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