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

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Abstract
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.
Keywords
HYDRAULIC RESISTANCE, FLOW RESISTANCE, FLOODPLAIN VEGETATION, SEDIMENT TRANSPORT, POSIDONIA-OCEANICA, AQUATIC VEGETATION, SHALLOW-WATER, CHANNELS, MACROPHYTES, DRAG, Open-channel flow, Roughness, Macrophytes, 2D modelling, Stream ecosystem

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Chicago
Verschoren, Veerle , Dieter Meire, Jonas Schoelynck, Kerst Buis, Kris D Bal, Peter Troch, Patrick Meire, and Stijn Temmerman. 2016. “Resistance and Reconfiguration of Natural Flexible Submerged Vegetation in Hydrodynamic River Modelling.” Journal of Environmental Fluid Mechanics 16 (1): 245–265.
APA
Verschoren, V., Meire, D., Schoelynck, J., Buis, K., Bal, K. D., Troch, P., Meire, P., et al. (2016). Resistance and reconfiguration of natural flexible submerged vegetation in hydrodynamic river modelling. JOURNAL OF ENVIRONMENTAL FLUID MECHANICS, 16(1), 245–265.
Vancouver
1.
Verschoren V, Meire D, Schoelynck J, Buis K, Bal KD, Troch P, et al. Resistance and reconfiguration of natural flexible submerged vegetation in hydrodynamic river modelling. JOURNAL OF ENVIRONMENTAL FLUID MECHANICS. 2016;16(1):245–65.
MLA
Verschoren, Veerle , Dieter Meire, Jonas Schoelynck, et al. “Resistance and Reconfiguration of Natural Flexible Submerged Vegetation in Hydrodynamic River Modelling.” JOURNAL OF ENVIRONMENTAL FLUID MECHANICS 16.1 (2016): 245–265. Print.
@article{7019358,
  abstract     = {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.},
  author       = {Verschoren, Veerle  and Meire, Dieter and Schoelynck, Jonas and Buis, Kerst and Bal, Kris D and Troch, Peter and Meire, Patrick and Temmerman, Stijn },
  issn         = {1567-7419},
  journal      = {JOURNAL OF ENVIRONMENTAL FLUID MECHANICS},
  language     = {eng},
  number       = {1},
  pages        = {245--265},
  title        = {Resistance and reconfiguration of natural flexible submerged vegetation in hydrodynamic river modelling},
  url          = {http://dx.doi.org/10.1007/s10652-015-9432-1},
  volume       = {16},
  year         = {2016},
}

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