Motion of water and sediment due to non-breaking waves in the swash zone*

A long wave run-up theory is applied to the modelling of wave-induced flow velocities, sediment transport rates and bottom changes in a swash zone. First, the properties of the water tongue motion and the resulting lithodynamic response are analysed theoretically. Next, an attempt is made to run the model for the natural conditions encountered on the southern Baltic Sea coast. The Lagrangian swash velocities are used to determine the Eulerian phase-resolved bed shear stresses with a momentum integral method, after which the motion of sand is described by the use of a two-layer model, comprising bedload and nearbed suspended load. Seabed evolution is then found from the spatial variability of the net sediment transport rates. The results presented are limited to cases of the small-amplitude waves that seem to be responsible for accretion on beaches.