Numerical experiments on subaqueous cyclic steps due to turbidity currents

摘要

A Froude-supercritical flow over an erodible bed may be subject to an instability which gives rise to the formation of cyclic steps, i.e. coherent, quasi-permanent trains of upstream-migrating steps bounded by internal hydraulic jumps in the flow above them. Cyclic steps have been observed and explained in bedrock streams and alluvium, but the possibility of cyclic steps due to turbidity currents in the subaqueous setting has not been explored. Yet turbidity currents are intrinsically more biased toward supercritical flows than rivers, suggesting that cyclic steps are at least as likely to be found in the subaqueous setting as in steep bedrock channels and alluvium. Here a numerical model is employed to explore these rhythmic bedforms generated by 20, 45 and 110-micron turbidity currents in an experimental setting. The results of numerical simulations offer an insight into what can be expected from laboratory experiments on cyclic steps.