Columbia-Pacific Northwest Region

American Falls Concrete Spillway Rehabilitation Project

Questions and Answers

What are the river flows below the dam going to be during the spring, summer and fall of 2022?

Outflow from American Falls Dam will be seasonal and is anticipated to be in the range of 12,000 to 15,000 cubic feet per second during peak irrigation delivery in the summer and will depend on other downstream water delivery obligations, including potential additional flow augmentation delivery and Idaho Power storage deliveries. In the fall season of 2020 and 2021, there were some adjustments to American Falls Dam outflows and Lake Walcott pool levels to extend the work window at American Falls Dam. In 2022, fall flows and Lake Walcott pool levels are anticipated to be normal with no plans to adjust Lake Walcott pool levels and associated American Falls Dam outflows.

Will there be fishing concerns this recreating season?

Outflows from American Falls Dam will continue to follow seasonal outflows for irrigation and other water deliveries. We do not anticipate any impacts to fishing. Anglers should be aware that flows can change at any time downstream of the dam.

What does water year mean?

The water year extends from the winter to fall of each year, e.g., mid-October 2021 to mid-October 2022 constitutes water year 2022.

What does non-irrigation and irrigation season mean?

The non-irrigation season extends from mid-October to late March when irrigation is generally not occurring through the winter months. The irrigation season extends from late March to mid-October each year when crops are being irrigated.

The American Falls Dam concrete spillway rehabilitation project resumes on or around May 9, 2022. Construction activities are expected to continue no later than Oct.15, 2022.

What are the river flows below the dam going to be during fall 2021?

Outflows from American Falls will follow seasonal outflow for downstream irrigation deliveries until approximately late Sept. From late Sept. to mid-Oct., outflow from the dam will be lower than actual downstream irrigation use by approximately 1,800 cfs to allow Lake Walcott’s pool elevation to be lowered, in anticipation of higher than the typical non-irrigation season outflow for American Falls Dam after mid-Oct. The typical non-irrigation season outflow is 350 cfs. From mid-Oct. through the 2021 construction period, outflow will be 1,000 cfs, which corresponds to the minimum flow that can pass through the powerplant units at American Falls Dam, allowing work in the stilling basin area to be done after the irrigation season ends.

How will Lake Walcott levels be affected this fall?

There are no anticipated affects to Lake Walcott’s pool level in 2022 due to the American Falls Spillway Rehabilitation Project. Lake Walcott levels are anticipated to follow normal seasonal levels in 2022.

Reclamation is actively working with the Idaho Department of Fish and Game, Idaho Department of Parks and Recreation, Idaho Department of Environmental Quality, U.S. Fish and Wildlife Service, and Idaho Power, to monitor for potential affects to river conditions downstream of American Falls throughout the spillway rehabilitation project.

Reference
Upper Snake River Systems Water Operations >>