Preliminary debris-flow assessment at the regional scale_ a GIS-based approach

Cavalli M., Crema S., Trevisani S., Marchi L., 2018, Preliminary debris-flow assessment at the regional scale_ a GIS-based approach, GIT 2018, Sarzana (SP), 11-13/06/2018,

Debris flows are widespread phenomena in mountain catchments that often cause damage to urbanized areas and transport routes. The spatial characterization of the affected areas is a major issue in the framework of watershed management. We developed a simple and fast semi-automated and low data-demanding procedure for regional-scale identification of debris-flow prone channels and alluvial fans. A GIS-based approach enables a preliminary mapping of potentially debris-flow affected areas and provides information for the priority ranking of channels and alluvial fans exposed to debris flows. The methodology exploits Digital Elevation Models (DEMs) to derive geomorphometric parameters analyzed for the identification of debris-flow triggering areas and their propagation along the channel. Potential initiation sites of debris flows are identified as those exceeding a threshold of local slope versus contributing area, while channel reaches corresponding to debris flows propagation, deceleration and halting conditions are derived from thresholds of local slope. An analysis of longitudinal channel profiles, which considers the traveled distance and the local slope, is used for the computation of the debris-flow runout. The procedure takes into account the presence of hydraulic control works (i.e. check dams) along with information on erosion-resistant bedrock channels and sediment availability. This approach has been validated by means of field checks and through its extensive application in the eastern Italian Alps. The developed methodology has been implemented in a set of freely-available software tools ( in order to facilitate its application and further validation in different environments.

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