Initiation of erosion in unidirectional flow using a synchronized imaging technique

The introduction of non-cohesive sediment (sand) into cohesive sediment (mud) may produce a mixture with erodibility characteristics, unlike the two individual constituents (Sanford 2008). Suspended sediment entrainment has been found to occur intermittently in turbulent flow (e.g., Drake et al. 1988). Therefore, instantaneous turbulent velocity fluctuations are used to characterize sediment entrainment events in this study. Our goal was to obtain the instantaneous turbulent fluid velocity fluctuations adjacent to an erosional zone in a sand–clay sediment mixture to evaluate the Taylor frozen turbulence hypothesis (TFTH) and demonstrate that it is valid near the erosional sediment surface. The TFTH assumes that the advection contributed by the turbulence itself is small; therefore, a field of turbulence advects with the mean flow, while the fundamental properties of the turbulence remain unchanged (Taylor 1938). We validated the TFTH using spatial and temporal spectra for this case (e.g., Pope 2000).