Water levels in the Eastern Snake Plain Aquifer are back down

In 2015, cities and farmers came together to replenish the declining Eastern Snake Plain Aquifer. Despite their efforts, water levels are back down, almost reaching pre-agreement lows. Still, state water managers warn the situation could have been much worse.

The aquifer, one of the largest in the U.S, lies beneath eastern and south-central Idaho, providing drinking water to about 300,000 people and irrigation for over two million acres of farmland.

However, since the 1950s, it has been declining, largely because of increased efficiency in irrigation practices – reducing the amount that naturally seeped into the ground – and urban growth. The growing demand eventually outpaced supply, leading to legal disputes that brought stakeholders to the table to work out a solution.

In the first few years after the 2015 ESPA agreement, aquifer levels began to climb. A few snowy winters helped, plus the state set a goal of sending an average of 250,000 acre-feet of Snake River water back into the aquifer each year to revive it, with funding from the legislature. Farmers who rely on groundwater also agreed to reduce their pumping.

Now, after a few years of severe drought, the aquifer has dropped once again, and is currently about 300,000 acre-feet below 2015 levels, according to well measurements taken by the Idaho Department of Water Resources this spring.

Last year alone, the aquifer lost one million acre-feet of water, Mike McVay, a hydrologist for IDWR, told board members this week.

“It’s painful,” he said. “But that’s where we’re at.”

 A chart showing water levels in the Eastern Snake Plain Aquifer over time

Idaho Department of Water Resources

Water volume in the Eastern Snake Plain Aquifer from 1912 to 2023.

Water managers emphasize that the 2015 agreement’s recharge and pumping reduction efforts have prevented a worse scenario.

“It’s significantly better than what it would have been if we hadn’t done all the work that’s been done,” Wesley Hipke, who manages ESPA recharge for IDWR, said in an interview.

Still, the dry years have meant benchmarks intended to reverse the aquifer’s decline are not being met.

The state has recharged slightly less water on average per year than it set out to, in part because when there’s a drought, there’s little excess water available for the program beyond what’s already reserved for irrigation. Plus, groundwater users haven’t reduced their consumption enough, according to reviews by the department.

Going forward, groundwater levels would need to increase nearly 10 feet by 2026 to meet the targets outlined in the 2015 agreement.

One solution the state is focused on is expanding its recharge program, especially in the northern part of the aquifer towards Idaho Falls.

Four new sites are being developed there and three could be ready next spring. Those additions would create more chances to make deposits to the bank beneath the surface.

“The aquifer leaks,” McVay said. “We’ve got to keep going, because anytime we stop, all those gains are lost.”

However, recharge still depends on strong snowpack, and climate change has made this less predictable, with a higher proportion of spring precipitation expected to fall as rain instead of snow.

But Hipke said when those good water years come, the state is now better situated to put excess water back into the aquifer than it was in the past.

Find reporter Rachel Cohen on Twitter @racheld_cohen

Copyright 2023 Boise State Public Radio

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