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Erosion patterns in a sediment layer


Eric Clement, Florent Malloggi (LMDH, University of Paris VI, France)
Adrian Daerr , Laurent Limat (MSC, University of Paris VII, France)

Many natural patterns coming from erosion have been described by
geomorphologists. Erosive patterns are common in situations implying dense
sediment transport, but so far, a complete understanding of all the
physical processes involved is still a challenging issue. We report here on
laboratory-scale experiments which reproduce a rich variety of natural
patterns[1] with few control parameters. In particular, we observe
intriguing rhomboid structures often found on sandy shores and flats. It
turns out that the standard views based on surface waves fall short to
explain the phenomenon. We argue that the small thickness of the flowing
layer at the onset of grain carriage instead leads to a strongly non-linear
erosion-deposition process. From the experimental parameters, the relevance
of some possible erosion mechanisms can be analyzed.
Also using the same experimental set-up we produce underwater avalanches
displaying, in some cases, a fingering instability of the front. We discuss
the mechanisms leading to the instability propose an analysis of the wave
selection dynamics .
1. A.Daerr, P. Lee, J.Lanuza and E. Clement Erosion patterns in a sediment
layer  Phys. Rev. E 67 (2003) 065201