Land subsidence in the Los Banos-Kettleman City area, California: Past andfuture occurrence

Land subsidence in the western San Joaquin Valley has been studied and moni tored for almost six decades. Especially in the 1950s and 1960s, land subsi dence 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 g roundwater withdrawal, following the importation of surface water to the Va lley in late 1960s. The land subsidence in the Valley potentially could be a serious issue if the existing surface water supplies cannot meet increasi ng water demands during future critical drought periods. In this respect, t his paper proposes a preliminary analysis to predict magnitudes of subsiden ce for the period 2000 to 2040, based on historical occurrences. In this st udy, extrapolation from earlier subsidence is based on: (1) knowledge of re cent post-drought records at extensometers, (2) assumption of a single time porosity scenario, and (3) the premise that pumpage from the confined aqui fer gradually will decrease as a result of progressive water quality degrad ation. Predicted magnitudes of land subsidence in the Los Banos-Kettleman C ity area are expected to be in the range 0.5 to 4.0 m for the next 4 to 5 d ecades under the scenario considered in this paper.