Ides, S.

Meire, P.

Plancke, Y.

Smolders, S.

Temmerman, S.

Open Marine Archive

 - 85 -  
Marsh development in Saeftinghe and impact on storage of storm 
water 
Smolders Sven
1,2
, Stefaan Ides
3
, Yves Plancke
2,3
, Patrick Meire
1
 and Stijn Temmerman
1
 
1 
Ecosystem Management research group, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, 
Belgium 
E-mail: sven.smolders@ua.ac.be , patrick.meire@ua.ac.be , stijn.temmerman@ua.ac.be  
2
 Flanders Hydraulics Research, Berchemlei 115, 2140 Antwerp, Belgium  
E-mail: sven.smolders@mow.vlaanderen.be , yves.plancke@mow.vlaanderen.be  
3  
Antwerp Port Authority, Havenhuis, Entrepotkaai 1, 2000 Antwerp, Belgium 
E-mail: Stefaan.ides@haven.antwerpen.be , Yves.plancke@haven.antwerpen.be  
 
The Saeftinghe marshes have developed since the 1930’s from large intertidal flats to high elevated 
marsh. A huge amount of sediment is captured in this area and this volume is lost for water storage 
during storm tides. With a 2D hydrodynamic Telemac model different scenarios for the Saeftinghe 
area were analysed: from huge tidal flat as it was in 1931 to an intermediate situation in 1967 and 
the situation as it is today. The impact of the storage area today was tested by excluding the area 
from the model. 
 
The model was calibrated extensively on water levels and was validated even for a storm tide. 
Changes in the Saeftinghe area affected water levels from Terneuzen till the sluices at Merelbeke. 
When Saeftinghe was excluded from the model water levels at Antwerp were 15cm higher for spring 
tide and 20cm for a storm tide (return period of 2,5 year). When more storage area was provided, 
i.e. when Saeftinghe was more like a huge intertidal flat like in 1931, water levels at Antwerp were 
18cm lower for spring tide, but for storm tide the differences were smaller, only 5cm. The latter 
shows that, for a storm tide, the presence of the marsh as a storage area is more important than its 
elevation. The water level of the storm tide grows far above the marsh level so the difference in 
storage area at lower levels becomes less important. This shows that even old marshes can play an 
important role in the water level and flood risk management of the estuary. 
 
The effect of plants on the filling of Saeftinghe was investigated using a different friction coefficient 
in the model for the Saeftinghe area. A Manning coefficient of 0.1 was used to mimic marsh 
vegetation compared to the 0.025 of the tidal flat situation. The plants slow down the filling of the 
area considerably. At a certain moment the water level in the main navigation channel is 40cm 
higher than at the marsh at the back of the Saeftinghe area near the dike. The effect however on the 
water levels in the navigation channel was limited. 
 
This study clearly shows that large marsh areas like Saeftinghe not only have a great ecological 
function, but function also as large storage areas for storm tide water. The fixed morphology of 
Saeftinghe at this moment, caused by the fixation of the position of the navigation channel, 
prevents rejuvenation of the marsh and so extra storage area. For a storm tide the elevation of the 
marsh is of less importance compared to its presence. For a normal spring tide the elevation of the 
marsh has large effects on the water level up- and downstream of Saeftinghe. 
 
 


Marsh development in Saeftinghe and impact on storage of storm water

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