Plant stiffness and biomass as drivers for drag forces under extreme wave loading: A flume study on mimics

Maike Paul*, Franziska Rupprecht, Iris Möller, Tjeerd J. Bouma, Tom Spencer, Matthias Kudella, Guido Wolters, Bregje K. van Wesenbeeck, Kai Jensen, Martin Miranda-Lange, Stefan Schimmels

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

34 Citations (Scopus)


Moving water exerts drag forces on vegetation. The susceptibility of vegetation to bending and breakage determines its flow resistance, and chances of survival, under hydrodynamic loading. To evaluate the role of individual vegetation parameters in this water-vegetation interaction, we conducted drag force measurements under a wide range of wave loadings in a large wave flume. Artificial vegetation elements were used to manipulate stiffness, frontal area in still water and material volume as a proxy for biomass. The aim was to compare: (i) identical volume but different still frontal area, (ii) identical stiffness but different still frontal area, and (iii) identical still frontal area but different volume. Comparison of mimic arrangements showed that stiffness and the dynamic frontal area (i.e., frontal area resulting from bending which depends on stiffness and hydrodynamic forcing) determine drag forces. Only at low orbital-flow velocities did the still frontal area dominate the force-velocity relationship and it is hypothesised that no mimic bending took place under these conditions. Mimic arrangements with identical stiffness but different overall material volume and still frontal area showed that forces do not increase linearly with increasing material volume and it is proposed that short distances between mimics cause their interaction and result in additional drag forces. A model, based on effective leaf length and characteristic plant width developed for unidirectional flow, performed well for the force time series under both regular and irregular waves. However, its uncertainty increased with increasing interaction of neighbouring mimics.

Original languageEnglish
Pages (from-to)70-78
Number of pages9
JournalCoastal Engineering
Publication statusPublished - 1 Nov 2016
Externally publishedYes


  • Biomass
  • Drag force
  • Frontal area
  • Plant mimics
  • Stiffness
  • Wave forcing


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