Impact of the Eastern Scheldt Storm Surge Barrier on the Morphodynamics of the Ebb-Tidal Delta

Abstract

Threatened by rising sea levels and other climate change induced hazards, there is an increased need for coastal flood protection, such as storm surge barriers. However, the construction of such barriers may lead to unwanted coastal changes. This thesis examines the effect of the Eastern Scheldt storm surge barrier on sediment pathways and the implications for coastal erosion. In addition, possible sediment-based interventions to redirect the current with the aim of reducing coastal erosion were investigated. First, a literature study was performed to provide historical context on the natural and human induced development of the ebb tidal delta. A data analysis on the sediment budget of the ebb tidal delta was performed, which showed that from 1960 to 1987 the ebb tidal delta gained sediment, from 1987 to 2010 it lost sediment, and from 2010 to 2019 it gained sediment again. A numerical model in Delft3D FM was used to produce sediment transport vector fields over a morphologically representative tidal cycle, which were then visualized using SedTRAILS. The research found that the barrier decreased the strength of the ebb current on the entire ebb tidal delta. The Roompot Zuid has a predominantly ebb-dominant character before the barrier in 1976 but changes to a flood-dominant character due to the construction of the barrier, which weakened the ebb-current. In 2019, part of the Roompot Zuid regained an ebb-dominant character. The Schaar van Onrust also became flood-dominant due to the barrier, eliminating the sediment-retaining effect the ebb dominated current in this channel. This shift indicates that sediments that previously stayed in front of the coast of Noord-Beveland are now redistributed further along the coast in south western direction, which led to a sediment deficit and erosion at the coast. The tested interventions seem to induce little structural changes in the tidal currents. The removal of sediment causes the sediment transport patterns to converge into the dredged area, suggesting deposition. Therefore the tested interventions do not seem effective from a coastal management perspective. The approach used here may also be useful for the assessment of sediment transport impacts at other sites where the construction of similar barriers is being considered.