Aquifer recharge

Managed aquifer recharge is conducted at the Milepost 31 site operated in American Falls Reservoir District No. 2 in Magic Valley.

BOISE — Idaho has nearly met a long-term goal set in 2009 of minimizing its annual impact on the Eastern Snake Plain Aquifer by 600,000 acre-feet, according to state water officials.

The analysis will be included in a January report to Idaho House Speaker Scott Bedke, R-Oakley, who requested a 10-year review of the state’s Comprehensive Aquifer Management Plan for the ESPA.

The CAMP plan — drafted based on recommendations of a diverse group of stakeholders — was intended to reverse a decades-long trend of declining groundwater levels within the ESPA, where water calls have pitted surface water irrigators with senior water rights against well irrigators with junior water rights. Officials initially thought it would take at least three decades to reach the lofty bar set by CAMP.

Neeley Miller, a senior planner with the Idaho Department of Water Resources, presented on the state’s progress toward reaching the 600,000 acre-foot goal during an Oct. 23 committee meeting.

Initial draft estimates Miller presented show work by the various ESPA stakeholders would reduce the average annual impact on the aquifer by 550,000 acre-feeet.

The original CAMP goals called for achieving 150,000 acre-feet of the 600,000 acre-foot reduction in consumptive use through managed recharge, explained Wesley Hipke, who coordinates the state’s managed aquifer recharge program. Recharge entails intentionally running surface water through strategically located unlined canals — or dumping water into adjacent spill basins — and letting it seep into the aquifer to replenish water pumped by irrigators.

Essentially, the aquifer serves as a natural storage reservoir, trapping surface water at times when flows exceed users’ ability to put the full volume to good use. The recharge effort stalled out, due to a lack of funding, until 2014, when the state Legislature opted to budget recharge funding on a continual basis.

The following year, the Legislature approved a resolution to be averaging 250,000 acre-feet of annual recharge by 2024. In 2016, irrigators with the Surface Water Coalition settled a water call against junior groundwater users. As part of the settlement, the groundwater users agreed to reduce their annual consumption by 240,000 acre feet.

The draft report shows the state nearly hits the 600,000 acre-foot goal when the settlement reduction and recharge program are combined with savings from pivot end-gun removal programs, other water-conservation efforts and cloud seeding programs.

Hipke said the state has averaged 249,000 acre-feet of annual recharge during the past five years, but that was a wet period and he believes more infrastructure will be needed to meet goals during future dry years.

The state’s natural-flow recharge right came into priority on Oct. 23 in the Lower Snake below American Falls Reservoir. The right enables Hipke’s program to recharge in the Lower Snake throughout winter until the irrigation season resumes.

As of Oct. 29, he was recharging about 200 cubic feet per second of water in the Lower Valley. Before the end of December, Hipke should have the infrastructure to accommodate more than 1,000 cfs in the Lower Valley. He explained the Milepost 29 recharge spill basin, located off of the Milner-Gooding Canal, has been closed for construction and will reopen in mid-December. Furthermore, the state intended to open its new Wilson Reservoir recharge spill basin off of Northside Canal on Oct. 30, adding roughly 250 cfs of additional capacity.

The Idaho Water Resource Board has also approved construction of two recharge injection wells off of Twin Falls Canal and four injection wells off of the A&B Irrigation District pipeline. The board is also finishing a project to expand its recharge capacity on the Egin Bench near Rexburg and will review concepts for developing another large-scale Upper Valley project at its November meeting.

In the Upper Valley, Hipke said the state has been recharging storage water for the Surface Water Coalition and Idaho cities.