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Scientists Flood Almond Orchards To Restore Groundwater in California

Curtis Jerome Haynes / Courtesy

Storm water floods six acre almond orchard in Modesto. UC Davis scientists are using the orchard to see how well it recharges the groundwater.

Curtis Jerome Haynes / Courtesy

Almond farmers in California’s Central Valley have been villainized in the drought. The crop needs a gallon of water to grow a single almond.

Now scientists are studying whether almond orchards can be used to help restore water to depleted aquifers. Some almond growers are flooding their orchards as part of the experiment. 

On Nick Blom's farm in Modesto, water pours out of an irrigation valve. Pretty quickly, it begins to cover six acres of almond trees in standing water. Blom says normally he wouldn’t water the trees this time of year.

"I did have some concerns. You do risk root damage and other kinds of things that can happen to your trees," says Blom.

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L to R: Ken Shackel, with UC Davis; Nick Blom, almond farmer; and Helen Dahlke with UC Davis 

Curtis Jerome Haynes / Courtesy

An aquifer lies about 45 feet under the surface. Blom had to use that water this summer when surface supplies were cutback in the drought. Now, he’s trying to restore it.

Blom says he's over-irrigating right now. "The trees aren’t using it. So you’re basically putting water on the soil," says Blom. "So you’re getting 100 percent of that water percolating down and it goes into the groundwater and now it’s in your water table."

Scientists at UC Davis are studying whether flooding almond orchards during the winter time can help pull California out of a chronic groundwater overdraft, at least in some areas. UC Davis hydrologist Helen Dahlke says soils have to be suitable for it – but researchers have mapped that out.

"There are between 3.6 and 5.6 million acres where groundwater recharge could be done most likely," says Dahlke.

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Water from nearby canals pour out of irrigation valve on Nick Blom's almond orchard. 

Curtis Jerome Haynes / Courtesy

Coincidentally it’s pouring rain on Blom’s orchards. But it’s these El Nino rains that farmers hope to use to deliberately flood fields. Blom says water from Modesto’s stormdrains feed into a canal system that he can use on his orchards.

“If we weren’t doing this experiment all the water would just end up in the river,” says Blom.

It would end up in the Tuolumne River. But recharging groundwater this way is no easy task.  

“It’s a great idea using agricultural fields to recharge the groundwater, but there’s a lot of ducks that need to be in a row and the first duck is that we don’t want to kill the trees,” says Ken Shackel with the UC Davis Department of Plant Sciences.

Shackel says he’s set up underground cameras to observe the tree roots. He’ll monitor for potential damage or disease. Another risk is that fertilizers could also seep into the groundwater. Shackel says farmers may need to change the way they operate.

“They may need to change the way they fertilize the trees so that by the time we get to the winter time and the recharge events, then the water is fairly pure that’s in the ground," says Shackel. "Trees will use nitrogen. Nitrate is the big issue, but there’s a lot of other things too.”

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Nick Blom checks irrigation valve on his almond farm. 

Curtis Jerome Haynes / Courtesy

This is the third time researchers have flooded Nick Blom’s almond orchard as part of the experiment. Helen Dahlke says they’re getting a good idea how quickly the water seeps into the aquifer.

“The first one has happened roughly two weeks ago and the water had infiltrated within 24 hours, it was gone from the surface,”says Dahlke.

By the end of the experiment, Blom’s almond orchard will have received nearly two feet of water. The Almond Board of California is funding the research, which involves three different orchards. Nick Blom says he’s hopeful the experiment will only bring benefits.

“It’s helpful. It’s a benefit to everybody because we do sit in a basin of water. So if we can put water into that basin throughout our area, it’s going to help everybody’s groundwater. So all the wells will be fine,” says Blom.

Researchers are hopeful too. Previous tests on alfalfa, grapes and pistachios showed it didn’t harm the crops or affect drinking water.

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 Six acre almond orchard that is part of UC Davis experiment.

Curtis Jerome Haynes / Courtesy