The shoreface-connected ridges along the central Dutch coast — part 2: morphological modelling

The long-term (decades, centuries) morphological behaviour of the shoreface-connected ridges along the central Dutch coast was studied with a simplified modelling approach, consisting of a 1D current model (Trenchflow), combined with a 2DV morphodynamic model (Sutrench). The analysis focused on a cross-section of a single sand bank, assuming that the interaction of the water motion and morphology could be considered a local phenomenon. The modelling was used for a sensitivity analysis of the relevant processes. The present model reveals a positive feedback: the schematized sand bank is predicted to grow, while there is no damping, even not during high waves. However, using the observed flow response, which differs from the theoretical flow response as described in Part 1 of this paper, actual growth rates are close to zero. The modelling shows that the ridges are stable on a time scale of years to decades, while they may be considered active on the time scale of thousands of years. Calculated migration rates of the ridges are in the order of 1 m/yr. Morphological time scale and migration rate correspond to the results from a geological reconstruction.