The city of Ouzinkie, near Kodiak is working quickly to prevent their 25-year-old wooden dam from collapsing. Extensive rot was discovered on the Mahoona Dam earlier this summer and further inspections have shown that it could collapse at any time.
The dam provides drinking water and affordable electricity for the 161 year-round residents of the Spruce Island community.
Charles Cobb is the state dam safety engineer for the Department of Natural Resources. Cobb was first to inspect the dam earlier this year. He says a collapse could be devastating.
“The hydroelectric generator is just downstream of the damn. It’s a good ways but it’s still in the drainage. If the dam were to fail not only would there not be any water supply to the generator, the flood wave would knock out the generator building,” Cobb said.
The state requires all dams to be inspected every three to five years, depending on their classification. The dam was last inspected in 2007 and should have been inspected again in 2010, but it wasn’t. He says owners, in this case the City of Ouzinkie, are responsible for hiring engineers to conduct inspections.
“I was just following up on the overdue inspection and encouraged the mayor to get an engineer to look at it and he did. That’s when we discovered that the problem was much more substantial than it was several years ago,” Cobb said.
The dam was built in 1986 and was improved 10 later. It had a 20-year life expectancy, according to Ouzinkie City Mayor Dan Clarion. Clarion says the hydropower plant houses several hundred thousand dollars worth of new equipment that was recently purchased with money from the Denali Commission and without the hydropower generator the city would have to rely on diesel generators that would likely double or triple energy costs. If the city can get the water level down from 13 feet to about four or five feet, Clarion says damage will be limited.
“Yeah, we’re kind of on borrowed time right now. The recommendation by DNR is that we dewater the dam and keep it as low as we can and still maintain our water and our hydro system,” Clarion said.
Clarion added that their salmon stream is in the drainage and would be damaged if the dam collapsed at full capacity.
Right now the city is hurrying to install a new valve that would help bring the water level down and allow for further drainage in case of heavy precipitation. Engineers are trying to figure what is the lowest water level at which the dam can still operate. Until the new valve is installed Cobb says the dam can only lose water through the hydropower generator.
“If it rains faster than they can generate electricity it’ll fill back up again to the spillway level. That’s where we have some concerns. When it’s high enough to spill out of the spillway that’s a full load on the dam and it definitely raises some concerns,” Cobb said.
As for a back up plan for drinking water, the city is working to rehabilitate and old infiltration gallery setup at the river. Still, if the dam collapses before the water level is significantly decreased it could take that out as well.
Clarion says with any luck the new valve should be operable within the month. Structural repairs to the dam are still being considered, although the fixes would be temporary. The city has applied to the Alaska Energy Authority for money from their renewable energy fund that would help pay for a design plan and the survey work required for dam permitting. The city still needs to find an estimated $6 million to replace their crumbling dam. That’s something those involved say could take a few years.