The spatial distribution of wave overtopping volumes over a composite smooth impermeable seawall with an impermeable berm

The distribution of overtopping volumes is crucial for understanding the coastal areas impacted by overtopping events. Accurate predictions of how far overtopping will extend landward are essential for assessing coastal safety in light of potential wave overtopping hazards, especially in a changing climate. This study introduces, for the first time, a comprehensive series of laboratory-scale physical modelling experiments aimed at investigating the spatial distribution of overtopping volumes behind a composite smooth impermeable seawall with an impermeable seaward berm. The hydrodynamic conditions were designed to simulate random sea states that follow the JONSWAP spectrum ( γ = 3.3). The analysis focuses on how wave characteristics and seawall structure parameters affect the landward distribution of overtopping water. The results show that the spatial distribution of overtopping water can be accurately described by an exponential function of the distance ( x ) behind the seawall crest, alongside a spatial decay coefficient ( k ). The value of k , which determines the shape of the landward distribution, is influenced by the combined effects of wavelength ( L 0 ), structure freeboard ( R c ), water depth on the berm ( d s ), and berm width ( B An empirical equation for the spatial decay coefficient k was developed using Buckingham's π theorem to predict the distribution of overtopping water behind the seawall. The proposed equation showed satisfactory agreement with the experimental measurements. However, the applicability of the relationship is limited to the tested configurations, as the crest elevation, foreshore slope, and landward slope angles remained constant throughout the study. The findings of this study will equip coastal engineers with a new predictive tool for evaluating overtopping risks and refining the design of composite seawall configurations across a range of wave conditions.