Wave overtopping of a vertical seawall in a surf zone: A joint analysis of numerical and laboratory data

This research uses physical and numerical experiments to investigate the wave overtopping of a vertical seawall in an uneven surf zone. The numerical experiments exploit two approaches, which differ in vertical resolution and computational time: CFD-RANS and SWASH. The tests were conducted with and without the wall, allowing the analysis of the spectral evolution in shallow water and its relationships with wave overtopping. The study assesses the performance of numerical models with different levels of complexity and uses laboratory and numerical data to understand the key variables that control the phenomena under study. The results indicate that while CFD-RANS is quantitatively in line with the laboratory measurements, SWASH overestimates the spectral moments and underpredicts the overtopping rate by a factor of 2. However, the numerical tools satisfactorily reproduce the physics of the processes, allowing us to focus on some aspects of engineering relevance. Laboratory and numerical data indicate that the overtopping rate depends not on the wave spectrum shape but on the high percentiles of the wave elevation distribution. This outcome clarifies that wave setup is a critical variable for prediction purposes. Finally, the article highlights that the surf zone's spectral moments are correlated. The correlation structure is such that the mean spectral periods became proportional to the local wave energy despite these quantities being independent in deeper water. We warn that this phenomenon could result in spurious, unphysical relationships between mean spectral periods and overtopping rates. The analysis of further literature data corroborates this conclusion.