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The Rio Grande is an interstate and international stream which begins in high mountains of Colorado, flows across New Mexico, and forms the boundary between Texas and Mexico. Precipitation ranges from 8 inches (20 em) to more than 30 inches (76 em), but irrigation is required for growing crops throughout the region. The population of the region has been increasing rapidly, from 750,000 in 1929 to 1, 700,000 in 1970, and it is expected to increase to 2,500,000 by 2020. The basic economy of the region was agricultural until recent years. Since 1950, the mining and petroleum industries have increased much more rapidly than agriculture. Annual precipitation on the region is about 86 million acre-feet (110,000 hm 3); however, all but 4 million acre-feet (4,900 hm 3) is returned to the atmosphere by evapotranspiration. The groundwater reservoirs contain an aggregate of 5,800 million acre-feet (7,200,000 hm 3) of fresh and slightly saline water in storage, which could be withdrawn through wells. In contrast, the surface reservoirs have a combined storage capacity of only 18 million acre-feet (22,000 hm 3). Thick deposits of valley fill in stream and intermontane valleys comprise the principal groundwater reservoirs. In most areas they are capable of yielding large supplies of water to wells. In some areas, limestone constitutes major aquifers. Withdrawal of ground water in the region in 1970 was 2.7 million acre-feet (3,300 hm 3), of which 88 percent was used for irrigation. About 53 percent of the water withdrawn was consumed. Ground water has been "mined" in some areas, and severe declines in water levels have resulted. The loss of water by evapotranspiration in wetlands and phreatophyte areas is 2.5 million acre-feet (3,100 hm 3) per year. In comparison, about 3. 7 million acre-feet (4,600 hm 3) per year of surface water and ground water is consumed by man's activities. Salvage of water lost to noneconomic evapotranspiration in wet and phreatophyte-infested areas offers the greatest possibility of improving the effective water supply in the region. Salvage of half the water lost would increase the effective supply by 1.2 million acre-feet (1,500 hm 3) per year. The usable water supply could be increased tremendously by drawing on the large reserve of ground water in storage, but this withdrawal could affect the flow of streams in some areas. The region appears to offer several possibilities for utilizing underground space for purposes other than the withdrawal of water, such as waste disposal, artificial recharge, water-quality control, and development of geothermal energy. Planners for groundwater management should have detailed information on the physical parameters that affect ground water, so improved management would be possible. D1 D2 SUMMARY APPRAISALS OF THE NATION'S GROUNDWATER RESOURCES management. Although ground water comprised 21 percent of the water used in the United States in 1970, planning for groundwater development has been limited to the municipal, water district, or private level, except for a fe...

The High Plains in Texas occupy an area of about 35,000 square miles extending from the northern boundary of the Panhandle southward about 300 miles, and from the New Mexico line eastward an average distance of about 120 miles to a boundary which in most places is sharply defined by a bold escarpment several hundred feet in height. The region is noted for its abundant supply of ground‐water, most of which is found in the Ogallala formation, a sandy deposit lying at or near the surface throughout most of the region, and reaching a depth of between 200 and 300 feet. The Ogallala formerly extended over a much greater area, but it has been removed by erosion from much of the territory it once occupied. The areas in which it remains are the High Plains, which are bounded by prominent escarpments both on the east and on the west, and are traversed in Texas by the Canadian River, which is deeply entrenched in the older rocks. The water‐bearing sands of the Ogallala in both segments are cut off in all directions from any underground connection, except through the underlying older rocks which contain highly mineralized water unlike the fresh water in the Ogallala. The source of the fresh water, therefore, is within the High Plains themselves, and is from the rain and snow that falls on the surface of the Plains.

Although ground water is generally available in most parts of Mitchell County, Tex., for stock and domestic use, wells of large yield have not been reported until recently. In the past, Colorado City has had considerable difficulty in obtaining enough water for public supply from ground water in the immediate vicinity of the city. Reports of irrigation wells yielding more than 1,000 gallons a minute in east-central Mitchell County, therefore, have attracted considerable interest, particularly as the water was discovered during a period of severe drought. This memorandum is based on a brief investigation made in May 1953. Pre vious investigations have been made in various parts of Mitchell County, particularly in the vicinity of Colorado City, but this investigation is concerned mainly with irrigation wells in the northeastern piart of the county. There are about 65 to 70 irrigation wells in Mitchell County Records were obtained for 48 of these wells, samples of water were taken from 21 wells for chemical analyses, and drillers' logs of 19 wells were Obtained, These data are recorded in tables at the end of this memorandum The irrigation wells range in depth from 115 to 315 feet but most of them are 150 to 200 feet deep. The groundwater reservoir is composed of sand and gravel beds of Triassic age. In most places aquifers are found at two different depths, the upper between depths of 20 and 50 feet, and the lower between 100 and 200 feet" Some of the water is obtained from alluvium. No large quantity of water has been found below 300 feet. The cost of irrigation wells has been relatively small because the cost of drilling is about $1.50 per foot and not much casing is required. Many wells have 20 to 50 feet of casing in them but some wells have no casing at alL It was not possible to measure static water levels in many of the wells because most of the wells had been pumping continuously for about 3 months. Static levels for a number of wells were measured in January 1953= It is reported that the static water levels in January, before pumping started, ranged from about 15 feet below the land surface in the northern part of the area to about 65 feet in the southern part. Most of the wells yield 200 to 250 gallons a minute, but the Granite 25

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