Idaho Department of Water Resources Director Mathew Weaver on Dec. 6 issued a final order identifying an end-of-season shortfall of 44,900 acre-feet of water to the Twin Falls Canal Company’s reasonable carryover storage volume.

The order is part of the ongoing 2005 Surface Water Coalition’s (SWC) conjunctive administration delivery call.

Water users with groundwater rights from the Eastern Snake Plain Aquifer (ESPA) with priority dates later than Jan. 25, 1970, who are not covered by an approved mitigation plan have 14 days from the date of the order to demonstrate they can mitigate for the shortfall.

Junior groundwater users failing to establish the ability to mitigate with an approved mitigation plan face curtailment.

Groundwater users

The order follows six months of upheaval between senior surface water users and junior groundwater users before they agreed on a stipulated mitigation plan in November.

All members of the Idaho Ground Water Association are protected under that plan, said Thomas J. Budge, IGWA’s attorney.

“Groundwater users who comply with approved mitigation plans have safe harbor from curtailment under the methodology order,” he said

IDWR’s “methodology order” prescribes how water rights are administered under the SWC delivery call. Under the order, IDWR evaluates the water supply and water demand of the SWC at several intervals during the irrigation season, and then orders curtailment if the predicted water demand is greater than the predicted water supply.

Reservoir storage

The latest curtailment order is based on impacts to the amount of water SWC members have in their reservoir storage accounts at the end of the irrigation season, he said.

“Although the irrigation season has ended, prior court decisions entitle SWC members to a certain amount of ‘carryover’ storage. When a shortfall occurs, IDWR orders curtailment, as with the latest order,” he said.

Since the irrigation season has ended, the curtailment applies to non-irrigation diversions that are not covered under an approved mitigation plan, he said.

“The ability for IDWR to order curtailment under the methodology order at various intervals throughout the irrigation season makes sense on paper. But it is extremely problematic in practice because it puts water users at risk of curtailment with little or no advance notice and can result in water being turned off to large amounts of growing crops and growing livestock,” he said.

Safe harbor

“This latest curtailment order highlights the value of the 2024 Stipulated Mitigation Plan, which prescribes a more pragmatic approach to managing groundwater supplies and meeting water needs of senior surface water users,” he said.

Groundwater users covered by the following approved or pending stipulated mitigation plans are not affected by the order, if they are in compliance with their mitigation plan:

• The 2024 SWC/Ground Water District Stipulated mitigation plan.

• The A&B Irrigation District mitigation plan.

• The Coalition of Cities mitigation plan.

• The Southwest Irrigation District mitigation plan.

• Water Mitigation Coalition mitigation plan.

“The majority of water users in the ESPA are in an approved mitigation plan and the impacts from this finding are relatively minor because of the smart foresight of water users in adopting these mitigation plans,” Director Weaver said.