The penstock at the Salmon Creek Dam in Juneau was damaged last week in a landslide caused by heavy rains. The penstock is a steel pipe that carries water between the dam and the powerhouse. According to Alaska Electric Light & Power (AEL&P), the damage occurred about 1,000 feet downstream of the dam. AEL&P provided the following comment to the Landmine:
The valve that controls the water flow from the reservoir into the penstock was closed remotely from our operations center when loss of penstock pressure was detected at the plant. This damage to the penstock did not result in any downstream flooding and the Salmon Creek Dam was not damaged. All monitoring equipment for the dam has remained fully functional. Because of the damage to the penstock, the plant will remain out of service until repairs can be made.
The Salmon Creek dam is safe and all inspections and testing have been completed. After the inspection of the dam and the penstock it became clear that the repairs to the penstock would not be a quick fix, so the low level outlet valve at the base of the dam was opened to 25%. This was done in order to keep the reservoir elevation at normal levels. AELP is in compliance with all plans and regulations that relate to the dam. AELP has notified the Federal Energy Regulatory Commission (FERC) about the damage to the penstock and will continue to keep FERC updated on the plans for repairs to the penstock.
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As a result of the landslide the Salmon Creek Trail will remain closed until AEL&P can make repairs. It won’t be clear how long the repairs will take until AEL&P fully assess the damage. AEL&P has shifted the load to other hydroelectric plants to cover the loss of power from the Salmon Creek Dam. In a normal water year Salmon Creek provides 6% of megawatt hours. All of Juneau’s power comes from several hydroelectric power plants run by AEL&P.
The Salmon Creek Dam was built in 1914. It was the first constant-angle arch dam built in the world. The dam provides hydroelectric power generation to Juneau. The reservoir provides drinking water to Juneau and water for a salmon hatchery. The current reservoir elevation is 1,128.3 feet. The control height is 1,140 feet and the spillway is located at 1,172 feet.