Nnafie, A.

Van Oyen, T.

Open Marine Archive

87 
 
Effects of extreme wave and wind events on morphodynamics of 
estuaries:     An idealized model study 
Abdel Nnafie and Tomas Van Oyen 
Flanders Hydraulics Research, Antwerp, Belgium, 
abdel.nnafie@mow.vlaanderen.be; abnnafie@gmail.com 
 
 
Introduction 
Estuaries are often situated in very densely populated areas with high economic activities that often 
strongly conflict with their ecological values. Understanding of the long-term (order decades to 
centuries) morphodynamic evolution in estuaries is of great importance to successfully manage these 
areas, such as maintaining shipping routes and preserving ecosystems. Climate scenarios generally 
predict an increased storminess in the future, where extreme wave and wind events are expected to 
occur more often. Little is known about the impact of these events on morphodynamics of estuaries, 
and particularly, how tidal channels and shoals will respond to these events.  
 
The overall aim of this study is to improve fundamental understanding of how an increased storminess 
affect estuarine morphodynamics on medium and long time scales. Specifically, first, impact of 
extreme wave and wind events on the evolution of tidal channels and shoals is examined. Second, 
sensitivity of model results to intensity of extreme events as well as to their strength and chronology of 
their occurrence is investigated.  The Scheldt estuary is used as a case study (Figure 1). 
 
Methodology 
In this study the coupled SWAN-Delft3D numerical model is used, which accounts for both flow, 
waves and wind. This model has been successfully applied to morphodynamic modeling of estuaries 
and other coastal systems. A curvilinear grid is created, which extends from Ghent to 30 km seaward 
(Figure 1). Size of grid cells ranges between 100 m and 300 m in the area of interest (Western Scheldt 
and its mouth area) and it increases to ~ 2.5 km at the offshore boundaries. Model experiments start 
from an idealized bathymetry, which is obtained by averaging the measured bedlevel over the width of 
the domain. As boundary conditions, the model is forced by a tidal wave with three harmonic 
constituents M2, M4 and M6 at the seaward boundaries (southern, western and northern boundaries in 
Figure 2).  
 
 
 
Figure 11 Delft3D computational grid (red), which covers entire Scheldt estuary and part of the North Sea. 
Focus area of present study (Western Scheldt and its mouth area) is indicated by white rectangle. The white 
arrow indicates direction of the propagating tidal wave in the North Sea (south-north). 
  


Effects of extreme wave and wind events on morphodynamics of estuaries: An idealized model study

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