Field studies of borehole gamma-ray spectrometer methods for mineral exploration; a selected bibliography

A finite-difference digital model was developed to simulate the effects of a proposed well field on the water levels in existing wells in the Salt River Indian Reservation, which is in the southeastern part of Paradise Valley in central Arizona. The model area includes about 600 square miles in Paradise Valley and the adjoining Salt River Valley. In 1975 about 37,500 acre-feet of ground water was withdrawn for irrigation in the Salt River Indian Reservation. The proposed well field would withdraw as much as 45,000 acre-feet per year of additional irrigation water north of the Arizona Canal. The model was calibrated by using measured water-level declines for 1923-76 and simulated declines for 1946-75. The calibrated model was then used to predict water-level declines, based on projected amounts of pumpage, after 20 years of pumping. The rate of water-level decline would be an additional 2 to 6 feet per year in existing wells after 20 years of pumping in the proposed well field. The model was more sensitive to changes in pumpage distribution and in pumpage and recharge amounts than to changes in transmissivity and specific yield. (USGS)