Research Outputs

Abstract

Intertidal areas often host tidal marsh vegetation, which plays a crucial role in influencing hydrodynamic processes. This study investigates the influence of saltmarsh vegetation on fringing and mid-channel flats on currents in the Western Scheldt, the Netherlands. We quantify how and over which spatial scale vegetated intertidal areas affect estuarine currents, and how this varies over time when vegetation cover changes. Using vegetation maps spanning ca 25 years, we assessed changes in saltmarsh vegetation extent and distribution, with notable vegetation expansion on mid-channel flats. A depth-averaged Delft3D-FM model was adopted to quantify the effect of both mono-specific and multi-species vegetation on peak ebb and flood currents. Results indicate that species diversity is particularly important when considering currents at the marsh-mudflat scale, and its effect is negligible at the broader estuarine scale. During storm conditions, mono-specific and multi-species vegetation reduced peak velocities by 10–80% on the vegetated zone, and by 1–30% in the surroundings, over an area comparable to or smaller than the vegetated zone. During calm-weather conditions, the effect was limited to the vegetated zone (10–80%, although with smaller magnitude and extent compared to storm conditions). Over the period 1993–2016, both bathymetrical changes and changes in vegetation had a comparable magnitude of impact on altering current velocities over the saltmarshes. These findings emphasize that saltmarsh vegetation alters currents at the marsh-mudflat scale in particular. This will have estuary-wide implications for sediment dynamics, morphology and ecology over a timescale of decades.