Years of local avalanche mitigation efforts have resulted in the use of new techniques, equipment and institutional knowledge in related Juneau businesses.
Alaska Electric Light & Power protects its Lake Snettisham and Lake Dorothy hydroelectric power transmission lines from avalanche damage through passive and active preventative measures, such as avalanche diverters.
AEL&P contracted work on its three steel avalanche diverters at miles three through four of the Snettisham line; two are finished and one started.
“This is heavy construction work that we don’t have any specialty in,” Scott Willis, AEL&P spokesperson, said in a recent email interview.
The large wedge-shape steel structures AEL&P uses to protect certain towers on its power lines are a unique solution for a unique Southeast problem. Typically avalanche diverters are large earthen berms or concrete structures built up around vulnerable towers. The remote location of the company’s at-risk towers, about 40 miles from Juneau, is accessible by helicopter only. Due to this constraint, AEL&P’s steel diverters are transported in pieces and assembled on site.
“Our diverter designs are somewhat innovative, in that they have to be large enough to resist the forces of the avalanches,” Willis said, “but come in pieces that are small enough to be set by a helicopter and erected by crews without access to large pieces of heavy equipment.”
AEL&P contracted Juneau-based Coastal Helicopters to transport materials and North Pacific Steel Erectors to construct the structure, Willis said.
“Coastal Helicopters provided all the normal helicopter support, lifting crews and most of the equipment to the work site each day,” Willis said.
Active avalanche mitigation
AEL&P started contracting avalanche specialists after the large avalanche that cut hydro power to Juneau for over a month in 2008, Willis said. For the past few years the specialists have been AEL&P seasonal employees.
“Early each morning our specialist looks at the weather patterns and prepares a forecast of the probability of avalanche activity,” Willis explained. “During the week he makes field trips to measure, test and otherwise assess the snowpack.”
At first when the utility’s specialists decided the snowpack was “ripe for active avalanche control,” he said. “In the first few years this meant throwing sticks of dynamite out the door of a flying helicopter to induce smaller avalanches” so a big avalanche doesn’t come down all at once.
Dynamite is hazardous and its use rife with regulations. To avoid these pitfalls AEL&P started using a Daisy Bell.
“I understand we had one of the first two of these devices in the country,” Willis said.
The bell-shaped device is slung beneath a helicopter and flown up to high-risk avalanche areas. A charge of hydrogen and oxygen is injected into the bell from attached tanks and ignited over an avalanche area.
“The resulting explosion directs a shock wave down at the snow and if conditions are right, makes a little avalanche,” Willis said.
“We have worked a lot with AEL&P on their avalanche mitigation,” Mike Wilson, general manager for Coastal Helicopters said in an email interview. “In fact our work on avalanche mitigation has roots back into the 80's and 90's working with Echo Bay mines on the sheep creek portal area.”
Coastal Helicopters is contracted to fly the Daisy Bell to mitigation sites. The company first began using it in 2010 and have had moderate success in reducing the size of potential avalanches, Wilson said.
“Unfortunately the avalanche cycle that cause the highest level of danger also does not allow for use of the Daisy Bell or any helicopter supported mitigation techniques,” Wilson said. “The avalanche diverters are, in my belief, a good step in mitigating the dangers of avalanche for the power line.”
Coastal has also worked with Alaska Avalanche Specialists on heli-ski education and mitigation and study work on the urban avalanche zones in Juneau, Wilson said.
Eric Eriksen, vice-president of transmission and distribution at AEL&P said in an interview with KTOO, that he believes the company is leading the industry in avalanche mitigation efforts, education and modeling. The upshot is AEL&P is becoming a mentor in the industry.
“We get a lot of inquiries,” Ericksen said in the interview.
• Contact reporter Russell Stigall at 523-2276 or at email@example.com.