Process-based modelling of a shoreface nourishment

A state-of-the-art process-based model is applied to hindcast the morphological development of a shoreface nourishment along the barrier island of Terschelling, The Netherlands. The applied morphodynamic model is Delft3D for fully three-dimensional flow and sediment transport in coastal environments. Owing to a complex geomorphological setting of the study area, the curvi-linear model includes adjacent tidal inlets and covers 40×70 km with an increasing grid size resolution towards the nourishment site in the center of the island. In 1993, a total of 2 Mm³ of sand was supplied to the nearshore bar zone off Terschelling, filling up the trough between the middle and outer bar. By spring 1994, most of the nourished sediment had been redistributed onshore and welded onto the middle bar where it remained in the following years. The morphodynamic model is applied to the prediction of this rapid nearshore profile behaviour. The calibration of the model against an extensive set of full-scale hydrodynamic data at several locations throughout the nearshore bar zone shows a good representation of the measured hydrodynamics. Morphodynamic results show a dependency on spatial scale: on the scale of precise bed level evolution with respect to bar migration and growth, model predictions are poor as the nearshore bars are predicted to flatten out. Resorting to bulk volumes integrated over larger spatial scales, the model clearly has skill in predicting the overall effects of the nourishment. The lack of phase shift between sediment transport and bathymetry is identified as the key controlling factor for the poor sandbar predictions.