Geodetic Survey Data Used as Subsidence Observations for Model Calibration, Central Valley, California
Description
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 observations (measurements) using geodetic surveys during 1926–2021 by USGS, Bureau of Reclamation (Reclamation), California Department of Water Resources (DWR), National Geodetic Survey (NGS), and San Luis and Delta-Mendota Water Agency (SLDMWA). In the context of this report, subsidence is defined as the lowering of the land-surface elevation as a result of aquifer-system compaction and is calculated by differencing repeated measurements. While the model only goes through 2019, the 2021 data is included in this data release for completeness. For a more detailed description of geodetic survey methods, please see Poland and others (1975) and Sneed and others (2020).