Spatial distribution of wave-by-wave overtopping behind vertical seawall with recurve retrofitting

Abstract

Understanding the spatial distribution of wave overtopping water behind coastal protection structures is essential for assessing the safety level of coastal regions behind the coastal defences. The spatial distribution of wave overtopping volume determines the planning and arrangements of critical infrastructures (e.g., railways, roads and buildings) in coastal regions. This study presents a series of laboratory-scale physical modelling experiments to investigate the spatial distribution of wave overtopping volume behind plain vertical seawall and seawall with recurve retrofitting. The hydrodynamic conditions are designed to mimic both swell and storm sea conditions. Tests were conducted for a range of relative freeboard and empirical-based predictive equations were derived for both mean and extreme overtopping events under impulsive and non-impulsive wave conditions. Test results showed that overtopping impact hazard zone reduces up to 87% with the increase of relative freeboard (Rc/Hm0). The hazard zone for extreme overtopping events was found to be up to 3 times of the mean overtopping volumes. The effectiveness of recurve retrofitting on mitigating spatial distribution of wave overtopping were investigated with three recurve prototypes of varying overhang length and recurve's height. It was found that increase in overhang length provides higher reductions in the spatial distribution of hazard zone behind the wall and improve the climate resilience of the seawall. The results highlight that recurve retrofitting is more effective in reducing the length of hazard zone under impulsive wave conditions. The findings of this study provide key data and predictive formulae for robust assessments of the hazard zones behind the key coastal defence infrastructures during mild and extreme climatic events.