Assessment of a geomorphologically highly active catchment in the Northern Apennines, Italy: linking sediment sources mapping with a morphometric connectivity approach

This study was carried out in the upper Val d’Arda catchment (Northern Apennines, Italy). The study area is highly susceptible to soil erosion and mass movements, which significantly contribute to land degradation and reservoir siltation. Sediment sources were extensively mapped to elaborate an inventory map providing the extent and distribution of sediment-related processes and landforms. A morphometric connectivity model (IC) was applied to semi-quantify the structural (de)coupling relations of sediment source areas with respect to the catchment outlet, main channels, and reservoir. Furthermore, a DTM-based terrain analysis was performed to assess morphometric features of selected geomorphic systems. Lastly, the IC was validated by means of detailed field surveys. The results show that landslides are the dominant geomorphic processes, although badlands, upland erosion and fluvial erosion are representative sources of sediments. Large earthflows are the major geomorphic processes in shaping the general topography as well as local morphometric heterogeneity. Likewise, both configuration and density of the drainage system are affected by landslide extent and distribution, thus influencing the sediment connectivity at catchment scale. Finally, landslides combine and overlap with badlands and other fluvial processes producing complex and polygenetic geomorphic systems. Their connection with the channel network is highly influenced by the structural connectivity, often presenting variable degrees of linkage from source to sink. This study is a key step for a suitable watershed management aimed at dealing with sediment-related impacts. Further improvement of the model should be considered to account for land use heterogeneity and anthropic landforms locally disconnecting sediment cascade.