Flow-path changes in the incised channel of the Illgraben torrent

The Illgraben near Leuk-Susten is the most active debris-flow torrent of Switzerland with several events per year. In the departure zone of the Illgraben, enormous amounts of heavily disintegrated quartzite, limestone and gypsum are easily mobilized during precipitation events. In addition, mass movements regularly delivered debris into or close to the channel, allowing the formation of one of the largest debris-flow cones of the European Alps over the Holocene. After a first series of analyses conducted on the cone (also see overbank sedimentation events out of the current channel at Illgraben), investigations focussed on recent flow-path changes in the deeply incised channel in summer 2007. A total of 315 cross-sections, wedges and increment cores of broadleaved trees (Alnus sp., Betula sp., Populus sp., Salix sp., Sambucus nigra) were extracted and spatio-temporal patterns of past debris-flow activity are currently being reconstructed through the analysis of the wounds identified in the selected trees.. While the analysis of the comparably young broadleaved trees will not deliver extensively long time series of past events, it will provide very detailed insights into the recent activity as well as into the healing and wood anatomy of wounds in broadleaved trees. First results are expected to be available by mid 2008.


Mandators: Swiss Federal Office for the Environment (FOEN), Cantonal Department for Traffic, Construction and Environment (Canton of Valais)

Project duration: August 2007 – September 2008

Contact: Markus Stoffel


Arbellay, E., Stoffel, M., Bollschweiler, M. (2010): Wood anatomical analysis of Alnus incana and Betula pendula injured by a debris-flow event. Tree Physiology 30: 1290–1298. [PDF]

Arbellay, E., Stoffel, M., Bollschweiler, M. (2010): Dendrogeomorphic reconstruction of past debris-flow activity using injured broad-leaved trees. Earth Surface Processes and Landforms 35: 399–406. [PDF]