Central Valley Hydrologic Model version 2 (CVHM2): Subsidence and Aquifer-System Compaction Data Used as Observations

The Central Valley, and particularly the San Joaquin Valley, has a long history of land subsidence caused by groundwater development. The extensive withdrawal of groundwater from the unconsolidated deposits of the San Joaquin Valley lowered groundwater levels and caused widespread land subsidence—reaching 9 meters by 1981. More than half of the thickness of the aquifer system is composed of fine-grained sediments, including clays, silts, and sandy or silty clays that are susceptible to compaction. In an effort to aid water managers in understanding how water moves through the aquifer system, predicting water-supply scenarios, and addressing issues related to water competition, the United States Geological Survey (USGS) developed a new hydrologic modeling tool, the Central Valley Hydrologic Model (CVHM; Faunt and others 2009). The data presented in this data release will be used to facilitate updates to the original CVHM and represent subsidence and aquifer-system compaction observations (measurements) using various methods during 1926–2021. While the model only goes through 2019, the 2021 data is included in this data release for completeness. In the context of this data release, subsidence is defined as the lowering of the land-surface elevation as a result of aquifer-system compaction and is calculated by differencing repeated elevation measurements derived from geodetic surveys, continuous GPS (CGPS), and Interferometric Synthetic Aperture Radar (InSAR) techniques. Aquifer-system compaction is measured using vertical borehole extensometers to monitor changes in the distance between the top of a cable or pipe that is anchored or placed at depth, and a reference point at or near land surface. For more detailed information on the methods discussed in this data release, please see Sneed and others, 2013; 2018).