Monitoring the morphodynamics of the Zwin inlet. Interim report. 1 year after the extension works

The Zwin is a relatively small tidal inlet connected to the North Sea through a tidal channel. The inlet is flooded twice a day and is characterized by the presence of intertidal area with sand banks and salt marshes. From August 2016 until the opening of the dyke in February 2019, large intervention works were carried out to reduce the sediment silting and accretion processes by increasing the amount of water flowing in and out of the inlet (i.e. tidal prism). This project aims to evaluate the …

The Zwin is a relatively small tidal inlet connected to the North Sea through a tidal channel. The inlet is flooded twice a day and is characterized by the presence of intertidal area with sand banks and salt marshes. From August 2016 until the opening of the dyke in February 2019, large intervention works were carried out to reduce the sediment silting and accretion processes by increasing the amount of water flowing in and out of the inlet (i.e. tidal prism). This project aims to evaluate the success of the intervention work and to improve our understanding on the morphodynamics of the Zwin. Detailed topographic and hydrodynamic measurements were carried out in the entrance and inland inlet units before and after the opening of the dyke. The results indicate significant morphological changes in the entire inlet system where the channel has become deeper and wider. Although a high spatial variability with the onshore mobility of the sandy bedforms occurs in the entrance inlet, the sediment balance is stable there. In contrast, the inland inlet spatially experiences two morphological trends with the dominance of erosion in the middle and east side while accretion takes place westward. Future topographic and hydrodynamic monitoring will allow to monitor further the morphological response and to investigate the contribution of the different driving processes in the Zwin inlet.