Almond trees next to irrigation canal mrmagnificent/Thinkstock
California central valley Almond orchard next to irrigation canal

Soil characteristics, other factors critical for successful groundwater recharge

Ken Shackel said there are a number of “deal breaker ducks” when it comes to groundwater recharge that include environmental issues, water rights issues, and issues of ownership.

Ken Shackel, Dr. H2O to some due to area of expertise, lightened a discussion of the serious issue of groundwater recharge at a tree nut meeting in Tulare, Calif. by flashing a slide of ducklings in a perfect row flanked by their mother.

His point, “It’s a great idea using agricultural fields to recharge water, 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.”

In his slide, he pointed to the mama duck with the label “deal breaker…trees don’t die.”

Shackel is a pomologist, a professor who teaches soil, plant, and water relations in plant science at the University of California, Davis.

His talk was on “Using Almond Orchards for Groundwater Recharge,” something being explored by people from a variety of disciplines which has the Almond Board of California partnering with a number of entities and farmer cooperators.

Before launching into the challenges to recharge, he built the case that California’s groundwater levels are vital to farming success and those levels are dropping due to the state’s drought.

About 30 percent of California’s annual water supply comes from groundwater. In a dry year, Shackel said it’s about 60 percent. California’s groundwater storage capacity is more than ten times that of its surface water.

Overdraft forces people to deepen their wells which can cost as much as $500,000. Less than one percent of all the water on the planet is groundwater or in underground water reservoirs.

The very fact that many growers are moving to water-saving irrigation techniques – including subsurface drip – means less water is returned to the earth to bolster groundwater levels.

Shackel said there are a number of “deal breaker ducks” when it comes to groundwater recharge that include environmental issues, water rights issues, and issues of ownership.

For example, one of his slides showed a groundwater aquifer comprising soil, rock and bedrock, and the bedrock slants in such a way that recharge at one point leads to water sent elsewhere.

“Even though you put water on your farm, it can flow to somebody else’s farm,” Shackel said. “Will growers cooperate? It may not benefit (a particular person), but it benefits the industry.”

One grower believes the State Groundwater Management Act will result in greater cooperation and foster more of a regional approach. Still remaining, however, said grower Don Cameron of Terranova Ranch, is the question “Who will pay for it?

Cameron is a pioneer seeking to recharge aquifers on his farming operation, but has not been concentrating on almonds. Instead, water is left standing in open land and vineyards.

“We have to have flood water to make it work,” Cameron said.

In 2011, water was made available, and Cameron embarked on infrastructure developments with help from a $5 million grant from the Kings River Conservation District. He put up $2 million of his own money.

It’s expected some dirt will be moved sometime in 2017 for the Terranova project.

If there were “a consigned basin,” he said it would be simpler. “It would be filling the bowl back up, but if it moves, then what?”

Cameron said reaching this point has been “a slow process - there are a lot regulations to be met. It takes a lot of patience.”

But he believes the project will be successful, and in fact is now looking at flooding walnuts this summer planted in the Biola area (Fresno County).

Shackel pointed out that soil characteristics help determine suitability for mounting a recharge project. UC has come up with what it calls a Soil Agricultural Banking Index. This index looks at such factors as hydraulic conductivity, occurrence of water restrictive layers, topographic limitations such as sloping land, chemical limitations, and surface conditions such as erodibility.

Questions Shackel and others are wrestling with include whether it is okay for almonds to be flooded when they are dormant, what happens to root and tree health over the long run, and what happens to the water and environment?

Shackel has set up underground cameras to observe the tree roots and monitors for potential damage or disease. Another risk is that fertilizers could also seep into the groundwater. Shackel has said farmers may need to change the way they operate, being assured the water left for recharging is fairly pure.

“If you are recharging, there’s a need to use fresh water,” he said. “Water gets saltier as it moves through soil.”

Sometimes part of the challenge is making sure there’s an infrastructure in place to provide needed water that goes beyond flood runoff. For example, the City of Modesto took runoff from the city and put it into a system that connected to ditches used by a water district. It’s a matter of being able to transport the water to where it’s needed.

There are two commercial almond orchard sites where recharge projects were started in 2015 – in Modesto and Delhi. At these sites, tree health and yield are being monitored. So far, there has been neither a positive nor a negative impact on yields.

Root health is being checked by testing for water stress, learning if roots are able to supply water the trees’ need.

This includes the use of a pressure chamber to measure the level of water suction in the plant. Shackel said it’s like measuring the “blood pressure” of the plant. Shackel believes multiple treatment years – at least three or four – will be required to evaluate the potential long term effects in almonds.

The Almond Board of California (ABC) is taking a multi-tier approach to the recharge effort. This includes partnering with Sustainable Conservation, a nonprofit conservation organization, plus the research consulting firm Land IQ, which will help identify areas potentially suitable for ground water recharge by mapping in detail where almond production and associated infrastructure merge.

The ABC also has a partnership with the Lawrence Berkeley National Laboratory to address the issue.

Gabriele Ludwig, the ABC’s director of sustainability and environmental affairs, said a preliminary analysis of almond acreage indicates that nearly 675,000 acres are moderately good or better in their ability to recharge groundwater.

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