Assessing geomorphic changes induced by a debris-flow: a case study in the Dolomites

The study of landscapes and of their dynamics has become fundamental to understand natural hazard mechanisms and the better planning of mitigation measures to prevent damages and losses. Debris flows are a common natural hazard for mountain areas. One major event occurred on the August 5th, 2017 in the Prags-Braies valley (Italian Alps). Heavy rainfall triggered the movement of loose sediments from talus slopes within the Schade catchment into the village of Schmieden-Ferrara. This study aims to analyze the debris-flow event by using a DEM of Difference (DoD) approach to estimate the mobilized materials and identify the spatial patterns of erosion and deposition in the catchment. Two different methods to estimate the error and propagate uncertainty of DTMs into the DoD were tested and compared: i) spatially uniform constant error threshold, and ii) spatially variable uncertainty through a fuzzy approach. The elaboration was carried out using the fuzzy approach as this was considered the most reliable for the study case. The result showed a net balance of -115,719 +/- 46,043 m(3). This value was taken as a reference for the design of a sediment retention basin at the catchment outlet, currently under construction by the local Civil Protection Agency.