Abstract
Debris flows are among the most dangerous natural processes affecting the alpine environment due to their magnitude (volume of transported material) and the long runout. The presence of structures and infrastructures on alluvial fans can lead to severe problems in terms of interactions between debris flows and human activities. Risk mitigation in these areas requires identifying the magnitude, triggers, and propagation of debris flows. Here, we propose an integrated methodology to characterize these phenomena. The methodology consists of three complementary procedures. Firstly, we adopt a classification method based on the propensity of the catchment bedrocks to produce clayey-grained material. The classification allows us to identify the most likely rheology of the process. Secondly, we calculate a sediment connectivity index to estimate the topographic control on the possible coupling between the sediment source areas and the catchment channel network. This step allows for the assessment of the debris supply, which is most likely available for the channelized processes. Finally, with the data obtained in the previous steps, we modelled the propagation and depositional pattern of debris flows with a 3D code based on Cellular Automata. The results of the numerical runs allow us to identify the depositional patterns and the areas potentially involved in the flow processes. This integrated methodology is applied to a test-bed catchment located in Northwestern Alps. The results indicate that this approach can be regarded as a useful tool to estimate debris flow related potential hazard scenarios in an alpine environment in an expeditious way without possessing an exhaustive knowledge of the investigated catchment, including data on historical debris flow events.
Highlights
IntroductionSeveral studies have focused on analyzing channel processes in relation to hydrological, geomorphological and ecological systems; in particular, the concepts of coupling and connectivity are largely adopted for studying the interaction of hillslope and channel flows in order to model the hydrological response of catchments (Rickenmann, 1999; Michaelides and Wainwright, 2002; Glade, 2005; Michaelides and Chappell, 2009) and sediment dynamics (Iverson, 2003; Rickenmann et al, 2003; Berti and Simoni, 2005).Debris Flow Integrated StudySediment connectivity is a measure of the degree of linkage between sediment sources and downstream areas (Cavalli et al, 2013) and its spatial characterization in a catchment gives an estimation of the possible paths of sediment to reach a target zone
In Good Clay Maker (GCM) catchments, rocks are degradable and the unconsolidated material is less abundant if compared to Excellent Clay Maker (ECM) ones
Based on the dominant bedrock lithology characteristics reported in section “Study Area,” Rio Frejus is classified as Excellent Clay Maker based on the Clay Weathering Index (CWI) classification (Tiranti et al, 2014; Table 2)
Summary
Several studies have focused on analyzing channel processes in relation to hydrological, geomorphological and ecological systems; in particular, the concepts of coupling and connectivity are largely adopted for studying the interaction of hillslope and channel flows in order to model the hydrological response of catchments (Rickenmann, 1999; Michaelides and Wainwright, 2002; Glade, 2005; Michaelides and Chappell, 2009) and sediment dynamics (Iverson, 2003; Rickenmann et al, 2003; Berti and Simoni, 2005).Debris Flow Integrated StudySediment connectivity is a measure of the degree of linkage between sediment sources and downstream areas (Cavalli et al, 2013) and its spatial characterization in a catchment gives an estimation of the possible paths of sediment to reach a target zone. The geomorphic effect of the rainfall acting on sediment deposits may result in debris flow occurrence. Debris flows are one of the most dangerous phenomena within the Italian alpine environment. They have been responsible for the 36% of fatalities in the Italian alpine region during the last century (Tropeano et al, 2006). Mitigation of debris flow effects on human life has become one of the most important challenges of the scientific community
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