Flow‐induced reconfiguration of aquatic plants, including the impact of leaf sheltering

Zhang, Xiaoxia; Nepf, Heidi

doi:10.1002/lno.11542

“…With regard to the vertical profile of frontal area, Typha has a nonuniform distribution and Rotala has a uniform distribution. We note that under some flow conditions, aquatic plants exhibit reconfiguration (bending) in response to flow (e.g., Sand‐Jensen, 2003; Vogel, 1989) and that reconfiguration typically reduces the vegetation drag (e.g., de Langre et al, 2012; Fathi‐Maghadam & Kouwen, 1997; Harder et al, 2004) but can sometime increase the drag (Zhang & Nepf, 2020), both of which would impact vegetation‐generated turbulence. However, reconfiguration was not considered in this study, and for the flow and depth conditions considered here, the model plants did not reconfigure.…”

Section: Introductionmentioning

confidence: 99%

Measured and Predicted Turbulent Kinetic Energy in Flow Through Emergent Vegetation With Real Plant Morphology

Yuan

¹

,

Nepf

²

2020

Water Resources Research

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Velocity and forces on individual plants were measured within an emergent canopy with real plant morphology and used to develop predictions for the vertical profiles of velocity and turbulent kinetic energy (TKE). Two common plant species, Typha latifolia and Rotala indica, with distinctive morphology, were considered. Typha has leaves bundled at the base, and Rotala has leaves distributed over the length of the central stem. Compared to conditions with a bare bed and the same velocity, the TKE within both canopies was enhanced. For the Typha canopy, for which the frontal area increased with distance from the bed, the velocity, integral length-scale, and TKE all decreased with distance from the bed. For the Rotala, which had a vertically uniform distribution of biomass, the velocity, integral length-scale, and TKE were also vertically uniform. A turbulence model previously developed for random arrays of rigid cylinders was modified to predict both the vertical distribution and the channel-average of TKE by defining the relationship between the integral length-scale and plant morphology. The velocity profile can also be predicted from the plant morphology. Combining with the new turbulence model, the TKE profile was predicted from the channel-average velocity and plant frontal area.

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“…This approach was found to agree well with laboratory experiments, and the authors successfully reproduced the shelter effect originally noted in Seginer et al (1976). However, it did not include elastic forces, which Nepf (2012) experimentally demonstrated as one of the most important factors shaping the profile of seagrass (Zhang & Nepf, 2020). Dijkstra and Uittenbogaard (2010) applied a similar method as Abdelrhman (2007) by including the modulus of elasticity with good agreement to laboratory experiments.…”

Section: Introductionmentioning

confidence: 71%

“…Boothroyd et al (2016) recently highlighted the importance of resolving plant seasonal morphological change on river flow dynamics; however, it has not remained easy to resolve both plant morphological detail and motion to date. Zhang and Nepf (2020) revealed that multiple leaves play a significant role in the sheltering. Through simple extensions of the leaf object model to allow for branching at selected DEM nodes, the approach presented in this study can be further developed for simulating a wider variety of plant forms, thereby allowing simulations that can capture hydrodynamic changes that occur over the full plant life cycle.…”

