CHAPTER 183 SEDIMENT TRANSPORT UNDER (NON)-LINEAR WAVES AND CURRENTS

Two series of experiments were carried out in the Large Oscillating Water Tunnel of Delft Hydraulics, which was recently extended with a recirculation flow system. Combined wave-current boundary layer flows were studied with a mobile sand bed in the sheet flow regime. Detailed intra-wave concentration and velocity measurements were carried out and revealed a three-layer system, i.e. a pick-up layer, a sheet flow layer and a suspension layer. In the suspension layer time-lag effects of the sediment concentration led to sediment fluxes in upstream direction. The suspended sediment was more confined to the near-bed region than according to diffusion theories, most likely due to turbulence damping. The horizontal time-dependent and net sediment fluxes were concentrated in the sheet flow and pick-up layer. Measured net sediment transport rates could be described as a linear relation with the third-order velocity moment <U3> near the bed