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Human interventions like closure dams or storm-surge barriers can have serious consequences to the natural sediment budget of an estuary or tidal basin. A clear example is the Eastern Scheldt. The Eastern Scheldt tidal basin in the southwestern part of the Netherlands has seen dramatic changes due to human intervention in the past few decades. The construction of two back-barrier dams in 1965 and 1969 had a significant impact on the tidal hydrodynamics and sediment transport. The effects of these interventions were still ongoing when the hydrodynamic regime was altered again by the construction of the storm-surge barrier between 1983 and 1986.
In the decades before 1965, the Eastern Scheldt exported large quantities of sediment towards sea through its inlet. The implementation of the back-barrier dams caused a significant increase in the volume of water flowing through the inlet each tide, which was observable in the response of bathymetry. The export of sediment, the rates of channel deepening and the ebb-tidal delta volume all increased as soon as the dams were built.
After 1986, the average tidal flows inside and outside the basin decreased dramatically as a result of the storm-surge barrier. Inside the basin this has led to degradation of the intertidal area. Tidal current is the main process building up the shoals and maintaining the size of channels. Waves are the main process breaking down the shoals. Due to the barrier, the currents decreased, while the waves stayed the same. As a result, the shoals become lower and smaller, and the channels are silting up.
On the ebb-tidal delta, the effect of the barrier is that the morphological activity decreased. Apart from this, it seems that the barrier forms a blockage for the exchange of sediment between the basin and ebb-tidal delta. The ebb-tidal delta is losing sediment, but not towards the basin.