Hydro-sedimentary processes of mangrove wetland over a meso-macrotidal estuary

Mangrove wetlands play a vital role in reducing water flow and wave energy, facilitating sediment capture and accumulation, thereby stabilizing coastlines and protecting coastal zones. Nevertheless, few studies have comprehensively investigated the hydrodynamic and sedimentary processes from bare flat zone to the forest interior of mangrove wetlands. Therefore, this study collected comprehensive field data, including hydrological, sediment, and elevation measurements between 2020 and 2022, aiming to diagnosing the attenuation of hydrodynamic and sediment processes in an undisturbed mangrove wetland of the Nanliu River Estuary. Results showed both current velocity and wave height declined markedly landward, accompanied by spatial fluctuations. Specifically, mean flood velocity, mean ebb velocity, and mean significant wave height decreased by over 70 %, 40 %, and 50 %, respectively. Correspondingly, surface sediments showed a general fining trend landward, with localized variations reflecting spatial heterogeneity of hydrodynamic forces. Meanwhile, surface elevation in bare flat zone increased sharply landward at an average slope of 1.6 ‰, while vegetated zone displayed a much gentler profile, averaging around 0.3 m. Vegetated zone was in relatively stable state, typically undergoing weak erosion or strong accretion, whereas bare flat zone experienced pronounced erosion or minor deposition. Dense, mature mangroves could effectively dissipate wave energy and slowing tidal currents, reducing flood velocity, ebb velocity, and wave height by 0.42 %/m, 0.25 %/m, and 0.45 %/m, respectively. Typhoons not only triggered substantial erosion but also reshaped sediment characteristics, with their impacts modulated by water depth controlled by tidal cycle variations.