Evaluation of Wave Attenuation Performance of an Ecological Submerged Breakwater in the Sheyang Coastal Zone, Jiangsu Province, China

Under the combined pressures of natural variability and human activities, the area of tidal flats has been gradually decreasing, with most muddy coasts experiencing varying degrees of erosion. The central coast of Jiangsu Province, a world-renowned region for extensive tidal flats, has witnessed intensifying erosion of its muddy coasts in recent years. To mitigate further coastal erosion, an ecological submerged breakwater (ESB) was constructed in the intertidal zone north of the Sheyang River estuary to reduce wave impact on the shoreline. This study evaluates the wave attenuation performance of the ESB based on wave observations conducted at stations deployed on the seaward and landward sides of the structure in May 2025. Results indicate that the breakwater effectively reduces wave height, but its performance exhibits significant dynamic characteristics. During the observation period, the maximum attenuation rate for significant wave height (H1/3) reached 76.3%, with an average rate of 33.8%. Wave dissipation efficiency was closely related to sea state: under calm conditions (H1/3 < 0.4 m), the average attenuation rate was only 18.4%, whereas under severe sea states (H1/3 ≥ 0.4 m), it increased markedly to 57.6%. The wave transmission coefficients (Kt) span a wide range from 0.20 to 0.99, indicating a significant dynamic variability in the wave attenuation performance of the ESB. The performance of the ESB was primarily controlled by two key factors: incident wave height and submergence depth of the structure. Compared to “zonated” natural ecosystems such as oyster reefs, coral reefs, salt marshes, and mangroves, the ESB, as a “linear” engineered structure, achieves comparable wave attenuation within a limited spatial footprint. A promising future strategy involves using the ESB as a frontline defense, integrated with landward ecological restoration measures like salt marsh rehabilitation, to establish a hybrid “grey-green” coastal protection system that synergistically enhances both coastal resilience and ecological function. This study provides a scientific basis for the design and performance evaluation of ecological engineering solutions for protecting eroding muddy coasts.