Abstract ID: 3.11912 | Accepted as Talk | Talk/Oral | TBA | TBA

Cryosphere degradation in Alpine headwaters increases sediment supply, which can pose a hazard to valley bottoms only if sediments are both available for transport and effectively mobilized. Torrential systems play a crucial role in upstream-downstream sediment transfer. By re-establishing the torrent’s central role in propagating disturbances, we aim to assess a watershed’s susceptibility to transmitting sediments downstream. We analyze these processes through sediment cascades, which characterize sediment fluxes and storage across catchment units. While sediment connectivity is often reduced to topographic parameters, a more comprehensive approach is needed.

Our study combines regional and local-scale investigations. We develop a regional inventory of sediment transfer systems influenced by cryospheric processes using Geographic Information Systems. At the local scale, we conduct case studies in proglacial margins and permafrost areas in the northern French Alps. In the IMC Conferencewe will present preliminary results highlighting the diverse sediment dynamics observed.

We identified various sediment connectivity patterns. Some sites show high connectivity (e.g., La Bérarde, June 2024), while others act as sediment sinks (e.g., Le Pré de Madame Carle, Vallonbrun). In certain cases, sediment inputs from recurrent processes outweigh those linked to the cryosphere degradation, leading to sequenced connectivity (e.g., La Cros de la Vache, Glacier de l’Olan). In Le Vallon du Grand Tabuc, a rockfall from the Crête des Grangettes seems to feed a downstream fluviatile plain as a sediment sink, interrupting connectivity. Finally, slope erosion on some sites is dominated by periglacial processes, whereas sediment supply seems to originate more from torrential deposits removal (e.g., rock glacier in Vallon de l’Arcelle Neuve).

These field studies provide insights into sediment dynamics and their controlling factors. Preliminary results reveal spatial variability in sediment cascade efficiency and form the basis of a conceptual model identifying key drivers of sediment connectivity.

Finally, we aim to refine this model to assess sediment cascade efficiency at a regional scale. Our goal is to develop a sediment connectivity index and an atlas for northern French Alpine catchments. This atlas will support scientists, technical experts, and land managers in improving hazard assessment and risk management in Alpine environments under climate change.