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Show Weather Men Tell Army How Big Dams Must Be The "biggest rain" that might fall on a river or creek watershed is one of the things that engineers need to know in building a dam for flood control. This hypothetical rain must be at maximum intensity and duration. The run-off from such a rain determines the . size of the dam and more especially the size of the spillway. Huge losses may be avoided if the dam and spillway are big enough to withstand any flood that may. develop. Huge savings sav-ings result when construction does not exceed needs for which the dam is built. Rainfall records and hydromete-orological hydromete-orological specialists of the United States weather bureau provide the corps of engineers, United States army, with essential information on possible maximum precipitations in a number of watersheds or basins where flood-control projects are under un-der way. The figures turned over to the engineers by the river and flood division of the weather bureau, represent the maximum in rain intensity and duration that may be expected. The biggest rain that may be expected would equal any big rains that have fallen, or might fall, on the river basin in question. The Arkansas river basin above Caddoa, Colo., where a dam is to be built, is a good example. In checking its records, the weather bureau bu-reau considered all big rains in that part of the United States and determined de-termined whether or not they might have fallen on the upper Arkansas watershed. The probability of a bigger big-ger rain than the hypothetical rain is a virtual impossibility, says the weather bureau. The weather bureau has figures on the maximum rainfall for other such watersheds. Among them, the Arkansas river basin above Caddoa, Colo., the St. Francis river above Wapapello, Mo., the White river above the Mud Mountain dam3ite in Washington, Wolf creek above Fort Supply in Oklahoma, and Mill creek in Cincinnati. It is planned to make a similar study of all principal prin-cipal river basins in the country. |