LAND SUBSIDENCE IN THE LOS BANOS–KETTLEMAN CITY AREA, CALIFORNIA: PAST AND FUTURE OCCURRENCE

Abstract

Land subsidence in the western San Joaquin Valley has been studied and monitored for almost six decades. Especially in the 1950s and 1960s, land subsidence had tremendous negative environmental and socioeconomic implications. The rate of land subsidence in the Los Banos–Kettleman City area, however, has decreased during the last three decades as a result of a decrease in groundwater withdrawal, following the importation of surface water to the Valley in late 1960s. The land subsidence in the Valley potentially could be a serious issue if the existing surface water supplies cannot meet increasing water demands during future critical drought periods. In this respect, this paper proposes a preliminary analysis to predict magnitudes of subsidence for the period 2000 to 2040, based on historical occurrences. In this study, extrapolation from earlier subsidence is based on: (1) knowledge of recent post-drought records at extensometers, (2) assumption of a single time porosity scenario, and (3) the premise that pumpage from the confined aquifer gradually will decrease as a result of progressive water quality degradation. Predicted magnitudes of land subsidence in the Los Banos–Kettleman City area are expected to be in the range 0.5 to 4.0 m for the next 4 to 5 decades under the scenario considered in this paper. [Key words: subsidence, groundwater extraction, aquitard, inelastic compaction, active porosity, Los Banos-Kettleman City, California.]