Quantitative basin characterisation to refine debris-flow triggering criteria and processes: an example from the Italian Western Alps

Abstract

This paper investigates rapid channelized debris flow related to rainfalls in small alpine basins. Its goal is to evaluate and correlate different geological and technical aspects with predisposing and triggering factors that can control these phenomena. The study area is the upper part of the Susa Valley where 12 small basins were selected. For each of them, lithological, geomorphological, climatic and technical information were mapped and analysed. Debris-flow triggering conditions, flow and depositional processes were related to physical characteristics of the basin that can be easily measured and quantified. At least three different groups of basins were found: G1) basins with one event each 4-6 years, characterised by massive or blocky calcareous rocks, G2) basins with more than one event per year that show an abundance of layered or sheared fine-grained rocks and G3) basins with recurrence levels exceeding 10 years, activated only by heavy and prolonged rainfalls, marked by massive or blocky coarse-grained igneous rocks. Furthermore, important morphometric differences were found. These considerations are useful in terms of hazard zonation and risk mitigation.

Analysis of Rainfall-Induced Landslide on Unsaturated Soil Slopes

“…The morphological characteristics are summarized in Table 1. It can therefore be concluded that most debris flows will also originate at slope angles close to 30 • , and this observation is supported at other sites [26]. Field surveys revealed that landslide and debris flow in the Umyeonsan region were the result of three main steps: (1) initial failure produces a shallow landslide trace caused by the transitional sliding of the loose colluvium overlying gneiss bedrock (Figure 3a).…”

“…It can be deduced that the summer season receives a large portion of the annual rainfall [32]. Figure 6 shows the hourly and cumulative rainfall for [26][27] July 2011 recorded at the rain gauges installed at Seocho and Namhyun stations. The cumulative 24-h rainfall ending at 12:40 p.m. on 27 July 2011 was 364.5 mm and 425.5 mm, respectively (i.e., very heavy rainfall).…”

Risk management on an alluvial fan: a case study of the 2008 debris-flow event at Villar Pellice (Piedmont, N-W Italy)

“…The deposit of the debris flow shows a different horizontal gradation along the fan with clast-rich lobes, levee-like boulder train and distal sand-rich lobes that are characteristic of this type of catchment lithology group (Tiranti et al, 2008). Boulders could be found on the alluvial fan apex, while sand and silt in the more distal part.…”

An 1-D Integrated Hydro-Mechanical Model to Unravel Different Hydrological Triggering Processes of Debris Flows

“…The assessment of rainfall threshold values for debris flow initiation are based in most cases on statistical empirical approaches using large data sets without detailed knowledge of the different triggering processes and its influencing factors [2,29].…”