Author(s): Michele Trevisson; Olivier Eiff
Linked Author(s): Olivier Eiff, Michele Trevisson
Keywords: Fine-sediment ridges; Bedform morphology; Turbulent boundary layer
Abstract: Longitudinal bedforms, so-called sediment ribbons, are observed to form over uniform fine-sediment beds in fluvial environments. While the associated secondary flow structure has been investigated for stationary conditions on the basis of artificial ridges (Zampiron, 2021), the formation of sediment ribbons still remains largely unexplored. Colombini (1995) suggested the ribbons to be the result of a bed instability triggering the secondary flow. A top-down mechanism was instead proposed by Scherer (2022) on the basis of DNS simulations of an infinitely-large uniform sediment bed: the ribbons were found to be triggered by high and low-speed streaks in the outer flow. However, the ribbons were short-lived and replaced by ripples. Here, the aim is to experimentally analyze the initiation and long-term evolution of ribbons on a uniform sediment bed by combining time-resolved topographic measurements with time-resolved transverse-plane stereo-PIV measurements, allowing the bed evolution to be correlated with the turbulent structures across the entire flow cross-section.
Year: 2024