Modelling intertidal area evolution in the Western Scheldt: Hindcast (1964-2010) and forecast (2020-2100) under sea level rise scenarios
Van der Wegen, M.; Chaves Aguilera, M. (2025). Modelling intertidal area evolution in the Western Scheldt: Hindcast (1964-2010) and forecast (2020-2100) under sea level rise scenarios. Version 1.0. Deltares: Delft. 38 pp.
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Sea level rise; Intertidal Areas |
Contact detailsProposer: Ministerie van Infrastructuur en Waterstaat; Rijkswaterstaat (RWS) , more
| Authors | | Top |
- Van der Wegen, M., more
- Chaves Aguilera, M.
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| Abstract |
The Western Scheldt comprises about 92 km2 of intertidal areas, including sandy and muddy shoals and large marsh regions like the Land van Saeftinghe. Some areas are attached to the estuary’s shorelines, while others are surrounded by channels. These intertidal zones hold significant ecological value and contribute to flood protection through wave attenuation. Over time, the intertidal area slowly evolves in size and height due to tidal and wave forces, as well as human interventions such as dredging and disposal activities. Measurements indicate a 2% decrease in intertidal area and a 30% increase in mean intertidal area height from 1965 to 2010.
This study aims to assess the performance of process-based morphodynamic modelling (Delft3D) in predicting the evolution of intertidal flats in the Western Scheldt and to explore the potential impacts of sea level rise (SLR) and dredge-disposal strategies. The analysis focuses on morphodynamic hindcast results between 1965 and 2010 and forecast results from 2020-2100, examining intertidal area evolution in terms of general patterns, hypsometry, area and mean height. The Delft3D model is 2D, includes one, 200 μm sand fraction, dredging/disposal activities and a schematized, one-direction wind/wave field.
During the hindcast period, the model’s deviations from observations are in the same order of magnitude as the observed changes (~10% of the actually observed intertidal area and mean height). This indicates challenges in accurately reproducing observed variations. Initially, the model underestimated the increase in intertidal area and later overestimated the decrease. In the first decades, the model underestimated the increase in mean height, but the error became negligible after 45 years. Adding waves sometimes improved the model performance and sometimes not. Model performance was generally worse when subregions were analysed, suggesting that regional differences in model performance partly average out in the total area analysis.
The 80-year model forecast shows a clear declining trend in intertidal area under various scenarios with 3m/century SLR (-20 to -40%), while no-SLR scenarios maintain more intertidal area (-5 to +20%). Model deviations found in the hindcast (max 10% of the present area and height) remain lower than the extreme SLR impact. Intermediate SLR scenarios interpolate between these extremes. Model results indicate that a strategy disposing more sediments in the eastern part and deeper parts of the main channel leads to about 10% more intertidal area loss compared to a strategy disposing sediments near intertidal areas throughout the estuary.
Our analysis suggests that process-based modelling has potential in predicting long-term (>decadal) trends of intertidal flat evolution, especially when considering larger-scale interventions and long-term changes in forcing (SLR, dredging and disposal strategies). To improve model performance, future work may include 3D dynamics, mud, and more advanced schematizations of the wave field and dredging/disposal algorithms. Comparison results to other modelling efforts (ASMITA/ESTMORF/Delft3D hybrid) may enhance confidence in model predictions under SLR scenarios. |
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