Experimental Study on Wave Attenuation Characteristics of Hemispherical and Cage Oyster Reefs in Wave Flume

As a typical ecological engineering structure, oyster reefs can weaken wave energy while providing ecological restoration functions, serving as an important component of nature-based coastal protection solutions. This study systematically investigated the wave attenuation characteristics of two types of oyster reefs—hemispherical and cage structures—through physical model experiments in a wind-wave-current flume. A total of 43 test conditions were designed for the hemispherical reef experiments to analyze the influence of relative crest freeboard, wave steepness, and reef width on the transmission coefficient. Results showed that the transmission coefficient decreases as the relative crest freeboard increases. When wave steepness exceeds a certain threshold, the transmission coefficient becomes more sensitive to changes in wave steepness. Based on the experimental data, an empirical transmission coefficient formula for hemispherical oyster reefs under regular waves was fitted. For the cage reef experiments, the empty flume control method was employed to analyze the spatial wave height variation under different filling rates. It was found that, under the deeply submerged condition, higher filling rates result in more significant wave attenuation, and the roughness dissipation effect of the reef structure is more pronounced under the deeply submerged condition than under the shallowly submerged condition. The research findings can provide experimental evidence for the configuration selection and parameter optimization of wave attenuation units at the front of coastal ecological seawalls.