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Open Access Publications from the University of California

WESTSIM: A GIS-based application of the integrated GW surface water model (IGSM) to the Western San Joaquin Basin for conjunctive use plannning and drainage prediction


As a result of water redistribution under the Central Valley Project Improvement Act (CVPIA), numerous and varied conjunctive use, land retirement, and water transfer proposals are likely to be generated by local, state, and federal agencies, each of which will have an impact on Reclamation's facility operations and water availability. In addition, reductions in surface water deliveries under the CVPIA are likely to result in increased local reliance on groundwater. If groundwater recharge fails to keep pace with groundwater withdrawal, this increase will be accompanied by groundwater level declines, water quality degradation, land subsidence, and possibly interruptions or reductions in Reclamation's ability to meet delivery requirements. Reclamation's legal and operational actions in the San Joaquin Valley, including contract renewals, depend on an assessment of the site-specific impact of proposed or anticipated water redistribution activities. Therefore, the purpose of this project is to produce an integrated west side groundwater and surface water model that can be used to assess water district-level impacts such as agricultural drainage, groundwater safe yield, and land subsidence, for proposed land retirement, conjunctive use, water transfers, and surface water delivery changes. The expected applications of the model include land retirement in the Delta Division and San Luis Unit. The west side of the San Joaquin Basin will be assessed with the use of the Integrated Groundwater and Surface Water Simulation Model (IGSM), a comprehensive tool with surface water component used to route water through river and canal channels; and a groundwater component used to evaluate flow processes in subsurface formations. In addition, IGSM has the capability to handle land subsidence induced by lowering of the water table. Because of its varied capabilities, this model has been chosen to evaluate surface water and groundwater interaction of the area, for purposes indicated ab

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