was founded in 1929-inspired by the desolate 40 days & 40 nights in 1927 when the Mississippi drowned 20,000 square miles, drove 600,000 people from their homes, destroyed 4,000,000 acres of crops, took hundreds of lives. Congress voted $325,000,000 to tame the river, directed the U.S. Army Engineers to organize the Waterways Experiment Station. Engineers built a mighty model of the Lower Mississippi-nearly a quarter of a mile long, reproducing in detail every sand bar, tributary, levee and by-pass of the 16,000-square-mile area from Helena, Ark. to the Gulf.

By reshaping the model's channels this way & that, engineers have designed cutoffs which in the last ten years have straightened the Mississippi's most torturous meanderings and shortened the river by 120 miles. The flood menace has thereby abated. But much remains to be done, and the Mississippi model will be in operation for years to come.

No important hydraulic work is begun in the U.S. today without previous small-scale study at Vicksburg. The Waterways Station models now spread across more than 36 acres; through them it can pump 6,000 gallons a minute-enough water to supply a city the size of Springfield, Ohio. Waves are created by motor-driven triangular plungers, tides by valves controlled by a motor-driven cam, shaped like a polar graph of tidal fluctuation. Sand and gravel are simulated by crushed coal, silt by powdered gilsonite (a lightweight rock), beaches by fine sand. Dams and tunnels are often made of transparent pyralin to expose the waters within.

In the course of solving specific problems, the station's 150 engineers incidentally develop general hydraulic laws. Example: 19-ft. waves are more destructive to harbors than 24-ft. waves. Reason: the bigger waves break and dissipate their energy farther from shore.

The models often reveal that the original designs for river and harbor works are inadequate. For example, proposed works to eliminate shoals from Wilmington and Richmond harbors were found useless, and periodic dredging was recommended instead. Typical civilian projects, to be studied when military work ebbs:

P:Widening and deepening Atlantic City's Absecon Inlet-if it can be done without sending destructive currents along nearby resort beaches.

P:Preventing Gulf brine from seeping 100 miles up the Mississippi to New Orleans, where it is sucked into the city's water system.

P:Overpowering for good the three rivers* which converge menacingly on Johnstown, Pa., horribly deluged in 1889 and 1936.

Military work is also the chief present concern of the station's soil-mechanics laboratory, which was added in 1931 to study river silts and the shape, seepage and settling of levees and earthen dams. Soil engineers and chemists now study design of military airports, use of cemented soils for runways (TIME, Nov. 17). And a cell first designed to measure pressures within earthen dams is now used by the Army to record effects of explosions on experimental air-raid shelters.

*The Coneamaugh, Little Coneamaugh and Stony Creek Rivers.

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