Field observations of wave-current interaction at the sea bed.

Abstract

Field measurements are presented on the mean, turbulent, and wave induced velocities near the sea bed in combined wave plus current flow, with which to test theories of wave/ current interaction. A technique of splitting the variance within the velocity spectrum was developed to separate wave orbital velocities from turbulent fluctuations, which were often as large as the orbital velocities. The wave boundary layer was much thinner than the lowest measuring height (10 cm) and acted as a source of turbulence to the current boundary layer, analogous to an increased apparent bed roughness. This caused both the turbulent kinetic energy and the mean bed shear stress to increase strongly with the wave: current ratio. The results have implications for sediment transport, tidal dynamics, wave dissipation, and forces on pipelines. (A)