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Aggressive avalanche program reduces closures
while safeguarding motorist safety

Explosive measures were used this winter to cut avalanche-related closures in half on the state’s most avalanche-prone highway, Idaho 21. The route, one of Idaho's most popular winter recreation corridors and host to most of the state's highway avalanches, typically is closed 60 days per year. Because of an aggressive avalanche control program, the highway was closed just 30 days this winter.

District 3’s lead avalanche forecaster Jon Barker and his assistant Mick Riffie also spent two-and-a-half weeks in District 2 on the Lochsa River near Fleming, providing forecasting, mapping, and control assistance for U.S. 12.

An avalanche swept across the highway next to the Lochsa River, stranding a dozen semi-trucks and pushing a truck loaded with lumber products into the river. The heavily traveled east-west route was closed for more than two weeks while ITD crews removed debris from the highway. One of the numerous slides was estimated to be 30 feet high.

“Jon was asked to help in determining future avalanches during the crews’ cleanup efforts,” said District 3 Regional Engineer Tom Points. Barker advised the district not to re-open the road after a bad winter storm, even though the road had already been closed for several days, “and sure enough, within several hours of that recommendation another avalanche came down and blocked the entire highway again.”

Barker and Riffie also assisted with avalanche threats on U.S. highways 26 and 89, along the Palisades Reservoir and near Montpelier in eastern Idaho.

Explosives were used in southwest Idaho to bring down unstable snow shelves before they could slide and block the highway. Three different methods were used to deliver the explosive charges in this first-year program:

an avalauncher (a cannon-type device) that delivers explosives into avalanche chutes. The avalauncher was used several times this winter.
"Heliblasting" to drop explosives in avalanche-prone areas from a helicopter. Only two heliblasting missions were done. Because of the cost of helicopter rental, the method is used only in extreme circumstances. Still, more than 80 percent of the avalanche paths in the canyon can be accessed only by helicopter.
When conditions warrant, ITD avalanche-mitigation crews ski into areas and set charges by hand.

Despite the technological advances, this is still the method used most often.

Those triggers bring down snow that accumulates in the chutes, reducing avalanche hazards and allowing ITD crews to safely clear snow from the roadway.

Fifty-seven avalanches slid onto the roadway – “the second-highest number of slides ever recorded in one winter," according to Barker, who works out of the Lowman maintenance facility. Despite the avalanches, the road only closed 30 times last winter. The road never closed after Feb. 11, although storms dumped about 80 inches of additional snow on the region.

Overall, the Banner Summit region received 350 inches of snow this winter.

Barker credits the four months of uninterrupted travel this spring to vigilance.

“It was accomplished through very active forecasting, and keeping a constant presence in the canyon, monitoring changes in the snowpack,” he explained.

The effectiveness is a testament not only to the quick responses of ITD crews in plowing the highway, but it also speaks to their ability to mobilize equipment and position it for clearing the highway before an avalanche occurred.

“The new methods took the guess work out of it, to a large degree, and allowed us to clear the road very quickly,” Barker said.

The largest avalanche to crash onto the highway last winter measured more than 16 feet high.
Typically, avalanche season extends through the first weekend of May.

"This is a great accomplishment, given the heavy winter we had," Barker said.

ITD received a special-use permit from the U.S. Forest Service to use the preemptive measures to reduce the avalanche hazard on Idaho 21 between Grandjean Junction and Banner Summit.

The 11-mile Canyon Creek section, part of the Boise National Forest, has 64 documented avalanche chutes (up from what commonly was presumed to be 54 chutes) and experiences about 90 percent of the state's avalanches that affect roadways. The agencies worked together closely to ensure protection of natural resources in the region and to develop of a long-term avalanche control program.

The agencies continue collaborate, refining ITD’s work in the canyon. “By further enhancements to the program and refining our approach, we are confident we can reduce closure days even further,” Barker said.

Barker and Points have submitted a proposal to the Forest Service to gain further access to the avalanche-prone areas and to use explosives under any weather conditions, rather than for the limited circumstances.

The department also uses other tools to manage avalanche hazards. Information is gathered from weather stations and through snow-density testing to determine when avalanches are likely. ITD recently installed another weather station to provide the best possible weather-related information for avalanche forecasters.