Farm Progress

Winter flooding to recharge underground aquifers under the microscope

The researchers developed a soil agricultural groundwater banking index to evaluate whether different soil types, cropland, or topography would be suitable to flood to help recharge.

December 2, 2015

3 Min Read
<p>The group Sustainable Conservation conducted a pilot study in 2011 at Terranova Ranch to examine vineyard flooding to help groundwater recharge.</p>

A new multi-year collaboration with the University of California (UC), Sustainable Conservation, and the Almond Board of California (ABC) plans to study how the winter flooding of fields and orchards could help recharge underground aquifers.

The group effort builds on research conducted in 2011 by Sustainable Conservation based in San Francisco on the Terranova Ranch in Fresno County, says Daniel Mountjoy, the association’s director of resource stewardship.

In the project, the grower flooded a vineyard in June and kept the water on the vineyard floor until the leaves began to turn yellow. Two weeks after the grower removed the water the leaves were fully green again. Mountjoy found no long-term repercussions.

He says the collaboration has factored in the results of a study by University of California researchers and Cooperative Extension farm advisers. The study identified about 3.6 million acres of farmland statewide with potential to serve as percolation basins for groundwater recharge.

The researchers developed a soil agricultural groundwater banking index to evaluate whether different soil types, cropland, or topography would be suitable to flood to help recharge.

The study’s authors point out that this would not address the state’s lack of infrastructure to route large water volumes to farm fields during a short period of time. In addition, precipitation doesn't fall evenly throughout the state, and heavy rainfall doesn't necessarily occur close to areas with optimum recharge qualities.

A separate study commissioned by the California Water Foundation identified that redirecting excess river flow during the winter onto farmland for recharge could reduce groundwater overdraft on the San Joaquin Valley’s eastside by 12 percent to 20 percent annually.

The study area included parts of Merced, Madera, and Fresno counties, plus the City of Fresno.

As part of the collaboration, Mountjoy says Sustainable Conservation representatives are interviewing growers who have diverted surplus winter water onto fields and orchards in the past to learn more about the learned benefits and drawbacks.

“We’re learning from growers about the trees and the time of year, and finding that growers have pushed the limits far beyond UC recommendations,” Mountjoy said.

Sustainable Conservation hopes to enlist 10 growers of different crops, including almonds, to participate in a demonstration this winter for monitoring. The group hopes to encourage other growers to apply excess surface water independently to unmonitored blocks.

Mountjoy says the group focused on almonds since the nut crop covers more than one million acres of crop land in the state.

“We’re very interested in almonds since they have such a large footprint.”

Gabriele Ludwig, the ABC’s director of sustainability and environmental affairs, says the almond industry wants to help maintain a healthy groundwater supply.

“Fundamentally, better groundwater management is both important and mandatory for the long-term health of the Central Valley,” Ludwig said. “Given that almonds make up about one million acres, it makes sense to see if almonds can be part of the solution to groundwater management.”

Of the 10 sites, UC researchers will monitor three in almonds to document tree health, root conditions, and other physiological changes.

Ludwig says questions exist about pushing potential contaminants down to the groundwater, yet dilution could already be underway.

In almonds, she says the other big question is when the trees can handle irrigations with large amounts of water.

Sustainable Conservation has reached out to other commodity groups, including the California Association of Winegrape Growers and the California Fresh Fruit Association, to seek their participation.

In addition, the group is seeking partnerships with irrigation districts. The Madera Irrigation District will hold an informational meeting for growers on this issue in December.

Not only could the groundwater recharge help growers and local water managers, but Mountjoy hopes the results could aid state regulators involved in developing sustainable groundwater plans.

Mountjoy said some groundwater sustainability planning efforts focus more on reduced pumping, instead of on-farm flooding as a solution to increase the groundwater supply.

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