Experimental investigation on dispersion mechanisms in rigid and flexible vegetated beds

Serio, Francesca De; Meftah, Mouldi Ben; Mossa, Michele; Termini, Donatella

doi:10.1016/j.advwatres.2017.08.005

Cited by 42 publications

(35 citation statements)

References 62 publications

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“…(Nepf, ), which in turn cause variation in the dispersion processes. Therefore, the effects of vegetation on dispersion have been studied carefully so far (e.g., De Serio et al, ; Nepf et al, ; Shucksmith et al, ; Sonnenwald et al, ; White & Nepf, ).…”

Section: Introductionmentioning

confidence: 99%

Quantification of Vegetation Arrangement and Its Effects on Longitudinal Dispersion in a Channel

Park

Hwang

2019

Water Resources Research

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In nature, aquatic vegetation is one of the important factors—along with hydraulic characteristics and geometric configuration—determining the dispersion of scalars. Previous research has studied the effects of vegetation on longitudinal dispersion, varying plant population with uniform arrangement. However, since vegetation grows more often in clumped and heterogeneous rather than uniform patterns, the present work investigates the effects of the vegetation arrangement on the flows characteristics such as longitudinal dispersion, mean velocities, and drag coefficients. Several types of vegetation arrangement are described with the isometric and allometric concept and quantified with the standardized Morisita index. Laboratory experiments were performed to investigate variations of hydraulic parameters and longitudinal dispersion coefficients according to vegetation arrangements, which were quantified with the standardized Morisita index. The hydraulic parameters of mean velocity, turbulent kinetic energy, and drag depend on the vegetation arrangements, and in particular, the longitudinal dispersion coefficient varies with these arrangements by a factor of 4 or more.

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Section: Introductionmentioning

confidence: 99%

Quantification of Vegetation Arrangement and Its Effects on Longitudinal Dispersion in a Channel

Park

Hwang

2019

Water Resources Research

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“…In the jet flow-field, the longitudinal dispersion Kx decreases enough as compared to that in the ambient flow-field, promoting an increase of the vertical dispersion Kz, and consequently an increase of the jet width occurs. According to previous studies [31,44], the net dispersion coefficient can be generally determined as Figures 15 and 16 show that K x and K z roughly behave like L x and L z , respectively. These observation support the assumption that turbulent diffusion is proportional to the turbulent eddies length-scales.…”

Section: Turbulent Length Scales and Dispersion Coefficientsmentioning

confidence: 99%

“…The turbulent kinetic energy of velocity fluctuations cascades from large to small scales of motion. In the analysis of the flow-dispersion interaction, the turbulent kinetic energy (TKE) is important in determining the turbulent dispersion coefficient and thus the mass transport [31]. At equilibrium, the transport equation of the turbulent kinetic energy is expressed as: ∂k ∂t…”

Section: Theoretical Analysismentioning

confidence: 99%

“…This seems reasonable for the ambient flow where the vertical-velocity component is very small as compared with the streamwise component. [31,44], the net dispersion coefficient can be generally determined as Ki = αk ½ Li, where the scale factor α will differ between the vertical and horizontal diffusion and differ from a location to another within the jet flow-field. Following Nepf [44], the scale factor is of O(1).…”

Section: Turbulent Length Scales and Dispersion Coefficientsmentioning

confidence: 99%

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Turbulence Measurement of Vertical Dense Jets in Crossflow

Meftah

Mossa

2018

Water

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Turbulence measurement of a dense jet perpendicularly issued into a crossflow is investigated experimentally. The flow-velocity components were extensively measured with a high frequency Acoustic Doppler Velocimeter (ADV) system, whereas, a Micro Scale Conductivity Temperature instrument was used to measure the jet salinity. Special attention is given to understand the jet flow-structures in the flow symmetry plane. The flow velocity-fields, the jet trajectory, the turbulence intensities, the turbulent kinetic energy, the turbulent length scales, and the dispersion coefficients have been analyzed. The flow velocity-fields show that the dense jet is characterized by two distinct regions: an ascending region, of jet-like mixing, and a descending region of plume-like mixing. In this study, a new scaling approach of the jet trajectories, based on the jet characteristic length scales, is proposed, leading to an empirical closed-form expression to predict the jet trajectory. The turbulence analysis shows that the jet is accompanied by high levels of flow-turbulence intensities and large kinetic energy production. The results of the turbulent length scales indicate that the ambient flow-field, without jet effect, is an isotropic process. However, in the jet flow-field, a significant spatial-variation of the turbulent length scales was observed, indicating an anisotropic process. The trends of the dispersion coefficients follow those of the turbulent length scales. In comparison with the ambient flow, the jet flow-field shows a decrease of the longitudinal dispersion coefficient and an increase of the vertical one, leading to the increase of the jet width.

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“…In particular, vegetation attenuates the action of waves, slows down the flow, and promotes diffusion and deposition processes [6][7][8][9][10]. Accordingly, it (i) enhances particle removal and water quality [11][12][13]; (ii) positively affects the hydrochory and nautochory of seeds and organic matter [14][15][16][17]; (iii) reduces sediment erosion and resuspension, while enhancing sediment deposition [18][19][20]; and (iv) creates preferred paths for tracers' dissipation processes [21][22][23]. This is one of the main reasons for investigations of the interaction between vegetation and flow.…”

Section: Introductionmentioning

confidence: 99%

Wave Height Attenuation and Flow Resistance Due to Emergent or Near-Emergent Vegetation

Peruzzo

Serio

Defina

et al. 2018

Water

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Vegetation plays a pivotal role in fluvial and coastal flows, affecting their structure and turbulence, thus having a strong impact on the processes of transport and diffusion of nutrients and sediments, as well as on ecosystems and habitats. In the present experimental study, the attenuation of regular waves propagating in a channel through flexible vegetation is investigated. Specifically, artificial plants mimicking Spartina maritima are considered. Different plant densities and arrangements are tested, as well as different submergence ratios. Measurements of wave characteristics by six wave gauges, distributed all along the vegetated stretch, allow us to estimate the wave energy dissipation. The flow resistance opposed by vegetation is inferred by considering that drag and dissipation coefficients are strictly related. The submergence ratio and the stem density, rather than the wave characteristics, affect the drag coefficient the most. A comparison with the results obtained in the case when the same vegetation is placed in a uniform flow is also shown. It confirms that the drag coefficient for the canopy is lower than for an isolated cylinder, even if the reduction is not affected by the stem density, underlining that flow unsteadiness might be crucial in the process of dissipation.

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Experimental investigation on dispersion mechanisms in rigid and flexible vegetated beds

Cited by 42 publications

References 62 publications

Quantification of Vegetation Arrangement and Its Effects on Longitudinal Dispersion in a Channel

Quantification of Vegetation Arrangement and Its Effects on Longitudinal Dispersion in a Channel

Turbulence Measurement of Vertical Dense Jets in Crossflow

Wave Height Attenuation and Flow Resistance Due to Emergent or Near-Emergent Vegetation

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