Concrete rehabilitation work on the downstream side of American Falls Dam, which began in early June, is on schedule and expected to conclude in November of 2021, U.S. Bureau of Reclamation officials said.

Improvements to the spillway, the stilling basin immediately below it, and other parts of the 42-year-old dam aim to extend the life of the structure and modernize it.

The dam and the reservoir behind it, on the Snake River near American Falls, Idaho, supply water for irrigation, power production and other uses to much of the state’s south-central region.

Crews recently started upgrading concrete on parts of the downstream face, and soon will complete concrete repairs on entrance adits. Preparations are underway for placing concrete on part of the spillway.

Nicole Carson, project manager with Reclamation, said plans call for finishing work on the spillway apron this year, and in 2021 completing repairs to the stilling basin — an in-stream structure that dissipates the energy of water as it enters — more concrete upgrades to the dam’s face, and improvements to gate-operator decks. Work on the spillway apron and stilling basin involves replacing roughly 6-inch-thick concrete.

“Construction is proceeding as planned,” she said. “We are continuing to monitor and coordinate as we need to.”

Water-delivery operations have not been affected, and no impact is anticipated, said Brian Stevens, water operations manager for the Bureau’s Upper Snake field office.

Idaho Power said in a statement that downstream irrigators should not be impacted by the repair work, partly because Reclamation can use Lake Walcott to assure adequate supplies to make up for reduced outflows from American Falls.

Stevens said a group that includes Reclamation, Power County, Idaho Power and state Fish and Game and Environmental Quality departments frequently discusses project elements including potential impacts to water quality.

Water enters the river channel through the spillway or Idaho Power’s plant. Carson said the company and Reclamation would adjust flows to aid water quality if spillway or stilling-basin work changes river depth.

The approximately $7.8 million project is funded by Reclamation budget appropriations, Idaho Power Co., and reservoir space holders who have rights to water stored in the reservoir. Next year’s work is scheduled to start in June.

The contractor, Winspear Construction LLC, Boise, built a temporary access road as an alternative to State Highway 39.

American Falls Reservoir can hold up to 1,672,600 acre-feet of water. The dam, which replaced a predecessor, is 94 feet tall.