Source-to-Sink Sediment Tracing in the Glogn River Catchment

We aim at exploring the sedimentary source-to-sink pathways in the Alpine Rhine, Switzerland through integrating hydrological modeling, connectivity mapping, and field observations. We hypothesize that either rainfall-driven overland flow erosion or landsliding (Battista et al., 2020) are the main mechanisms contributing to the generation of sediment and controlling the source-to-sink transport of sediment in the basin. We test this hypothesis through mapping such sediment sources in the field and on lidar DEMs, and we conduct conceptual models to characterize the sensitivity of these sources to temporally and spatially varying rainfall rates (Demmel et al, 2024). We complement this analysis with a coupled hydrology-erosion model, through which we predict how the water and suspended sediment waves propagate downstream from the source through the channel network (Agostini et al, 2024). We then test these model-based predictions on rainfall-dependent source-to-sink sedimentary pathways with field data. We start with the 370 km-large Glogn river catchment, which is a tributary of the Alpine Rhine. In the headwater reaches, the Glogn catchment is made up of a dense network of channels that are perched on the hillslopes, whereas farther downstream, the basin hosts several deep-seated landslides that potentially supply large volume of sediment to the channel network (Cruz Nues et al, 2015). We proceed upon collecting data about the size of clasts and their petrographic composition to characterize the source signal for the bedload of the Glogn River, and we trace these signals from upstream to downstream. We complement this dataset with a petrographic characterization of the suspension load including the bulk geochemical and mineralogical composition of sand and the measurements of concentrations of cosmogenic 10Be and 26Al in riverine quartz minerals. We then apply a principal component analysis to this dataset to identify the material signals of the different sediment sources, and we estimate the relative contribution of material from tributary basins through mixing modelling. We postulate that in the upstream, less dissected part of the basin, overland flow erosion constitutes the major mechanism of the sediment production, whereas in the downstream area where the Glogn has deeply dissected into the substratum, mass failure processes such as landsliding is the most important mechanism contributing to the production of sediment. References: Agostini, L., Demmel, S., Garipova, S., Sinclair, S., Schlunegger, F., Molnar, P. (2024) Suspended sediment transport in river network models: testing signal propagation and modelling approaches. EGU24. Battista, G., Schlunegger, F., Burlando, P., Molnar, P. (2020) Modelling localized sources of sediment in mountain catchments for provenance studies. Earth Surf. Process. Landforms, 45, 3475 3487. Cruz Nues, F., Delunel, R., Schlunegger, F., Akar, N., Kubik, P.W. (2015) Bedrock bedding, landsliding and erosional budgets in the Central European Alps. Terra Nova, 1-10. Demmel, S., Agostini, L., Garipova, S., Leonarduzzi, E., Schlunegger, F., Molnar, P. (2024) Climatic triggering of landslide sediment supply. EGU24.