Reconstruction Project on Ashton Dam Begins This Week
July 20, 2010
ASHTON, Idaho—After extensive planning, the project to improve the Ashton Dam to modern construction standards will begin this week with construction of a bypass tunnel to allow the Henry’s Fork River to pass around the dam while the work on the dam is conducted in 2011. The entire project is scheduled to be completed in 2012.
Because the tunnel will be constructed through bedrock at the side of the dam, drilling and blasting will be required. Residents near the dam and reservoir may notice the sound of drilling and will likely hear loud reports from the blasting as the tunnel is constructed. This work could begin as early as Wednesday, July 21. The work to build the tunnel is expected to take much of the next five months.
PacifiCorp, which operates as Rocky Mountain Power in Idaho, has worked for several years with federal and state officials and interested stakeholders on the planning and preparations for this project. Project planning was closely coordinated with environmental, federal, state regulatory and permitting agencies who have authority over hydroelectric projects. Extensive consultation and planning for safety and water quality considerations have been a priority in this process.
Warning horns will be sounded before detonating each blast, and surface blasting will take place only during daylight hours. Drilling and blasting inside the tunnel will be conducted during daylight and nighttime hours. These activities will likely be heard by those living close to the project, particularly downstream from the dam. Others in the surrounding area may hear this work, as well.
PacifiCorp has selected W.W. Clyde & Co., headquartered in Springville, Utah, as its contractor in the first phase of its three-year project to improve Ashton dam. The company was selected by PacifiCorp because of its expertise in this type of construction.
“We recognize that this construction has an impact on both residents and recreationalists as we embark on this large and important project,” said Robert Atwood, project manager. “Our company is committed to long term and continuous operation of the Ashton hydroelectric project because it produces low-cost electricity for our customers. Our first concerns are for the safety of the general public and of employees and contractors working on or near the project.
“We also respectfully request that people not attempt to view the construction up close,” Atwood said. “Because of the emphasis on safety, no public viewing of the construction will be allowed at this time. PacifiCorp employees or representatives are required to escort any persons away from areas near the project site to safe locations.”
PacifiCorp has been working with the Federal Energy Regulatory Commission and the Idaho Department of Water Resources Dam Safety since 2004 to evaluate the structural conditions of the dam and determine scope of work required to upgrade the structure to modern standards.
The utility consulted with qualified structural engineers and engineering geologists, all with extensive experience with the design and construction of embankment dams like Ashton.
The need to pursue a more detailed evaluation of the dam’s condition was identified in spring 2004 and that evaluation was conducted periodically over several years, requiring adjustments of the reservoir level from time to time. Throughout the evaluation phase, company officials met periodically with those who use Ashton Reservoir for irrigation and for recreation to keep them informed of the project and the schedule of work as it developed.
About Ashton Hydro Plant
The Ashton Hydro Plant is operated by PacifiCorp Energy, which provides electric generation services to Rocky Mountain Power and Pacific Power. The project is located on the Henry’s Fork of the Snake River, approximately 2.5 miles west of the city of Ashton, Idaho. The project began operating in 1914 and was later purchased and expanded in 1925 by Utah Power & Light Co. (a predecessor company of Rocky Mountain Power). The project consists of a dam and powerhouse with three generating units. The dam is a rock and earth filled structure, 60 feet tall and 226 feet long, with a 70-foot-wide concrete intake and 82-foot-long spillway. A roller compacted concrete cap was installed in 1991 to protect the embankment during flood flows. Unit No.1 is rated at 2.85 megawatts. Units No.2 and No. 3 are rated at 2.5 megawatts.
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