%0 Conference Proceedings %F Poster %T The influence of flood frequency, riparian vegetation and threshold on long-term river transport capacity %+ Géosciences Rennes (GR) %A Croissant, Thomas %A Lague, Dimitri %A Davy, Philippe %< avec comité de lecture %B European Geosciences Union General Assembly 2016 %C Vienne, Austria %V 18 %P EGU2016-13276-1 %8 2016-04-12 %D 2016 %Z Sciences of the Universe [physics]/Earth Sciences/GeomorphologyConference poster %X Climate fluctuations at geological timescales control the capacity of rivers to transport sediment with consequenceson geochemical cycles, sedimentary basins dynamics and sedimentation/tectonics interactions. While the impactof differential friction generated by riparian vegetation has been studied for individual flood events, its impacton the long-term sediment transport capacity of rivers, modulated by the frequency of floods remains unknown.Here, we investigate this effect on a simplified river-floodplain configuration obeying observed hydraulic scalinglaws. We numerically integrate the full-frequency magnitude distribution of discharge events and its impact on thetransport capacity of bedload and suspended material for various level of vegetation-linked differential friction.We demonstrate that riparian vegetation by acting as a virtual confinement of the flow i) increases significantly theinstantaneous transport capacity of the river independently of the transport mode and ii) increases the long termbedload transport rates as a function of discharge variability. Our results expose the dominance of flood frequencyrather than riparian vegetation on the long term sediment transport capacity. Therefore, flood frequency has to beconsidered when evaluating long-term bedload transport capacity while floodplain vegetation is important only inhigh discharge variability regimes.By comparing the transport capacity of unconfined alluvial rivers and confined bedrock gorges, we demonstratethat the latter always presents the highest long term transport capacity at equivalent width and slope. The lossof confinement at the transition between bedrock and alluvial river must be compensated by a widening or asteepening of the alluvial channel to avoid infinite storage. Because steepening is never observed in natural system,we compute the alluvial widening factor value that varies between 3 to 11 times the width of the bedrock channeldepending on riparian vegetation and discharge variability. This result is well supported by measurements madein natural river systems in different worldwide locations (Taiwan, Himalayas and New Zealand). Although bankcohesion is often invoked to as a property that sets alluvial river width, we propose unconfinement as anotherimportant control factor. %G English %L insu-01308941 %U https://insu.hal.science/insu-01308941 %~ INSU %~ UNIV-RENNES1 %~ UR2-HB %~ CNRS %~ GR %~ OSUR %~ GIP-BE %~ UR1-HAL %~ UR1-SDLM %~ UR1-SDLMJONCH %~ GR-DIMENV %~ UNIV-RENNES2 %~ OSUR-OSU %~ TEST-UNIV-RENNES %~ TEST-UR-CSS %~ UNIV-RENNES %~ INRAE %~ UR1-ENV %~ GR-R