Digital model of the Hollister Valley ground-water basin, San Benito County, California
A two-dimensional finite-difference digital model was constructed to simulate effects of proposed pumping and recharge schemes on water levels in the Hollister Valley ground-water basin. Pumping rates in the valley are expected to increase from 24,000 acre-feet per year in 1968 to an ultimate rate of 38,500 acre-feet per year. The model was calibrated for the period 1940-51 and tested by simulating water-level changes from 1951 to 1968. Model-generated water levels were generally within 15 feet of observed water levels for the calibration period. For the testing period, computed and observed water levels differed by as much as 35 feet in parts of the study area. Discrepancies in the test results may be caused by errors in historical pumpage data or by unidentified faults or local semiconfined conditions. Under one proposed development scheme, model-predicted water levels to the year 2020 declined up to 170 feet in previously undeveloped areas. For developed areas near the city of Hollister, water-level declines of 100 to 125 feet were predicted for the same period. (Woodard-USGS)