Mobile layer in oscillatory sheet flow

Abstract

Measurements are reported of mobile layer thickness and the velocity and concentration distributions within the mobile layer in oscillatory sheet flow. Tests were carried out with sand, PVC, and acrylic granules in an oscillatory water tunnel. Velocities were measured with a laser Doppler anemometer, and concentrations were measured with conductivity probes. The measurements of mobile layer thickness appear to confirm the importance of the parameter S = (ρU0ω/(ρs−ρ)g). At low values of this parameter the measurements tend toward the unique curve which would be expected if pressure gradient and inertia effects were negligible. On the other hand, the velocity profile measurements show some influence of pressure gradient and inertia even for values of S as low as 0.12. At higher values of S a type of plug flow is observed in which the sediment comes to rest as the flow reverses and then begins to move again as a solid block.