California drought may have pushed parts of the Sacramento Valley aquifer toward permanent collapse

Over time, heavy water extraction has contributed to changes in the aquifer systems under the San Joaquin and Sacramento valleys. Although some of these changes can be reversed, a new study, published in the Proceedings of the National Academy of Sciences, indicates that large parts of the Sacramento Valley may have undergone irreversible ground compaction during recent droughts, leading to a permanent loss of groundwater storage.

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Pumping water out of aquifers lowers underground water pressure, which can make the land surface sink in a process called land subsidence. Moderate sinking can be reversible when water returns because of the elasticity of underground pore spaces. However, intensive pumping can permanently and inelastically compress the sediments that hold water, resulting in a permanent reduction in water storage space. Land subsidence also results in visible sinking of the surface.

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Well measurements can show where water levels stand but can miss stress changes in other underground layers. The study authors say that space-based geodetic techniques, such as the Global Navigation Satellite Systems (GNSS) and Interferometric Synthetic Aperture Radar (InSAR), can enhance aquifer monitoring by enabling measurements of surface deformation with far better spatial coverage, decameter resolution and millimeter-level accuracy in annual depth changes.

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