Linking debris flow erosion to channel-bed parameters: Geotechnical and remote sensing investigation of ten channels in Switzerland

Le résumé fourni par la source

Debris flow dynamic is governed by complex interactions between channel topography and the hydro-geomechanical characteristics of both the flow and its erodible bed. However, systematic field data linking sediment characteristics to debris flow erosion and deposition remain scarce, mostly due to the challenging accessibility of steep channels, and their heterogeneous poorly sorted materials. In this study, we investigated ten debris flow channels in Switzerland using repeated UAV surveys combined with geotechnical field and laboratory measurements. Multi-epoch digital surface models showed that erosion generally prevails over deposition where thalweg slopes exceed ≈ 20°, although both the magnitude and spatial patterns of erosion vary substantially among channels and between events. To explore the causes of these differences, we measured grain size distributions, saturated hydraulic conductivity ( K sat ≈ 10 −7 to 10 −3 m/s), and in-situ mechanical resistance. Channels composed of fine-rich, less permeable sediments exhibited greater average erosion, possibly because reduced permeability hinders pore pressure dissipation during undrained loading. Penetrometer and vane shear tests further indicated that freshly deposited wet sediments were mechanically weaker than coarser materials left after erosion. The strength of the deposits then increased rapidly upon drying. Erosion also increased for larger channels and catchments. By integrating geomorphological and geotechnical parameters, we classified the studied channels into four behavioral types, ranging from small, coarse gullies to large, fine-rich channels. This multi-site dataset offers rare field constraints on the relationship between sediment properties and debris flow erosion, providing essential parameters for the calibration and validation of next-generation hydro-mechanical debris flow models.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.