In the spring of 2008 and winter 2009, two large avalanches caused damage to several towers along a 43-mile power line route from the Snettisham Lake hydroelectric facility. As a result AEL&P had to use backup diesel generators to meet power demand.
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.
"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 addition to completing the protective structure at tower 4/5 this season, crews were also able to prepare the site and install foundations for a diversion structure at tower 4/4. This will allow for completion of that structure in a future field season and at a lower cost than having to mobilize crews to do foundation work a second time.
The cost for constructing a diversion structure is roughly $2.2M each. AEL&P received a grant of $2M 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 as necessary to prevent the buildup of larger potential avalanches.
