The effect of wave directional spread on coastal hazards at coastlines fronted by a coral reef

Abstract

Many coastlines fronted by a coral reef are threatened by wave driven flooding. For this reason, waves in coral reef environments has been topic of many studies. However, most are focused on a 1D simplification of the coral reef environment. These studies neglect the impact of 2D processes, for example wave directional spread. In this study an attempt is made to understand and investigate the influence of wave directional spread on wave runup. XBeach Non-Hydrostatic with an additional vertical layer is used to perform a great amount of digital experiments. A synthetic database is created consisting of 540 different model runs. The analysis showed that wave directional spread influences the wave runup by affecting the wave setup and low frequency runup. So, for the most accurate runup predictions it is advised to include directional spreading in the analysis. Furthermore, the complete exclusion of directional spreading in the runup analysis will lead to an over prediction of the runup, so current 1D models give conservative estimations of the runup. Lastly, it was found that the exact wave directional spread is not that important but it is advised to obtain information about the wave field that is dealt with and take that into account in the runup analysis.