By Joyce Edlefsen
REXBURG — A Rocky Mountain Power Co. official told the Henry’s Fork Watershed Council Tuesday in Rexburg that modifications and reconstruction of its Ashton Dam will take more time than originally announced.
The company wants to make sure it doesn’t run into icing problems as it does various phases of the project, according to Mark Stenberg. With the climate in the Ashton area offering a short construction season, the company wanted to be sure it could accomplish the work and still be able to bring the reservoir levels up to prevent icing.
So instead of starting a two-year project next month, the company’s contractors will begin a three-year project.
The first year will focus on construction of a bypass channel around the dam. The second year will include construction of a coffer dam. And the final year will include work on the embankment on the face of the dam.
Since announcing in December that the old dam would get major improvements to correct structural problems, company representatives have been met with affected irrigators and have been consulting with a plethora of federal and state agencies that must permit parts of the work or agree to the plans.
In response to concerns raised by the public when the company’s plans were announced, more focus has been placed on keeping sedimentation to a minimum during the work.
A sediment study is planned with ERI, the same company that conducted studies for the Chester Hydroproject, being retained to do that work.
As recommended by the U.S. Fish and Wildlife Service, the start date for drawing down the reservoir will be March 15 each year so the water levels will be down before waterfowl nest.
Historical significance of the structure also is being considered, and a 404 permit is being obtained from the U.S. Army Corps of Engineers.
The company has corresponded with the Idaho Fish and Game Department concerning compliance with its Federal Energy Regulatory Commission license provisions related to fish and wildlife.
FERC and a group of engineer consultants also are being consulted and are checking off on aspects of the projects as it proceeds, Stenberg said.
And by providing an update to the Watershed Council, the company is meeting its promise to keep the public informed about updates on the project.
Stenberg says the company discovered a map and survey that shows what the reservoir pool will likely look like when the water is drawn down to 5,130 feet, about the elevation the project will require.
At that elevation the reservoir will be about one-half its normal pool.