California pumps too much groundwater, especially during droughts. Now, it's learning to refill the overdrawn bucket.

From the article:

If the issue was too much water coming out of the ground, wouldn’t it be simplest to try to put some back whenever an opportunity arose?

That opportunity appeared in February of 2011. After a dry year, an unexpected storm dumped snow and rain, sending a long glug of extra water down the King’s River, which snakes along the edge of Terranova Ranch. Cameron diverted some of it into a series of deep canals and ditches built in anticipation of this exact moment, set up a series of small pumps, and pumped enough water onto a field of wine grapes to flood them nearly two feet deep.

His neighbors were aghast, thinking there was no way the plants would survive a drowning. But Cameron’s intuition told him otherwise—the wild ancestors of grapes evolved along rivers, after all. “I was pretty damn sure they could handle having their feet wet,” he laughs.

The water kept disappearing into the ground, so he just kept pumping—all the way through June, well after buds burst and leaves unfurled, for a total of 13 feet of water over the season: enough to cover a football field to well above the field-goal crossbar.

The grapes survived just fine. The bigger value of the experiment, though, was to pique others' interest. Cameron talked about his experiment constantly, hosting taco-truck talks at the farm and evangelizing the idea to scientists, policymakers, and farmers alike.

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The groundwater in the San Joaquin Valley is overdrawn by about 2 million acre-feet a year— about one-third as much as all Californians use in their homes. [...]

No one yet knows exactly how much of that deepening debt can even be repaid. Local water districts’ SGMA plans currently propose to fill about 40 percent of the hole with recharge. But an independent analysis from the PPIC found that recharge could fill only about 25 percent of the overdraft.

Ideally, water would be injected in confined zones where deposits of coarse gravel or sand offer a direct channel to an aquifer. Such “sweet” zones are rare, but Fukuda’s Tulare Irrigation District already uses one, and the state is spending $12 million to find more.

Stanford researchers led by geophysicist Knight have figured out how to find them from the air or by driving overland on a 4x4. Equipped with an instrument that maps subsurface geological structures by measuring their electrical conductivity, the team can tell gravel and sand—through which water travels easily—from clay, which stops its downward motion.

Hyper-effective recharge zones probably won’t be enough, though. Farmers will also need to be willing and ready to flood their fields.

[...]

If floodwaters could be peeled off and directed to groundwater recharge, the risk of damaging floods could be decreased at the same time, says DWR engineer Ajay Goyal. But there are legal and logistical hurdles. Complicated fights about who has rights to the “extra” water—and what exactly constitutes “extra”—are already brewing. Miles of aging, expensive infrastructure would need to be updated to accommodate even larger water pulses.