A snow shed, snow bridge or avalanche gallery is a type of rigid snow-supporting structure for avalanche control (avalanche defense) or to maintain passage in areas where snow removal becomes almost impossible. They can be made of steel, prestressed concrete frames, or timber. These structures can be fully enclosed, like an artificial tunnel, or consist of lattice-like elements. They are typically of robust construction considering the environments they must survive in.
Snow protection is particularly important when routes cross avalanche "chutes", which are natural ravines or other formations that direct or concentrate avalanches.
Snow sheds or avalanche galleries are a common sight on railroads in mountain areas, such as the Donner Pass in the United States or many of the Swiss mountain railways, where tracks are covered with miles of shedding. Although unused today, the Central Pacific railroad had a complete rail yard under roof in the pass. They are also found on especially hazardous stretches of roadway as well, such as the one in Snoqualmie Pass, or those on the Trans-Canada Highway between Revelstoke and Golden in British Columbia.
Snow bridges may superficially look similar to snow fences, but they act differently. Snow fences are built vertically and accumulate snow on their downwind side, while snow bridges are slanted or horizontal and hold snow on their top side.
Railway trains occasionally get blown off the tracks by high winds.
The Lanxin High-Speed Railway has particularly strong winds which blow on most days of the year; a 67-kilometre long wind-protection "gallery" has been proposed to be built in this region.
- Photographs of avalanche defences, FAO corporate document repository
- "Avalanche and torrent control in the Spanish Pyrenees"
- "Steel snow bridges"
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