%0 Conference Proceedings %F Poster %T Chasing waterfalls: Experimental controls on knickpoint form and migration processes %+ University of Edinburgh %+ Géosciences Rennes (GR) %A Baynes, Edwin %A Lague, Dimitri %A Attal, Mikaël %< avec comité de lecture %B European Geosciences Union General Assembly 2016 %C Vienne, Austria %V 18 %P EGU2016-3273 %8 2016-04-12 %D 2016 %Z Sciences of the Universe [physics]/Earth Sciences/GeomorphologyConference poster %X As the link between the fluvial network and hillslopes, bedrock channels mediate the response of the landscape tochanging boundary conditions, such as tectonics and climate. Such signals of transient forcing are manifested inbedrock river profiles through migrating ‘knickzones’ or ‘knickpoints’, that separate a downstream reach broadlyin equilibrium with the new conditions and an upstream reach which is yet to adjust. Knickpoints therefore marka dynamic boundary location within mountain landscapes, yet the complexities of the mechanisms of knickpointretreat are often ignored in studies of landscape evolution.We carried out a series of box flume experiments (65 cm long, 30 cm wide) to explore the importance ofknickpoint geometry, mean discharge and substrate strength on the form and migration of knickpoints in acohesive homogenous substrate. The retreat rate of knickpoints is found to be independent of mean discharge.Knickpoints retreat faster through a weaker substrate. The dominant control on knickpoint retreat, when dischargeand substrate strength are constant, is the knickpoint form which is set by the ratio of channel flow depth toknickpoint height. Where the knickpoint height is five times greater than the flow depth, the knickpoints developundercutting plunge pools, accelerating the removal of material from the knickpoint base and the overall retreatrate, possibly due to the trajectory of the jet at the knickpoint lip. Smaller knickpoints relative to the flow depth aremore likely to diffuse from a vertical step into a steepened reach or completely as the knickpoint retreats up channel.These experiments challenge the established assumption in models of landscape evolution that a simple relationshipexists between knickpoint retreat rate and discharge/drainage area. In order to fully understandhow bedrock channels, and thus mountain landscapes, respond to transient forcing, further detailed study ofthe mechanics of erosion processes at knickpoints, both experimentally and at the field/landscape scale, is required. %G English %L insu-01309188 %U https://insu.hal.science/insu-01309188 %~ 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