Abstract
This paper proposes a simplified GIS-based procedure which aims to preliminary assess areas exposed to debris flows by evaluating erosion and deposition area into channels and along alluvial fans. The methodology is based on the definition of several morphometric parameters on Digital Elevation Models (DEMs); it is independent from landslide volume and its rheological characteristics. By solving a set of parametric equations and excluding, from time to time, the unlikely areas by means of an analysis process that uses on/off-raster masks, potential erosion and deposition areas can be identified. The procedure was applied at six intra-mountain basins upstream of the village of Paupisi, Southern Italy, which was involved in multiple debris flow events in October 2015. The model estimated that a range between 15–21% of the selected basin drainage channels may be identified as erosion areas. Moreover, comparison of the recent debris flow paths with model outputs shows a good performance of the procedure, which was able to predict about 46% of the total actual propagation and invasion areas and about 62% of the distribution deposit areas. The methodology can be considered a useful screening for the identification of debris flow-susceptible channels, suitable for use in preliminary hazard evaluations.
Highlights
Debris flows are surging flows of water and saturated debris occurring in the steep channels of mountain environments [1]
The procedure previously described permitted introduction of a semi-automatized GIS-morphometrical model able to estimate erosion and deposition areas due to canalized water flow that may develop into debris flow responsible for fan accretion
In general terms, when trigger ratio (TR) increases, a higher number of cells pass under the 0.5 value, even though the predicted areas are always obtained by a combination of these cells with others that are defined by the slope and curvature thresholds
Summary
Debris flows are surging flows of water and saturated debris occurring in the steep channels of mountain environments [1] They are characterized by high destructive capacity due to both high velocity and the absence of clear premonitory signs [2], differing from slow-moving landslides, whose precursors are linked with progressive ante-event ground deformations often controlled by the geological-structural setting of the slope [3]. For this reason, hazards related to debris flows are a major concern for urban settlements and human activities on mountain environments and alluvial fans, due to their mutual interaction [4,5,6]. For correct land use planning and management, debris flow hazard and risk evaluation on fan areas requires the preliminary identification of drainage channels that periodically feed, with different magnitude, the fans themselves in relation to the features of the triggering rainstorm event and available material
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