Idaho starts anticipated large-scale recharge program

Storage water is recharged this fall into the New Sweden Irrigation District reservoir. The Idaho Department of Water Resources should have substantially more capacity to conduct recharge in the Upper Snake Valley this fall, and ample storage water to inject into the aquifer.

BOISE — Though the irrigation season has not yet concluded, the state has already started recharging 61,100 acre-feet of storage water that groundwater users provided as mitigation to senior Surface Water Coalition irrigators.

Idaho Ground Water Appropriators Inc. is obligated to give the coalition 50,000 acre-feet of storage annually under terms of a 2015 settlement to the coalition’s long-standing water call. It was filed based on declining Upper Snake River spring flows attributed to junior well irrigation.

Idaho cities that draw groundwater from the aquifer were also required to provide 2,600 acre-feet of mitigation water, and industrial processors reached their own agreement years ago to give the coalition 8,500 acre-feet.

The Upper Snake Reservoir system was still 69 percent full on Sept. 26, following an unusually wet water year. Twin Falls Canal Co. General Manager Brian Olmstead explained coalition members have no need for mitigation water this season, so they’ve donated it to support the state’s recharge program — which pays canal companies fees to inject surface water into the aquifer through their unlined canals and adjacent spill basins.

“I think we could have a really dry winter and still fill those reservoirs,” Olmstead said.

The state started recharging the storage water on Aug. 30 and now has recharge underway on three off-canal sites in the Upper Valley and one Lower Valley site, said Wes Hipke, recharge coordinator with the Idaho Department of Water Resources. The storage water alone will nearly equal the total volume of recharge the state conducted in the 2015-2016 season, before recharging a whopping 317,000 acre-feet in 2016-2017. Measurements taken late last March from sentinel wells used to track the settlement’s progress showed the aquifer gained 600,000 acre-feet in the span of a year, equal to half the capacity of Palisades Reservoir.

Hipke conservatively estimates the state’s program will recharge at least 240,000 acre-feet in the coming season — considerably more if canals are snow-free and capable of recharging flood-control releases in the Upper Valley next spring.

Further improving the water outlook, National Weather Service meteorologist Jay Breidenbach explained conditions in the Pacific Ocean now favor a La Nina weather pattern, resulting in slightly better odds of above-normal temperatures and precipitation throughout the Northwest.

In the Lower Valley, below Minidoka Dam, the state has a recharge water right that remains in priority throughout winter. Most years, Lower Valley winter flows are 500 cubic feet per second, but Hipke expects flows will range from 1,000 to 1,200 cfs this winter. The state has completed recharge infrastructure projects to boost its Lower Valley recharge capacity to roughly 900 cfs, compared to 250 cfs last winter.

Hipke said the state has allocated $4.2 million to build new recharge infrastructure in the current budget year, plus $460,000 to study more potential sites.

In the Lower Valley, Hipke hopes to commence construction this year on improvements to bypass hydro-power turbines on the North Side Canal to deliver up to 130 cfs of winter recharge water to Wilson Lake.

In the Upper Valley, Hipke expects to get studies back within the next few months on developing sites on the Snake’s South Fork, which could add 200 to 400 cfs of recharge capacity, and to commence construction soon thereafter. He also plans to start an expansion this month to add about 100 cfs of capacity to the Egin Bench recharge site in St. Anthony.

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