Effect of Bed Roughness on Time-Mean Drift Induced by Waves

Abstract

The results are reported of an experimental study of the Eulerian time-mean drift induced by progressive water waves over rough beds. Measurements were made in a laboratory flume with a laser Doppler anemometer, and two different two-dimensional artificial bed roughnesses were investigated. The measurements show that the maximum value of the time-mean drift velocity at the bed may be increased or decreased relative to the value predicted by Longuet-Higgins' theory for smooth beds. For a certain range of parameters, near-bed mean drift in the opposite direction to that of the wave propagation was observed.