Prediction of optimal safe ground water yield and land subsidence in the Los Banos-Kettleman City area, California, using a calibrated numerical simulation model

Land subsidence caused by the excessive use of ground water resources has t raditionally caused serious and costly damage to the Los Banos-Kettlerman C ity area of California's San Joaquin Valley. Although the arrival of surfac e water from the Central Valley project has reduced subsidence in recent de cades, the growing instability of surface water supplies has refocused atte ntion on the future of land subsidence in the region. This paper uses integ rated numerical ground water and land subsidence models to simulate land su bsidence caused by ground water overdraft. The simulation model is calibrat ed using observed data from 1972 to 1998, and the responsiveness of the mod el to variations in subsidence parameters are analyzed through a sensitivit y analysis. A probable future drought scenario is used to evaluate the effe ct on land subsidence of three management alternatives over the next thirty years. The model reveals that maintaining present practices virtually elim inates unrecoverable land subsidence, but may not be a sustainable alternat ive because of a growing urban population to the south and concern over the ecological implications of water exportation from the north. The two other proposed management alternatives reduce the dependency on surface water by increasing ground water withdrawal. Land subsidence is confined to tolerab le levels in the more moderate of these proposals, while the more aggressiv e produces significant long-term subsidence. Finally, an optimization model is formulated to determine maximum ground water withdrawal from nine pumpi ng sub-basins without causing irrecoverable subsidence during the forecast period. The optimization model reveals that withdrawal can be increased in certain areas on the eastern side of the study area without causing signifi cant inelastic subsidence. (C) 2001 Elsevier Science B.V. All rights reserv ed.