Almond orchard flooding in Modesto, California conducted for EESA's groundwater recharge demonstration project.

Almond orchard flooding conducted for the groundwater recharge demonstration project in Modesto, California. (Photo credit: Craig Ulrich/Berkeley Lab)

Groundwater—the water stored underneath the Earth’s surface between the cracks and spaces in soil, sand, and bedrock—is essential for the California residents and farmers who rely on it for up to 46 percent of their annual water use. Yet during the 2012-2017 drought, the state’s surface water supply was not sufficient to meet demand, resulting in excess groundwater pumping that caused land subsidence of up to 13 inches in some parts of the San Joaquin Valley.

Now a team of scientists at Berkeley Lab’s Earth & Environmental Sciences Area (EESA) is working with farmers and partners like the Almond Board of California and UC Davis to test on-farm banking, a new approach that has the potential to manage groundwater more sustainably. It’s an improvement on the age-old method of groundwater recharge, the process of replenishing aquifers by infiltrating water from the surface into shallow aquifers.

“On-farm banking has the promise of making the most productive use of the greatest amount of land possible while increasing the reliability and resiliency of California’s groundwater supply,” says EESA scientist Peter Nico, a soil and environmental biogeochemist.

Traditionally, groundwater recharge approaches mostly used either active injection through wells or dedicated infiltration ponds. But during dry periods, this land sits dormant. In contrast, on-farm banking “banks” groundwater by spreading excess surface water on flood-resistant crops, like wine grapes or almonds, during times of heavy rainfall.

“Due to the five-year drought, most places in California were overdrafting their groundwater,” said Nico, who heads EESA’s Resilient Energy, Water and Infrastructure program, and leads the Area’s collaboration with the Almond Board and UC Davis. “But by using a strategy like on-farm banking, you can potentially decrease the amount of overdrafting by replenishing groundwater more during wet periods.”

The drive to develop new approaches for groundwater management has been prompted by 2014 California legislation that aims to avoid depleting it through required regulation. The Sustainable Groundwater Management Act (SGMA) stipulates the creation of Groundwater Sustainability Agencies (GSAs). In turn, each GSA has to develop a plan to manage groundwater sustainably. Though SGMA will not be fully enacted until 2040, sustainability plans must be completed by 2020.

“There’s a rush to develop these plans,” Nico says. “And many groups are interested in figuring out how to recharge more groundwater.”

Data collection during almond orchard flooding in Delhi, California.

Data collection during almond orchard flooding in Delhi, California. (Photo credit: Craig Ulrich/Berkeley Lab)

To meet the increased interest in sustainable groundwater recharge, EESA, the Almond Board, and UC Davis are working together on an on-farm banking demonstration project at almond orchards in Modesto and Delhi, California.

While UC Davis is trying to understand on-farm banking’s effects on the almond trees and the root zone, EESA scientists are studying how the process filters water through the section of the Earth’s subsurface called the vadose zone—the area that’s sandwiched between the root zone and the saturated zone (the layer saturated with water). (Berkeley Lab’s Laboratory Directed Research and Development Program, as well as the Nature Conservancy, have funded EESA for related efforts).

“We are repurposing the knowledge and expertise we’ve already developed for Department of Energy-funded programs to look at the structure and chemistry of the vadose zone and the saturated zone,” Nico says. “But there’s still a lot we don’t know—for example, where the water goes in the vadose zone, how fast it moves, as well as what the water quality is once it gets there.”

Farmers and policymakers are also interested in how on-farm banking affects energy use and land subsidence, he adds, as a way to measure impact.

Flood gate for on-farm flooding. (Photo credit: Craig Ulrich/Berkeley Lab)

To answer all of these questions, EESA scientists are using time-lapse geophysical imaging, isotope chemistry, and are integrating advanced datasets into numerical models as a way to get a better understanding of the process.

Just as important as the science is taking the time to bring in the input and expertise of California’s winegrowers and almond farmers, says Craig Ulrich, EESA senior scientific engineering associate.

Recently, Ulrich got a chance to engage with wine growers about groundwater recharge and on-farm banking at a series of “tailgate talks” facilitated by the University of California’s Agriculture and Natural Resources Division and the San Joaquin Valley Winegrowers Association at held at two vineyards in the Fresno area. Thirty growers attended each talk. In addition to EESA and UC Davis, a local water irrigation district was also present to talk with growers.

“It’s a conversation with the people who have to make the decisions on how to manage their groundwater,” Ulrich said. “We wanted to find out what level of understanding they need, and bring them that information.”

In the long run, he adds, EESA hopes its research will empower policymakers, water managers, and farmers to make informed decisions about how to manage groundwater.

“The knowledge and level of understanding you need to manage groundwater sustainably has gone up several notches,” Nico says. “Yet at the same time, there isn’t a lot of information out there to make those decisions. Our goal is to help people understand how they can manage their groundwater water in a way they haven’t before.”