Modelling vegetation-induced wave attenuation: the impact of seagrass seasonal variability and biomechanical flexibility

Abstract. This study investigates wave attenuation induced by the non-linear interactions between wave dynamics and marine vegetation, focusing on Posidonia oceanica meadows along the Civitavecchia coastal zone (north-eastern Tyrrhenian Sea, Italy). To overcome the limitations of conventional models, which often oversimplify canopy–wave dynamics and lack the integration with observational data, this research employs a digital twin approach that enhances model fidelity by coupling numerical simulations with long-term in situ measurements. We refine the seagrass parameterization in a spectral wave model by incorporating an enhanced representation into the bottom dissipation source term, explicitly accounting for the effects of plant flexibility, seasonal growth patterns, and phenotypic traits, all informed by site-specific observations. Application to the Civitavecchia site demonstrates that the seasonal variability of the meadows drives significant temporal fluctuations in wave damping capacity, with a monthly variation of up to 10 %. Spatial analysis revealed wave height reductions of 10 %–40 %, averaging 18 % across Sites of Community Importance and 24 % over rocky substrates colonized by seagrass. These results highlight the necessity of resolving seasonal cycles and the biomechanical flexibility of aquatic vegetation.