The role of human activities on sediment connectivity of shallow landslides

Sediment connectivity within a catchment depends largely on the morphological complexity of the catchment and is strictly related to the anthropogenic modification of the landscape. In this context, the present research evaluates the role of anthropogenic effects on landscape modifications and the resulting influence on sediment delivery. An assessment of sediment connectivity was carried out for three different human impact scenarios: (i) drainage system density reduction, (ii) road network variation and (iii) land use changes. In addition, shallow landslides were used as sediment source areas to evaluate the potential connection between these sediment sources and downstream areas (e.g. main channels and road network). Two small catchments in the Oltrepò Pavese area (Northern Apennines, Italy), with different size and morphological setting, were analysed: the Rio Frate (1.9 km2) and the Versa (38 km2) catchments. In both areas, several shallow landslides were triggered in 2009 (Rio Frate and Versa) and in 2013 (Versa). Results highlight the role of the landscape complexity in coupling/decoupling upstream sediment sources, such as shallow landslides, from the main channel network and roads. In addition, the analysis identified instability phenomena characterized by high connectivity values, allowing determination of the areas in which mobilized sediment could potentially damage important infrastructures such as the road network or contribute to flooding induced by aggradation or obstruction of the river bed. The proposed approach provides a methodological framework to help improve watershed and land management strategies, especially in shallow landslides prone-areas.