Modelling morphodynamic response of a tidal basin to an anthropogenic effect: Ley Bay, East Frisian Wadden Sea – applying tidal forcing only and different sediment fractions

Morphodynamic response to an anthropogenic effect (construction of a peninsula) is investigated using the state-of-the-art Delft3D numerical model based on the Ley Bay area in the East Frisian Wadden Sea. Model simulations span a duration of 15 years applying tidal boundary forcing only and two bed sediment compositions; single (d50 = 0.2 mm)- and multiple (mud, fine-sand (0.25 mm) and coarse-sand (0.60 mm))-fractions. Finally, the effect of the initial distribution of sediment fractions is investigated. Application of the multiple sediment fractions resulted in strong sediment import into the Ley Bay in contrast with the case for a single sediment fraction. Temporal and spatial evolution of larger-scale basin elements (e.g. channels, tidal flats) indicate that the impact of the peninsula is better predicted using the multiple sediment approach. Agreement between the predicted morphology and the data is fair in deep water areas (> 3 m) compared to the shallow water areas (< 2 m) in the bay. These predictions are further improved after application of an initially distributed bed sediment composition. Therefore, the optimal prediction of the anthropogenic effect is obtained under the latter case implying the requirement of applying a stable bed sediment composition in line with the imposed boundary forcings. On-going work focuses on more detailed bed configuration around the peninsula (e.g. including possible dredging and dumping effects) and the wave boundary forcing.