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Show Recently the Upper Colorado River Basin Com- pact was approved under which the States involved can use their allotted portion of the Colorado River water within their States. It is possible that water can be diverted from the Colorado River into the Rio Grande Basin for use in Colorado and New Mexico since parts of both these States lie in both river basins. Conclusions While much coordinated planning has already been done, expanded cooperation of Federal, State, and local agencies for all aspects of water resources development is essential. A program of water resources and related land use should continue to recognize, as heretofore, the division of water be- tween States and other water use limitations im- posed by established water rights and compacts. 2. Extent and Nature of Programs Treating Irri- gated and Other Croplands, and Associated Sediment Problems The Problem The extent to which proper land use and im- proved irrigation practices may contribute to the conservation of limited water supplies and reduc- tion of sedimentation, and the extent to which such measures may be considered for complete water and related resources development of the basin. The Situation Water for irrigation is derived from both stream flow and ground water, principally the former. All of the water supplies have been appropriated and overdraft of the underground supply is occur- ring in the Pecos Valley. The problem of water shortage and the use of water on farmlands is so closely related to the problems of land treatment that they must be considered together. Croplands under irrigation in this semiarid region must be managed and protected to promote most efficient use of all available water supplies. The use of irrigation water and the installation of facil- ities must be directed toward methods that will not only prevent waste and loss of water but will also prevent destruction and loss of soil fertility. The land treatment problems for irrigated lands are serious and acute. Shortage of water, poor dis- tribution systems, improper use of irrigation water, inadequate drainage, and the sedimentation of existing reservoirs, river channels, and irrigation systems demand serious attention. Many irrigation systems need general overhauling; they need better location of distribution canals, land leveling, instal- lation of adequate headgates, canal structures, measuring weirs, and overnight storage ponds. Many ditches need to be lined and fields leveled to get efficient use of irrigation water. Productivity of many areas has been seriously reduced by exces- sive leaching of soil minerals from overirrigation, and by waterlogging and accumulation of alkali. Estimates for the 17 Western States indicate that water losses between points of diversion and fields under present practices average 38 percent; losses in the Rio Grande Basin exceed this average. This low water conveyance efficiency is caused largely by heavy seepage losses from unlined canals in highly permeable earth materials. Low water application efficiencies occur where farmers use obsolete irrigation systems, attempt to irrigate rough irregular land surfaces, and apply excessive amounts of water during the periods of heavy runoff. Studies show that average loam soil may retain from 1.0 to 1.5 inches of irrigation water per foot depth of soil. To obtain efficient use of irrigation water detailed information on type and depth of soil, permeability, and crop requirements is essential for each tract of land. This seepage and excessive use of water not only reduces water available for irrigation but also renders worthless, in many instances, productive irrigated land. Sediment depositions in the Rio Grande River Channel above the Elephant Butte Dam have de- stroyed or seriously impaired large areas of irrigated lands. Records indicate that in 1880,125,000 acres were under irrigation in the middle Rio Grande Valley below Cochiti and above the Elephant Butte Reservoir. By 1924, channel silting and water logging, together with water shortage and water dissipation, had reduced this to approximately 40,- 000 acres. During the late 1930's, drainage and flood protection structures reclaimed about 50,000 acres. The river bed near the abandoned town of San Marcial is between 15 and 17 feet higher than it was in 1880. Salt cedars and other nonbeneficial plants which have become established in the areas above McMillan Reservoir in the Pecos Basin and through the middle Rio Grande Valley above Ele- phant Butte Reservoir are estimated to consume between 300,000 and 400,000 acre-feet annually. These infestations are still spreading. In the lower Pecos River Valley, particularly in the Roswell artesian area, many irrigation wells 325 |
