Last year’s wet winter gave California Central Valley groundwater levels a major boost

California’s groundwater reservoirs got a major boost during last year’s record wet season, offering a glimmer of hope for the depleted underground aquifer’s that remain in a long-term deficit.

The 2023 water year, which was marked by above average rainfall and a concerted effort to recharge reservoirs, led to the addition of at least 4.1 million acre-feet of water underground, according to data released by the California Department of Water Resources.

That’s more than what Lake Oroville, the state’s second largest reservoir can hold — which is now 100% full. An acre-foot is the amount of water it takes to cover an acre with 1 foot of water and is generally enough to supply two California households for a year.

Much of that recharge took place in the San Joaquin Valley, where aquifers have been heavily taxed by pumping for agriculture. Glen and Colusa counties north of Sacramento saw major groundwater gains, as did Ventura and Santa Clara counties.

This groundwater boost was driven in part by deliberate efforts to recharge the state’s vast underground reservoirs, which accounts for about 40% of California’s total water supply and is relied on more heavily during periods of drought.

Most recharge is done by allowing water to pool on a piece of land, sometimes in specific recharge basins, and then slowly soak into the ground. Reduced groundwater pumping and enhanced conservation measures also played a role in stashing supplies underground.

RECHARGE BOOSTED BY LOCAL WATER AGENCIES

This latest groundwater data comes from water agencies, which were required to file reports with the state last month, and captures the last “water year” from Oct. 1 to Sept. 30.

The data is a product of the state’s Sustainable Groundwater Management Act, passed in 2014 as the state’s first effort to regulate groundwater. It requires local water agencies to manage their aquifers sustainable levels by 2040.

Local and regional water agencies such as the Westlands Water District, one of the state’s largest irrigation agencies that serves Fresno and Kings counties, last year bolstered new programs that encourage groundwater recharge.

Westlands spokesperson Elizabeth Jonasson said the agency recharged record amounts of water, nearly 162,000 acre-feet during the 2023 water year and around 200,000 acre-feet since then. She credited the programs’ success to the widespread availability of surface water.

The district received 100% of its requested water supplies from federal reservoirs in 2023, but so far will receive 40% this year.

“Groundwater recharge is hugely important because it allows us to capitalize on wet years and save it for dry years,” she said. “This past year showed us how much our growers are willing to step up and invest their own resources to capture as much water as possible for the sustainability of the aquifer.”