Comparison of Flexible and Rigid Vegetation Induced Shear Layers in Partly Vegetated Channels

Caroppi, Gerardo; Västilä, Kaisa; Gualtieri, Paola; Järvelä, Juha; Giugni, Maurizio; Rowiński, Paweł M.

doi:10.1029/2020wr028243

Cited by 51 publications

(35 citation statements)

References 97 publications

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“…In analogy to other environmental flows over porous obstructions [33], the presence of an inflection point makes the flow susceptible to Kelvin-Helmholtz (KH) type instabilities and the onset of large-scale vortices [31,34,35]. These vortices dominate the vertical transport of momentum, and by analogy of mass and energy, across the vegetated shear layer [36,37]. The vortex and the consequent shear penetration within the canopy define the exchange zone, i.e.…”

Section: Hydrodynamic Features Of Vegetated Floodplain Flowsmentioning

confidence: 99%

“…The extent of the exchange zone is a primary determinant of residence time in the obstruction [33,38] and has been found to scale upon the canopy drag length scale ⟨C D a⟩ p −1 . The canopy bulk drag ⟨C D a⟩ p is a key dynamic parameter governing the vegetated shear layer [36,38,39]. Experiments on flow over submerged canopies revealed the presence of a pronounced inflection point in the velocity profile only for sufficiently dense canopies, i.e.…”

Section: Hydrodynamic Features Of Vegetated Floodplain Flowsmentioning

confidence: 99%

“…While the use of simplified rigid surrogates can be sufficient to reproduce the flow features universally characterizing obstructed shear layers, simplified models do not catch the distinctive features of vegetated flows [33]. These features stem from the complex structure of vegetation, its flexibility and dynamic motion, inducing flow modifications that impact hydrodynamic and transport processes [36,[40][41][42][43]. For example, for canopies of tensile aquatic vegetation, differences in turbulent flow structure and momentum exchange have been observed in comparison with rigid cylinders [30,44,45].…”

Section: Hydrodynamic Features Of Vegetated Floodplain Flowsmentioning

confidence: 99%

“…For example, for canopies of tensile aquatic vegetation, differences in turbulent flow structure and momentum exchange have been observed in comparison with rigid cylinders [30,44,45]. For flows in partly vegetated channels, dynamically similar shear layers induced by rigid cylinders and flexible woody plants presented different extent of the exchange zone and momentum transport efficiency across the vegetated interface [36].…”

Section: Hydrodynamic Features Of Vegetated Floodplain Flowsmentioning

confidence: 99%

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Shear layer over floodplain vegetation with a view on bending and streamlining effects

Caroppi

Järvelä

2022

Environ Fluid Mech

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Shrubby and woody vegetation growing on floodplains profoundly influences hydrodynamic and transport processes in riverine systems. Existing hydrodynamic research is mostly focused on conditions with aquatic plants and rigid model vegetation. To appreciate the different hydrodynamic impacts of submerged floodplain and riverbank vegetation, a novel flume investigation was carried out. We simulated conditions found in riparian environments in terms of vegetation density, plant structure and flexibility, and presence of a grassy understory. Four experimental cases were defined so that vegetation exhibited different degrees of bending and streamlining. Extensive set of velocity measurements allowed reliable description of the double averaged flow. Vegetation morphology, with the flexibility-induced streamlining and dynamic motion controlled the magnitude and distribution of the vegetative drag, shaping the shear penetration within the canopy. The flows were highly heterogeneous, thus calling for spatially averaged approaches for the flow field investigation. The relative importance of dispersive momentum fluxes was high in the canopy bottom region where both Reynolds and dispersive stresses were small. The contribution of dispersive fluxes to momentum transport decreased with increasing reconfiguration. The results revealed the shear layers over floodplain vegetation to be dynamically similar to other environmental flows over porous obstructions. However, the velocity-dependent vegetative drag and deflected height introduced additional complexity in the flow simulation. Altogether our findings implied that accurate description of vegetated floodplain flows can be achieved only when plant morphology and flexibility are appropriately described in drag models. Article highlights A novel experimental setup with flexible woody plants and grasses was used to model the hydrodynamics of vegetated floodplains. Plant morphology and flexibility controlled the vegetative drag, affecting key shear layer features, including the shear penetration. The spatially heterogeneous flows had higher dispersive stresses at the canopy bottom, where the total fluid stress was small.

