Item: Reducing avalanche hazard to us route 89/91 in jackson wyoming using snow sails
Title: Reducing avalanche hazard to us route 89/91 in jackson wyoming using snow sails
Proceedings: Proceedings of the 2004 International Snow Science Workshop, Jackson Hole, Wyoming
Authors: Jamie Yount, Avalanche Technician, Wyoming Department of Transportation (WYDOT) Jackson Maintenance Facility, Rand Decker Professor and Chair, Department of Civil and Environmental Engineering, Northern Arizona University, Robert Rice Research Associ
Abstract: Snow sails are a form of passive avalanche starting zone defense. A deployment of snow sails work to disrupt the formation of continuous, coherent wind-slabs in avalanche starting zones. Snow sails are only effective on avalanche paths were the dominant avalanche mechanism is through the formation wind-slabs. The objectives of using snow sail defense structures at the 151-avalanche path in Jackson Wyoming are to cost effectively reduce the avalanche hazard to motorists and highway maintainers on US 89/91 and minimize the visual and terrain impacts. The 151-avalanche path is managed as critical big game habitat and is located adjacent to the residential areas of Jackson Hole. Heavy snows and consistent S-SW winds with a 1 mile fetch recurrently produce high hazard conditions, with snow slides frequently reaching the highway (~1.0/year). US 89/91 is the primary route for commuter traffic in the Jackson area and has recently been classified as the busiest primary highway in the state of Wyoming. In the autumn of 2002 a deployment of ~50 snow sails were fabricated, transported, and installed on the 151 avalanche path. The snow sails are removed annually in the spring and re-installed in the fall. This was required as a consequence of the National Environmental Policy Act (NEPA) Environmental Assessment (EA) to minimize year-round visual impact. After two seasons of operational use and continued evaluation, the project has proven effective in disrupting the formation of a coherent wind-slab in the 151 staring zone. However, widespread avalanche activity on January 1, 2004 produced an event at 151 depositing 10’ of debris across five lanes of highway. Continued evaluation will be required to determine the success of the snow sail deployment in reducing the avalanche hazard, and those conditions and configuration where the deployment is most effective.
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Keywords: passive avalanche mitigation, avalanche engineering, transportation
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