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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

Project Top | Authors 
  • Interregproject POLDER2C's, more

Contact details

Proposer: Vlaamse overheid; Beleidsdomein Mobiliteit en Openbare Werken; Vlaams Ministerie Mobiliteit en Openbare Werken; Departement Mobiliteit en Openbare Werken; Waterbouwkundig Laboratorium (WL), more


Authors  Top 
  • Schoutens, K., more
  • Temmerman, S., 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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