Assessing debris-flow activity and geomorphic changes caused by an extreme rainstorm: the case study of the Liera catchment (Dolomites, northeastern Italy)

Collecting information on sediment source areas and mobilized sediment volume is a fundamental step toward a better understanding of geomorphic changes caused by extreme events. This study aims to analyze the morphological changes caused by debris flows in a mountain catchment from both a quantitative (volume changes) and qualitative (spatial patterns of erosion and deposition) perspective in a catchment of the Dolomites (Liera catchment, 37.7 km2), which was severely affected by the Vaia storm (27th - 30th October 2018). The study of the geomorphic impacts of the Vaia storm in the Liera catchment, which was carried out in the frame of the Interreg SedInOut project (2019- 2022), includes: (i) the creation and comparison of pre- (2015) and post-event (2019) sediment sources inventories, (ii) the analysis of landforms evolution and, leveraging the availability of multitemporal high-resolution DTMs, (iii) the quantification of sediment volumes mobilized by debris-flows. The results show a substantial increase in sediment sources (mostly shallow landslides and debris-flow channels). Large sediment volumes were eroded and transported by debris flows, but the supply of sediment to the main channel was rather limited because most of the sediment was deposited on the alluvial fans of debris-flow catchments.