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Show A C. IRRIGATION AND DEVELOPMENT, tt>WER BASIN. Asrused here the term "lower basin" indicates the portion of the Colorado Basin below Boulder Canyon, but excludes the Gila, the waters of which are not available for the development of the lower basin. The lower basin in its characteristics is entirely different from the upper basin. Its valleys are arid and nearly frostless, with irrigation necessary the year through. The mean annual temperature is 74° F., and the mean annual precipitation is 3 inches. Its soils are recent unconsolidated silts, mostly very fertile and easily eroded: Its transportation needs are well served by ihe Santa Fe and Southern Pacific railroads. , As a whole, also, reclamation of the lands of "the lower basin by irrigation must be accompanied by flood protection. For discussion, the lower basin conveniently divides into two parts: That above Laguna dam, the head of the Yuma project canal, and that below Laguna dam. ABOVE LAGUNA DAM. Below Black Canyon, which is a continuation of Boulder Canyon, the river leaves the plateau and canyon region, where it has flowed in the immense canyons which characterize its whole middle course. It then enters a region of irregular mountain chains and valleys which continues until Laguna dain is reached. Long, narrow valleys alternate with canyons. The irrigable lands which can be reached by gravity lie in the flood plains of the river, from which the generally rough and broken valley sides rise steeply to confining mountains or hills. The fall of the river below Boulder Canyon averages 1.75 feet per mile, so that it is not possible to reach by gravity any land other than that in the flood plains unless a high diversion dam is constructed, and such a diversion could be made only at immense cost. Throughout most of its course irrigable lands can not be reached by practicable pumping lifts, but at one place, the Chucawalla Valley and Palo Verde mesa, a lift of 230 feet will reach a considerable area of land. A part of these flood plains is subject to periodical overflow, for protection against which levees are required. 93715-S. Doc. 142, 67-2------5 47 |
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Original book: [State of Arizona, complainant v. State of California, Palo Verde Irrigation District, Coachella Valley County Water District, Metropolitan Water District of Southern California, City of Los Angeles, California, City of San Diego, California, and County of San Diego, California, defendants, United States of America, State of Nevada, State of New Mexico, State of Utah, interveners] : |