Wave overtopping on a low-crested seawall under extreme waves

Abstract

Extreme waves in global nearshore regions, frequently accompanied by wave setup, can transform seawalls into low-crested structures. Such events pose threats to coastal infrastructure due to enhanced overtopping and intense hydrodynamic loads imposed on seawalls and related coastal defenses. This study investigates the wave overtopping dynamics on a low-crested seawall under extreme wave conditions through controlled wave flume experiments that have comprehensively measured wave elevations, free-surface profiles, overtopping volumes, and impact pressures. The temporal and spatial characteristics of wave overtopping and their dependence on water depth and wave parameters are examined. The results demonstrate a positive correlation between overtopping volume and wave amplitude, with localized impact pressures also intensifying as wave amplitude increases. Conversely, as wave peak frequency increases and seawall crest elevation rises, waves, especially those of larger amplitudes, tend to break earlier on the seaward slope. This earlier breaking dissipates a significant portion of wave energy, thereby reducing overtopping volumes and the impact pressures on the seawall. Furthermore, this study reveals that as the focusing position of the extreme wave group shifts landward, there is a notable reduction in the group's cumulative energy. This energy attenuation results in diminished overtopping volumes and lower impact loads. These findings elucidate the complex interplay between wave parameters, seawall height, and the dynamics of wave overtopping under extreme wave conditions as well as provide a theoretical framework for optimizing the design and resilience of seawalls to mitigate the adverse impacts of extreme wave events on coastal infrastructure.