Experiments to Systematically Evaluate the Role of Cohesion in Channel Initiation and Evolution

Nacere M Samassi, Fernando David Cúñez, Rachel Glade

Sediment cohesion has long been thought to exert a fundamental control on channel evolution and the wide range of channel forms observed on Earth and other planets. Here we present results from simplified laminar flume experiments to investigate how systematically increasing sediment cohesion affects erosional channel formation. Low cohesion leads to a subtle shift from highly mobile, braided-like to single-thread sinuous channels. At intermediate cohesion we observe an abrupt shift to straight, narrow, gully-like channels with retreating headcuts. Particle image velocimetry (PIV) shows that this change occurs despite similar sediment transport rates. At higher cohesion, bedrock-like headcut retreat and sediment transport rate decreases due to highly stabilized banks and the dominance of aggregates. Our work demonstrates that even in abstract, simplified experiments, changes in cohesion can produce a wide range of channel forms strikingly similar to those observed at a range of scales and environmental conditions on Earth and other planets.