Abstract
Vegetation is an important component of rivers, present naturally alongside the banks. In this research study, three-dimensional computational fluid dynamics (CFD) code ANSYS FLUENT was used to solve the Reynolds Averaged Navier-Stokes equations and to simulate flow features in an asymmetric vegetated compound channel. Three-dimensional flow characteristics and turbulence properties were captured well by the Reynolds stress turbulence model (RSM). A total of five flow cases were considered in this work. Among these, four cases were of circular vegetation patches present on the floodplain edge and one was of non-vegetated asymmetric trapezoidal compound channel. Impact of vegetation patch density, patch center to center (c/c) spacing and flow blockage area has been investigated on various flow features and compared with flow characteristics in a channel without vegetation. Flow features include mean and depth-averaged velocities, secondary flows, Reynolds shear and normal stresses, turbulence intensities and turbulent kinetic energy. The results show that the presence of vegetation patches along the floodplain imparted flow resistance which shifted the zone of higher velocities towards outer wall of main channel and floodplain. Increased velocities in the main channel up to 24.8% was observed for larger flow blockage (aD, where a is the density of the vegetation patch and D is the diameter of patch) and smaller normalized c/c spacing (L/D, where L is the c/c spacing between two patches and D is the diameter of patch) of patches. Large transverse shear stresses existed around the vegetated zone due to the gradient of velocities and vortices in the main channel and floodplain. Floodplain, especially vegetated zone acquires less Reynolds stresses and turbulence making it favorable for deposition of sediments and growth of ecological species.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Anjum N, Ghani U, Pasha GA, Latif A, Sultan T, and Ali S (2018) To investigate the flow structure of discontinuous vegetation patches of two vertically different layers in an open channel. Water 10(1):75, DOI: https://doi.org/10.3390/w10010075
ANSYS (2019) ANSYS guide, 2019. ANSYS, Incorporated, Canonsburg, PA, USA
Bousmar D (2002) Flow modeling in compound channels — Momentum transfer between main channel and prismatic or non-prismatic floodplains. PhD Thesis, Universite Catholique de Louvain, Ottignies-Louvain-la-Neuve, Belgium
Choi S, Kang H (2004) Reynolds stress modeling of vegetated open-channel flows. Journal of Hydraulic Research 42(1):3–11, DOI: https://doi.org/10.1080/00221686.2004.9641178
Fischer-Antze T, Stoesser T, BATES P, Olsen N (2001) 3D numerical modelling of open-channel flow with submerged vegetation. Journal of Hydraulic Research 39(3):303–310, DOI: https://doi.org/10.1080/00221680109499833
Folkard AM (2011) Flow regimes in gaps within stands of flexible vegetation: Laboratory flume simulations. Environmental Fluid Mechanics 11(3):289–306, DOI: https://doi.org/10.1007/s10652-010-9197-5
Helmio T (2002) Unsteady 1D flow model of compound channel with vegetated floodplains. Journal of Hydrology 269(1):89–99, DOI: https://doi.org/10.1016/S0022-1694(02)00197-X
Hubble T, Docker B, Rutherfurd I (2010) The role of riparian trees in maintaining riverbank stability: A review of australian experience and practice. Ecological Engineering 36(3):292–304, DOI: https://doi.org/10.1016/j.ecoleng.2009.04.006
Ibrahim ZB (2015) Flow behaviour due to floodplain roughness along riparian zone in compound channels. PhD Thesis, Universiti Teknologi Malaysia, Johor Bahru, Malaysia
Ibrahim ZB, Mazuki M, Ismail Z, Jumain M, Ibrahim N, Harun N, Katimon A (2012) Flood flow characteristics in vegetated straight channels: Physical models observations. Physical modeling application and technologies (PHYMAT2012) NAHRIM, September 25, Seri Kembangan, Malaysia
Jahra F, Kawahara Y, Hasegawa F, Yamamoto H (2011) Flow-vegetation interaction in a compound open channel with emergent vegetation. International Journal of River Basin Management 9(3–4):247–256, DOI: https://doi.org/10.1080/15715124.2011.642379
Jumain J, Ibrahim Z, Ismail Z, Ibrahim NH, Makhtar MR, Nordin MH (2013) Influence of two-line emergent floodplain vegetation on a straight compound channel flow. International Journal of Integrated Engineering 5(1):58–63
