Sea level rise in the Oosterschelde estuary

A study of the long-term morphological development of a model of the Oosterschelde with accelerated sea level rise if the storm surge barrier is removed

Master thesis (2022)

Authors

J. Wisse Civil Engineering & Geosciences

Contributors

S.G.J. Aarninkhof Hydraulic Engineering (graduation committee member)
Bram van Prooijen Environmental Fluid Mechanics - CEG (graduation committee member)
M. Eelkema (graduation committee member)
P.L.M. de Vet Coastal Engineering - CEG (graduation committee member)
M.C. Onderwater Coastal Engineering - CEG (mentor)
Faculty
Civil Engineering & Geosciences, Civil Engineering & Geosciences
Copyright: © 2022 Niels-Jan Wisse
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Published Date

07-10-2022

Language

English

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Faculty

Civil Engineering & Geosciences

Abstract

The Oosterschelde has been an area of morphological change for centuries. Both floodings and human influences have caused the Oosterschelde to have its current shape. During the last century before implementation of the Delta plan (1953) the estuary was still expanding as the channels deepened and the tidal flats increased. With the construction of the Delta works the tidal range decreased with 12 % whereas the tidal prism reduced with 31 %. As a consequence of this reduced tidal motion, the tide is not able anymore to counteract the erosion of the tidal flats which is caused by waves/wind. Therefore, the surface area and the height of the tidal flats reduces (‘Zandhonger’). This decrease of tidal area is an undesirable situation as the unique tidal nature of the Oosterschelde provides a lot of functions for both economy (oysters, mussels), ecology and recreation. Furthermore, the Oosterschelde is used as a transport route by cargo vessels.

This research studies the morphological development of a model of the Oosterschelde with two hypothetical interventions: removal of the storm surge barrier (SSB) and applying 2 metre sea level rise (SLR) in 50 years. This is done with four model scenarios: a run with SSB in place, without SLR (1), a run without SSB, without SLR (2), a run without SSB, with SLR (3) and a run with SSB, with SLR (4). This last run was used as sensitivity run in order to see which hypothetical interventions has more impact.

The model results led to conclusions which parts of the model are represented well and which parts of the model need to be improved. The results made clear that current model is promising as the tidal range was modelled correctly for the majority of the Oosterschelde. Also the model represented the tidal prism well compared to the calculated tidal prism (tidal prism = tidal range * wet surface area of the basin – the sediment volume of the tidal flats). It was found too that SLR can be modelled in a correct way by forcing a water level at the boundaries of the model.

It was found that wave activity is an important process with respect to the development of the tidal flats. Therefore, the frequency of the wave computations should be chosen in such way that reliable wave heights are present for each water level during the tidal cycle at all locations in the Oosterschelde. Another key factor which should be improved is the availability of sediment in the model as this determines the (desired) growth of the tidal flats with SLR. Processes/indicators which give information about this availability (ebb/flood dominance, sediment characteristics) can give insight in the development of the tidal flats. With improvement of modelling these two processes it may be possible to improve model capabilities.