The director of the Idaho Department of Water Resources has issued a methodology order for Snake River groundwater users, predicting a 162,600 acre-foot shortfall to senior priority surface water users in the Eastern Snake River Plain (ESPA) region in the 2022 irrigation season.

The shortfall prediction means that IDWR will curtail more than 328 groundwater rights with priority dates junior to Dec. 25, 1979, in the coming weeks if the holders of those water rights do not come into compliance with an approved mitigation plan with a groundwater district.

Curtailment will begin on May 20, according to the order, unless groundwater users have joined an approved mitigation plan prior to that time.

Currently, there are seven approved mitigation plans for the ESPA surface water delivery call. The approved plans came from the Idaho Groundwater Appropriators Inc. (IGWA), Southwest Irrigation District, Goose Creek Irrigation District, Coalition of Cities and Water Mitigation Coalition. Those entities will not need to show how they can mitigate for projected water shortfalls, the director’s order said.

The Department’s injury determination will be updated in July. Junior water users who could be affected by the order were sent a copy of the order last week.

"By law, we have to keep people with senior water rights whole, and we want to make the junior groundwater pumpers aware that despite the settlement agreements between the Surface Water Coalition (“SWC”), IGWA, and the Participating Cities, if junior groundwater pumpers are not participating in an approved mitigation plan, they could be subject to curtailment this year," said Mathew Weaver, deputy director of IDWR.

Much water litigation has resulted over conflicts between Snake River surface water users who have senior water rights under the basic principle of Idaho water law — first in time, first in right — and groundwater users with junior water rights in the ESPA. Consequently, the director of IDWR is required to issue an order at the beginning of the irrigation season, and then again in early July, determining any shortfall in water supply to the senior surface water right holders, and determining the obligations of junior groundwater pumpers to curtail water use or mitigate for depletions to the holders of senior priority water rights.

groundwater users who have joined an approved mitigation plan will avoid curtailment this year and in the future, and they will avoid future large-scale litigation issues related to water use in the ESPA area that could affect cities, commerce, industry, agriculture and the Southern Idaho economy, officials said.

If junior groundwater users do not join a groundwater mitigation plan or demonstrate to the director how their water use will not cause injury to senior surface water users in the next 14 days, their water rights will be curtailed, the order said.

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