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| Titel |
The effect of vegetation cover on the formation of glide-snow avalanches |
| VerfasserIn |
Thomas Feistl, Peter Bebi, Perry Bartelt |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091764
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| Publikation (Nr.) |
 EGU/EGU2014-6073.pdf |
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| Zusammenfassung |
| Glide snow avalanches release on steep, smooth slopes and can be prevented either by
protection forests or by artificial defense structures. To minimize the risk for people and
infrastructure, guidelines have been formulated concerning structure, height and distance
between avalanche prevention bridges. These guidelines assure the major functions of the
defense structures: first to prevent the release of avalanches and second to withstand the static
and dynamic forces of the moving snow cover. The major functions of protection forests are
generally similar and therefore guidelines on the maximum tolerable size of forest gaps exist
in Switzerland. These guidelines are based on a static relationship between the pressure of the
snow cover and the resistance of the defense structure and on empirical observations (forest).
Whereas ground friction is only qualitatively taken into account, we assume it to
play a crucial role in glide snow avalanche formation. To prove this assumption we
collected data on the predominant vegetation cover of 67 release areas in the region of
Davos, Switzerland. Our observations reveal a strong relationship between vegetation
cover type, slope angle and slab length. We were able to quantify the Coulomb
friction parameter μ by applying a physical model that accounts for the dynamic
forces of the moving snow on the stauchwall, the fixed snow cover below the release
area. The stauchwall resists the dynamic forces of the snow cover, until a critical
strain rate is reached and then fails in brittle compression. This failure strongly
depends on the friction between snow cover and soil. A typical value of μ for grassy
slopes is 0.2. Snow characteristics like density are implemented in the model as
constants. We compared the model results with the guidelines for defense structures
and forest gap sizes and found accordance for certain friction parameter values.
Forest gaps of 40 meter length and a 35° slope angle require friction values of 0.5
corresponding to stumps or tree regeneration to assure protection. Therefore forest gap
guidelines in Switzerland imply a relatively rough surface to prevent avalanche
formation. The calculated slope angle and slab length for smooth, grassy slopes
corresponds to defense structure distances for shallow snow heights. Guidelines
for defense structure distances correspond to a smooth surface like grass or low
dwarf shrubs which are common vegetation types for regions above the tree line.
Therefore we could confirm that artificial defense structures, built in accordance
with guidelines prevent glide snow avalanche releases, even on smooth terrain. |
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