Morphology of the Eastern Scheldt ebb tidal delta

Abstract

The Eastern Scheldt tidal basin and its ebb tidal delta have changed drastically in the recent centuries under the influence of natural processes and human interventions. A Storm Surge Barrier, one of constructions within framework of Delta Project in the Eastern Scheldt, is considered as the largest impact to changes in hydrodynamics and morphology of the ebb tidal delta. The barrier was built in 1987 to maintain the tide and to protect the area from flooding. The barrier closes under severe storm surge conditions and remains open during normal conditions to preserve the tide-dominated character of the ecosystem. However, this storm surge barrier caused a reduction of tidal volume and tidal current in the Eastern Scheldt. Since 1987, there has been a remarkable reduction of the tidal prism by 30%, of the average tidal range by 12% and of the average tidal current velocities by 33%. As a result, sediment export from the basin towards its ebb tidal delta has ceased. This led and still to changes in morphology of the ebb tidal delta. In order to adapt to changes in tidal volume, the tidal channels become sinks of sediment and this sediment has been and still is taken from the tidal shoals nearby. Sediment volume of these shoals therefore has decreased drastically. The deposition in channels and erosion on the shoals caused a number of negative effects to ecology, safety, navigation, recreations and fishery in the Eastern Scheldt. To analyse the morphological developments of the ebb tidal delta before, during and after the implementation of the Storm Surge Barrier in the Eastern Scheldt, bathymetry maps which present the changes in deposition and erosion parts in the ebb tidal delta in every four years (from 1960 to 2004) were used. In summary, the morphology of the Eastern Scheldt ebb tidal delta experienced enormous changes due to the Delta Project. These changes comprise shoaling and reorientation of channels- from updrift to downdrift (northward) migration of channels, landward migration of shoals, development and diminishing of ebb and flood chutes and development of scour holes near the entrance of the storm surge barrier. As a result, it would take a long time (centuries) to establish a new dynamic equilibrium between hydraulic conditions and geomorphology in the Eastern Scheldt inlet.