Implementation of Structural Control Measures to Mitigate Avalanche Hazard along Transportation Corridors

Abstract

Avalanche hazards along transportation corridors in the United States have traditionally been addressed by forecasting their potential and actively controlling them through explosive release while the roadway is closed. This approach reduces the threat of avalanches cascading onto the roadway and thus reduces danger to the traveling public. However, active control methods cannot always be implemented in a timely fashion, can be ineffective, and can have large associated economic impacts. An alternative to active control is passive, structural avalanche defenses. They are passive in that they do not require maintenance during winter storm periods. Structural defense measures include snow sails, snow-supporting structures, and snow sheds. Despite their extensive use in Europe and their potential for effectively reducing avalanche hazards, few examples are found in the United States. The potential for negative impacts to the visual attributes of the landscape has been a significant reason for their lack of domestic use. This paper discusses several types of structural defense measures, criteria for their selection at a given site, and their relative effectiveness. Passive structural defense measures designed for implementation at the Milepost 151 avalanche on US Route 89/191 near Jackson, Wyoming, are described. Details are given on important collaborations between landscape architects and engineers that led to successfully addressing National Environmental Policy Act requirements for retention of visual attributes at the Milepost 151 avalanche site in the presence of snow support structures deployed for the purpose of avalanche hazard reduction.