Bulk drag of a regular array of emergent blade-type vegetation stems under gradually varied flow

Busari, A. O.; Li, Chi Wai

doi:10.1016/j.jher.2016.02.003

Cited by 12 publications

(14 citation statements)

References 18 publications

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“…The water flow resistance of farmland vegetation is the ability of the crop to resist the action of hydraulic erosion and prevent soil loss. The vegetation induced resistance coefficient depends on the properties of vegetation (Busari & Li 2016;Zhang et al 2016). The experimental results of farmland vegetation water resistance are of great value to improving the soil and water conservation of farmland.…”

Section: Resultsmentioning

confidence: 99%

Simulation study of anisotropic flow resistance of farmland vegetation

Zhang¹,

Yin²,

Zhang³

et al. 2017

Soil & Water Res.

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Farmland vegetation is commonly cultivated with uniform planting spacing and heights. The effect of these features on resistance to hydraulic erosion is unclear. Hydraulic model experiments with the angle between the crop rows and the water flow direction set at 15°, 30°, 45° or 90° were conducted to analyze variation in the law of water flow resistance under partial or complete submergence of the crop. Cultivation can impact the flow resistance on slopes and this effect was greater when the crop was partially submerged. When planting spacing, slope, and water depth were constant, the change of the water flow Darcy-Weisbach resistance coefficient f with crop row-water flow angle was f 15° > f 30° > f 45° > f 90°. This suggests that flow resistance of farmland vegetation is anisotropic. The water flow resistance coefficient of crops that were partly submerged increased with water depth, but decreased with water depth when the crop was completely submerged. At the critical change from partial submergence to complete submergence, the water flow resistance coefficient was the highest when water depth was equal to crop height. These results may be useful for optimizing farmland planting and soil and water conservation.

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Section: Resultsmentioning

confidence: 99%

Simulation study of anisotropic flow resistance of farmland vegetation

Zhang¹,

Yin²,

Zhang³

et al. 2017

Soil & Water Res.

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“…where V is the water velocity; m is the motion viscosity coefficient and R is the hydraulic radius (Busari & Li 2016). The mechanical significance of Fr is used to analyse a ratio of the inertial force of water flow to gravity.…”

Section: Discussionmentioning

confidence: 99%

“…Re was calculated in this study, using Eq. :

R e = \frac{V R}{ν}

where V is the water velocity;

ν

is the motion viscosity coefficient and R is the hydraulic radius (Busari & Li ).…”

Section: Methodsmentioning

confidence: 99%

The effects of vegetation distribution pattern on overland flow

Zhang

Liu

et al. 2018

Water & Environment J

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Soil erosion is a major environmental problem. Vegetation, on the other hand, plays an important role in controlling soil erosion. The goal of the study is to examine the effects of the distribution pattern of vegetation on water flow. The vegetation parameters involved included the direction of plant rows, plant stem diameter and row spacing. To study how vegetation affects the flow of water on slopes, flume simulation experiments were conducted using three different plant row directions, three different plant diameters and three row spacing. Experimental slope is fixed, slope ratio of 1.0%. The hydraulic characteristics of the slope under the three vegetation distribution patterns are explored. The results showed that the pattern of vegetation distribution significantly affected the resistance of vegetation to water flow and pattern on this slope. When the angle (θ) between plant row and water flow directions decreased, the plant diameter (d) increased, or the row spacing (a × a) decreased, the Darcy–Weisbach resistance coefficient (f) for water flow became larger. Simultaneously, the Reynolds and Froude numbers (Re and Fr) both became smaller. In experimental procedure condition, the change rate of f, Re and Fr were analysed by linear regression, the θ decreased every 10°, the average increase rate of f was 6.6%, the average decrease rate of Re and Fr were 2.0 and 3.0%. The d increased every 0.001 m, the average increase rate of f was 41.6%, the average decrease rate of Re and Fr were 11.2 and 12.2%. The a × a decreased every 0.01 m, the average increase rate of f was 45.2%, the average decrease rate of Re and Fr were 11.7 and 10.7%. The flow depth h increased every 0.01 m, the average increase rate of f and Re were 13.6 and 25.2%, and the average decrease rate of Fr was 10.4%. The experimental procedure results will be valuable for not only revealing the hydraulic characteristics of flow over vegetation land, but also the optimisation of the distribution of vegetation on a slope.

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“…For vegetation with rigid stems it is often simulated by a group of cylinders or rectangular plates. The bulk drag coefficient will depend on the shape of individual vegetation elements and the areal density of the stems, as well as the distribution pattern of the vegetation elements (Busari & Li, 2016;Stone & Shen, 2002;Tanino & Nepf, 2008).…”

Section: Determination Of Drag Coefficientmentioning

confidence: 99%

“…The dependence of bulk drag on vegetation density for cylindrical stems has been shown experimentally by Stone and Shen (2002) for staggered arrangement of stems, and by Tanino and Nepf (2008) for random arrangement of stems. For blade-type vegetation with rectilinear arrangement of vegetation elements, Busari and Li (2016) showed that the bulk drag is not only dependent on vegetation density, but also on the longitudinal and lateral separation of adjacent stems. The generalization of the results by using an empirical formula is not straightforward as there are many parameters involved, such as the cross-sectional shape of the vegetation element and the relative location of adjacent elements.…”

Section: Introductionmentioning

confidence: 99%

Hybrid modeling of flows over submerged prismatic vegetation with different areal densities

Busari

2019

Engineering Applications of Computational Fluid Mechanics

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In the modeling of vegetated flows an efficient approach is to solve the Double Averaged Navier Stokes (DANS) equations, which are obtained from the spatial and temporal averaging of the Navier Stokes equations. The resistance effects of vegetation are modeled by a drag force density term with an empirical bulk drag coefficient, as well as by turbulence terms characterized by a length scale parameter. These empirical parameters are dependent on the areal density of vegetation and the spatial distribution pattern of vegetation elements and have seldom been studied. In this work the effect of spatial distribution of vegetation elements on the bulk drag coefficient is investigated by computing explicitly the flows around the vegetation elements. The results show that the bulk drag coefficient increases with the longitudinal vegetation element spacing, decreases with the lateral vegetation element spacing and can have multiple values for a given areal density of vegetation. In the DANS model the vegetation induced turbulence is simulated by a novel k-type model embracing an empirical length scale parameter. The length scale parameters are calibrated against previous experiments and a new set of experiments with high areal density of vegetation. The DANS model is subsequently verified by two cases with the same vegetation density and different distribution patterns.

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Bulk drag of a regular array of emergent blade-type vegetation stems under gradually varied flow

Cited by 12 publications

References 18 publications

Simulation study of anisotropic flow resistance of farmland vegetation

Simulation study of anisotropic flow resistance of farmland vegetation

The effects of vegetation distribution pattern on overland flow

Hybrid modeling of flows over submerged prismatic vegetation with different areal densities

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