By the time California finally began regulating groundwater use in 2014, most of the San Joaquin Valley was in critical overdraft. The Public Policy Institute of California estimates that groundwater pumping in the region has exceeded replenishment by an average of 1.8 million acre-feet per year over the last few decades. This imbalance was even worse during our last drought, when overuse shot up to 2.4 million acre-feet per year.
Overpumping puts groundwater aquifers at risk of compaction, permanently reducing their water storage capacity and making surface lands sink. Now, however, San Joaquin Valley groundwater managers must find and implement a fix. The state’s Sustainable Groundwater Management Act mandates balancing the region’s pumping with replenishment by 2040.
Managed aquifer recharge — diverting excess flood water so it can soak into the ground — is an obvious remedy. But accelerating recharge in the San Joaquin Valley is easier said than done. “Recharge is slow in silt and clay, and these are ubiquitous across the Central Valley,” explains Graham Fogg, an emeritus hydrogeologist at UC Davis.
Fogg and colleagues have found a new way to speed recharge in the Central Valley: ancient river channels where water can shoot underground.
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