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AEL&P: Avalanche mitigation pays off

Diversion structure protects tower from 30-year avalanche

Posted: March 18, 2012 - 12:08am
An avalanche diverter is seen here near an electrical transmission tower in this undated photo provided by Alaska Electric Light & Power. (Photo courtesy Michael Janes, AEL&P)  Photo courtesy Michael Janes,AEL&P
Photo courtesy Michael Janes,AEL&P
An avalanche diverter is seen here near an electrical transmission tower in this undated photo provided by Alaska Electric Light & Power. (Photo courtesy Michael Janes, AEL&P)

Alaska Electric Light & Power didn’t dodge a bullet during a recent avalanche so much as deflect it.

The utility’s avalanche mitigation efforts paid off in early March when an installed diversion structure shunted a 30-year avalanche away from its 4/6 transmission tower.

“The dry blast from this avalanche was estimated to be a 3.5 out of 5 on the avalanche scale — termed medium to large — with the potential to occur every 30 years,” Debbie Ferreira, vice president and director of consumer affairs for AEL&P stated in a release.

Wet snow from the avalanche buried the 35-foot barrier to its mid-point and continued past the structure down to the ocean. And lights stayed on in Juneau.

But the winter isn’t over yet.

A large avalanche on April 16, 2008 spurred the construction of the diversion.

The avalanche forced the utility to run expensive diesel generators during the months-long repair.

In that avalanche, five transmission towers were downed and two others damaged.

“To date, we have greater snow load than we had in April of 2008 — when the first avalanche hit,” Ferreira said. “As temps are gradually warming, we anticipate more avalanche activity.”

Activity tends to increase in April, she said.

An avalanche in November 2011 put the utility on 60 percent diesel power during repairs.

AEL&P uses diversion structures and purges avalanche areas with preventive releases to keep its 40-mile transmission line intact.

The utility uses a concussion release mechanism called the Daisy Bell. The bell is flown in by helicopter and a gas charge is remotely detonated within the bell, triggering an avalanche.

Though the diversion saved Juneau’s electrical lifeline this time, the utility’s work is not done, Ferreira said.

“Our avalanche team continues to forecast avalanche risk, monitor the line and mitigate as necessary,” Ferreira said. The utility plans to install two additional diversion structures in next year.

• Contact reporter Russell Stigall at 523-2276 or at russell.stigall@juneauempire.com.

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