Bottom Shear Stresses in the Boundary Layers Under Waves and Currents Crossing at Right Angles

This paper describes a two year experimental research programme investigating the influence of non-linear wave-current interactions on wave and current characteristics. The tests focus on the mean and oscillatory velocity components and shear stresses within the bottom boundary layer over a rough bed for cases where waves propagate at right angles to the line of the current flow. Bed shear stresses have been measured directly by means of a novel shear plate device. The aim of the research is to generate a reliable data set for use by modellers.Results show that currents experience a significant change both in mean bed shear stress and apparent bed roughness when waves are superimposed. However, the oscillatory, wave-induced, bottom shear stress has been shown to be insensitive to the addition of an orthogonal current.