Sediment and large wood supply in proglacial streams: insights from the Upper Navisence catchment monitoring.

Preliminary analyses of data collected during 2023 and analyses of archived data provided new insights into the sources of wood and sediment in this river corridor. These analyses have highlighted the primary supply processes accountable for these materials and some important feedback mechanisms. We found that the Torrent de l’Arpitettaz channel shifted across a forested area in 2019, driven by a large debris flow sequence (started in August) originated from recently exposed moraine deposits located on the north-facing valley flank. We observed that the stream is still progressively recruiting large wood pieces across the forest during the summer floods. This large-wood input temporarily and locally stabilises the channel bed and promotes a multithread planform, as the wood forms large jams with standing trees and boulders. The understanding and prediction of the complex cascade processes that govern the transient morphodynamic evolution of proglacial streams present a formidable challenge within the current context of climate change. The monitoring framework introduced in this study will offer a more comprehensive and holistic understanding of these phenomena. This work is supported by the CLIMACT UNIL-EPFL under the starting grant assigned to the ‘NaviSedWood’ project, and the Swiss National Science Foundation project PCEFP2_186963