A second avalanche diverter protecting Juneau’s major power source has been completed.
It’s part of AELP’s plan to mitigate powerful snow slides that threaten towers along the Snettisham line.
The company has been working on the plan since 2008, when a series of huge slides – considered a one-hundred year event – severed the capital city from low-cost hydroelectric power for 45 days, forcing the company to burn expensive diesel fuel.
Eric Ericksen is vice president of transmission and distribution for Alaska Electric Light and Power. He says most of the mountainous terrain along the line is avalanche prone, but the site near Snettisham is the steepest and spans about a 10-thousand foot section of line, where there are eight towers.
The diverters are large steel column and beam structures bolted to the bedrock, surrounding the transmission towers. The first was completed in 2009 to protect tower 4-6. It was truly put to the test this past March when snow from a massive avalanche reached about the 24-foot level of the 40-foot diverter, Ericksen says.
“The structure is about 200-thousand pounds of steel sitting in a wedge shape right in front of it and (snow) plowed into and kind of curled around the edges,” he says. The tower was not damaged. “So we were happy and we’re moving forward with plans to build more.”
The latest diverter protects tower 4-5; the foundation is already in for the third to be built around tower 4-4.
In addition to the three steel diverters, the mitigation system includes a number of actions. One particularly vulnerable tower has been taken out and the transmission line moved, other towers have been beefed up, and break-away links installed, so if there is damage to any structures, it will not have a cascading effect among other towers.
AELP also conducts avalanche control on the Snettisham line, to bring down snow before it builds up.
“We get a lot of inquires, so I like to think that we’re at this point kind of leading the industry in the country on avalanche mitigation and students and modeling and that, trying to evaluate options,” Ericksen says.
Each diversion structure costs about $2.2-million, covered in part by a grant from the state’s Renewable Energy Fund. AEL & P rate payers are paying the rest, factored into current rates.