Simulation and prediction of swash oscillations on a steep beach

This paper presents numerical simulations and analytical predictions of key aspects of swash oscillations on a steep beach. Simulations of the shoreli ne displacement based on bore run-up theory are found to give excellent agr eement with recent experimental data for regular waves, wave groups and ran dom waves. The theory is used to derive parameters that predict the onset o f swash saturation and the spectral characteristics of the saturated shorel ine motion. These parameters are again in good agreement with the measured laboratory data and are also consistent with previous experimental data. Si mulation of irregular wave run-up using a series of overlapping monochromat ic swash events is found to reproduce typical features of swash oscillation s and can accurately describe both the low and high frequency spectral char acteristics of the swash zone. In particular, the low frequency components of the run-up can be modelled directly using a sequence of incident short w ave bores, with no direct long wave input to the numerical simulations. Thi s suggests that wave groupiness must be accounted for when modelling shorel ine oscillations. (C) 1999 Elsevier Science B.V. All rights reserved.