Abstract
Vegetation in watercourses can influence different aspects of flow structure, subsequently affecting many processes of flow, such as pollutant transportation, sediment deposition and hydrophyte habitat distribution. Vegetation often occurs on one side of a channel, which requires understanding the effects of partial vegetation on the flow. Although many studies have been done on flows through uniform vegetation, this type of flow is unrealistic, as in natural floodplains, the vegetation in riparian zones is usually non-uniform. There is little study on the hydraulic characteristics of the flow with the co-existence of short and tall vegetation under either emergent or submerged conditions. In this paper, a novel experiment with rigid vegetation of two heights in one side of a channel was conducted to understand flow characteristics such as velocity profile, turbulence intensity, Reynolds stress, and discharge distribution. Experimental results revealed that the velocity is almost constant over the short vegetation height and increases sharply with the depth just above the short vegetation. Similarly, the Reynolds stress had little variation in the short vegetation layer, but started to increase rapidly from the top of the short vegetation to the water surface, which indicates the presence of strong mixing layer near the top of the short vegetation. Additionally, a strong shear layer existed between non-vegetated and vegetated zones, indicating the reduction effect of vegetation on the flow velocity. Furthermore, modifications are needed to properly calculate the hydraulic radius and Manning's coefficient for the flow with double-layered vegetation.
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References
Chen SC, Chan HC, Li YH (2012) Observations on flow and local scour around submerged flexible vegetation. Adv Water Resour 43(6):28–37
Shen HW, Tabios G III, Harder JA (1994) Kissimmee River restoration study. J Water Resour Plan Manag 120(3):330–339
Yan XF, Wai WHO, Li CW (2016) Characteristics of flow structure of free-surface flow in a partly obstructed open channel with vegetation patch. Environ Fluid Mech 16(4):807–832
Nezu I, Onitsuka K (2002) PIV Measurements of side-cavity open-channel flows—Wando model in rivers. J Vis 5(1):77–84
Nezu I, Onitsuka K (2001) Turbulent structures in partly vegetated open-channel flows with LDA and PI V measurements. J Hydraul Res 39(6):629–642
Ghani U, Anjum N, Pasha GA, Ahmad M (2019) Numerical investigation of the flow characteristics through discontinuous and layered vegetation patches of finite width in an open channel. Environ Fluid Mech 19(6):1469–1495
Huai WX, Zhang J, Wang WJ, Katul GG (2019) Turbulence structure in open channel flow with partially covered artificial emergent vegetation. J Hydrol 573:180–193
Anjum N, Tanaka N (2020) Hydrodynamics of longitudinally discontinuous, vertically double layered and partially covered rigid vegetation patches in open channel flow. River Res Appl 36(1):115–127
Chow VT (1959) Open-channel hydraulics. The Blackburn Press, West Caldwell
Pertryk S, Bosmajian G (1975) Analysis of flow through vegetation. J Hydraul Div 101(7):871–884
Yen BC (2002) Open channel flow resistance. J Hydraul Eng 128(1):20–39
Huang HQ, Nanson GC (1997) Vegetation and channel variation: a case study streams in southeastern Australia. Geomorphology 18(3):237–249
De Doncker L, Troch P, Verhoeven R, Bal K, Meire P, Quintelier J (2009) Determination of the Manning roughness coefficient influenced by vegetation in the river Aa and Biebrza river. Environ Fluid Mech 9(5):549–567
Bakry MF, Gates TK, Khattab AF (1992) Field-measured hydraulic resistance characteristics in vegetation-infested canals. J Irrig Drain Eng 118(2):256–274
Kitsikoudis V, Yagci O, Kirca VO, Kellecioglu D (2016) Experimental investigation of channel flow through idealized isolated tree-like vegetation. Environ Fluid Mech 16(6):1283–1308
Wu FS (2007) Study on flow resistance of flexible plants, Nanjing Hydraulic Research Institute, Nanjing. The first China water conservancy doctoral forum (in Chinese), Nanjing, 7th Nov 2007. pp 283–287.
