Predicting Extreme Wave Run-Up on Natural Beaches for Coastal Planning and Management

Abstract

A simple empirical model is proposed for predicting extreme wave run-up on natural beaches during severe wave events (deep water wave heights H 0 ≳ 8 m or return periods of about 50 years). The new model departs from traditional approaches that use the slope of the beach face ßf and the Iribarren number ξ0 s parameters for predicting run-up and instead uses the distance offshore xh , to water depth h to estimate a near-shore profile slope as S = h/xh , where the depth of closure is the proposed choice for h. Extreme run-up Rx is then expressed in terms of S as Rx/H0 = CS 2/3. Observations from recent severe storm events in South Africa are used to estimate the dimensionless coefficient C ≃ 7.5. The data are also compared with those of Holman [1986] and the results verify his regression equations and confirm they are valid for significant wave heights extending to 8.5 m for beach-face slopes around 0.1. The run-up predictions of Holman [1986], Nielsen and Hanslow [1991] and Stockdon et al. [2006] are compared to those of the proposed new model. The results suggest that the new model reduces the uncertainties in predicting wave run-up on natural beaches compared with previous models, and thus enables improved estimates of extreme wave run-up and the upper limit of beach change for coastal planning and management.