BOISE, Idaho — The Idaho Supreme Court has rejected surface water irrigators’ arguments that they should automatically be made whole for their full water rights when they issue calls against junior groundwater pumpers.

In its Dec. 17 opinion, the high court upheld a district court ruling supporting current Idaho policy, requiring that groundwater pumpers mitigate only for the actual amount of water senior surface water irrigators need to raise their crops.

Surface and groundwater are hydrologically connected in the Snake River Plain, and groundwater pumping can decrease the system’s natural flows.

In court documents, the Surface Water Coalition — representing several state irrigation districts and canal companies — has maintained that “a decreed or licensed water right creates a presumption that the full extent of the right has already been defined by its beneficial use.”

Lynn Tominaga, executive director of Idaho Groundwater Appropriators, believes his side “won all of the important issues,” and the Supreme Court ruling will maximize water irrigators can put to good use.

However, coalition attorney Travis Thompson is also claiming victory, believing the ruling clarifies policy and affords greater flexibility for water regulators to make in-season adjustments to mitigation obligations as weather conditions change.

The ruling comes 19 months after the Supreme Court heard the case, which stems from a 2005 water call.

After the original call, former Idaho Department of Water Resources Director Karl Dreher issued an order requiring that mitigation be no greater than flows needed to irrigate senior right holders’ crops. The surface irrigators appealed the order to District Judge John Melanson, and both sides appealed aspects of his ruling to the Supreme Court.

The current methodology sets the annual mitigation obligation based on a surface water irrigator’s usage during a reference year or years with similar storage, natural flows and snowpack. The IDWR director is expected to determine that obligation annually by early April.

Under the current methodology, pumpers’ mitigation burdens can be reduced if the season proves to be wetter than reference years, but they can’t be forced to increase their obligations if the season is drier than expected. Thompson explained the Supreme Court affirmed that projections set prior to the irrigation season must also be adjustable for dry weather.

“I think we’re pleased with the adjustable baseline conditions,” Thompson said.

IDWR Deputy Director Mathew Weaver said neither side likes the methodology for determining mitigation obligations. The department has continued using the methodology and stayed multiple challenges to it since 2009, pending the recent Supreme Court ruling. Weaver expects hearings will soon commence to update the methodology.

In its ruling, the Supreme Court also upheld Melanson’s decision that groundwater pumpers shoulder the burden of proof to demonstrate that their wells won’t hurt senior surface water rights, and that the standard they bear is “clear and convincing evidence” rather than the more lenient “preponderance of the evidence” standard. Furthermore, Thompson noted the ruling adds a requirement that groundwater pumpers include contingency measures in their mitigation plans in case deals fall through for the replacement water they lease.

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