The Idaho Water Resource Board this winter will modify part of its annual effort to put Snake River surface water back into the Eastern Snake Plain Aquifer.

IWRB passed a resolution saying it will not divert 200 cubic feet per second of streamflow at Milner Dam from Dec. 1 to Feb. 15. That water will remain in the river for hydroelectric power production and other uses below the dam.

Streamflow of 1 cfs equals about 2 acre-feet per day.

The Snake River disappears underground downstream of Milner before re-emerging at Thousand Springs. IWRB’s water rights for pumping river water into the aquifer allow it to divert up to 7,769 acre-feet at or upstream of Milner Dam. Exercising the rights in full could shut off all outflow.

Idaho Power Co. has told state water managers that allowing some water to flow past Milner in the winter would be valuable for hydropower production, the board said in a news release.

The resolution, in effect for one year, calls on Idaho Power to provide replacement water from its right in American Falls Reservoir upstream if the state falls short of its 250,000-acre-foot recharge target this winter.

IWRB aims to put an average of 250,000 acre-feet of water back into the aquifer annually to restore it to sustainable levels.

“The board intends to work cooperatively with all stakeholders to explore opportunities to benefit all uses on the system,” Board Chairman Roger Chase said in the release. “We learn as we go.”

Idaho Power “appreciates the opportunity to work with board members to find balance between the state’s managed-recharge program and downstream beneficial uses,” Kresta Davis, the company’s senior manager for water resources and policy, said in an email to Capital Press. The resolution “demonstrates both the success of the current recharge program and willingness to include stakeholder interests.

“These winter flows will increase Idaho Power’s ability to use our lowest-cost generating resource, our hydroelectric system,” she said. “That helps keep prices low for our customers and also supports our goal of reducing carbon emissions.”

“Up till last year, the program did not have capacity to take that water,” Wesley Hipke, the board’s ESPA recharge manager, told Capital Press. Following infrastructure projects, “in January 2020, we had the capacity to then divert all of that water. We could take that flow to zero at Milner.”

IWRB’s resolution “points to the complexities of managing this large of a system, and all the different uses and demands on it,” he said. “It’s going to take a lot of cooperative work to be able to balance all the different and competing uses, and that is what the board is working on navigating.”

The board said it has added about 2.2 million acre-feet to the aquifer since starting the recharge program in earnest in 2015. Surface-water and groundwater amounts vary each year based on snowpack and precipitation, irrigation demand and other factors.