Run-up characteristics of regular wave breaking on vegetated sloping beaches

Abstract

As an emerging “soft protection” measure for coastlines, coastal vegetation offers significant potential for disaster prevention and ecological service. This study investigated the run-up characteristics of breaking waves under the influence of vegetated slopes through physical experiments and numerical simulations. The numerical model used OpenFOAM® to solve the Reynolds-averaged Navier-Stokes equations and the stabilized k-ω SST turbulence model, which was adjusted to account for the influence of vegetation. The accuracy of the model was verified using experimental data. Then, the maximum wave run-up height (R_u) and its variations with slopes (m), vegetation density (N_v), vegetation zone length (L_v), and seaward horizontal distance of the vegetation zone (b) under different wave types were analyzed. The results show that the vegetated slopes can significantly reduce wave height along the sloping beach. In most scenarios, vegetated slopes contribute to reducing R_u. Specifically, an increase in N_v generally leads to decreased R_u on the slope, with a maximum reduction of up to 70.3% observed at N_v = 590 elm/m². However, when L_v and b are relatively small, the presence of vegetation can increase R_u. The maximum increase in wave run-up height is observed to be 17.9% at L_v = 0.8 m and b = 0.5 m. Changes in slope m and the position of vegetation on the slope effect wave-breaking characteristics, which in turn affect wave run-up. The reduction in R_u is most significant when waves break within the vegetated zone. Finally, a prediction formula for R_u as a function of the surf similarity parameter, wave, and vegetation parameters was developed using the multivariate non-linear regression method. In addition, extra cases were employed to validate the reliability of the prediction formula, which is expected to provide certain help in the design of coastal ecological protection measures.