Understanding the Mixed Velocity Scale in Relation to the Peak Reynolds Shear Stress in Open Channel Flows

Recent data analyses have demonstrated a strong correlation between sediment discharge and the mixed velocity scale instead of the shear velocity, albeit through an empirical approach. This paper seeks to advance the understanding of this relationship by conducting additional experimental and analytical research. First, a series of experiments was conducted under both plane bed and dune bed conditions with the aim of quantifying the peak Reynolds shear stress. This parameter is crucial as it represents the near-bed shear stress due to turbulence, which has a significant influence on sediment transport. The experimental results revealed a robust correlation between the mixed velocity scale and the peak Reynolds shear stress. This correlation is further substantiated by a conceptual model that is developed in accordance with the phenomenological theory of turbulence. These insights provide an alternative rationale for the preference of the mixed velocity scale over the conventionally applied shear velocity in the analysis of sediment discharge.