Effect of removal of the Oosterschelde storm surge barrier

Abstract

The research objective of this thesis is to determine the new hydrodynamic and morphodynamic situation in case the Oosterschelde storm surge barrier is removed, with emphasis on the development of the intertidal area. To reach the objectives of this study a literature study is performed which describes the impact of the Deltaworks. An analytical model is developed to evaluate the effect of the Philipsdam and Oesterdam on the hydrodynamics in the Oosterschelde when the barrier is removed. Besides that a Delft3D model, the Kustzuid model, is used to determine the effect of bathymetric changes, removal of the barrier and realignment of the basin. Several adaptations have been made to the Kustzuid model to improve the performance. A theory by [Friedrichs and Aubrey, 1988] is used to analyse the distortion of the water level and discharge signal. The applied theory uses the relative phase of the M2 and M4 component to indicate the asymmetry. Removal of the barrier causes an increase of the tidal range by 10 to 20%. This is indicated both by the analytical model as by the Delft3D model. The tidal range will not get as large as it was before the Deltaworks. Removal of the barrier will cause an increase of the tidal prism and strengthen the ebb dominance of the basin. Besides that shoal build up will be enforced by the higher current velocities. Simulations with different bathymetries dating from 1983, 2008 and 2100 indicate that the loss of sediment from the shoals to the channels leads to a less ebb dominant system. A sligthly less ebb-dominant system is found in 2008 compared to the 1983 scenario. Ongoing loss of sediment from the intertidal area leads to a scenario without intertidal flats in 2100. In the 2100 scenario without barrier the system gets flood dominant in the eastern parts of the basin. Flood dominance throughout the entire basin is found when the barrier is still in place in 2100. Large scale realignment of the Oosterschelde is simulated by adding intertidal area to the Oosterschelde without increasing the channel volume. These simulations show increased ebbdominance, leading to export of sediment. The set back of part of the dikes will increase the flow velocities inside the basin, however not enough to cause shoal build up. When the barrier is removed in combination with realignment, shoal build up will occur. Based on empirical relations, realignment of the Oosterschelde is not expected to have a large effect on the relative flat area.