Experimental study on wave attenuation by vegetation under variable water levels

Coastal vegetation serves as a natural and eco-friendly approach for wave energy dissipation, which is crucial for mitigating coastal erosion and enhancing resilience under variable water levels caused by climate change. This study investigates the wave energy dissipation capacity of salt marsh vegetation under varying water depths, focusing on the influence of stem-leaf structure on wave attenuation mechanisms. Through wave flume experiments, the wave-attenuating effects of Suaeda salsa models and cylindrical rod models were compared. A stem-leaf correction factor ( φ ) was introduced to optimize existing models' representation of complex vegetation structures. Results indicate: Due to its complex stem-leaf structure, the Suaeda salsa model exhibits a relative wave height ( K v = H₁ / H₀ , where H₁ is transmitted wave height and H₀ is incident wave height) approximately 22.67% lower than the rigid cylindrical rod model, demonstrating significantly enhanced wave attenuation capacity (Analysis of Variance (ANOVA): F -statistic = 38.7, p -value <0.01). The stem-leaf correction factor exhibits a nonlinear relationship with water depth (showing significant variation in shallow water and stabilizing in deep water). Its incorporation improves the fitting accuracy of the drag coefficient ( C d ) and Keulegan–Carpenter number (KC) ( R 2 = 0.53) and enhances the consistency between the corrected damping coefficient ( β cv ) and experimentally measured values ( β m ). The improved vegetation wave attenuation model proposed in this study deepens the understanding of vegetation structure's role in wave dissipation, providing theoretical and experimental foundations for designing eco-friendly coastal protection technologies. • A stem-leaf correction factor was proposed to improve traditional vegetation-based wave attenuation models. • The study revealed a nonlinear relationship between the stem-leaf correction factor and water depth, enhancing model fitting performance. • The Suaeda salsa model demonstrated superior wave energy dissipation with approximately 22.67% lower wave height attenuation coefficient than rigid cylindrical rods, due to its complex stem-leaf structure. • The corrected damping coefficient ( β cv ) achieved higher consistency with experimental measurements, improving wave energy dissipation calculation accuracy.