Swash Zone Modeling - Essay Example

However, an accurate model is still lacking for at least a couple of reasons (Nielsen et al., 2001). Firstly, the water motion in the swash zone is quite different from that in the inner surf zone and not well understood. In particular, the bed shear stresses have not been measured. Secondly, there is a possibility that perpendicular to the sand surface (in/exfiltration or ventilation) and/or strong horizontal pressure, gradients near bore fronts could influence the sediment motion significantly in the swash zone.

In the swash zone, the bore collapses at the shore, surface rollers are not present and consequently the velocity distribution given by Eq. (1) is not valid. Thus, this dissipation mechanism (i.e. surface roller concept) cannot be applied in this region. Instead of this, the eddy viscosity concept is adopted in order to simulate the dissipation due to turbulence in the swash zone (the run-down point is considered as the offshore limit of the swash zone). Details can be found in Karambas and Koutitas (2002).

The numerical solution of the Boussinesq-type equations is based on an accurate higher order numerical scheme, which has been developed by Wei and Kirby (1995). They used a fourth-order predictor-corrector scheme for time stepping and discretize the first-order spatial derivatives to fourth-order accuracy. This discretization automatically eliminates error terms that would be of the same form as the dispersive terms, and which must therefore be corrected for if lower order scheme are used. In order to validate the above model, Karambas and Koutitas (2002) compared the numerical results with experimental data (including swash zone).

As mentioned by Turner and Masselink (1998), vertical flow through a porous bed induces two effects: (a) bed stabilization-destabilization, and (b) thickening or thinning of the boundary layer. On the uprush, downwards-directed piezometric head gradients (infiltration) will increase the effective weight of sediment (i.e. bed stabilization), thereby decreasing the potential for sediment transport