Debris-flow hazard assessment related to geomorphological and geological setting and to shallow-landslide occurrence

摘要

Debris-flows hazard assessment related to shallow landslide occurrence is evaluated by means of AFHE (Alluvial Fan Hazard Evaluation) and SLHA (ShallowLandslide Hazard Assessment) methods. Both methodologies are based on the combination of weighted thematic maps, whose weights are calculated following the system theory approach. Results are obtained by means of GIS analysis. The AFHE method allows the calculation of the catchment hazard index and the production of the alluvial-fan hazard maps. The catchment hazard index describes the hillslope proneness to deliver sediment to channels and the capability of the latter to transfer this sediment to the apex of an alluvial fan. The alluvial-fan hazard-map is a raster map, where the alluvial fan is partitioned into square cells, each one characterised by specific coefficients, ranging from 0 (very low hazard) to 1 (very high hazard). Values are given based on process energy, event frequency, prevailing geomorphological processes and hydraulic studies. The SLHA method allows the identification of potential sediment sources for debris-flows. This procedure is applied to obtain the shallow-landslide susceptibility for the catchment area by combining weighted thematic maps. Maps are related to the factors that control the occurrence of shallow landslide: geomorphology (slope, landslide presence), soil geotechnical properties, land cover, land use, soil permeability etc. The coupled methods were applied in a mountain area of the western Italian Alps. The proposed procedures are effective both at regional and at local scale, allowing a simple and quick preliminary hazard assessment.