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Irrigation development in Box Butte County, an area of 1,067 square miles on a plain in northwestern Nebraska began about 40 years ago. Since then, pumpage of ground water has caused a steady decline of water levels in the High Plains aquifer system underlying the east-central part of the County. Comparison of maps of the potentiometric surfaces of the aquifer system in 1938 and 1980 indicates that water levels declined by more than 10 feet in an area of 336 square miles and by more than 30 feet in an area of 17 square miles. Quantitative studies of field data for the aquifer system indicate that hydraulic conductivity ranges from 6 to 60 feet per day and exceeds 25 feet per day in 21 percent of the County; specific yield ranges from 12 to 21 percent and averages about 15 percent; saturated thickness varied in 1938 from 190 to 510 feet and averaged about 342 feet. Recharge to the aquifer system, which comes mainly from precipitation averaging 17.1 inches annually, varied from 0.06 to 4.33 inches annually and averaged about 1.6 inches. The estimated volume of water stored in the aquifer system in 1980 is 80.3 million acre-feet; of water recoverable in 1980, 34.4 million acre-feet; and of water pumped in 1980, 104,000 acre-feet. Results of digital flow model simulation indicate that by 1992 the area of water-level decline of 10 feet or more will increase from 336 square miles (1981) to 630 square miles (1992), and that the area of decline of 30 feet or more will increase from 17 square miles (1981) to 240 square miles (1992) if pumpage continues to increase at the maximum annual rate recorded from 1938 through 1981. However, if pumpage is held to the 1981 rate, the area of decline of 10 feet or more will increase from 336 square miles (1981) to 530 square miles (1992). The maximum projected declines in water levels for the period 1981 to 1992 are 29 feet if pumpage is continually increased at the maximum annual rate recorded and 13 feet if pumpage is not increased beyond 1981.

Hydrologic analysis of the High Plains aquifer system in Box Butte County, Nebraska