Swash oscillations on a natural beach

Run‐up (swash) oscillations were measured on a gently sloping beach face for a variety of incident wave conditions. Run‐up energy spectra at wind wave frequencies show an ƒ −3 dependence and energy levels that are independent of incident wave height. This suggests saturation. In contrast, run‐up energy at surf beat periods increase approximately linearly with increasing incident wave energy. Thus, in the inner surf zone, where wave breaking limits the energy at wind wave frequencies, the principal manifestation of large incident wind waves is energetic surf beat.