Sheet flow layer structure under oscillatory flows

Abstract

Under large near-bed oscillatory velocities, sediment transport mainly occurs within a thin layer, known as the sheet flow layer. The structure of the sheet flow layer changes along the wave cycle, with maximum thickness around maximum onshore and off-shore velocities and minima at flow reversals. These changes are intimately related to the lower and upper bounds of the sheet flow layer. In the present work, the intra-wave changes of the sheet flow thickness for oscillatory flows, with acceleration and velocity skewnesses, are analysed based on detailed measurements of the sediment concentration within the bed layer and the backscattered signal of an Acoustic Doppler Velocity Profiler, located above. The results from both measurements are compared and discussed as a function of the physical forcing parameters: net current, flow acceleration and velocity skewnesses.