Flow characteristics in an alluvial channel covered partially with submerged vegetation

Devi, Thokchom Bebina; Kumar, Bimlesh

doi:10.1016/j.ecoleng.2016.06.018

Cited by 26 publications

(18 citation statements)

References 55 publications

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“…At position 5, the Reynold's stress in the vertical section changes little under L0; whereas that under L4, L8, and L12 increases until a maximum is reached near the top of the plant, and then decreases along the vertical direction. A similar phenomenon is observed in other studies [30,31]. There is a great difference in velocity at the top of the plant, resulting in the formation of a large number of vortices, and thus significant changes in the momentum exchange.…”

Section: Reynold's Stresssupporting

confidence: 86%

Effect of the Number of Leaves in Submerged Aquatic Plants on Stream Flow Dynamics

Yan

Tian

Lei

et al. 2019

Water

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The main purpose of this study is to investigate the effects of aquatic plants with no leaves (L0), 4 leaves (L4), 8 leaves (L8), and 12 leaves (L12) on the mean streamwise velocity, turbulence structure, and Manning's roughness coefficient. The results show that the resistance of submerged aquatic plants to flow velocity is discontinuous between the lower aquatic plant layer and the upper free water layer. This leads to the difference of flow velocity between the upper and lower layers. An increase of the number of leaves leads to an increase in the flow velocity gradient in the upper non-vegetation area and a decrease in the flow velocity in the lower vegetation area. In addition, aquatic plants induce a momentum exchange near the top of the plant and increase the Reynold's stress and turbulent kinetic energy. However, because of the inhibition of leaf area on the momentum exchange, the Reynold's stress and turbulent kinetic energy increase first and then decrease with the increase in the number of leaves. Quadrant analysis shows that ejection and sweep play a dominant role in momentum exchange. Aquatic plants can also increase the Reynold's stress by increasing the ejection and sweep. The Manning's roughness coefficient increases with the increasing number of leaves.

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Section: Reynold's Stresssupporting

confidence: 86%

Effect of the Number of Leaves in Submerged Aquatic Plants on Stream Flow Dynamics

Yan

Tian

Lei

et al. 2019

Water

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“…The numerical studies on investigating the flow structures in vegetated open channels utilizing CFD tool FLUENT have also been reported (Anjum & Tanaka, 2020; Lima, Janzen, & Nepf, 2015). However, in riparian environments or flood plains of several natural rivers, finite length vegetation can occur as partial distribution, with submerged as well as emergent condition of constant vegetation heights (Devi & Kumar, 2016; Devi, Sharma, & Kumar, 2019). Sometimes the vegetation with varying heights (Huai, Wang, Hu, Zeng, & Yang, 2014; Liu, Diplas, Hodges, & Fairbanks, 2010), that is, vertically double layered with short vegetation such as shrubs and grasses are submerged due to flood, whereas the tall vegetation such as trees remains non‐submerged.…”

Section: Introductionmentioning

confidence: 99%

Investigating the turbulent flow behaviour through partially distributed discontinuous rigid vegetation in an open channel

Anjum

Tanaka

2020

River Research & Apps

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Riparian vegetation does not only affect the channel flow carrying capacity, but also plays significant roles in water management, stream restoration, and river rehabilitation. This study numerically investigates the flow characteristics through longitudinally discontinuous rigid vegetation occupying half width of the channel, with the help of three-dimensional software FLUENT in which a Reynolds stress turbulence model was adopted. Three varying conditions of vegetation were considered comprising of vertically double-layered vegetation (DLV), submerged vegetation (SV), and emergent vegetation (EV) while keeping the same vegetation density, as well as a varying discharge condition against DLV was also tested. The results indicated that the flow distribution becomes more complex through DLV and SV followed by multiple layers with an inflectional instability in the vertical velocity profile around submerged canopy top, as compared to the flow through EV where the uniform distribution of flow over the canopy column was observed. The velocity in the canopy zone decreased considerably because of the resistance due to vegetation, which influenced the channel carrying capacity, in comparison to that in the non-vegetated zone. The flow velocities through the obstructed part of the channel, that is, canopy zone, in DLV arrangement reduced by a percentage difference of approximately 42 and 37% compared to that of SV and EV arrangements, respectively; whereas it was reduced by approximately 55% when the discharge was twice while keeping the same configuration of DLV. The inflectional instabilities and estimated mixing layer over the interfacial zone suggested a stronger lateral exchange of momentum for DLV configuration in comparison to that of SV and EV. Within the gaps between the patch zones, the flow velocity, turbulent kinetic energy, and turbulent intensity reduced significantly due to blockage effect and sheltering offered by the vegetation patches, signifying a positive flow response towards aquatic life and sediment deposition.

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“…In recent years, an increasing number of studies have been carried out to investigate the relationship between different types of vegetation and flow characteristics. Some of these studies have addressed fully flexible and fully submerged vegetation, such as grass and macrophytes (Temple, 1999;Yen, 2002;Carollo et al, 2005;Kirkby et al, 2005;Bal et al, 2011;Nepf, 2012;Li et al, 2014;Bebina Devi and Kumar, 2016;Errico et al, 2018). The results that were obtained are robust, but their field of application is quite restricted (mainly grassed waterways and narrow streams).…”

Section: Introductionmentioning

confidence: 99%

Flow resistance of partially flexible vegetation: A full-scale study with natural plants

Chiaradia

Gandolfi

Bischetti

2019

J Agricult Engineer

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Riparian vegetation plays a crucial role in riverine ecosystems, providing many types of benefits to nature and humanity. However, a high vegetation density can reduce the conveyance capacity of a watercourse, particularly in the case of shrubs, which are very common within riverbeds and widely used in river and channel restoration works. In this paper, we study the influence of three species of shrubs (white and goat willows and black alder) on the hydraulic resistance factor of a real-scale channel under controlled flow conditions. A system for the anchorage of shrubs to the channel bed allowed us to carry out repeated experiments with the three plant species and with varying plant densities and flow rates. The experimental results provided a range of values for the additional contribution of the vegetation to the hydraulic resistance factor from 0.004 to 0.071 m–1/3s, in terms of Manning’s coefficient. This variability is related to the vegetation setup (plant species and density) but also to the increasingly hydrodynamic configuration assumed by plants at higher flow velocities and submergence ratios. We found that these factors can be summarised quite effectively by the product of elasticity (E), plant density (M), and plant area index (PAI). At small (E∙M∙PAI) values (<108) the resistance coefficient is less than 0.01, while it increases of up to one order of magnitude when (E∙M∙PAI) exceeds 1010. Furthermore, our results show a distinct two-stage trend of the value of the additional contribution to the n coefficient of a given vegetation setup at varying velocities and submergence levels, with values decreasing when a threshold of velocity and submergence ratio is exceeded. The position of this threshold point appears to be related to the geometrical and mechanical characteristics of the plants. Although our experiments do not provide enough data to identify a functional relationship between n and specific characteristics of the plants and of the flow, they show that the effect of shrubs on hydraulic resistance is highly variable with the flow conditions and that the conveyance capacity may be significantly larger than expected.

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Flow characteristics in an alluvial channel covered partially with submerged vegetation

Cited by 26 publications

References 55 publications

Effect of the Number of Leaves in Submerged Aquatic Plants on Stream Flow Dynamics

Effect of the Number of Leaves in Submerged Aquatic Plants on Stream Flow Dynamics

Investigating the turbulent flow behaviour through partially distributed discontinuous rigid vegetation in an open channel

Flow resistance of partially flexible vegetation: A full-scale study with natural plants

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