The Arkansas-White-Red Region, an area of265,000 square miles (6.86x1011 square metres), is characterized by diversity in geography, climate, and geology and, in turn, by diversity in water resources and water problems. The western semiarid part of the region is water deficient, that is, potential evapotranspiration exceeds precipitation. The eastern, humid part has a surplus. Water use in the region in 1970 averaged 10 billion gallons per day (438 cubic metres per second), of which more than 65 percent was ground water. The largest use of ground water was for irrigation of crops, mostly in the water-deficient areas of Texas, Oklahoma, Kansas, and Colorado. Because of its ready availability and widespread occurrence, ground water is used throughout the region to supply municipal and rural water needs. The most productive aquifers, capable of yielding more than 50 gallons per minute (0.0032 cubic metres per second) to individual wells, are alluvium, carbonate. rocks, gypsum, and sandstone. Fresh water in storage in aquifers in the region is estimated to be 2 billion acre-feet (2.5x1012 cubic metres). In addition, a large, unmeasured volume of saline water (containing more than 1,000 milligrams per litre of dissolved solids) underlies the fresh water at depths generally less than 500 feet (150 metres).
The flow of water in each aquifer depends upon the physical and hydrologic characteristics of the aquifer, the climate, and the relation to, and the character of, adjacent rocks and streams. These factors also determine the effect of water-supply development or other man-induced stresses on the flow and the quality of water in the aquifers. Analog and digital models of aquifers can be used to evaluate stresses on aquifers and thereby provide water managers and planners with efficient tools for planning the development and continued use of aquifers.
