Long-term interaction between the Dutch coast and the tidal basins

Rijkswaterstaat is responsible for the maintenance of the coastal foundation. More insight into the interaction between the tidal basins in the Wadden Sea and the Western Scheldt and the coast is very important for the management of the Dutch coast. This study aims to answer the followin research questions: - How do the developments of the tidal inlets on the long-term look like? - What are the possible effects for the sand-balance of the Dutch coast? - Which processes govern the developments? - What are the influences of the development on the coast erosion of the island-heads and on the sand nourishments requirements for the coast maintenance? The Western Scheldt is deepening due to export and sandmining. It is expected that the export wil continue in the coming period, with an order of magnitude of 1 Mm3/year. The development of this estuary has only limited effect on the sand-balance of the Delta Coast. Ignoring the export from this estuary in considering the coastal maintenance would be justified. Tideal asymmetry is commenly identified as an important mechnism influencing the residual sediment transport. For the Western Scheldt this seems not to be the case. The change form import to export near Vlissingen-Breskens cannot be explainted by the initial modelling of tidal transport. The Wadden Sea basins are importing about twice the amount of sediment than required for compensating sea-levle rise, due to the human interferences. The impact of the closure of the Zuiderzee will still be influencing the development of the system for centuries. The total sediment demand for restoring the morphological equilibrium of the Marsdiep-Vlie system is estimated to be in the order of 100 million m3. The import forms an important item for the sand-balance of the Dutch coast. Under accelerated sea-level rise this import will even increase in the future, although the increase will be less than proportional to the rate of sea-level rise.