Evaluation of a technique for simulating a compacting aquifer system in the Central Valley of California, USA

Large volumes of water have been pumped from the Central Valley aquifer system since the early 1900's. Water levels in the most heavily pumped areas had declined as much as 120 m by 1970. These large water-level declines resulted in approximately 21,000 hm3 of water released by inelastic compaction of numerous compressible fine-grained deposits. The principal technique used to evaluate the aquifer system was a three-dimensional computer program that solves the basic ground-water flow equation. The program was modified to incorporate water released by inelastic compaction of the fine-grained deposits by making storage a function of hydraulic head. The computer-simulated volume of water released from inelastic compaction for the period from 1961 through 1977 was 6 percent of the estimated volume. The technique could be used in other areas where water is released as a result of inelastic compaction of fine-grained deposits.