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Abstract:
Sediment transport in glacierized catchments responds to glacier retreat and changing hydrology. The changing sediment export from these catchments impacts downstream morphodynamics, ecosystems, communities, and hydropower infrastructures. Here, we present a catchment-scale numerical model of alpine geomorphic processes, including fluvial transport of subglacial and proglacial sediment transport. The model's simplicity allows us to apply it in a Monte Carlo framework to data collected over 7 years from the Fieschertal catchment in the Swiss Alps, while the catchment’s glacier underwent roughly 500 m of glacier retreat. Model outputs, supported by the observational data, suggest that the catchment has transitioned to a regime where sediment transport depends on the carrying capacity of the water instead of sediment availability. Results suggest that the proglacial area experiences increasing sediment deposition towards the end of the study period in 2020. Hence, the proglacial area can serve as a sediment source and sediment sink. As a result of the dependence of sediment transport on water discharge, the amount of sediment discharged from the catchment is forecasted to diminish from the 2050s onwards at the latest, when water discharge from the catchment substantially declines from the reduced glacier melt. Together, the model and its application quantify the interaction and evolution of multiple geomorphic processes in the catchment as hydrology and glacier cover evolve. Furthermore, the results suggest that increases in sediment discharge rely upon increased transport capacity of water, in addition to more significant sediment inputs from mass movements and increased subglacial sediment discharge.
