MORPHOLOGICAL EFFECTS OF THE EASTERN SCHELDT STORM SURGE BARRIER ON THE EBB-TIDAL DELTA

The morphology of the Eastern Scheldt inlet in the southwestern Netherlands has been changing for the past 25 years in response to the construction of the Eastern Scheldt storm-surge barrier in 1986. As a result of the barrier, there has been a decrease in tidal amplitudes, tidal volumes, and average flow velocities, and there is hardly any sediment exchange through the barrier. Bathymetrical measurements of the ebb-tidal delta show multiple effects: (1) An overall decrease in sediment volume, (2) a decrease in morphological activity, (3) erosion of the shoals and sedimentation in most channels, (4) northward reorientation of channels and shoals, and (5) an increase in wave-driven features. Results from a process-based model show that the erosion is related to the wave action, and the reorientation is related to the interaction between cross-shore and alongshore tide. The steady erosive trend, combined with the decline of morphological activity, points toward a system dominated by relatively small and mostly negative bed-level changes. This system is still far from any kind of equilibrium, and is still adapting itself to the new hydraulic forcing regime, even though sediment transport capacities have decreased.