Nezu I, Nakagawa H (1993) Turbulence in open-channel flows. Routledge, London
Tang X (2019) A mixing-length-scale-based analytical model for predicting velocity profiles of open channel flows with submerged rigid vegetation. Water Environ J 33(4):610–619. https://doi.org/10.1111/wej.12434
Vivoni ER (1998) Turbulence Structure of a Model Seagrass Meadow. PhD. Thesis, Massachusetts Institute of Technology, Cambridge
Tang X (2019) Evaluating two-layer models for velocity profiles in open-channels with submerged vegetation. J Geosci Environ Prot 7(1):68–80. https://doi.org/10.4236/gep.2019.71006
Stone BM, Shen HT (2002) Hydraulic resistance of flow in channels with cylindrical roughness. J Hydraul Eng 128(5):500–506
Okamoto T, Nezu I (2013) Spatial evolution of coherent motions in finite-length vegetation patch flow. Environ Fluid Mech 13(5):417–434
Nepf HM (1999) Drag, turbulence, and diffusion in flow through emergent vegetation. Water Resour Res 35(2):479–489
Martino R, Paterson A, Piva M (2012) Double-average mean flow and local turbulence intensity profiles from PIV measurements for an open channel flow with rigid vegetation. Environ Fluid Mech 12(1):45–62
Maji S, Pal D, Hanmaiahgari PR, Gupta UP (2017) Hydrodynamics and turbulence in emergent and sparsely vegetated open channel flow. Environ Fluid Mech 17:853–877
White BL, Nepf HM (2007) Shear instability and coherent structures in shallow flow adjacent to a porous layer. J Fluid Mech 593:1–32
Huai W, Zhao L, Li D, Li Q (2009) Experimental analysis of vertical profiles of stream-wise velocities in flows through vegetation with PIV. J Exp Fluid Mech (in Chinese) 23(1):26–30
Huai W, Han J, Zheng Y, Yang Z (2009) Experimental study on hydraulic behaviors of steady uniform flow in open channel with submerged flexible vegetation. J Hydraul Eng (in Chinese) 40(7):791–797
Zhao F, Huai W (2016) Hydrodynamics of discontinuous rigid submerged vegetation patches in open-channel flow. J Hydro-environ Res 12:148–160
Yilmazer D, Ozan AY, Cihan K (2018) Flow characteristics in the wake region of a finite-length vegetation patch in a partly vegetated channel. Water 10(4):1–16
Huai W, Wang W, Hu Y, Zheng Y, Yang Z (2014) Analytical model of the mean velocity distribution in an open channel with double-layered rigid vegetation. Adv Water Resour 69:106–113
Rahimi H, Tang X, Singh P, Li M, Alaghmand S (2020) Open channel flow within and above a layered vegetation: experiments and first-order closure modeling. Adv Water Resour. https://doi.org/10.1016/j.advwatres.2020.103527
Raupach MR, Finnigan JJ, Brunnet Y (1996) Coherent eddies and turbulence in vegetation canopies: the mixing layer analogy. Bound-Layer Meteorol 78(3–4):351–382
Nepf HM (2012) Hydrodynamics of vegetated channels. J Hydraul Res 50(3):262–279
Zheng S, Wu YH, Baiyin B, Wu X (2017) Experimental research on Manning’s roughness coefficient of an open channel with aquatic vegetation. J Hydraul Eng (in Chinese) 48(7):874–881
Poggi D, Porporato A, Ridolfi L, Albertson JD, Katul GG (2004) The effect of vegetation density on canopy sub-layer turbulence. Bound-Layer Meteorol 111(3):565–587
Liu D, Diplas P, Hodges CC, Fairbanks JD (2010) Hydrodynamics of flow through double layer rigid vegetation. Geomorphology 116(3–4):286–296
Ren HQ (2013) Preliminary study of the plants on the flow structure mechanism. MSc thesis (in Chinese), Changsha University of Science & Technology, Changsha
Rahimi HR, Tang X, Singh P (2019) Experimental and numerical study on impact of double layer vegetation in open channel flows. J Hydrol Eng 25(2):04019064
Cheng N-S, Nguyen HT (2011) Hydraulic radius for evaluating resistance induced by simulated emergent vegetation in open-channel flows. J Hydraul Eng 137(9):995–1004
Cheng N-S (2015) Single-layer model for average flow velocity with submerged rigid cylinders. J Hydraul Eng 141(10):06015012
Tang X, Rahimi H, Singh P, Wei Z, Wang Y, Zhao Y, Lu Q (2018) Experimental study of open-channel flow with partial double-layered vegetation. In: Proceedings of the 1st international symposium on water resource and environmental management (WREM 2018), 28–29 Nov 2018, Kunming, China. E3S Web of Conferences 81, 01010 (2019), London: EDP Sciences, Hamilton House. https://doi.org/10.1051/e3sconf/20198101010.
Acknowledgements
This research was partly supported by XJTLU via the Research Development Fund (RDF-15-01-10, RDF-16-02-02) and Key Programme Special Fund (KSF-E-17, KSF-A-19) and by the National Natural Science Foundation of China (11772270).
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Tang, X., Rahimi, H., Guan, Y. et al. Hydraulic characteristics of open-channel flow with partially-placed double layer rigid vegetation. Environ Fluid Mech 21, 317–342 (2021). https://doi.org/10.1007/s10652-020-09775-1
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DOI: https://doi.org/10.1007/s10652-020-09775-1