Section: Water Resources Researchmentioning

confidence: 99%

Integration of submerged aquatic vegetation motion within hydrodynamic models

Nakayama

¹

,

Shintani

²

,

Komai

³

et al. 2020

Preprint

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Aquatic models used for both freshwater and marine systems frequently need to account for submerged aquatic vegetation (SAV) due to its influence on flow and water quality. Despite its importance, parameterizations are generally adopted that simplify feedbacks from SAV, such as canopy properties (e.g., considering the deflected vegetation height) and the bulk friction coefficient. This study reports the development of a fine-scale non-hydrostatic model that demonstrates the two-way effects of SAV motion interaction with the flow. An object-oriented approach is applied to capture the multiphase phenomena, whereby a leaf-scale SAV model based on a discrete element method is combined with a flow dynamics model to resolve stresses from currents and waves. The model is verified through application to a laboratory-scale seagrass bed. A force balance analysis revealed that leaf elasticity and buoyancy are the most significant components influencing the horizontal and vertical momentum equations, respectively. The sensitivity of canopy-scale bulk friction coefficients to water depth, current speeds, and vegetation density of seagrass was explored. Deeper water was also shown to lead to a smaller decrease in vegetation height. The model approach can contribute to improving assessment of processes influencing water quality, sediment stabilization, carbon sequestration, and SAV restoration, thereby supporting an understanding of how waterways and coasts will respond to changes brought about by development and a changing climate. Plain Language Summary Aquatic system models that capture aquatic vegetation are increasingly important to help us understand processes controlling carbon budgets (e.g., "blue carbon") and for planning restoration efforts (e.g., Adams et al., 2016, https://doi.org/10.1002/lno.10319). Current models all rely on "static" approaches to account for vegetation via bulk parameterizations, though we know vegetation motion is important (e.g., Abdolahpour et al., 2018, https://doi.org/10.1002/lno.11008). Our study is the first to model the feedback between blade-scale vegetation motion and hydrodynamics to show it is crucial in shaping bottom mixing processes with implications for carbon and nutrient deposition.

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“…Boothroyd et al (2016) recently highlighted the importance of resolving plant seasonal morphological change on river flow dynamics; however, it has not remained easy to resolve both plant morphological detail and motion to date. Zhang and Nepf (2020) revealed that multiple leaves play a significant role in the sheltering. Through simple extensions of the leaf object model to allow for branching at selected DEM nodes, the approach presented in this study can be further developed for simulating a wider variety of plant forms, thereby allowing simulations that can capture hydrodynamic changes that occur over the full plant life cycle.…”

Section: Discussionmentioning

confidence: 99%

“…This approach was found to agree well with laboratory experiments, and the authors successfully reproduced the shelter effect originally noted in Seginer et al (1976). However, it did not include elastic forces, which Nepf (2012) experimentally demonstrated as one of the most important factors shaping the profile of seagrass (Zhang & Nepf, 2020). Dijkstra and Uittenbogaard (2010) applied a similar method as Abdelrhman (2007) by including the modulus of elasticity with good agreement to laboratory experiments.…”

Section: Introductionmentioning

confidence: 99%

Integration of Submerged Aquatic Vegetation Motion Within Hydrodynamic Models

Nakayama

¹

,

Shintani

²

,

Komai

³

et al. 2020

Water Resources Research

View full text Add to dashboard Cite

Aquatic models used for both freshwater and marine systems frequently need to account for submerged aquatic vegetation (SAV) due to its influence on flow and water quality. Despite its importance, parameterizations are generally adopted that simplify feedbacks from SAV, such as canopy properties (e.g., considering the deflected vegetation height) and the bulk friction coefficient. This study reports the development of a fine‐scale non‐hydrostatic model that demonstrates the two‐way effects of SAV motion interaction with the flow. An object‐oriented approach is applied to capture the multiphase phenomena, whereby a leaf‐scale SAV model based on a discrete element method is combined with a flow dynamics model to resolve stresses from currents and waves. The model is verified through application to a laboratory‐scale seagrass bed. A force balance analysis revealed that leaf elasticity and buoyancy are the most significant components influencing the horizontal and vertical momentum equations, respectively. The sensitivity of canopy‐scale bulk friction coefficients to water depth, current speeds, and vegetation density of seagrass was explored. Deeper water was also shown to lead to a smaller decrease in vegetation height. The model approach can contribute to improving assessment of processes influencing water quality, sediment stabilization, carbon sequestration, and SAV restoration, thereby supporting an understanding of how waterways and coasts will respond to changes brought about by development and a changing climate.

show abstract

Flow‐induced reconfiguration of aquatic plants, including the impact of leaf sheltering

Cited by 27 publications

References 41 publications

Measured and Predicted Turbulent Kinetic Energy in Flow Through Emergent Vegetation With Real Plant Morphology

Measured and Predicted Turbulent Kinetic Energy in Flow Through Emergent Vegetation With Real Plant Morphology

Integration of submerged aquatic vegetation motion within hydrodynamic models

Integration of Submerged Aquatic Vegetation Motion Within Hydrodynamic Models

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