1 M.G. Aguilera Chaves, 2 M. van der Wegen, 3 M. Taal. M, 4 A. Colina Alonso, 5 B. Röbke.
1 Deltares, The Netherlands; 2 Deltares & IHE, The Netherlands; 3 Deltares, The Netherlands; 4 Deltares & TU Delft, The Netherlands; 5 Deltares, The Netherlands;
* Corresponding author: monica.aguilerachaves@deltares.nl
Introduction
Climate change and its effect on sea level rise (SLR) is increasing pressure in coastal areas. Moreover, SLR is expected to accelerate in the coming decades. The uncertainty associated to SLR rates raises concerns regarding the impact on coastal regions, particularly the ones that are relevant for their socio-economic and/or ecological value. Tidal basins and estuaries are examples of coastal systems that are vulnerable to accelerating SLR. Their existence depends on the balance between the creation of accommodation space under SLR (sediment demand), and the capacity of the coastal system to fill in this space (sediment supply) (Wang et al., 2018).
The Western Scheldt is an estuary located in the southwest of the Netherlands. It offers access to the port of Antwerp (Belgium) by means of a main navigation channel. In addition, there are intertidal flats along the basin that form habitats for marine species and birds (Elmilady, et al., 2022). These intertidal areas are prone to drowning under accelerating SLR. Therefore, understanding the development of the Western Scheldt under SLR, particularly the evolution of its intertidal flats, becomes crucial. Such knowledge allows planning an adequate coastal management for the long-term preservation of this system.
Objective and Methods
The objective of this research is to study the response of intertidal flats in the Western Scheldt to extreme SLR. For this purpose, a process-based model (Delft3D 4) is used. This corresponds to the Delft3D-Scheldt-SLR Model, which was developed by Röbke et al. (2020). This previous study aimed at determining the relative impact of SLR and different sediment strategies on the long-term hydrodynamics and morphodynamics in the Western Scheldt (period 2020-2100). As a sub-study, this research focusses on the behavior of intertidal area. The sediment strategies refer to the comparison of two dredging and dumping scenarios named current DAD and future DAD. Where dumping volumes vary. For the current DAD the material is placed on the shoals and in the channels of the estuary. While, for the future DAD, the sediment is dumped primarily in the deeper parts of the channels more located in the eastern part. The global SLR scenarios re based on the IPCC report (Church and Clark, 2013, and Le Bars et al., 2017). Various combinations of different SLR scenarios were performed with the two sediment strategies, and with multiple sediment fractions (sand only and sand-mud models).
Results
Here, the results are summarized for the sand-mud model with the current DAD. When there is no sea level rise (No SLR), the intertidal area increases over time in the Western Scheldt, mainly in the central part. Dumping of sand, from dredging activities, directly on top of the intertidal flats contributes to their expansion. In the landward side, even though the intertidal area remains constant, its composition changes. Sand volume decreases, while mud deposits increase.
The Western Scheldt is mostly flood dominant, but with SLR, this flood dominance decreases (Röbke et al., 2020). This causes mud import in the system to decrease. Under SLR, the intertidal areas decrease almost everywhere. The presence of sand drops along the estuary, especially near the landward side. Mud deposits near to the landward boundary. Despite the elevation of intertidal flats increasing with SLR, the sediment supply (even the one coming from the dredging activities) is not sufficient to maintain them. They start drowning with extremer SLR.
References
Church, J. and P. Clark, 2013. Sea level change. In T. Stocker, M. t. S. t. J. t. A. t. Y. t. V. t. D. QIN, G.-K. Plattner and P. Midgley, eds., Climate change 2013: the physical science basis. Contribution of working group I to the fifth assessment report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge. Pp. 1137–1216.
Elmilady, H., van der Wegen, M., Roelvink, D., van der Spek, A., 2022. Modeling the morphodynamic response of estuarine intertidal shoals to sea-Level rise. Journal of Geophysical Research: Earth Surface 127: e2021JF006152. https://doi.org/10.1029/2021JF006152
Le Bars, D., Drijfhout, S. and de Vries, H., 2017. A high-end sea level rise probabilistic projection including rapid Antarctic ice sheet mass loss. Environmental Research Letters 12: pp. 1–9. doi:10.1088/1748-9326/aa6512
Röbke, B., Elmilady, H., van der Wegen, M., Taal, M., 2020. The long-term morphological response to
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Wang, Z. B., Elias, E. P. L., Van Der Spek, A. J. F., & Lodder, Q. J., 2018. Sediment budget and morphological development of the Dutch Wadden Sea: Impact of accelerated sea-level rise and subsidence until 2100. Netherlands Journal of Geosciences, 97(3), 183–214. https://doi.org/10.1017/njg.2018.8
