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Reclamation to begin repairing spillway at Alcova Dam in October

The Wyoming Area Office of the U.S. Department of Interior’s Bureau of Reclamation says it is preparing for contract construction work at Alcova Dam following the 2020 irrigation season.

“Completion of this project is important in order to ensure the continued reliability of the spillway structure,” said Wyoming Area Manager Carlie Ronca. “It includes replacing deteriorated concrete on the downstream spillway and stilling basin retaining walls, retaining wall caps, and floor slabs in designated areas. Additionally, it will replace downstream spillway and stilling basin handrails and chain-link fence.”

To accommodate the construction work, the reservoir will be temporarily lowered an additional 29 feet below the normal winter operating elevation of 5,488 feet, down to elevation 5,459 feet, which is below the level of the spillway crest.

Reservoir levels will not be affected during the summer and will remain at normal levels through the end of September. Spillway and stilling basin access work will start after Oct. 1 and be completed by March 31, 2021, to avoid peak spillway discharge season.

During October, Alcova Reservoir will be lowered 39 feet at an average rate of about 15 inches per day. In a normal year, the reservoir is lowered about 5 inches per day for a total of 10 feet. The flows below Alcova and Gray Reef dams during October 2020 will be about 2,000 cubic feet per second (cfs) through Oct. 20 and then be reduced to the normal winter flow rate of 500 cfs. Alcova Reservoir is planned to be refilled to normal winter operating elevation in the last half of December. This will result in temporary higher than normal releases through the Miracle Mile and from Pathfinder Dam and minor declines in reservoir levels in Seminoe and Pathfinder reservoirs. By Jan. 1, 2021, Alcova Reservoir will be restored to its normal winter operating range.

Alcova Dam, on the North Platte River in Wyoming, is a zoned earthfill structure rising 265 feet above its foundation and containing 1,635,000 cubic yards of material. It was completed in 1938. The dam impounds water for a 41.4-MW hydroelectric powerhouse that was built in 1955 and is located on the right bank of the river, opposite the toe of the dam. Reclamation did not indicate if the work will affect generation from the facility.

Reclamation is the largest wholesale water supplier and second largest producer of hydroelectric power in the U.S. Its facilities also provide substantial flood control, recreation opportunities, and environmental benefits.