Item: Wet-snow avalanche interacting with a deflecting dam: field observations
Title: Wet-snow avalanche interacting with a deflecting dam: field observations
Proceedings: 2010 International Snow Science Workshop
Authors: Betty Sovilla1, Ilaria Sonatore1,2, Stefan Margreth1 and Marc Christen1 1WSL Institute for Snow and Avalanche Research SLF, Flüelastrasse 11, Davos Dorf, 7260, Switzerland 2 Università degli Studi di Milano - Bicocca, Dipartimento di Scienze Geolog
Abstract: In 2008 a large wet-snow avalanche occurred in the region of Klosters, Switzerland. The avalanche reached the valley bottom and interacted with a deflecting dam that was constructed after the avalanche winter 1999, overflowing it at its lower end. To document this extraordinary event, we performed airborne laser-scanning immediately after the avalanche. This data, together with a video sequence made during the avalanche descent, provided a unique data set to study the dynamics of a wet-snow avalanche and its flow behavior around the deflecting dam. The avalanche hit the dam with deflecting angles of 10-30°. We could observe that, for smaller deflecting angles, the friction of the avalanche as it flowed alongside the dam slowed down the avalanche front, but, for higher deflecting angles, the avalanche suddenly accelerated increasing its run-out distance. Additionally, we could observe that snow deposits left by the avalanche exhibited strong pattern formation, which reflected the history of the wet flow. In particular, we could detect high levees running parallel to the curvature of the dam indicating the dam influenced the lateral spreading and we estimated that the whole deposit area was deviated from its original direction by approximately 25°. Furthermore, we observed the formation of numerous rolls-waves, which increased the avalanche flow depth and caused the overflow of the dam. Based on our analysis, we propose recommendations to take into account the effects of wet-snow avalanche flow for practical design of deflecting dams.
Keywords: wet-snow avalanche, avalanche deflecting dam, airborne laser-scanning