Quantification of sediment supply and availability from hillslope to channel network: the case study of the Tenetra Creek (Marche, Italy)

Intense rainfall events are the primary cause of landslides and heavy torrential flows, two of the most hazardous processes that can occur along hillslopes. When a rainstorm event causes many highly-mobile landslides at the same time in a large area, the considerable input of the moved material that these events rapidly throw into the hydraulic network can start a chain reaction of further dangers. These can be combined with the phenomena of forced erosion by the surface water drainage. For this reason, it is of fundamental importance to study the sediment productivity of the river basin, taking into consideration the transport connectivity between the slopes and the involved riverbeds. A remarkable weather event occurred in the Marche region on September 15–16, 2022, with localized rainfall of 419 mm in twelve hours, a record intensity over the previous decades. A self-regenerating storm system produced this enormous amount of precipitation causing the watercourses overflow and extensive flooding. Peak rainfall intensities reached 90 mm/h. The research focuses on the study of a small torrential basin, the Tenetra Creek, which has minimal anthropogenic influences. The rainfall event triggered several highly mobile landslides, most of them represented by debris flows, that in some cases reached the river network, contributing to the increase in river solid transport and causing considerable morphological changes. The methodology of this work started with a detailed basin-scale analysis of regional landslides databases (Italian Landslide Inventory, ISPRA; Hydrogeological Planning, Authority Basin) and a comparison of the mapped elements with the mass movements during the 2022 event in order to determine the source areas of material and the availability of material on the slopes. Then, the sediment connectivity index, based on the tool developed by Crema and Cavalli (2018), was used to investigate the mobilization of material according to topographic laws and to quantify the topographic control on sediment connectivity. The index expresses the potential connection between different parts of the catchment area; in particular, it describes the probability that sediments eroded from hillsides will reach the drainage network defined as a target. Since the sediment balance in a basin system is modelled also by the input of sediment bank collapse within the high water levels, we effectively evaluated the lateral changes in banks in relation to the 2022 event, by utilizing hydraulic sections within GIS environmental models. Geomorphic Change Detection software allowed for precise calculations of volumetric changes in storage, underscoring the significance of monitoring such alterations for future flood management strategies. The intricate relationship between flooding and geomorphological landscapes reveals the profound impact that natural occurrences can have on our environment. Understanding all the above-mentioned changes to which it is subject is essential for effective flood management, which necessitates continuous research and adaptive strategies to respond to evolving conditions. Implementing integrated methodologies allows for a comprehensive assessment of sedimentary supply in non-man-made river systems, providing crucial insights into the dynamic processes at play.