The project required historical research into the original construction of the nearly 100-year-old dam, careful construction techniques and a three-year phased construction schedule.
The reconstruction of the Ashton Dam was a unique project in the history of PacifiCorp, which operates as Rocky Mountain Power in Idaho, Utah and Wyoming. The project required historical research into the original construction of the nearly 100-year-old dam, careful construction techniques and a three-year phased construction schedule.
The utility worked with federal and state officials and interested stakeholders for a number of years on this project. Detailed planning and coordination with numerous groups was required to meet the needs of state and federal water quality requirements, farmers who use the Ashton reservoir for irrigation and sport fishing groups concerned about the impact of the project on a world-famous fishing area.
“We extend our special thanks to the nearby property owners and farmers who use Ashton reservoir for irrigation and recreation, together with the community of Ashton,” said Troy Stout, project manager, PacifiCorp. “We appreciate their patience and understanding during the course of this project. We are also grateful for the work of state and federal agencies, sport fishermen and the Henry’s Fork Foundation, who assisted us with the planning and execution of the reconstruction. It has been a very productive partnership.”
The project was closely coordinated with environmental, federal, state regulatory and permitting agencies who have authority over hydroelectric projects. Extensive consultation and planning for the safety of workers and the public — as well as water quality and fishery considerations — have been a priority in this process.
The project featured extensive preparatory steps, including explorations and design that began in 2003. Jack Kolkman, hydro operations manager, said a number of alternatives for dam reconstruction were considered. The company sought the least disruptive options for water quality and consideration for those who use the reservoir for agriculture and recreation.
The company decided that complete restoration was the best option, rather than lesser measures that might have solved the problems of the aging structure, but were less-certain. Permitting for the project began in 2007.
PacifiCorp worked 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 construction method chosen was an industry standard, but because of the age of the dam, its interior structure was not completely known. This required a series of core samples to be taken to determine the materials and conditions in the interior of the dam.
The level of the reservoir was carefully managed during the evaluation and construction process. Residents near the area and farmers who use the reservoir for irrigation were contacted directly to inform them in advance when the reservoir was lowered or raised to allow for evaluation and construction activities to proceed.
The first step was construction of a diversion tunnel around the dam beginning in July 2010. This provided a way to redirect, yet maintain stream flow and allow the dam reconstruction to proceed. Preparation continued in 2011 and early 2012 with connection of the tunnel to the reservoir and construction of cofferdams both downstream and upstream of the dam to allow the work to proceed.
In January, March and April of 2012, replacement and repair of concrete supporting structures was completed on the downstream side of the power house. Continuing work through summer and fall of 2012 included excavation and reconstruction of the earthen and rock-fill portion of the dam on the upstream side and replacement of the dam’s concrete crest.
“This has been a career project for me; and I’ve been here 30 years. There has been nothing really like it in my experience,” Jack Kolkman, director of hydro plant operations for PacifiCorp Energy, said.
To completely rebuild Ashton Dam has been extremely challenging, but also fascinating and rewarding, according to Roger Raeburn, environmental manager for PacifiCorp Energy.
“This kind of work had no modern precedent at PacifiCorp. After all, there are no new dams being constructed. The coordination that was required among state and federal agencies, property owners, farmers and recreational users was extensive. We are grateful for the cooperation and input of these organizations, which greatly contributed to the project’s success.”
Project cost is approximately $25 million. PacifiCorp provided all funding.
A number of contractors and consultants were involved in the project.
W. W. Clyde & Company of Springville, Utah, was the principal contractor for construction services. URS Corporation, headquartered in San Francisco, Calif., served as project engineer, designer, and construction manager, while Cirrus Ecological Solutions, LC, of Logan, Utah, was principal environmental consultant for sediment, water quality, and spawning gravel assessments.
Historic and cultural resources consultant SWCA, Inc, based in Phoenix, Ariz., also participated in the job, as did Cornforth Consultants, Inc., of Portland, Ore., which handled ongoing dam instrumentation data collection and reporting. Bear River Electric of San Mateo, Calif., was responsible for installation of the instrumentation.
