Abstract
Large‐scale subsidence due to aquifer‐overdraft is an ongoing hazard in the San Joaquin Valley. Subsidence continues to cause damage to infrastructure and increases the risk of extensional fissures.Here, we use InSAR‐derived vertical land motion (VLM) to model the volumetric strain rate due to groundwater storage change during the 2007–2010 drought in the San Joaquin Valley, Central Valley, California. We then use this volumetric strain rate model to calculate surface tensile stress in order to predict regions that are at the highest risk for hazardous tensile surface fissures. We find a maximum volumetric strain rate of −232 microstrain/yr at a depth of 0 to 200 m in Tulare and Kings County, California. The highest risk of tensile fissure development occurs at the periphery of the largest subsiding zones, particularly in Tulare County and Merced County. Finally, we assume that subsidence is likely due to aquifer pressure change, which is calculated using groundwater level changes observed at 300 wells during this drought. We combine pressure data from selected wells with our volumetric strain maps to estimate the quasi‐static bulk modulus, K, a poroelastic parameter applicable when pressure change within the aquifer is inducing volumetric strain. This parameter is reflective of a slow deformation process and is one to two orders of magnitude lower than typical values for the bulk modulus found using seismic velocity data. The results of this study highlight the importance of large‐scale, high‐resolution VLM measurements in evaluating aquifer system dynamics, hazards associated with overdraft, and in estimating important poroelastic parameters.
Highlights
Groundwater is an essential resource for agriculturally productive regions across the world that suffer from low annual precipitation and limited surface water availability
We assume that subsidence is likely due to aquifer pressure change, which is calculated using groundwater level changes observed at 300 wells during this drought
Subsidence continues in the San Joaquin Valley due to the compaction of aquifer fine‐grained material
Summary
Groundwater is an essential resource for agriculturally productive regions across the world that suffer from low annual precipitation and limited surface water availability. The Central Valley in California holds the second largest underground aquifer in the United States, which delivers an essential proportion of the freshwater supply in central California The presence of this aquifer has supported extensive irrigation of cropland since the late 1800s, allowing it to become one of the most agriculturally productive regions in the United States (Faunt, 2009). Recent increases in groundwater withdrawal are linked to replacing seasonal crops with perennial crops and orchards, which are more profitable, and more water‐intensive (Borchers et al, 2014). This historic and modern groundwater use has caused a steady decline of water tables in the Central Valley, in the dryer San Joaquin Valley, located in the southern half of the Central Valley. Lowering of water tables has forced deeper well drilling, which is costly and more energy‐intensive (Perrone & Jasechko, 2019)
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