Farmland may provide key to replenishing groundwater

People huddled around
UC Davis faculty work out details of groundwater-recharge project with almond growers in Fresno. From left: George Goshgarian, Sr.; Professor Ken Shackel; George Goshgarian, Jr.; Professor Helen Dahlke; and Professor Astrid Volder.

Replenishing supply may benefit everyone in the drought-stricken Golden State.

California’s aquifers are shrinking as more growers pump groundwater to keep crops alive. But that fertile farmland may also provide the means for replenishing groundwater to benefit everyone in the drought-stricken state.

UC Davis researchers are encouraged by early results from tests to see if intentionally flooding farmland in winter can replenish aquifers without harming crops or drinking water.

“On-farm flooding looks very promising,” said Professor Helen Dahlke with the Department of Land, Air and Water Resources. “We’re pleasantly surprised by how quickly water tables responded to on-farm flooding without damage to crops.”

Toby O’Geen, a UC Cooperative Extension specialist with the Department of Land, Air and Water Resources, evaluated all of California’s farmland for its potential to bank groundwater. He determined about 3.6 million acres of farmland have good recharge potential because they could likely accommodate deep percolation with little risk of crop damage or groundwater contamination from salt and nitrates in the soil.

O’Geen, Dahlke, and their team are working with alfalfa growers in Siskiyou County and will test flooding on almonds in the Central Valley this winter, looking at plant physiology, infiltration rates, water quality, and costs. They are building on previous groundwater-banking research in the Kings River Basin where 75 percent of diverted floodwater percolated to aquifers.

“We flooded pistachios, alfalfa hay, and wine grapes,” said Don Cameron, manager of Terranova Ranch along the Kings River in Fresno County. “Our wine grapes were under water for five months, which raised a few eyebrows, but they did fine. Diverting floodwater to farms can recharge groundwater and reduce the risk of downstream flooding. It’s a good situation all around.”

This winter, Dahlke and professors Ken Shackel and Astrid Volder with the Department of Plant Sciences will flood portions of three Central Valley almond orchards and monitor how flooding affects tree physiology, root health, and water quality.

In spring 2015, the team applied 140 acre-feet of water to alfalfa at Bryan-Morris Ranch in Siskiyou County, more than double the irrigation the field normally gets in a year.

“It was amazing to see how well the land absorbed the water and how quickly the water table rose,” said Jim Morris, Bryan-Morris Ranch manager. “That’s good news for farming and the environment.”