published on March 3, 2016 - 9:37 PM
Written by The Business Journal Staff
Valley farmers report that any flooding of their nut and fruit orchards during the current El Niño condition would likely do more good than damage to their trees.

In fact, some farmers plan to deliberately flood their orchards as part of testing the benefits of winter flooding.

By doing so, they not only ensure the trees have enough water, but they are also helping recharge the groundwater basin in winter when more water is available.

California gets its bulk of rainwater from December to March. This year some storms caused brief flooding on farms.

Although the Valley has had a break from storms for most of February, El Niño continues and additional heavy rains are possible.

Harnessing winter storm or drainage water can help slow the fall of groundwater levels during the drought.

It was once thought that natural flooding of orchards during winter would be harmful to the tree crops. But that view is changing.

“There is no ill effect,” said Barry Bedwell, president of the California Fresh Fruit Association. “I have heard no complaints about too much water.”

He added that tree roots are actually stronger when they’ve been soaked with drainage water. He said some water districts have drainage water available that can be guided into orchards.

Bedwell said the snowpack in the Sierra is also key to replenishing the groundwater basin. And the snowpack is very good this year.

But it is important not to let the snowmelt water, which fills the reservoirs, be allowed to flow to the ocean, Bedwell said.

The idea of intentionally flooding orchards is being tested by researchers at University of California Davis. Helen Dahlke, a professor and hydrology expert with the UC Davis, Department of Land, Air and Water Resources, reported recently that on-farm flooding looks promising.

She said researchers are pleasantly surprised by how quickly water tables respond to on-farm flooding without damage to crops.

Dahlke and her research team are testing use of orchard flooding on Central Valley almonds this winter. She is looking at plant physiology, infiltration rates, possible water quality concerns and costs involved in flooding orchards.

Dahlke reports that as much as 15 million acre feet of flood flows could be saved during a wet California winter.

That is important when considering many farmers depend on well water to keep their orchards alive.

Although the drought continues, this season is better suited than recent winters for testing the flooding of fields. As of Feb. 9, Fresno had received 9.62 inches of rain for the season, compared to 3.87 on the same date last year.

And more rain is expected in late February and March.

Dahlke’s team is building on previous research in the Kings River Basin where as much as 75 percent of diverted floodwater percolates down to the underground aquifer.

The previous project was conducted in winter of 2011 when waters in the Kings River were high enough to allow for flooding of farms.

As part of the project, researchers flooded pistachio trees, alfalfa hay and wine grapes at Terranova Ranch along the Kings River in Fresno County. Don Cameron, manager of Terranova Ranch, said his wine grapes were underwater for five months, but came out fine.

Still, researchers point out that a lot must be considered before flooding a farm or orchard.  The soil must be fairly loose and permeable.

Also not all crops tolerate extra irrigation in winter.

In addition, Valley farmers must consider if flooding fertilized farmland or saline soil will leach the chemicals into the groundwater.

And flood plans must comply with regulations in California’s Sustainable Groundwater Management Act of 2014.

The legislation provides a framework for sustainable management of groundwater supplies by local authorities, with a limited role for state intervention only if necessary to protect the resource.

On the positive side, certain levels of flooding could dilute salt and nitrate concentrations leading to no groundwater contamination.

Cameron said that besides the need for more rain water to fill the Kings River, farmers need the infrastructure to carry excess drainage water from water districts out to farms.

But so far, the winter flooding idea has attracted plenty of interest from farmers, he said.

Winter flooding of almond orchards
Meanwhile, Ken Shackel professor with the UC Davis Department of Plant Sciences has designed a two-year project to test floodwater on almonds in the Central Valley. In December, his team began applying two feet of water over 60 days to a small portion of almond orchards in Modesto and Merced.

In addition, impacts of flooding in spring will be tested at a Fresno County almond orchard to see how flooding affects trees after bloom.

The UC Davis project is funded by the Almond Board of California in Modesto, which anticipates that some almond orchards will be good candidates for groundwater recharge.

Also helping in the testing process is a California organization called Sustainable Conservation. That group is working with 20 Valley growers to determine winter flooding impact on various crops.

Sustainable Conservation officials point out that groundwater pumping provides around 35 percent of all freshwater used in California during average years. During drought years, that percentage can creep past 60 percent. So it considers groundwater recharge as vital.

The group’s project is not funded by the Almond Board of California, but the two organizations collaborate on project work and results. “We are hopeful to find ways to make this work,” said Gabriele Ludwig, director, sustainability and environmental affairs for the Almond Board of California.

She said growers want to be sure winter flooding of crops works.

Some crops are more sensitive than others
Shackel pointed out that almond trees are more sensitive to being underwater than grape vines. So he said it will be important to thoroughly examine the trees in spring.

May and June will be key months to see if the trees show negative symptoms, Shackel said.

Valley trees were still dormant in mid-February, but Shackel found that the almond trees looked healthier from ground level to the top of the tree. How the roots survive the heavy water use will be of vital importance.

So will the amount of blossoms and quality of nuts on the tree.

Shackel said almond growers are anxious to see if the winter flooding system works. “There’s a lot of excitement,” he said.

Bee health improving
Flooding farms and a wetter winter have improved conditions for bees in the Central Valley. Bedwell reported that bees, — vital to all crops — are doing better this season.

Hives were put out on farms and near orchards in early February.

“Bee health continues to improve,” Bedwell said.

Last year, bee populations, already in decline, suffered from too little water. Beekeepers called on farmers to put water out for the thirsty bees.

“Bees need fresh water,” said Elina Nino, head of Apiculture Extension & Research at UC Davis. “They need something on the surface to take back to the hive.”

Some farmers use small pools or soaker hoses to keep the bees hydrated. With flooding of orchards, bees have plenty of water at least for a while.

But as the season progresses and weather becomes hot and dry, bees need another water source.

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