Transient swash motions on a gently-sloping beach

Spectral and wavelet analyses are used to investigate run-up motion on a gently sloping beach with special attention devoted to the coupling between the long-period swash oscillations and the wave grouping outside the surf zone. Run- up elevations were measured under random-wave conditions during the laboratory GLOBEX experiments carried out along a 1:80 sloping, fixed beach. A capacitance wire was deployed parallel to the bottom in order to detect the swash edge. The low Iribarren numbers involved in the experiments led to swash motions dominated by surf beat. High correlation levels between the scale-averaged wavelet power and the run-up suggest that low-frequency swash motions are still associated with the modulation of offshore swell waves. In addition, wavelet analysis supports the idea that swash-swash interactions are important in controlling swash oscillations