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Show Water Salvage River-bottom vegetation such as salt cedars, cottonwoods, willows, and baccharis consume enor- mous quantities of water. Studies of the areas above McMillan Reservoir on the Pecos River and in the Safford Valley of the Gila River, made in 1940 and 1941, showed that this vegetation may consume twice as much water as would cultivated crops. These invaders which thrive especially on sediment deposits and along stream channels where the waters are definitely saline, are continually spreading. Between Gochiti and San Marcial in 1947 there were more than 60,000 acres of this high-water-con- suming vegetation which were estimated to deplete the annual stream flow by 238,000 acre-feet. A similar growth on some 15,000 acres of the delta above McMillan Reservoir is estimated to use nearly 90,000 acre-feet of water annually. Smaller areas of this vegetation are established and are beginning to spread in the newer deltas above Alamogordo and Red Bluff Reservoirs on the Pecos River and above Caballo Reservoir on the Rio Grande. Other areas are found along the lower river. The floodway, an authorized part of the Middle Rio Grande Project, is expected to lower the ground water level in the area just above Elephant Butte Reservoir. This will decrease the amount of water available for transpiration by the native vegetation. This is expected to save about 60,000 acre-feet an- nually. A proposed bypass channel around the McMillan delta would reduce the recharge to this area, lower the water table, and save about 30,000 acre-feet. Various methods, both chemical and mechanical, for eradicating salt cedar growth are being tested by the Bureau of Reclamation and the Fish and Wildlife Service. More research is neces- sary to determine the most effective means of con- trol at least cost. These growths can be cleared out and regrowth controlled but the cost may be high. In the in- stances that have been studied it appears that the value of water that could be salvaged by replacing these plants with useful grasses would exceed the estimated cost of eradication and control. Overuse of the range has stimulated invasion of range land by mesquite and juniper. By overuse of range grasses, seedlings of these brushy plants were able to take over the range. Inferior range has resulted, but of even greater concern, these plants are also reducing the water supply. Their deep root system takes much more water from the soil than did native grasses, and their spreading crowns cause evaporation of much larger amounts of water than did the grasses. Weeds which replace grass on overgrazed range use much more water than does grass. The eradication of these useless plants and better range management would salvage some of the water now lost. Present information suggests that it is doubtful if any method other than livestock reduc- tion for a reasonable period would be economically feasible. Several shallow lakes have been created by sediment bars across river channels. Typical of these are Kaiser Lake above McMillan Reservoir and San Marcial Lake above Elephant Butte Reser- voir. Much water is lost through evaporation from these open water surfaces and by transpiration from aquatic plants. Draining these shallow lakes would further reduce the total water losses. Assuming that important areas of bottom land and range land can be cleared of most worthless plants and that open lakes and marshy areas are drained, an estimated annual saving of about 275,- 000 acre-feet of water is possible. Irrigation authorities agree that less than half the water available for irrigation is actually used by crops. Water diverted from streams is lost by seepage from main canals and laterals and by evap- oration and seepage from storage reservoirs. Vary- ing amounts of the water delivered to farms are lost because of inadequate preparation of land for irrigation, faulty lay-out of farm ditches, and poor management of the water. Irrigation efficiencies range from 80 down to 30 percent. Many ways are known for saving water lost be- tween the source and its use by crops, but their adoption in full may not be justified by values of salvaged water. The Department of Agriculture estimates, however, that if all practical improve- ments were made in canals and canal structures, operating procedures for distributing water in these systems, and land preparation and farm ditch lay- outs, and if proper use were made of water on farms, at least 25 percent of all the water now used for irri- gation in the Rio Grande Basin could be saved for other uses. Public Water Supply With very few exceptions all community water systems in the Colorado and New Mexico portions of the Rio Grande Basin use water from under- 911610-51- -22 307 |