Satellite imaging to identify pathways for recharge of the confined aquifers in California's San Joaquin Valley

Groundwater overdraft has been occurring for decades in California’s San Joaquin Valley, an alluvial basin consisting of unconfined, semi-confined and confined aquifers. Excessive pumping of groundwater is exceeding the natural recharge of the aquifers; this is causing land subsidence which has a significant negative economic impact through infrastructure damage. A solution is to supplement natural recharge through managed aquifer recharge, which can be implemented by the spreading of water on the ground surface, or by the injection of water in wells. Because subsidence of the ground surface occurs primarily due to compaction in the confined aquifers, there is a need to prioritize recharge of the confined aquifers. This requires identifying locations where there are permeable pathways that can be accessed by recharge operations to reach the confined aquifers. Recent studies have shown that high resolution interferometric synthetic aperture radar (InSAR) data, when processed to extract seasonal deformation timing and amplitude information, reveal seasonal uplift patterns associated with natural recharge into the confined aquifers.  We find coherent signals in three regions in the InSAR data from the 2017, 2019 and 2023 water years which represent “wet years”, i.e. the years with high volumes of precipitation and surface runoff. For each of the three regions, we used an interpolated 3D sediment-type model derived from airborne electromagnetic data to identify the permeable pathways that enter the confined aquifer. In two of the regions, pathways to the confined aquifer exist at the margins of the Corcoran Clay, the major confining aquitard of the valley. In the third region, the Corcoran Clay is thin and intersected by pathways of coarse material. The ability to utilize satellite imaging to inform the design of recharge operations can contribute significantly to achieving sustainable groundwater management.