Juneau still on hydropower, even after controlled avalanche took out transmission line

Thane pole structure
Pole structure holds up a set of electrical transmission lines along Thane Road in Juneau. (Photo by Matt Miller/KTOO)

Earlier this month, a controlled avalanche damaged a power transmission line along Thane Road. It’s the main power line that runs from two major hydroelectric facilities at Lake Dorothy and Snettisham, southeast of Juneau.

But Juneau is still running off that hydropower because there’s a second, parallel transmission line that runs underground beneath an active avalanche path.

“Both these lines are typically in service during normal operations,” said Debbie Driscoll with Alaska Electric Light and Power, Juneau’s electric utility. “They offer some redundancy, which is great in the event that one line needs to be taken out of service for maintenance or repairs.”

Driscoll said damage to the overhead line during the controlled avalanche was limited because the transmission lines are connected to pole structures with what are called breakaway links.

“We use breakaway links on that section of lines so that the line will just break free from the poles,” Driscoll said. “That minimizes the chance that the poles themselves would break or be damaged.

Driscoll said it makes their repairs easier whenever there is an avalanche.

“And then we only have to rehang the line as opposed to having to replace the pole structures as well,” she said.

So the lines aren’t broken. They’re just disconnected from the poles.

Driscoll said their crews cannot safely return and rehang the lines until the state Department of Transportation resumes avalanche control operations above Thane Road. She said that will happen after the current cycle of storms.

In 2008 and 2009, avalanches destroyed up to three towers near Snettisham for the above-ground transmission line providing hydropower for Juneau. The city ran on backup diesel generators for several weeks or months in both cases, and residents paid dramatically higher electric bills.

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