The state of groundwater recharge in the San Joaquin Valley – from the Public Policy Institute of California (PPIC)

By Ellen Hanak

When strong winter rains finally ended the recent five-year drought, many water districts seized the opportunity to recharge depleted aquifers. How did they do, and what barriers did they face? A public forum brought more than 30 experts together to discuss the benefits, opportunities, and barriers to groundwater recharge. The event was hosted by the California State Board of Food and Agriculture and the state Department of Water Resources.

My presentation focused on recharge in the San Joaquin Valley—a region that is home to more than four million people, half the state’s agricultural output, and most of its critically overdrafted groundwater basins, where pumping exceeds replenishment. Consequences include dry wells, sinking lands, and reduced supplies to weather future droughts.

As part of our ongoing work to explore practical and effective solutions to the region’s water challenges, the PPIC Water Policy Center recently surveyed local water districts about their groundwater recharge efforts. Although such efforts have been underway for decades in some parts of the valley, the state’s 2014 groundwater law has increased interest in using recharge to bring basins into long-term balance.

About 75% of respondents to our survey said they were actively recharging this year. Large water districts with formal recharge programs are doing the lion’s share of recharge, but there’s lots of interest from smaller agencies in getting in on the act.

Agricultural districts are already employing a broad mix of recharge tools, and many see potential for expansion. In contrast, urban districts—most of which rely heavily on groundwater—are much less active. The most widespread methods—used by two-thirds of agricultural districts surveyed—include allowing water to seep through unlined canals and irrigating crops with surface water instead of groundwater, which enables basins to recharge naturally (a method known as “in-lieu” recharge). Other popular options—used by half of agricultural districts—include directing water to dedicated “recharge basins” and applying extra water on irrigated cropland. Some districts also spread water on fallowed land and open space. Of these tools, recharge basins are being used most intensively, storing more than half of total recharge reported (roughly four maf). One caveat to this last finding is that many districts have been using some popular methods (cropland irrigation, in-lieu recharge, and unlined canals) without formally accounting for how much recharge occurs.

 

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