Hydrodynamics and Cross-Shore Sediment Transport in the Swash-Zone of Natural Beaches: A Review

The high velocities and suspended sediment concentrations in the swash-zone mean that the sediment transport processes in this zone are likely to be important contributors to shoreline erosion and accretion. However, studies of hydrodynamics and sediment transport in the swash-zone have been relatively few compared with those in the rest of the nearshore zone. Studies of swash-zone hydrodynamics have included run-up measurements using electrical resistance and capacitance devices, as well as cameras. Run-up has been modelled mostly using the non-linear shallow water equations. Sediment transport studies in the swash-zone require instrumentation which can unobtrusively obtain measurements close to the bed, therefore, very few data exist so far. Studies have been performed in incident –wave dominated relatively low energy conditions on steep reflective beaches, measuring individual swash events, and the sediment transport processes modelled with reasonable success on the uprush only. Studies made on high energy dissipative beaches have found the swash to be dominated by oscillations at infragravity frequencies, with suspended sediment concentrations being 3 to 9 times higher in the swash-zone than the inner surf-zone. The added complication of groundwater influx and outflux is also recognised as an essential area of study, whose processes should be included in any model of the swash-zone sediment transport.