Tidal marsh stability under very high flow velocities: experiment in the tidal flume facility at the UAntwerp in context of the dike breach experiments in the Hedwige-Prosperpolder as part
of the INTERREG POLDER2C's project
Schoutens, K.; Temmerman, S. (2021). Tidal marsh stability under very high flow velocities: experiment in the tidal flume facility at the UAntwerp in context of the dike breach experiments in the Hedwige-Prosperpolder as part
of the INTERREG POLDER2C's project. INTERREG project POLDER2C’s. Universiteit Antwerpen (UA): Antwerp. 19 pp.
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| Keywords |
Hydraulic structures > Dikes, shores and other flood defenses > Erosion protection
Physical modelling
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Contact detailsProposer: Vlaamse overheid; Beleidsdomein Mobiliteit en Openbare Werken; Vlaams Ministerie Mobiliteit en Openbare Werken; Departement Mobiliteit en Openbare Werken; Waterbouwkundig Laboratorium (WL) , more
| Abstract |
Intense storm or high water events can cause severe stress on dikes eventually leading to a dike breach. Analysis of dike breaches during the North Sea flood in 1953, revealed that the presence of forelands or tidal marshes seems to reduce the dimensions of the dike breach, which limits the volume of flood water and therefore reduces flood risks and increases the time for evacuation. Nevertheless, little is known about the stability, more specific the resistance against erosion, of tidal marsh soils and vegetation under the extreme flow conditions that are generated during a dike breach.
Within the framework of the Interreg Polder2C’s project, a controlled lab-flume experiment was conducted in the tidal flume at the University of Antwerp to study the erosivity of a tidal marsh. In winter 2021, marsh monoliths (80 x 120 x 40 cm) were extracted in reed marshes in front of the dikes of Living Lab Hedwige-Prosperpolder (LL HPP*) and installed as a 10 m test section in the lab-flume. Both sediment bed dynamics and vegetation responses were quantified over 6 experimental runs. During each run, extreme flow velocities which can be expected during a dike breach, were applied for 2 hours (up to 2 ms-1 compared to 0-0.2 ms-1 during normal spring tides).
First results indicate that the tidal marsh is highly stable. Apart from the organic debris layer which flushed away in the first experimental run, erosion was limited even when aboveground vegetation was removed. During the runs, the reed stems were strongly bent by the water, however the shoots recovered rapidly when the flow stopped. These results emphasize the potential safety function of tidal marshes in the context of nature-based levee and bank protection, even during a dike breach hazard.
*Living Lab HPP is a temporary stretch of about 3 km of levees at the Dutch Belgian border available for the (research) experiments and (training) exercises thanks to the realization of the depoldering of Hedwige-Prosperpolder within the framework of the updated Sigmaplan. |
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