Coastal protection service of a seagrass meadow in a fetch-limited, non-tidal environment

Seagrass meadows have been proposed as a nature-based coastal protection measure to reduce incoming wave energy. Although numerous studies have demonstrated the capability of seagrass meadows to attenuate waves, their real-world effectiveness in providing coastal protection remains uncertain. The aim of this study was to quantify the influence of a Zostera marina meadow located in a non-tidal fetch-limited environment on three coastal protection metrics: wave runup at the shore, the storm-induced erosion of dunes, and the longshore sediment transport. Field observations were combined with numerical wave simulations using the open-source model SWAN. The field study encompassed one year of wave observations along a transect from 1.5 to 8.0 m depth, using a wave buoy and six pressure sensors. Seagrass characteristics were mapped on four occasions to capture seasonal variability. The effect on wave attenuation of the seagrass meadow was isolated from other dissipation processes by comparing model scenarios with and without vegetation. Results showed that maximum wave attenuation occurred under high-energy conditions, with a maximum wave height attenuation of 12%. However, as depth-induced breaking became the dominant dissipation process, the contribution of the seagrass meadow diminished, leading only to modest reductions in wave runup (1.0%), storm erosion volume (4.0%), and longshore sediment transport (0.6%). These findings indicate that seagrass meadows situated in relatively deep, fetch-limited environments offer limited potential for wave energy dissipation and coastal protection.