Item: Permanent avalanche defense structures in japan
Title: Permanent avalanche defense structures in japan
Proceedings: 1990 International Snow Science Workshop, Bigfork, Montana USA, October 9-13
Authors: Mrs. Jacqueline D. Decker and Dr. Rand Decker
Abstract: The defense against avalanche hazards in Japan is based primarily on permanent structures; wind fences, starting zone snow rakes and sheds, diversions and "jungle gyms" in the track and run-out. The choice of these technologies has resulted from the fact that roads, railways and buildings are usually the avalanche targets. Relatively small, planned, artificially (explosively) released avalanches would not provide the necessary protection, A unique defense structure is the "jungle gym'. This is a large scale avalanche flow energy dissipater. These steel and concrete structures are often 3 to 10 meters in height and will span the entire width of the avalanche track. The concept behind this form of defense is that as the avalanche passes through the interlocking web of steel columns and beams, its flow energy is sufficiently damped that its run-out distance will be greatly shortened. These "jungle gyms" are used operationally in sites where starting zone defense is not feasible and the avalanche targets in the run-out are so spread-out that sheds and diversions would not be practical. The expense of construction and maintenance of avalanche defense structures is not small and is distributed equally amongst the national, prefectural (state), and local governments. The technologies and politics in Japan, associated with the use of permanent avalanche defense structures may provide a good model for other countries considering these methods for avalanche hazard mitigation.
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Keywords: wind fences, starting zone, diversions, permanent, defense, hazard
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