[H-GM03] Geomorphology

[HGM03-06] Laboratory model experiments of bedrock channels with a subsurface layer limiting downward incision

*Hiroto Igawa¹, Noritaka Endo¹ (1.Graduate school of science and technology, Kanazawa University)

Keywords:Mountain river, bedrock channel, Downward incision, Lateral erosion , Laboratory model experiment

In a large timescale, mountain rivers make a significant contribution to mountain landscapes. Mountain rivers are fundamentally bedrock rivers, and alluvial deposits exist only in parts and temporarily. During the development of mountain rivers, downward incision, and lateral erosion resulting in valley widening and channel migration take place. A previous laboratory experiment modelling basin-scale mountain rivers showed that lateral migration of the stream channels became dominant after a transition from the early stage where the denudation rate was below the total uplift per unit time to the latter stage of a dynamic equilibrium state, which suggested that lateral erosion became active after downward incision became inactive. In our previous study of laboratory experiment modelling channel-scale bedrock rivers, the wooden plank as a non-erodible layer was embedded at a certain depth from the channel base. During this experiment, it was observed that lateral erosion became active where the plank were exposed by downward incision and then downward incision was restricted. The completely unerodible layer such as the plank, however, seems to be somewhat an unnatural object. In the present study, a subsurface layer harder than the surrounding substrate that is less erodible but not perfect unerodible was installed instead. As a result, lateral erosion tended to become more active when the hard layer was exposed and downward incision became slow. This result agrees with our previous study, suggesting negative correlation between activeness of downward incision and lateral erosion of bedrock river channels under certain conditions.