3D COMPUTATIONS OF WAVE-DRIVEN LONGSHORE CURRENTS IN THE SURF ZONE

This study aims at improving the computation of the wave-driven longshore currents in the surf zone. The vertical distribution of wave-driven currents often deviates from a logarithmic vertical distribution, due to the vertical mixing induced by wave breaking. 3D modeling of these currents provides the opportunity to take this vertical variation into account. The current method of computing the bed shear stress in the 3D approach of Delft3D is dependent on the thickness of the near-bed vertical computational layer: the thinner this layer, the larger the bed shear stress and the smaller the wave-driven longshore currents. Computing the bed shear stress using the velocity at the edge of the wave boundary layer avoids this layer dependency. With this method good agreement with measured velocity data from laboratory experiments and field experiments is obtained, except for very close to the shore. Although Delft3D in 2DH and 3D model have similar skill in simulating longshore currents, the 3D approach is recommended for wave-driven sediment transport related problems as it more realistically represents the cross-shore current and suspended concentration profile.