The Idaho Department of Water Resources projects a shortfall to senior water rights in the Eastern Snake River Plain this season.

The director of the Idaho Department of Water Resources has issued a water order predicting a 29,000 acre-foot shortfall to senior surface water rights in the Eastern Snake River Plain.

If the early forecast plays out, some groundwater users could be subject to curtailment this irrigation season if they are not participants in an approved mitigation plan or are out of compliance with an approved plan.

At this point, the department doesn’t know how many water rights the curtailment could affect, Mathew Weaver, IDWR deputy director, said.

IDWR is coordinating with groundwater districts and the Idaho Ground Water Association to determine if any junior water right holders are not in good standing, which would leave them subject to a curtailment, he said.

After that process, IDWR will issue another order in May identifying water rights that might be curtailed, he said.

While runoff at the Heise gauge of the Snake River from April to July is expected to be near-normal this year, IDWR also factors in the Snake River Plain Aquifer level in its forecast supply. Although some recovery of the aquifer has occurred due to the state’s recharge efforts, it’s not back to a level that would avoid curtailment, he said.

About 855 water rights are junior to the Aug. 25, 1991, curtailment date identified in IDWR’s order regarding the April forecast supply, he said.

But those water right holders would be protected from curtailment if they are participating in a mitigation plan and are in good standing due to the safe harbor provision in those plans, he said.

Weaver said it’s too early to know if a shortfall to senior water rights will occur, but IDWR is required to determine if one is anticipated before the irrigation season begins.

The department does its best to forecast, but it won’t really know what the demand will be until the middle of the irrigation season, he said.

In determining injury to senior water rights, the courts have directed IDWR to err on the side of senior water users, and an injury determination is made in more years than not, he said.

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