Mojave Groundwater Resources
Mojave Land-Subsidence Studies
In cooperation with the Mojave Water Agency (MWA), the U.S. Geological Survey (USGS) has documented localized land subsidence in the Mojave River and Morongo groundwater basins in the southwestern Mojave Desert of California for various periods since 1944. The land subsidence is caused by the compaction of clay layers within the aquifer system in response to groundwater-level declines. Differential land subsidence (subsidence occurring at different rates across the landscape) can alter surface drainage routes, cause ground failures including fissures, and damage surface and subsurface infrastructure (Holzer and Pampeyan, 1981). An explanation of the mechanics of land subsidence caused by aquifer-system compaction is available here.
Land subsidence in the Mojave River and Morongo groundwater basins was first characterized by comparing Global Positioning System (GPS) survey results from 1998 with historical elevation data (from topographic maps or leveling surveys) at selected benchmarks, some with data as early as 1944 (Sneed and others, 2003). More recently, Interferometric Synthetic Aperture Radar (InSAR) methods were utilized to determine elevation changes beginning in 1992, when InSAR data were first collected for this area. Although repeated leveling surveys can measure land subsidence with greater vertical accuracy than InSAR, the spatial and temporal distributions of measurements are sparse. Analyses of the spatially detailed (high resolution) maps generated from the InSAR data have enabled researchers to detect five localized areas of subsidence and are the most efficient means to characterize the location, extent, timing, and magnitude of subsidence throughout the nearly 5,000 square-mile MWA management area.
Five USGS reports document land-subsidence analyses in the MWA management area. The first three reports describe land subsidence and groundwater levels for the periods 1944–99 (Sneed and others, 2003), 1999–2004 (Stamos and others, 2007), and 2004–09 (Solt and Sneed, 2014). The results from the latter two reports were integrated with results from other USGS/MWA cooperative groundwater studies into the broader scoped USGS Mojave Groundwater Resources Website, which includes an interactive map. The fourth report combines groundwater level data and InSAR derived subsidence for 1992–2009 with lithology from the three previous subsidence reports and distills the data and analyses into a longer-term context (Brandt and Sneed, 2017). The fifth report describes subsidence and groundwater levels from 2014 to 2019 and combines the results with previous analyses to generate a nearly 30-year examination of groundwater levels and InSAR-measured land subsidence (Brandt and Sneed, 2021).