Development and calibration of a two-dimensional digital model for the analysis of the ground-water flow system in the San Antonio Creek Valley, Santa Barbara County, California

A two-dimensional finite-difference model was used to simulate ground-water flow conditions in San Antonio Creek valley. The model was calibrated to simulate steady-state conditions as approximated by ground-water conditions in 1943 and transient conditions during the period 1944-77. The transmissivity of the aquifer and the vertical hydraulic conductivity of the confining bed underlying Barka Slough at the western edge of the basin were calibrated during the steady-stage simulation. Calibrated transmissivity values ranged from more than 20,000 feet squared per day along the axis of the valley to less than 100 feet squared per day along the perimeter. Net flux values (the difference between recharge and net discharge) along the San Antonio Creek channel were determined during the transient-state simulation by a least-squares calibration technique. Results of the calibration indicated that the net flux out of the system along the stream channel increased by about 4,030 acre-feet per year from 1943 to 1977. The model simulated that about 70 percent of the increase in net flux was derived from the reduction in ground-water discharge to Barka Slough and about 30 percent from water coming out of storage. (USGS)