The first major challenge was evaluating the condition of the dam and evaluating all options, according to Kolkman. When reconstruction was selected as the most prudent option for the utility’s customers, a detailed evaluation was conducted, including core samples to determine the internal conditions of the dam.
The level of the reservoir needed to be coordinated with the needs of farmers who use the water for irrigation and the requirements of the reconstruction project. A detailed schedule of reservoir level changes was developed and shared with stakeholders to accommodate both the needs of agriculture and the construction project.
During the construction phases it was necessary to relocate fish as water was diverted from areas near the dam during the work. This work was accomplished in cooperation with the Idaho Department of Fish and Game using specialized equipment to stun the fish with electric shocks, net them and relocate them unharmed outside the work area.
Three relocation efforts were needed and were judged highly successful. One of the largest concerns of residents and recreational users in the area was about potential negative impact of sediment that might be introduced during reconstruction.
Both state agencies and fishing enthusiasts were wary because of sediment problems that occurred in 1992 with work on the Island Park Dam, upstream of Ashton. PacifiCorp project managers conducted and participated in many extra meetings to explain all they were doing to control sediment into the river and minimize environmental impacts of the reconstruction. The results were impressive, even to skeptics.
“I’m pretty happy with the way things have turned out,” said Dan Garren, Fish and Game’s fisheries manager in the Upper Snake Region.
“They avoided a large-scale sediment event and, when you think about the scope of the project up there, that’s pretty amazing.”
Garren believes the power utility’s communication and outreach to anglers was “awesome. PacifiCorp listened and I really think they stepped up their efforts,” Garren said.
Brandon Hoffner, executive director of the Henry’s Fork Foundation, said the utility was great to work with.
“They have been very responsive to our concerns,” he said. “We are very happy with the fact they were able to get the project done with what looks like minimal effects to the river.”
The project involved a large selection of equipment. The fleet at work included:
• Caterpillar articulating 730 and 740 dump trucks (with and without ejector), used to transport existing dam material waste and import new material.
• Caterpillar 375, 330BL, 330CL, 325C, 345B, and 304D trackhoes, which handled dam excavation, material placement, and loading trucks with new dam material.
• Caterpillar 623F paddle-wheel scraper, used for new core material excavation.
• Putzmeister Telescopic TB 130 belt conveyor, which carried out material placement in the reservoir, new embankment filter, and material placement.
• Caterpillar TH-6 and TH-560B telehandlers, utilized for miscellaneous site work.
• Caterpillar 988B and 950G front end loaders, for material loading and stockpiling.
• Grove RT855B and 890E cranes, used for concrete placement and formwork, scaffolding construction, and material placement in otherwise unreachable locations.
Employee staffing was between 25 and 75 depending on the nature of construction activity.
Subcontractors and consultants employed by principal contractor W. W. Clyde & Company included CDM-Smith, of Cambridge, Mass., subconsultant for the Phase 2 cofferdam and dewatering design. Butte, Mont.-based O’Keefe Drilling Company, constructed the upstream dewatering wells, and Portadam, Inc., headquartered in Williamstown, N.J., served as supplier and constructor of the downstream cofferdam. Other W. W. Clyde & Company subcontractors included Rain-for-Rent (dewatering) and A-Core, Inc. (concrete demolition), both of Idaho Falls, Idaho, Independent Drilling, based in Blackfoot, Idaho (downstream dewatering wells), Swiss Precision of Ashton, Idaho (labor and fencing), Harris Rebar (rebar supplier and installer), and Nicholson Construction (drilling and grouting for left-abutment grout curtain) both headquartered in Salt Lake City, Utah, as well as Walters Ready Mix, of Rexburg, Idaho (concrete supplier), Superior Blasting, Inc. based in Nampa, Idaho (blasting), and Potable Divers, Inc, in Vernal, Utah (cofferdam inspection).
URS Corporation also engaged subcontractors for the project. Materials, Testing, and Inspection (MTI), based in Ontario, Ore., handled third-party quality control testing for them, while third-party quality control laboratory TerraSense, LLC, located in Totowa, N.J., was responsible for select soil testing.