Moyie dam receives repairs
The Moyie dam has received repairs of the concrete to the (left) western wall, spillway and the center wall. Further repairs will be made to the east (right) side of the dam next year.
(Photo by Cynthia Bonsant)
BONNERS FERRY — The first two phases of improvements to Moyie Dam have been completed by resurfacing the west spillway, west wall and center wall.
Mike Klaus, city engineer, said that the dam was completed in 1948 and after 70 years of deterioration, the face of the structure was in need of repair.
City Administrator Lisa Aliport said repairs to the city-owned dam were needed to keep it operational and for Bonners Ferry to keep its license in good standing with the Federal Energy Regulatory Commission. The project was funded by a $4.125 million bond which passed in May.
Some places on the spillway required almost a foot of new concrete, Klaus said. After the old concrete was removed with a high powered water hose, the face of the dam was kept dry for remodeling by directing water to the valve which takes it to a turbine in the water house. Water was then re-released into the river without passing over the dam.
Concrete today is made from crushed gravel and angular rocks, however when the dam was built, the most available rock was rounded river rock that was likely found near the job site, Klaus said.
“I know that the terms concrete and cement are used interchangeably, but it turns out that cement is one of the components of concrete,” Klaus said.
Concrete is typically comprised of cement, water, fine aggregates (crushed rock or sand), coarse aggregates, physical admixtures such as fibers, and chemical admixtures that facilitate placement of the concrete and add air.
The expansion and contraction of concrete that can lead to cracking can be mitigated by adding air, he said. This is also called air entrainment. Air entrainment is provided when a chemical is added that creates little air bubbles in the concrete once it is placed. Those little air bubbles help absorb the forces of expansion and contraction, reducing the potential for cracking, Klaus said.
Klaus said that when the dam was originally built, it likely didn’t have air entrainment. This left the dam’s surface more susceptible to cracking due to natural freeze and thaw cycles. In addition, the occasional log coming over the dam’s face also contributed to damage sustained over the years.
Klaus said that patchwork was done in the 1980s and 1990s, which has helped maintain the dam.
The west spillway has been repaired in the first two phases. The east spillway and east wall will be repaired in the third phase of the project next year. Construction crews “beefed up” the dividing wall of the two spillways, by adding more concrete and widening the center wall.
The Moyie Dam provides 25% to 30% of the overall electricity needed in Bonners Ferry. Klaus said that if the city can keep the dam operational then they won't have to spend money on power through Bonneville Power Administration.
When the bond passed overwhelmingly in support for the improvements of the dam, Klaus said that this told city officials that ratepayers find value in having a dam in working and operational use. He said in order to keep it operating, the Moyie Dam has to be maintained.
Since it is a run-of-a-river dam, its production and energy waxes and wanes per season. The goal, said Klaus, is to keep the dam operational for the next 100 years.