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Modelling Belgian Coastal zone and Scheldt mouth area. Sub report 14: Scaldis-Coast model – Model setup and validation of the morphodynamic model

With the increasing awareness of sea level rise, the Flemish Authorities initiated the Complex Project Kustvisie(CPKV) in order to start together with all involved stakeholders to define the overall long-term coastal defence strategy for the Belgian Coast. In order to analyze the impact of sea level rise on the morphology of the coast and to assess proposed mitigation measures on their efficiency the need for a flexible coastal model for the Belgian coast and Scheldt mouth area was revealed. Therefore, in 2015 it was decided to build an integral coastal model within the TELEMAC-MASCARET model suite. The present report describes the setup and validation of the sediment transport and morphodynamic part of the model. Scaldis-Coast consists of a morphodynamic module, a 2D TELEMAC hydrodynamic module and a TOMAWAC wave propagation module. The Scaldis-Coast model is a highly efficient and flexible model that is applicable for short and long term morphodynamics both in the tidally driven off-shore and wave driven near-shore part of the Belgian coastal zone and Scheldt mouth area. The computational domain spans from the French coast near Calais to the Dutch coast between the Eastern Scheldt and the Grevelingenmeer, including the Eastern and WesternScheldt estuary. The offshore boundary is at at a distance of about 30 km from the coast. The resolution of the model varies from 750 m offshore to 25 m nearshore with automatic refinement around complex geometries like breakwaters, but also at locations with steep slopes in the bathymetry. With a morphological acceleration factor of twenty (MORFAC = 20) the computational cost is about 1,5 to 2 days on a 100-cores high performance computer for a ten years morphological run. The long term coastal morphodynamics are validated against the historical evolution of the seabed in the large area around Zeebrugge after the extension of the outer port in 1986. In general, the large-scale trends are well represented. This is the systematic erosion in front of the extended port and the sedimentation at the sand bank of the Paardenmarkt. In the last decade both the erosive trends in front of Zeebrugge and the sedimentation trends at Paardenmarkt tend to slow down. This is less obvious in the model. This can be attributed to the presence of resistant mud layers in the surrounding of Zeebrugge, whereas the model is a pure sand model. First steps have been made in including cohesive sand dynamics in the model. Also, the formation of the Baai van Heist is not accurately represented. This is something that has been noticed before in other sand-based morphodynamic models for Zeebrugge, but also at other locations as IJmuiden. However, preliminary results of a combined sand-mud model show promising steps forwards for this complex morphodynamic behaviour. With respect to the near- and onshore morphodynamics driven by the littoral drift, the model has been proven to perform well. On the midterm, i.e. annual erosion/sediment trends, the model has been validated against erosion trends at Wenduine and sedimentation trends of the fairway to the Blankenberge marina. First steps have been made in implementing cross-shore sediment transport processes. However, at this moment they are not yet implemented in the Scaldis-Coast model. This makes the model less suitable for estimating beach and foreshore storm responses. Nevertheless, the extensive siltation of the Blankenberge marina access channel due to one storm event, was been reproduced accurately by the model.
November 2023
Scheepvaart, waterwegen en zeewezen
G. Kolokythas, S. Fonias, L. Wang, B. De Maerschalck, J. Vanlede
WL Rapporten 15_068_14