Abstract: As a critical engineering measure for coastal protection, the application of submerged breakwaters on coral reefs requires further investigation. Existing research on wave types in shallow reef waters remains limited, and systematic analysis of nonlinear wave propagation characteristics in such environments is still insufficient. Consequently, this study utilizes physical flume experiments to systematically explore the influence of submerged breakwaters, positioned on the fore-reef slope, on the propagation characteristics of cnoidal waves over coral reef topography. Focus is placed on analyzing the effects of incident wave height, water depth over the reef flat, and wave period on local mean wave height, wave setup, wave run-up, and wave nonlinear features. The results indicate that submerged breakwaters significantly enhance wave reflection and shallow-water deformation, causing the wave breaking point to shift seaward. This effectively reduces transmitted wave heights on the reef flat, thereby mitigating erosive damage to the reef substrate and ecological environment. Furthermore, the submerged breakwater weakens the enhancement of nonlinearity induced by increasing incident wave heights and reduces wave asymmetry. It causes the peak skewness to shift toward the vicinity of the breakwater and significantly suppresses nonlinear variations during propagation. Experimental data also reveal that water depth over the reef flat significantly influences the wave-dissipation performance; under the conditions of this study, optimal wave attenuation is achieved at a water depth of 0.030 m. The findings of this research provide a theoretical foundation for the design of coastal protection works on coral reefs, balancing enhanced protection efficiency with the stability of the reef flat ecosystem.

Key words: cnoidal wave, coral reef, submerged breakwater, nonlinear characteristics, hydrodynamic characteristics