MODESTO — In an effort to restore California’s desperately depleted ancient aquifers, scientists are testing an approach that seizes surplus winter rain and delivers it to where it’s most useful: idle farms and fields.

On Tuesday, roiling, muddy water from the storm drains of the city of Modesto flooded an almond orchard, where UC Davis researchers will track its progress as it slowly percolates — over weeks, months, even years — into a 45-foot-deep underground reservoir.

“If we can recharge our basin during the wet years, that’s water we have banked away for dry years,” said farmer Nick Blom, who authorized the experiment on his orchards southwest of Modesto, where hundreds of trees are in winter slumber.

The UC Davis team seeks to answer some hard questions: Is the water clean enough? Will it drown the valuable trees? Could it introduce waterborne diseases or make trees more vulnerable to insect pests?

If the technique is proven safe and effective, the scientists will encourage its broader use on California’s 3.5 million to 5.6 million acres of suitable soils.

The approach replicates Mother Nature’s eons-old pattern, with wet winter storms restoring the state’s depleted aquifers. But this balance has been upset by excess agricultural and urban “overdrafting” of this water supply. In short, we’re taking more than we’re giving.

Both farmers and state water experts urgently need a solution to the problem, which has stressed 21 of the state’s aquifers, especially in Tulare County, in the southern San Joaquin Valley. In some areas, it is so severe that the land is subsiding — permanently in some cases.

The state’s first-ever groundwater protection law, passed by the Legislature in 2014, calls for “sustainable” aquifer management, said Helen Dahlke, assistant professor of UC Davis’ department of land, air and water resources.

To achieve the necessary balance between supply and demand, it’s not enough for farmers to simply reduce how much water they pump; they also need to return the water to its source, she said.

That’s a tall order for many agriculturally rich parts of the state, especially the most arid regions.

If this experiment works, scientists envision pulling floodwaters off rivers such as the Sacramento and diverting them to dry regions via the state’s vast network of canals. This would not only ease the risk of flooding but could also deliver water to drought-ravaged parts of the state.

Meanwhile, farmers elsewhere are enlisting other approaches. In the Pajaro Valley, farmers have dug small “percolation ponds” on the edges of their fields. Along the Consumnes River and Yolo Bypass, there are newly widened levee setbacks, giving river water more time to drain and recede.

“Hopefully, we can come up with a system so we can at least maintain the water table where it is right now,” Dahlke said.

Such recharge strategies could face political, legal and economic challenges, the UC Davis team says.

Many people claim rights to the state’s water the moment it lands from the sky. And the delivery canals aren’t historically available in the winter. This is the time when they are cleaned and maintained.

Tuesday’s experiment — flooding a 5-acre field with 6 inches of water — was possible only because the Modesto Irrigation District provides water to both the city of Modesto and surrounding farms. So it has control over water use and also has access to the intricate web of delivery canals.

If not diverted to the Blom farm, the storm drain water would have flowed into the nearby Tuolumne River. The experiment is funded by the Almond Board of California.

Scientists will monitor any root damage with underground cameras, inserted 3 feet deep through plastic tubes. They will also watch next spring to see if the trees bloom and leaf normally. And they will measure the orchard’s almond production to see if yields decline.

To track water flow rates, they use temperature sensors; water retains heat more than the surrounding soil.

And they will test the loamy soil to make sure the water isn’t delivering nitrates, salts or dangerous pollutants.

This Modesto basin could be quick to recover because it’s shallow and relatively healthy. But other basins, such as those in the southern San Joaquin Valley, may need 20 years before the surface water gets to where it’s needed — and flows may need to be repeated annually, said Ken Shackel, a professor in the department of plant sciences at UC Davis.

If successful, “there is enough acreage in almonds and similar crops that it could make a huge different to the state water balance,” Shackel said. “And it is a lot cheaper than building a reservoir.

“We are thinking about this as the first step in a very long-term strategy.”

Contact Lisa M. Krieger at 650-492-4098. Follow her at Twitter.com/LisaMKrieger and Facebook.com/LisaMKrieger.