An experimental study on sediment transport and bed evolution under different swash zone morphological conditions

In this study, new large‐scale experimental data are presented showing evidences of a link between the swash zone dynamics and the surf zone morphodynamics. Two sets of large‐scale experiments are presented. The first set of experiments investigates the swash and surf dynamics under the same hydrodynamic forcing but with two different swash zone morphological conditions, one of which was created by manual reshaping of the sub-aerial beach face. It is shown that more dissipative swash zone conditions (a more mildly sloping beach face) significantly reduce the rate of seaward sandbar migration such that it almost ceases during the performed experimentation time. This behavior is compared to a second set of experiments which shows the natural sand bar offshore migration under almost identical hydrodynamic forcing. The changes in the sandbar migration are investigated in terms of the differences in the swash zone dynamics. The more reflective swash zone is characterized by more intense backwashes that, in turn, promote significant quantities of sediment suspension during the interaction of the backwash with the subsequent bore. The dissipative swash zone leads to a larger number of wave–swash interactions, reducing the backwash magnitudes and the magnitude of suspended sediment concentration events in the swash zone, with a corresponding reduction in the offshore suspended sediment transport. The total offshore sediment transport rates are also shown to reduce, leading to the observed modification of the sandbar migration.

► Evidences of a link between the swash and surf zones sediment dynamics are presented.
► We examine the effect of two different swash zone morphological conditions.
► More dissipative swash zone conditions significantly reduce the rate of seaward sandbar migration.
► The dissipative swash zone leads to a larger number of wave–swash interactions.
► This reduces the backwash magnitudes and the offshore suspended sediment transport