Citation

Decker R, Rice R, Wells L, Yount J. Transp. Res. Circular 2004; (E-C063): 645-655.

Copyright

(Copyright © 2004, U.S. National Academy of Sciences Transportation Research Board)

DOI

unavailable

PMID

unavailable

Abstract

Snow sails are a form of passive avalanche-starting zone defense. A deployment of snow sails will disrupt the snowpack in an avalanche-starting zone and inhibit the formation of coherent, continuous avalanche wind-slabs. Snow sails were first constructed from on-hand materials and deployed in the European Alps in the late 1940s through the 1950s. They were known in German as "kolktalfen," which translates literally as (airflow) eddy (generating) tables. Snow sails are only applicable to certain specific avalanche environments, including sites where the dominant avalanche mechanism is through the formation of wind slabs. The objective of the Milepost 151 avalanche project was to assess, test, and install an operational deployment of approximately 50 snow sails in the avalanche-starting zone as a means of cost-effectively reducing the avalanche hazard, due primarily to wind-slab avalanching, for motorists and Wyoming Department of Transportation maintainers on US-89/191. The 151 avalanche is located adjacent to a populated residential area of Jackson, Wyoming, and is also a critical, managed big game winter habitat. After 4 years of pilot-phase trials and technology demonstrations, a complement of 60 snow sails was fabricated, transported, and installed during the autumn of 2002. The final sail design was similar to the initial trial design. Helicopter-supported logistics were used to transport 50 of the preassembled snow sails, earth pin anchors, and cabling from the Jackson valley floor to the 151 avalanche site. Unlike other forms of constructed, passive avalanche-starting zone defense facilities, snow sails may be removed annually in the spring and reinstalled in the autumn. This minimizes their year-round visual impact. The 151 avalanche snow-sail deployment has undergone a requisite U.S. Department of Agriculture Forest Service/National Environmental Policy Act Environmental Assessment. The finding was one of no significant impact.