Experimental study on flow analysis and energy loss around discontinued vertically layered vegetation

Anjum, Naveed; Tanaka, Norio

doi:10.1007/s10652-019-09723-8

Cited by 20 publications

(10 citation statements)

References 40 publications

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“…However, the variation of relative backwater rise is very small against the selected range of Froude numbers as compared to backwater rise as shown in Figure 2b. It is resulted that the initial depth (ho) has a very small effect on backwater rise as similar results are reported previously (Ahmed & Ghumman, 2019;Anjum & Tanaka, 2019;Pasha & Tanaka, 2017).…”

Section: Effect Of Initial Froude Number (Fr O ) On Backwater Risesupporting

confidence: 88%

“…The flow hydrodynamics in a compound channel is also studied numerically (Ahmad et al, 2020). Anjum and Tanaka (2019) investigated the energy reduction of flood flow experimentally for vertically double-layered vegetation in an open channel (Anjum & Tanaka, 2019). Laboratory experiments have also been conducted to evaluate rapidly varied flow affects between the floodplain and the main channel flow (Peltier, Proust, Riviere, Paquier, & Shiono, 2013).…”

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confidence: 99%

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Experimental investigation of flood energy reduction through vegetation at various angles

Ahmed

Valyrakis

Ghumman

et al. 2021

River Research & Apps

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The efficiency of flow energy reduction past emergent vegetation has been typically studied assuming a right angle of the vegetated corridor to the flow direction. However, in many real-world cases the riparian zones of natural, restored, or engineered rivers and waterways, are found at an oblique angle to the flood flow direction. In the current study, the effect of vegetation angle with respect to the flow direction is investigated experimentally in an open channel rectangular flume. The experiments are conducted under a range of subcritical steady flow conditions, with varying Froude number (Fr o ). The vegetation cover is placed at various angles to the flow direction (90 , 45 , and 30 ), for a sparse and intermediate vegetation density, defined from the ratio of spacing of each vegetation element in the cross stream direction (B), and the diameter of vegetation element (d) (B/d = 2.13 and 1.09, respectively). Detailed water surface profiles are obtained for all those cases, demonstrating a considerable backwater rise, increasing with increasing vegetation density, Froude number, and flow approach angle. The energy reduction decreased by increasing the Froude number for the perpendicular (90 ) and increased for oblique vegetation (45 and 30 ). For the perpendicular vegetation, the average energy reduction rate for sparse (90VS) and intermediate (90VI) vegetation densities are 25.44% and 31.44%, respectively. The range of average energy reduction for sparse vegetation at 45 (45VS) and at 30 (30VS) are 18.3-19.8% and 18.7-19.7%, respectively. Similarly, range of average energy reduction for intermediate vegetation at 45 (45VI) and at 30 (30VI) are 21.4-22% and 18.8-22%, respectively.

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Section: Effect Of Initial Froude Number (Fr O ) On Backwater Risesupporting

confidence: 88%

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confidence: 99%

Experimental investigation of flood energy reduction through vegetation at various angles

Ahmed

Valyrakis

Ghumman

et al. 2021

River Research & Apps

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“…The steepness of water surface slopes is mainly due to Wv, and the increased ht' is due to the increment of the density of each V. However, the increment of Hm' makes the water surface slopes steeper in all cases considered. The increment in vegetation density and the steeper water slope caused air bubble entrainment within the V, which can play a significant role in energy dissipation (Figure 1f,g) [23,35]. However, due to limitations of the experimental facility, the air bubble entrainment was not quantified, hence, not discussed here.…”

Section: Water Surface Slope Within the Vegetation Modelmentioning

confidence: 99%

“…Pasha and Tanaka [22] reported that a band of densely distributed emergent vegetation provides the maximum energy reduction of the tsunami flow, but it is very difficult to implement a dense coastal forest. An experimental investigation by Anjum and Tanaka [23] clarified the effectiveness of patch-type vertically double-layered vegetation, but, in that case, a large space is required, and space is limited along the shoreline in many areas. Coastal vegetation effectively reduced the energy of an overtopping tsunami flow by posing resistance to the flow when it was implemented behind a seaward embankment [14].…”

Section: Introductionmentioning

confidence: 99%

Flume Experiments on Flow Analysis and Energy Reduction through a Compound Tsunami Mitigation System with a Seaward Embankment and Landward Vegetation over a Mound

2021

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As a countermeasure against tsunami inundation, the present study conducted a series of laboratory experiments using a compound mitigation system in which a seaward embankment (E) followed by landward coastal vegetation (V) over a mound (M) (EMV) was investigated in supercritical flow conditions. The changes of flow around the mitigation system and energy reduction were clarified under varying conditions of mound height and vegetation density. Cases of an embankment followed by only a mound (EMNV) were also considered for comparison. Experimental results showed that three basic types of flow structures were observed within the mitigation system in EMV cases. A water cushion was created within the mitigation system mainly due to the combined effects of the mound and vegetation. It significantly reduced the maximum total energy in EMV cases by approximately 41%66%, whereas in EMNV cases, the maximum energy reduction was found to be 23%65%. Increments in both mound height and vegetation density increased the intensity of the water cushion within the mitigation system by offering more drag and reflecting the flow, and hence, significantly reduced the energy of the flow.

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“…Horstman et al (2018) tried to replicate a real mangrove vegetation distribution in the laboratory and found that there was a reduction of strength in heterogeneous canopy layer as compared with homogeneous type. Different numerical and analytical models of heterogeneous vegetation also indicate the difference in treatments concerning homogeneous vegetation (Anjum & Tanaka, 2020a, 2020b; Huai et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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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Experimental study on flow analysis and energy loss around discontinued vertically layered vegetation

Cited by 20 publications

References 40 publications

Experimental investigation of flood energy reduction through vegetation at various angles

Experimental investigation of flood energy reduction through vegetation at various angles

Flume Experiments on Flow Analysis and Energy Reduction through a Compound Tsunami Mitigation System with a Seaward Embankment and Landward Vegetation over a Mound

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

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