Environmental Fluid Mechanics

, Volume 16, Issue 1, pp 245–265 | Cite as

Resistance and reconfiguration of natural flexible submerged vegetation in hydrodynamic river modelling

  • Veerle VerschorenEmail author
  • Dieter Meire
  • Jonas Schoelynck
  • Kerst Buis
  • Kris D Bal
  • Peter Troch
  • Patrick Meire
  • Stijn Temmerman
Original Article


In-stream submerged macrophytes have a complex morphology and several species are not rigid, but are flexible and reconfigure along with the major flow direction to avoid potential damage at high stream velocities. However, in numerical hydrodynamic models, they are often simplified to rigid sticks. In this study hydraulic resistance of vegetation is represented by an adapted bottom friction coefficient and is calculated using an existing two layer formulation for which the input parameters were adjusted to account for (i) the temporary reconfiguration based on an empirical relationship between deflected vegetation height and upstream depth-averaged velocity, and (ii) the complex morphology of natural, flexible, submerged macrophytes. The main advantage of this approach is that it removes the need for calibration of the vegetation resistance coefficient. The calculated hydraulic roughness is an input of the hydrodynamic model Telemac 2D, this model simulates depth-averaged stream velocities in and around individual vegetation patches. Firstly, the model was successfully validated against observed data of a laboratory flume experiment with three macrophyte species at three discharges. Secondly, the effect of reconfiguration was tested by modelling an in situ field flume experiment with, and without, the inclusion of macrophyte reconfiguration. The inclusion of reconfiguration decreased the calculated hydraulic roughness which resulted in smaller spatial variations of simulated stream velocities, as compared to the model scenario without macrophyte reconfiguration. We discuss that including macrophyte reconfiguration in numerical models input, can have significant and extensive effects on the model results of hydrodynamic variables and associated ecological and geomorphological parameters.


Open-channel flow Roughness Macrophytes 2D modelling Stream ecosystem 



Characteristic area of the plant (m2)


Total wetted plant surface (m2 m−2)


Vogel exponent (–)


Chézy coefficient of the bed (m1/2 s−1)


Drag coefficient (–)


Modified drag coefficient to account for flexible vegetation (–)


Experimental drag coefficient (–)


Representative Chézy value for vegetation (m1/2 s−1)


Cylinder diameter (m)


Drag force of the vegetation (N)


Gravitational acceleration (m s−2)


Water depth (m)


Vegetation height (m)


Variable vegetation height in function of stream velocity (m)


Shoot height of Callitriche platycarpa (m)


Shoot height of Potamogeton pectinatus (m)


Shoot height of Potamogeton natans (m)


Number of cylinders per m2 horizontal area (m−2)


Manning coefficient (s m−1/3)


Nash-Sutcliffe coefficient (–)


Discharge (m3 s−1)


Hydraulic radius (m)


Water level slope (–)


Flow velocity (m s−1)


Angle with horizontal bed and shoot (°)


Density of water (kg m−3)


Von Kármán constant (–)



Data used in this paper can be accessed via the authors ( V.V. thanks the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen) for personal research funding. D.M. would like to thank BOF (Bijzonder Onderzoeksfonds, UGhent) for funding personal research. J.S. is a postdoctoral fellow of FWO (project no. 12H8616N). K.D.B. would like to acknowledge the financial support of the South African National Research Foundation (NRF). This research was partly executed with the financial support of the FWO for the Scientific Research Network (WOG) “the functioning of river ecosystems through plant-flow-soil interactions”.


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Copyright information

© Springer Science+Business Media Dordrecht 2015

Authors and Affiliations

  • Veerle Verschoren
    • 1
    Email author
  • Dieter Meire
    • 2
    • 3
  • Jonas Schoelynck
    • 1
  • Kerst Buis
    • 1
  • Kris D Bal
    • 1
    • 4
  • Peter Troch
    • 2
  • Patrick Meire
    • 1
  • Stijn Temmerman
    • 1
  1. 1.Department of Biology, Ecosystem Management Research GroupUniversity of AntwerpWilrijkBelgium
  2. 2.Hydraulics Laboratory, Department of Civil EngineeringGhent UniversityGhentBelgium
  3. 3.Flanders Hydraulics ResearchAntwerpBelgium
  4. 4.Department of BiodiversityUniversity of LimpopoSovengaSouth Africa

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