International Symposium on Mitigative Measures against Snow ...

<strong>International</strong> <strong>Symposium</strong> on Mitigative Measures against Snow Avalanches
Egilsstaðir, Iceland, March 11–14, 2008
3. VALIDATION
There is considerable uncertainty about the effectiveness of dams to deflect and, in particular, to
stop, snow avalanches. The new dam height criteria have been compared to a data set of run-up
marks on man-made dams and natural obstacles from Norway (Harbitz and Domaas, 2006), Iceland
and France. The run-up data can only be partially reconciled with the theoretically predicted
run-up ranges as the run-up marks are in some cases substantially higher than the predictions
(Jóhannesson and others, 2008b). However, the validation shows that the run-up marks of several
medium-sized and large avalanches are in rough agreement with the proposed criteria, and
that the overall variation of the run-up with normal velocity is in general agreement with the
new criteria. The high observed run-up of some of the avalanches indicates a large uncertainty
in the estimated velocity or some run-up mechanism that is not accounted for in the theoretical
analysis. Some of the highest run-up marks may be caused by the impact of the saltation or
powder components of the avalanches, which may, for example, damage forest considerably
higher up than the highest point reached by the dense core. Pressure from the saltation or powder
layers can, however, not account for the complete overflow of dense-flow avalanches over
obstacles as has been observed in at least one case with high run-up.
An analysis of overrun of avalanches at the Ryggfonn test site in Norway (Gauer and others,
2005) also indicates that avalanches are in some cases able to overrun dams, in particular
catching dams, more easily than the dam design criteria predict. These observations need to be
taken as reminders of the still imperfect dynamic basis of the proposed run-up criteria, in spite
of the advances that have recently been made, indicating that natural avalanches are perhaps of
several different types, which are not adequately described by a single dynamic framework.
ACKNOWLEDGEMENTS
This work was carried out as a part of the research project CADZIE (grant EVG1-1999-00009)
and SATSIE (grant EVG1-CT-2002-00059) with support from the European Commission.
Support to finalise a book about the new design criteria has been provided by the Icelandic
Avalanche and Landslide Fund.
REFERENCES
Gauer, P., and K. Kristensen. 2005. Avalanche studies and model validation in Europe, SATSIE;
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Jóhannesson, T., P. Gauer, K. Lied, M. Barbolini, U. Domaas, T. Faug, C. B. Harbitz, K. M.
Hákonardóttir, D. Issler, F. Naaim, M. Naaim and L. Rammer. 2008a. The design of
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