Ripple formation and sediment-suspension events in unsteady depth-varying open-channel flow

The development of ripples and its effects on suspended sediment during unsteady flow was studied experimentally to understand and quantify the processes during floods. Quasi-instantaneous profiles of velocity and sediment concentration were taken simultaneously and co-located by combining an acoustic Doppler and imaging method (ADVP) with Particle Tracing Velocimetry (PTV) for suspended sediment particle tracking. During the final phase of the accelerating flow range, a ripple pattern appeared almost instantaneously along the whole reach of the fine sediment bed. It developed rapidly, and its dimensions remained nearly stationary from then onward. Sediment suspension occurs as individual events, and can be linked to coherent flow structures. Sediment suspension in the final phase of accelerating flow and the subsequent steady flow is controlled by large-scale turbulence processes comparable to those reported for steady flow in the literature. The height and the intensity of the upward suspension were related to the ripple dimensions.