Exploring the relative importance of wind for exchange processes around a tidal inlet system

Abstract

Considering scenarios of sea level rise, the sediment budget of the Wadden Sea is of interest for both coastal safety and for the maintenance of values of this unique environment. Sand nourishments are foreseen on the ebb-tidal deltas of the Wadden Sea to increase the sediment budget, which requires us to predict the fate of the nourishment. This study focusses on the exchange of water and sediment between the North Sea and the Wadden Sea through Ameland Inlet. Based on a combination of field observations from the extensive 40 days Kustgenese2.0/SEAWAD field campaign in fall 2017 and Delft3D modelling results, the flow conditions are explained and the contribution of different forcing mechanisms is unravelled. Residual flows and sediment transport at the ebb-tidal delta were found nonstationary due to the action of waves, but also due to local wind-shear stresses. The wind-driven exchange with neighbouring basins over the tidal watersheds leads to significant residual flows through Ameland Inlet, which increases the importance of wind for the system functioning. The many shallow areas and the orientation of the system in relation to the prevailing wind direction for strong winds are believed to make wind forcing as important as observed around Ameland Inlet.