TWIN FALLS, Idaho — An early assessment by the Idaho Department of Water Resources determined irrigators relying on the Twin Falls Canal Co. will face a shortfall of 74,100 acre-feet this irrigation season.

The injury to the Twin Falls Canal Co. was calculated to occur between the Blackfoot and Minidoka reach of the Snake River. TFCC has senior water rights dating to October 1900.

All groundwater users who draw water from the Eastern Snake Plain Aquifer with a priority date junior to March 31, 1954, must be covered by an IDWR-approved mitigation plan by May 2 or face curtailment.

An order relaying the finding went out to water users on Thursday.

This is just step one in the process, with IDWR looking at the reach gain analysis, said Jay Barlogi, TFCC general manager.

“We’ll have to see how the season works out,” he said.

Junior rights

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 senior surface water right holders and the obligations of junior groundwater pumpers to curtail water use or mitigate for depletions.

There was good snowpack this year in the mountains, and reservoirs are full. But the water supply is also determined by the Eastern Snake Plain Aquifer, he said.

“In recent years, it’s declined significantly,” he said.

The 74,100 acre-foot shortfall is based on the April 4 forecast of 3.37 million acre-feet of water flow at the Snake River Heise gage from April 1 through July 31.

The forecast is calculated by the Bureau of Reclamation and U.S. Army Corps of Engineers based on mountain snowpack and predicted streamflow runoff. The April forecast flow volume equates to 102% of the average.

The shortfall determination also considers current groundwater levels in the aquifer. Despite concerted management efforts, levels measured in the spring of 2023 were at or near all-time lows dating back to the 1950s. The low ESPA groundwater levels affect spring flows and surface water flows in the Snake River.

No guarantee

“We hope the springs, reach gain and flows will hold up to provide that water we need so badly to get to the end of the irrigation season. But there’s no guarantee,” he said.

The aquifer hit a historic low in 2022 and another new low in 2023. There’s no indication it’s going to get better in 2024, he said.

The weather ahead could be cool and wet, which would decrease demand. But it could also get hot and dry, leading to greater demand than currently anticipated, he said.

The shortfall is enough to cover 74,100 acres with a foot of water.

“Typically across the state, farmers need between 2 feet and 4 feet of water to raise their crops,” he said.

There are some mitigation plans in place from the 2015 Groundwater Settlement between surface and groundwater users, and they’re meant to handle this situation, he said.

“But it has been a bit of a struggle in recent years,” he said.