The amount of water returned to the Eastern Snake Plain Aquifer so far this year is down 29.2% from last year because of the drought.
Idaho in 2014 started an annual program in the irrigation offseason to return surface water to the large aquifer beneath the state’s south-central and southeast regions.
Wesley Hipke, recharge program manager for the Idaho Water Resource Board and state Department of Water Resources, said about 40,000 acre-feet of water was returned from Oct. 20 to Dec. 5. That’s down from 56,500 acre-feet during the same period a year ago.
“There is just less water available because of the dry year we had” in 2021, he said.
For the full 2020-21 campaign, the state returned 130,000 acre-feet of water to the aquifer. Hipke said he expects a 2021-2022 total of 130,000 to 150,000 unless conditions change.
The state targets an annual average of 250,000.
From Dec. 1, 2020, to Feb. 15, 2021, the Idaho Water Resource Board agreed not to divert some water under its recharge water right at Milner Dam, the farthest downstream of the Upper Snake River dams, to help with power production. The total was about 27,000 acre-feet.
Hipke said this year’s drought left many reservoirs with below-average amounts of water following the irrigation season and “has really affected how much water is available for recharge right now.”
He said Minidoka Dam, between the American Falls and Milner dams, is releasing around 400 cubic feet per second of water compared to the roughly 550 considered normal this time of year.
“They’re trying to capture as much as they can to fill the reservoirs,” Hipke said.
Concerns about the aquifer’s decline date back decades. Causes range from drought, population growth and more groundwater pumping to more efficient irrigation systems that return less water to the aquifer.
Hipke said Idaho aims to return as much as possible in good water years “because we know we are going to have these low years when we know we are going to be significantly below that 250,000 (acre-foot) mark.”
Since the state started the recharge program, the aquifer benefited from several good water years, a 2015 settlement between groundwater and surface water users and construction of additional recharge facilities, he said.
Hipke said the recharge program “is not done developing capacity, especially in the upper valley above American Falls.” That would increase capabilities to use a wet year’s excess water “to benefit the aquifer both in the short term and the long term.”