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Section: Hydrodynamic Features Of Vegetated Floodplain Flowsmentioning

confidence: 99%

Section: Hydrodynamic Features Of Vegetated Floodplain Flowsmentioning

confidence: 99%

Section: Hydrodynamic Features Of Vegetated Floodplain Flowsmentioning

confidence: 99%

Section: Hydrodynamic Features Of Vegetated Floodplain Flowsmentioning

confidence: 99%

See 2 more Smart Citations

Shear layer over floodplain vegetation with a view on bending and streamlining effects

Caroppi

Järvelä

2022

Environ Fluid Mech

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“…The volume of fluid (VOF) method was used to investigate the internal flow characteristics of an air induction nozzle (AIN). Caroppi et al [40] studied the impacts of embedding natural plants in the experimental simulation of flow in partly vegetated channels. They found that the normalized shear penetration was 6-10 times greater than observed for rigid cylinders, resulting in wider zones significantly exchanging momentum with the adjacent open water.…”

Section: Introductionmentioning

confidence: 99%

Assessment of flow characteristics through a grassed canal

Gad¹,

Sobeih

Rashwan

et al. 2021

Innov. Infrastruct. Solut.

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Vegetation is defined as a kind of surface roughness, which reduces the capacity of the channel and retards the flow by causing loss of energy through turbulence and drag forces of moving water. In water channels, vegetation maybe used to stabilize the water surface and prevent erosion caused by concentrated water flow. In terms of channel lining, grass offers the least expensive option and is the most esthetically pleasing. Most previous studies on this subject were conducted using artificial vegetation in laboratory experiments; research conducted in canals with natural vegetation is lacking. In this study, flow characteristics through a natural grassed canal are studied. In addition, the Manning coefficient and specific energy were determined based on field measurements for both grassed and un-grassed canals. The fieldwork was conducted on Ganabia 9B, southeast of El-Mahalla El Kubra, El-Gharbia, Egypt. The average heights of vegetation in the grassed canal ranged from (28 to 100) cm and the values of flow rate range from (0.0504 to 0.1127) m 3 /s. The number of tests is 42 tests for the un-grassed canal and 205 tests for the grassed canal. This study indicated that the Manning coefficient increased with an increase in energy and momentum coefficients. The energy coefficient increased with a decrease in relative specific energy and an increase in grass height. The un-grassed canal exhibited a smaller relative specific energy than the grassed canal. The momentum coefficients for the non-grassed and grassed canals were 1.015-1.517 and 1.003-1.655, respectively. Therefore, the un-grassed canal showed a higher momentum coefficient than the grassed canal at a ratio of 0.264-1.196%. The relative specific energy was calculated in two ways: (i) using the actual energy coefficient values and (ii) setting it equal to one. As such, the error percentages of the specific energy for the grassed and un-grassed canals were 0.000105-0.1652% and 0.0048-0.2194%, respectively. The results obtained herein were compared with those obtained in previous studies, showing good agreement, but differ in the accuracy of predicting values. Three programs, i.e., gene expression programming, Statistical Package for the Social Sciences, and artificial neural network, were employed to create empirical formulas for modeling the Manning coefficient and relative specific energy for the grassed and un-grassed canals. Gene expression programming was found to be the best modeling program.

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Flow behaviour in a multi‐layered vegetated floodplain region of a compound channel

Barman

Kumar

2022

Ecohydrology

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Riparian vegetation plays a crucial role in determining the flow behaviour in the channel. The effect of flow on the slope and main channel varies based on the size, type, and density of floodplain vegetation in a compound channel. Though real field vegetation distribution is non‐uniform, most studies mainly concentrate on uniformly distributed vegetation with fixed vegetation height. This paper attempts to address this issue through laboratory studies as it was not explored properly. Flow properties like velocity, Reynolds shear stress, turbulence intensities, and turbulent kinetic energy behave differently in heterogeneous vegetated channel compared with the homogeneous vegetated channel. These flow properties in the slopes and main channel section are more pronounced for uniformly distributed vegetation than non‐uniform distribution. The multi‐layered/varying vegetation height showed higher velocity, turbulent intensity, and turbulent kinetic energy than single‐layered/constant vegetation height on slopes and main channel sections. Integral scales (Taylor and Euler) analysis showed greater magnitude for uniform multi‐layered vegetation than non‐uniform multi‐layered vegetation. Further, the study of octant analysis reveals that internal outward and internal inward interaction events dominate the slope floodplain interaction section, which is not seen in no‐vegetation cases. These studies give a better perspective to understand flow in heterogenous vegetation and move closer to real field scenarios.

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Comparison of Flexible and Rigid Vegetation Induced Shear Layers in Partly Vegetated Channels

Cited by 51 publications

References 97 publications

Shear layer over floodplain vegetation with a view on bending and streamlining effects

Shear layer over floodplain vegetation with a view on bending and streamlining effects

Assessment of flow characteristics through a grassed canal

Flow behaviour in a multi‐layered vegetated floodplain region of a compound channel

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