Modelling of time-dependent sand transport at the bottom boundary layer in the surf zone

The present paper is aimed to formulate a numerical model for calculating the time-dependent velocity field and the space and time distribution of sand concentration inside the bottom boundary layer in the surf zone. The numerical results are compared with recent laboratory data. The 2DV (two-dimensional vertical) numerical module for the velocity field is based on the Reynolds averaged form of the Navier-Stokes equations while the sand transport module uses the turbulent convection-diffusion equation. The equiphase mean values for the horizontal and vertical velocities within the bottom boundary layer (the flow field) and the equi-phase mean values for the sand concentration are obtained. A transformation of the coordinate system is performed in order to enable the easy implementation of the numerical modelling. Details of the numerical modelling together with discussions on the boundary conditions are also presented. The comparison of numerical and laboratory results reveals relatively good agreement within certain limitations of the present model. The laboratory data, which are used to compare the hydrodynamic numerical model have been obtained in the surf zone while the ones for verifying the sand concentration numerical model are obtained as a result of pure oscillatory movement.