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Show through construction of numerous reservoirs in the headwaters of rivers draining from west Texas to the Gulf of Mexico for which larger main stem reservoirs have been planned. It would also in- clude provision for domestic water supply in the development of the Canadian River in the Ar- kansas Basin. This would provide another example of multi- ple-purpose development. West Texas munici- palities are ready to pay in full for such water supply as is used first to supplement the under- ground water supply for municipal and industrial purposes and then, after treatment, for irrigation. In the northern half of the region, the Mis- souri Basin development program will substan- tially relieve principal water supply deficiencies as well as reduce damage from floods and sedi- mentation. Similar help in the High Plains por- tion, from southern Nebraska into New Mexico and the Panhandle of Texas, will come from the full development of the Arkansas River Basin, including its tributary Canadian River. The main water management problem in the entire region involves making the best possible use of severely limited resources both in surface and ground waters with special emphasis on (a) hold- ing use within the limits of available supply, (b) preventing ground and surface water develop- ments from conflicting with each other, and (c) dealing with the threat of excessive sedimentation to the continued serviceability of water resources projects. The Western Mountain Region, extending from the foothills and frontal ranges of the Rocky Mountains to the Pacific coast, includes both the wettest and the driest areas in the Nation. Pre- cipitation varies from as much as 200 inches a year on the Olympic Peninsula in northwest Washington to 3 to 12 inches on desert areas of the Southwest. In this region precipitation occurs largely from the late autumn through spring but, except in the crest areas of the mountains, it is less than the potential evaporation. Except in the mountain ranges the yearly runoff is negligible. Broadly speaking, the region receives most of its runoff when the sun melts winter snow in the mountain areas, with great releases of water in spring in the South and in early summer in the North. This may generate damaging main stem floods in the Columbia River Basin. Foothill and mountain areas adjacent to the Pacific coast have winter-rain floods. The spring floods in the Colorado Basin are controlled by Hoover Dam and are damaging mainly to the extent that they bring down great loads of sediment. Many river valleys and intermountain basins throughout the region are of a geological struc- ture that provides important ground water reser- voirs. Those already developed produce more ground water than all the remainder of the Na- tion. Those in California and Arizona have been well developed and are, to a great extent, serving to hold a large portion of the water already used for irrigation and thus give it multiple use. For instance, in the Sacramento Valley alone the total underground reservoir storage capacity, between the depths of 20 and 200 feet, is esti- mated at about 34 million acre-feet. This is more than equivalent to the usable capacity behind Hoover Dam in Lake Mead. It compares with the somewhat more than 160 million acre-feet capacity of all man-made surface reservoirs in the United States. Similar valleys in the Great Basins of Utah and Nevada are relatively undeveloped. As already indicated, they offer considerable promise of in- creased supplies of water when water-wasting vegetation has been controlled. These basins, with their great ground water storage capacity, stand out as a bright spot in the Western water picture, and many of them can be developed successfully without interbasin or interstate complications. They raise, however, certain problems in the field of water resources policy for, in important instances, water stored in surface reservoirs for irrigation ultimately serves, in part, to recharge ground waters. Here again, and most clearly, the need for joint management of surface and ground waters is indicated. Because of the characteristic concentration of runoff from the mountains in the periods of win- ter rains and spring or early summer snow-melt, systems of surface storage reservoirs throughout the region are essential to full utilization of the 117 |