Are Flooded Fields and Orchards the Answer to California’s Groundwater Shortage?

It’s a good water year in California. As of early April, the snowpack in the Sierra Nevada mountains was 110 percent of average. Winter rain storms have filled reservoirs, creeks, streams and lakes. And as the mountain snow melts, more water will be added. 

For almond grower Christine Gemperle, it means that, for the second year in a row, she will open the gates of the irrigation canal next to her orchard located in the Turlock water district of California’s Central Valley and flood her property. As the water in the canal permeates the soil, it will travel deep below the surface, recharging depleted groundwater reserves. 

The groundwater versus surface water distinction is important, especially for dry regions such as the Golden State. Surface water is just what it sounds like: water available from the Earth’s surface, in rivers, lakes and streams. Groundwater, conversely, is water held underground in rock or soil aquifers. The only way to access it is through digging wells or pumps underground—but digging too many wells can have negative consequences, including altering the Earth’s spin. 

Gemperle Orchards recharging underground aquifers. Photography via California Almond Board.

During normal years, groundwater accounts for almost 40 percent of California’s water supply. In dry years, this grows to 60 per cent. California’s groundwater reservoirs are able to hold 850 million acre-feet of water, compared to the state’s 50 million acre-feet of surface water capacity. However, there is still a deficit most years, with 1.8 million acre-feet of groundwater pumped out annually that isn’t replenished. 

A 2020 report by the Public Policy Institute of California paints a dire picture. Between 1988 and 2017, the region’s annual groundwater overdraft was almost two million acre-feet. The deficit is largely attributed to agricultural water use. The report suggests that at least a quarter of the overdraft could be mitigated with expanded groundwater recharge efforts and managing demand. California’s Sustainable Groundwater Management Act (SGMA) was enacted in 2014 to do just that, and it requires local agencies to have the infrastructure in place by 2042 to limit further depletion of the resource.

There has been some progress. Westlands Water District covers more than 1,000 square miles of agricultural land in the San Joaquin Valley. In the year leading up to this past February, it had recharged 380,000 acre-feet of surface water back into the district’s aquifers. “Hats off to district farmers for their commitment and contributions to this significant achievement,” said Allison Febbo, the district’s general manager, in a press release. 

But wide-scale restructuring takes time, and droughts that deplete surface water resources are frequent. Between 2020 and 2022, California experienced the driest years in more than 126 years. So much groundwater is pumped by farmers trying to keep their crops alive during drought years that thousands of wells have gone dry.

“During the last drought, my neighbour’s well went dry because we were all pumping to keep our crops alive,” says Gemperle. 

In a good water year, Gemperle may be allotted 48 inches of surface water to irrigate her almond trees. In drier years, this can fall to 24 inches. It makes groundwater reserves and on-farm recharge even more critical for growers looking to make up for the lack of available surface water.

Helen Dahlke heads a research group at the University of California, Davis that studies surface and groundwater use. “We are telling growers if they have suitable soils that are coarse or porous, this would be a good location to recharge,” she says.

Dahlke recommends flooding fields during dormant periods of growth—and preferably with perennial crops such as almonds or grapes. Flooding during dormancy, when less water is being used by the plant, allows for the water to seep through the underlying soil layers quickly with little adverse effect on crops. 

Jesse Roseman, an analyst with the Almond Board of California, says that surveys done by the board indicate that 11 percent of California almond growers are now so convinced in the value of groundwater recharge that they are regularly flooding their fields, filling up farm recharge ponds or re-directing water to unlined irrigation canals where it will seep into the ground. 

For Dahlke, this is only the beginning of what’s possible. “There are eight million acres of irrigated farmland in California that could be utilized for on-farm groundwater recharge,” she says. 

But as great as it sounds, Mother Nature is still in charge. “We did a study on the availability of surface water for recharge,” says Dahlke. “Wet years, particularly in the San Joaquin Valley, only occur every four to five, maybe seven years.” For growers such as Gemperle, there are also bureaucratic kinks to be worked out.

“Even though I put all that water in the ground, none of it is mine,” she says. It will be administered by the district, and she may never see a drop of it. She points out that it’s a lot of work for a grower to open the irrigation gates and go out in stormy weather to monitor the process, not to mention the money spent to maintain the equipment needed to transport the water. 

Christine Gemperle. Photography via California Almond Board.

“The biggest benefit to growers is when there is an incentive,” says Joe Choperena, with Sustainable Conservation, a non-profit organization promoting stewardship of California’s land, air and water. He cites the example of the Tulare Irrigation District, where growers who help to recharge groundwater can be granted permission to pump more water than their neighbors.

Last fall, Bill SB 659, co-sponsored by the California Association of Winegrape Growers, directed the California Department of Water Resources to identify immediate recommendations that could increase the state’s groundwater supply, including better methods to capture stormwater run-off. In February, the California state governor’s office published a list of how it is addressing the need for improved groundwater capacity in 2024. The state has distributed nearly $1 billion to support recharge and other stormwater capture projects that will add more than 28 billion gallons to the state’s water supplies every year. 

Every drop of water in California matters, and this past winter, Gemperle added 30 acre-feet of the precious resource to recharge groundwater reserves. 

“The water went down even faster this year,” she says.