Page 4

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Title
Page 4
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Colorado River problem
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http://digital.library.unlv.edu/u?/dig,8
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308 THE COLORADO RIVER PROBLEM to use all the water available and that all the power that can be developed in the main section of the river will be needed. The plan of development, therefore, should provide that: 1.—Losses from evaporation should be kept to a minimum. 2.—All available head should be used for power. 3.—Storage for regulation of flow should be located above the Canyon Section so that the equated flow can be used through the greatest practicable head. 4.—Storage in and below the Canyon Section should be limited to that necessary for re-regulation of flow for irrigation in the Lower Basin plus such quantity as is essential for immediate flood relief of existing developments in the Lower Basin. Failure to conform to this provision will mean ultimate duplication of storage capacity and consequent curtailment of irrigation due to unnecessary evaporation losses. There are reservoir sites in the Upper Basin of sufficient capacity to provide regulation of flow. The first cost of such reservoirs per acre-foot of storage will be more than that for sites in the lower Canyon Section, but they will be worth as much for irrigation, three times as much for power, and, on account of regulated flow, will make possible material savings in cost of power dams built below them. Moreover, they can be developed successively as needed so that if interest on investment is considered, their ultimate cost may not be much greater, even on an acre-foot basis. Present developments in the Lower Basin are subject to damage by floods. The development of storage in interest of power will relieve the flood menace in part. Full protection, in so far as it can be obtained by storage, requires that the storage capacity be available at the beginning of each flood season. Storage for power on the other hand should be operated to keep reservoirs as full as practicable at all times. The United States Bureau of Reclamation estimates that ultimately 4,000,000 acre-ft. will suffice for flood protection. As will be shown hereafter, 4,000,000 acre-ft. is all that is justified at present. Flood storage to afford the greatest benefit should be as far down stream as practicable. Flood Protection The Lower Basin is menaced by floods from both the Gila and the Colorado Rivers. The Gila floods are produced by winter rains and generally occur between November 30 and March 1. They reach a maximum flow of about 200,000 sec-ft. (approximately the flow over Niagara Falls). They are extremely flashy and, therefore, produce higher flood stages and greater velocities than the more deliberate floods of the Colorado. As long as the Gila remains uncontrolled, it will determine the height to which levees must be maintained at and below Yuma. There is general agreement that, although the Gila, until controlled, will require maintenance of levees at present heights, it will never seriously inundate the Imperial Valley, because it discharges no water for a large part of the year. There are several irrigation and power projects under consideration,

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