BOISE — The Idaho Water Resource Board is projecting that it will recharge approximately 170,000 acre-feet of water into the East Snake Plain Aquifer in winter 2018-19, a lower amount than the 250,000 acre-foot annual goal.

The reason for the decrease is mainly because of limited water availability, combined with construction projects and canal maintenance requirements, officials said at the board meeting last week.

The board’s four major Magic Valley-area partners will have shorter recharge seasons this year because of existing construction and maintenance projects in the Milner pool affecting Southwest Irrigation District, Milner-Gooding Canal, North Side Canal and Twin Falls Canal, said Wesley Hipke, recharge project manager for the board.

The board set a record in winter 2017-18 by recharging more than 525,000 acre-feet of water into the aquifer, more than doubling the average annual goal. In June last year, hydrologists with the Idaho Department of Water Resources noted that the aquifer rose by more than 1.7 million acre-feet in one year, the largest single-year increase in 80 years. The increase was due to aquifer recharge efforts, two consecutive robust winters, the 2015 water settlement between the Surface Water Coalition and the Idaho Ground Water Appropriators and surplus water from high reservoir storage.

The board has recharged 63,293 acre-feet of water into the aquifer so far this year, Hipke said. The winter 2018-19 recharge season began in mid-August and recharge water from nine sites in the Upper Snake River Valley led to 57,147 acre-feet of water flowing into the aquifer from that region, he said.

Having only average reservoir carryover this year in the Upper Snake, combined with construction and maintenance constraints, will likely lead to a smaller volume being recharged into the aquifer, he said. Looking back to previous years with average reservoir carryover and projected drier El Niño winters, the board was only able to recharge 60,000 to 70,000 acre-feet of water into the aquifer. The higher amount projected for this year is due to expanded recharge infrastructure and more participating canals, Hipke said.

He added that once the construction projects are complete on Milner-Gooding Canal and the North Side Canal, the board will have even larger capacity for recharge when surplus flows exist. The board has spent more than $20 million dollars from 2013 through fiscal year 2019 on recharge infrastructure

improvements to increase managed recharge throughout the aquifer. For fiscal year 2019, the board budgeted $8 million for managed recharge infrastructure projects and investigations.

In a related issue, officials notified the board that under the 2015 water settlement, the groundwater appropriators more than doubled the amount of water it was obligated to conserve under the settlement with a reduction in use by 512,508 acre-feet of water. The annual target is 240,000 acre-feet, or a reduction of 13 percent among all ground water districts in the aquifer region.

“They knocked it out of the park,” said Brian Ragan, of the board’s Water Distribution Section.

The board independently verifies the amount of water conserved by groundwater users under the settlement agreement by monitoring 20 sentinel wells. The groundwater appropriators’ own accounting showed that they had reduced groundwater use by 474,078 acre-feet.

The conservation gains reduce depletion of aquifer volume and will help the groundwater appropriators meet future milestones in the settlement agreement, Ragan said.

In other action, the board was informed that a new study, called the “Treasure Valley Managed Recharge Feasibility Study,” is getting under way to assess the potential for managed aquifer recharge in the valley. The $200,000 study will be conducted by consultant Brown & Caldwell.

The study will examine how much water is potentially available for managed recharge, what locations may hold promise for recharging aquifers, and infrastructure requirements for developing recharge sites. The study is expected to be complete in late summer or fall 2019.

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