Sediment transport under a swash event: the effect of boundary conditions

Using a Lagrangian framework, we obtain predictions for suspended sediment transport under a swash event described by a recently proposed shallow-water model in which the swash is driven by a sustained off-shore bore and the sediment supply from the bore may vary with time. Although the hydrodynamics of the ‘modified’ swash flows differ somewhat from the classic Shen–Meyer description, the overall patterns of sediment transport are shown to be rather robust to this difference. In particular, it appears that in order to determine whether the swash zone imports or exports sediment, it is still crucial to determine accurately how much sediment is suspended by the incoming bore and advected into the swash zone by the flow following bore collapse. Both the total amount of this ‘pre-suspended’ sediment and its phasing relative to the swash inflow are important if net deposition patterns are to be predicted accurately.