av diversion

Avalanche Diversion

Avalanche diversion structures now guard the Snettisham line


- (above) AEL&P Avalanche Field Technician Ed Shanley stands in front of our newest avalanche structure. Photo by Mike Janes.

Three massive avalanche diversion structures protect three transmission towers in an avalanche-prone area about four miles south of the Snettisham Hydro Project, Juneau's primary source of hydropower.

"These diversion structures are huge steel "wedges" constructed uphill of the transmission tower," said Eric Eriksen, vice-president of Transmission and Distribution. "If an avalanche comes toward the tower, these structures are designed to split the avalanche and divert it around the tower." In March of 2012, the diversion structure above tower 4-6 successfully diverted a medium-large avalanche away from the tower and prevented a major outage. AEL&P has focused its avalanche protection efforts in the area of mile 3 and mile 4 of the Snettisham transmission line. The towers in this area are the ones that were damaged in the avalanches of 2008 and 2009.

The cost for constructing a diversion structure is roughly $2.2 million each. AEL&P received a grant of $2 million from the State of Alaska Renewable Energy Fund to assist in the cost of constructing the diverters.

"While all our costs are recovered through electric rates," explained Eriksen, "with the grant from the State, we were able to build these structures through our normal capital budgeting process. The cost of this year's work is already included in our current rates." In addition to building protective structures at specific towers, AEL&P also performs active avalanche control on the Snettisham line. An avalanche specialist on AEL&P's staff monitors weather and snow conditions in the area on a daily basis, and performs controlled releases of the snowpack using the new Daisy Bell Helicopter Avalanche Control System, see below. This control work is necessary throughout the winter and early spring to prevent the buildup of larger potential avalanches.

Daisy Bell

The Daisy Bell Helicopter Avalanche Control System is designed to be slung under the aircraft where it uses an oxygen and hydrogen mix to produce very controlled blasts to move snow safely down a slope. AEL&P has been using the system since 2010.