Economic and Social Impacts of Land Subsidence in the San Joaquin Valley, California
Abstract: Extensive groundwater withdrawal from the unconsolidated deposits in the San Joaquin Valley, California, caused widespread land subsidence during some periods since the 1920s. During 2015–22, annual subsidence rates locally exceeded 0.3 m at times, resulting in nearly 2 m of subsidence. Land subsidence has caused damage to structures including aqueducts, levees, dams, roads, bridges, pipelines, and well casings. Sociologically important and expensive damages and repairs include the loss of conveyance capacity in canals that deliver water or remove floodwaters; the realignment of canals as their constant gradient becomes variable; the raising of infrastructure such as canal check stations, levees, and dams; the releveling of furrowed fields; and the drilling of new wells. Costs from these damages during 1955–72 have been estimated at $1.3 billion (2013 dollars). Although few data are available to quantify total damages during 2015–22, repair of the Federally-owned Friant-Kern Canal to recover lost conveyance is estimated to cost $500 million alone. The impacts of subsidence to smaller water purveyors and the communities they serve are far worse because there are fewer available resources to mitigate such direct impacts. Indirect impacts of subsidence include increased severity of floods (area, depth, and duration) and long-term environmental effects (altered stream gradients, channel courses, water depths, and water temperatures). Improved understanding of the true economic and social impacts of land subsidence is needed for more informed decision-making by resource managers.
Biography: Michelle Sneed is a hydrologist with the U.S. Geological Survey. She spent 25 years leading land subsidence research in the California Water Science Center and now serves as the Technical Support Coordinator for Groundwater Science in the Office of Quality Assurance. She received her BS and MS degrees in geology from California State University, Sacramento, where she subsequently taught geology classes for 10 years. She has published many studies of land subsidence related to fluid-pressure changes in areas throughout California and other areas in the Western U.S., which often have a focus on subsidence impacts to water-conveyance infrastructure. She is a member of the UNESCO Land Subsidence International Initiative, the recognized leader in promoting global land subsidence studies.