Z.B. Wang

Impact of Back-Barrier Dams on the Development of the Ebb-Tidal Delta of the Eastern Scheldt

Abstract Elekema, M.; Wang, Z.B., and Stive, M.J.F., 2012. Impact of back-barrier dams on the development of the ebb-tidal delta of the Eastern Scheldt. The Eastern Scheldt tidal basin in the SW 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 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. This research describes the hydrodynamic and morphological evolution of the Eastern Scheldt ebb-tidal delta between 1960 and 1983, before construction of the storm surge barrier started. The analysis focuses on how the back-barrier dams changed the tidal flow on the ebb-tidal delta and how these altered hydrodynamics influenced sediment transport and morphology. It starts with a description of the observed hydrodynamic and bathymetric changes. These observations are used as input for a process-based numerical model (Delft3D FLOW), which is used to simulate situations before and after channel closures. In the decades before 1965, the Eastern Scheldt exported large quantities of sediment towards the sea through its inlet. The implementation of the dams caused a significant increase in tidal prism, which was observable in the response of the bathymetry; the export and the rates of channel deepening and ebb-tidal delta growth both increased. Analysis of tidal-flow measurements and model output show a persistent trend for sediment transport towards and out of the Eastern Scheldt inlet. The construction of the back-barrier dams only amplified this export by increasing the tidal prism and pushing the basin out of equilibrium even more than it apparently already was.

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.

Tidal Wave Propagation in the Yellow Sea

To investigate the near-field and far-field hydrodynamic conditions along the Jiangsu Coast in large scale, a two-dimensional tided wave model which covers the Bohai Sea, the Yellow Sea and the East China Sea is developed and validated. After a brief review of previous models, some influencing factors, such as tide generating force, river discharges as well as shoreline changes due to land reclamation, are examined in this study. We suggest that whether these factors should be considered in the model depends on the different purposes and geographical regions of interest. Then, a series of experiments are designed to further investigate the previously proposed important factors of influence [i.e. local bathymetry and the role of Shandong Peninsula (SDP)] on the tided motions in the Yellow Sea. The numerical experimental results show that the interaction between the tidal wave system in the northern Yellow Sea and the incoming tidal wave plays a main role on the formation of the rotating tidal wave system in the southern Yellow Sea, whereas the role of geometric position of the SDP is secondary. With respect to the tidal current, it is found that the radial shape of it is independent of the local bathymetry, but may be generated by the convergent tidal wave formed by the meeting of the rotating tidal wave in the southern Yellow Sea and the incoming tidal wave from the East China Sea. Furthermore, a certain water depth is crucial for the intensity of current velocity to generate the special topography of radial sand ridges.