Hydrodynamic effects of porous trapezoidal artificial reefs on the wave transformation and wave setups at uneven coral reefs

In recent years, the combined impacts of global climate change and human activities have resulted in the continued degradation of coral reef ecosystems, weakening their role as natural coastal barriers. This not only threatens the safety of reef infrastructure but also poses substantial risks to the safety and livelihoods of coastal residents. In this context, the construction of coral reefs urgently necessitates efforts to enhance wave attenuation capabilities while promoting the restoration of coral reef ecosystems, in order to address the increasingly severe environmental challenges. Artificial reefs (ARs), serving as coastal protection facilities with dual functions of wave attenuation and ecological restoration, have been widely deployed worldwide. However, most existing research predominantly focuses on the effects of ARs on flow fields, with limited attention given to their influence on wave propagation and evolution characteristics over coral reef. Therefore, this study analyzes the influence of porous trapezoidal ARs on wave propagation and evolution over uneven coral reefs, based on physical experiments and numerical simulations. We systematically analyze key factors, including incident wave height, submergence water depth, wave period, number of artificial reef rows, and artificial reef pore size, to assess their impact on local wave height, wave setup, and reflection coefficients. The experimental results indicate that the arrangement of ARs helps to compensate for the elevation differences between the inner and outer reef flats, thereby enhancing the reflection of waves and intensifying the shoaling effect, which, in turn, causes the wave breaking earlier. High-resolution numerical simulations further reveal that the complex vortex field within ARs substantially enhances wave energy dissipation. The combined effects of these mechanisms enable ARs to effectively reduce local wave height and wave setup on the inner reef flat, thereby significantly influencing wave propagation characteristics. In conclusion, this research provides both theoretical support for coral reef ecological restoration and technical support for coastal engineering design and implementation.