Snow Supporting Structures for Avalanche Hazard Reduction, 151 Avalanche, Highway US 89/191, Jackson, Wyo. - FHWA-WY-09/05F
The 151 Avalanche, near Jackson, Wyoming has, historically, avalanched to the road below 1.5 to 2 times a year. The road, US 89/191 is four lanes and carries an estimated 8,000 vehicles per day in the winter months.
The starting zone of the 151 Avalanche is 1,140 vertical feet above the roadway. With the adjacent development of the South Park areas of the Jackson Hole Valley, using explosives for avalanche control is unacceptable. As a consequence, this project has led to the design and configuration of a deployment of snow supporting structures, that if implemented, would provide a more effective avalanche defense system. This has resulted in a unit structural and foundation design for seventy (70) snow supporting structures.
The unit design will support a maximum 6.6' snowpack. The 70 structures, deployed with a separation of 50' longitudinally, will cover the dominant portions of the 151 Avalanche starting zone. Moreover, novel deployment configuration has been developed to also retain the visual characteristics of the starting zone as seen from the Jackson Hole valley floor. This factors critically into the National Environment Policy Act (NEPA) rule-making responsibilities of the USDA Bridger-Teton National Forest and their resulting favorable Decision Memo.
The resulting design of a snow supporting structure is 12' long and 5.5' high, installed nearly perpendicular to the slope which is inclined at 35 degrees. A single structure weights 1,400 pounds, and the cost is estimated at $16,600 per structure; fabricated, transported and installed.