The Central Valley covers about 20,000 square miles and is one of the most productive agricultural regions in the world. Because the valley is semi-arid, surface-water availability varies substantially. Agricultural demand for irrigation is heavily reliant on surface water and groundwater. In the last few decades, land-use changes and limitations to surface-water availability—including drought and environmental flows—have increased pumping, causing groundwater-level and groundwater-storage declines, renewed subsidence, decreased stream flows, and changes to ecosystems. As these recent trends continue, monitoring, data compilation, and modeling are critical to understanding the dynamics of groundwater use and developing management strategies. [...]
Summary
The Central Valley covers about 20,000 square miles and is one of the most productive agricultural regions in the world. Because the valley is semi-arid, surface-water availability varies substantially. Agricultural demand for irrigation is heavily reliant on surface water and groundwater. In the last few decades, land-use changes and limitations to surface-water availability—including drought and environmental flows—have increased pumping, causing groundwater-level and groundwater-storage declines, renewed subsidence, decreased stream flows, and changes to ecosystems. As these recent trends continue, monitoring, data compilation, and modeling are critical to understanding the dynamics of groundwater use and developing management strategies. The U.S. Geological Survey (USGS) developed the Central Valley hydrologic model (CVHM) to quantitatively assess aquifer-system responses to climatic variation, surface-water deliveries, and groundwater pumping. To simulate the recent groundwater levels and the spatial distribution, timing, and magnitudes of subsidence, the CVHM has been updated into a new version, referred to as CVHM2. The simulation code for CVHM2, MODFLOW-OWHM, has been enhanced to simulate the timing of subsidence more accurately by incorporating effects layers that delay deformation, changes in altitudes caused by subsidence, and separation of the inelastic and elastic portions of subsidence. CVHM2 includes several enhancements: adding water-banking data, simulating pumping with multi-aquifer wells and at actual wells for urban and domestic pumping, adding inflows from small watersheds, and including recent data to extend the simulation through 2019, and include additional observation data to calibrate CVHM2 to recent groundwater-level and subsidence data. CVHM2 provides a more up-to-date and detailed set of data and a tool to analyze changes in groundwater availability and subsidence. It can be used to assist decision-makers in making water management decisions necessary to achieve effective conjunctive use. This model is the updated version of the Central Valley model. The data release for the original model can be found at https://doi.org/10.5066/F79S1PX3.
Benefits to California Water Managers
The CVHM2 helps to address water competition issues such as:
Conjunctive water use (interdependent use of surface water and groundwater)
Conservation of agricultural land
Land-use change, including environmental concerns and urbanization, and its effects on water resources
Faunt, C.C.; Traum, J.A.; Boyce, S.E.; Seymour, W.A.; Jachens, E.R.; Brandt, J.T.; Sneed, M.; Bond, S.; Marcelli, M.F. Groundwater Sustainability and Land Subsidence in California’s Central Valley. Water 2024, 16, 1189. https://doi.org/10.3390/w16081189