TY - JOUR

T1 - Plant stiffness and biomass as drivers for drag forces under extreme wave loading

T2 - A flume study on mimics

AU - Paul, Maike

AU - Rupprecht, Franziska

AU - Möller, Iris

AU - Bouma, Tjeerd J.

AU - Spencer, Tom

AU - Kudella, Matthias

AU - Wolters, Guido

AU - van Wesenbeeck, Bregje K.

AU - Jensen, Kai

AU - Miranda-Lange, Martin

AU - Schimmels, Stefan

N1 - Funding Information: We thank all of the staff at the Grosser Wellenkanal as well as B. Evans, J. Tempest, K. Milonidis and C. Edwards, Cambridge University, and D. Schulze, Hamburg University, for their invaluable logistical assistance. Our gratitude also goes to two anonymous reviewers whose comments greatly helped to improve the manuscript. The work described in this publication was supported by the European Community's 7th Framework Programme through the grant to the budget of the Integrating Activity HYDRALAB IV , Contract no. 261529 and a grant from The Isaac Newton Trust, Trinity College, Cambridge ( 11.35(s) ). M. Paul acknowledges funding by the German Science Foundation (grant no. PA 2547/1-1 ).

PY - 2016/11/1

Y1 - 2016/11/1

N2 - 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.

AB - 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.

KW - Biomass

KW - Drag force

KW - Frontal area

KW - Plant mimics

KW - Stiffness

KW - Wave forcing

UR - http://www.scopus.com/inward/record.url?scp=84982860073&partnerID=8YFLogxK

U2 - 10.1016/j.coastaleng.2016.07.004

DO - 10.1016/j.coastaleng.2016.07.004

M3 - Article

AN - SCOPUS:84982860073

VL - 117

SP - 70

EP - 78

JO - Coastal engineering

JF - Coastal engineering

SN - 0378-3839

ER -