Hydrodynamic influences of offshore submerged breakwater on wave properties of tsunami-like wave over coral reefs

In recent years, coral reefs in tropical and subtropical regions have been increasingly exposed to tsunami disaster risks, primarily due to the degradation of coral reef ecosystems that has significantly reduced their natural capacity for wave attenuation. Currently, there is an urgent need to implement effective strategies to enhance the wave attenuation and coastal protection capabilities of coral reefs. However, most traditional hard coastal protection measures exhibit notable limitations in addressing extreme climate events and long-term sea-level rise, primarily characterized by low ecological compatibility, substantial maintenance costs, and disruption of the natural coastal dynamic equilibrium. The offshore submerged breakwater (SBW) shows better friendliness in terms of ecological environment adaptability and is helpful in reducing the disturbance to the marine ecosystem. As an initial research attempt, this study conducts the corresponding physical experiments and high-resolution numerical simulations to investigate the impacts of segmented offshore SBW on the wave hydrodynamics of tsunami-like waves over coral reefs. The hydrodynamic effects of several key parameters, including incident wave height, submergence water depth, and relative gap width of offshore SBWs, have been thoroughly examined through experimental investigation. The complex flow field generated during the interaction between segmented offshore SBWs and tsunami-like waves is also numerically simulated. The research findings indicate that the presence of segmented SBW can significantly influence the transforming and breaking characteristics of tsunami-like waves over coral reefs. The complex interactions between tsunami-like waves and wave-induced flows within the spacing gaps of segmented SBWs effectively dissipate a considerable amount of incident wave energy, resulting in an elevated wave reflection coefficient and a reduced wave transmission coefficient. These effects collectively lead to a significant decrease in the run-up height of tsunami-like waves on the backreef slope, thereby providing effective wave attenuation and coastal protection.