Khademishamam M, Omid MH, Farhoudi (2014) Flow and bedload transport in a straight compound channel with vegetation roughened floodplains. River flow- The 7th international conference on fluvial hydraulics, September 3–5, Lausanne, Switzerland
Mulahasan S, Stoesser T, Alvarez F (2015) Visualization of shear layers in compound channel flows. 10th pacific symposium on flow visualization and image processing, June 15–18, Naples, Italy
Mulahasan S, Stoesser T, McSherry R (2017) Effect of floodplain obstructions on the discharge conveyance capacity of compound channels. Journal of Irrigation and Drainage Engineering 143(11), DOI: https://doi.org/10.1061/(ASCE)IR.1943-4774.0001240
Myers WRC, Lyness JF, Cassells J (2001) Influence of boundary roughness on velocity and discharge in compound river channels. Journal of Hydraulic Research 39(3):311–319, DOI: https://doi.org/10.1080/00221680109499834
Nepf HM (1999) Drag, turbulence, and diffusion in flow through emergent vegetation. Water Resources Research 35(2):479–489, DOI: https://doi.org/10.1029/1998WR900069
Nepf HM, Ghisalberti M (2008) Flow and transport in channels with submerged vegetation. Acta Geophysica 56(3):753–777, DOI: https://doi.org/10.2478/s11600-008-0017-y
Nepf HM, Vivoni ER (1999) Turbulence structure in depth-limited, vegetated flow: Transition between emergent and submerged regimes. 28th IAHR congress, August 22–27, Graz, Austria
Ozan AY (2018) Flow structure at the downstream of a one-line riparian emergent tree along the floodplain edge in a compound open-channel flow. Journal of Hydrodynamics 30(3):470–480, DOI: https://doi.org/10.1007/s42241-018-0052-3
Pasche E, Rouve G (1985) Overbank flow with vegetatively roughened floodplains. Journal of Hydraulic Engineering 111(3), DOI: https://doi.org/10.1061/(ASCE)0733-9429(1985)111:9(1262)
Pasha GA, Tanaka N (2016) Effectiveness of finite length inland forest in trapping tsunami-borne wood debris. Journal of Earthquake and Tsunami 10(2):1–26, DOI: https://doi.org/10.1142/S1793431116500081
Pasha GA, Tanaka N (2017) Undular hydraulic jump formation and energy loss in a flow through emergent vegetation of varying thickness and density. Ocean Engineering 141:308–325, DOI: https://doi.org/10.1016/j.oceaneng.2017.06.049
Pasha GA, Tanaka N (2020) Characteristics of a hydraulic jump formed on upstream vegetation of varying density and thickness. Journal of Earthquake and Tsunami 14(3), DOI: https://doi.org/10.1142/S1793431120500128
Pasha GA, Tanaka N, Yagisawa J, Achmad FN (2018) Tsunami mitigation by combination of coastal vegetation and a backward-facing step. Coastal Engineering Journal 60(1):104–125, DOI: https://doi.org/10.1080/21664250.2018.1437014
Rezaei B, Safarzade A (2016) Numerical modeling of flow field in prismatic compound channels with different floodplain widths. Journal of Applied Research in Water and Wastewater 3(2):260–270
Sanjou M, Nezu I (2011) Turbulence structure and concentration exchange property in compound open-channel flows with emergent trees on the floodplain edge. International Journal of River Basin Management 9(3–4):181–193, DOI: https://doi.org/10.1080/15715124.2011.584511
Shiono K, Knight DW (1991) Turbulent open-channel flows with variable depth across the channel. Journal of Fluid Mechanics 222:617–646, DOI: https://doi.org/10.1017/S0022112091001246
Sun X, Shiono K (2009) Flow resistance of one-line emergent vegetation along the floodplain edge of a compound open channel. Advances in Water Resources 32(3):430–438, DOI: https://doi.org/10.1016/j.advwatres.2008.12.004
Tanaka N, Yasuda S, Iimura K, Yagisawa J (2014) Combined effects of coastal forest and sea embankment on reducing the washout region of houses in the Great East Japan tsunami. Journal of Hydro-Environmental Research 8(3):270–280, DOI: https://doi.org/10.1016/j.jher.2013.10.001
Tang X, Knight DW (2009) Lateral distributions of streamwise velocity in compound channels with partially vegetated floodplains. Science in China Series E: Technological Sciences 52(11):3357–3362, DOI: https://doi.org/10.1007/s11431-009-0342-7
Terrier B (2010) Flow characteristics in straight compound channels with vegetation along the main channel. PhD Thesis, Loughborough University, Loughborough, UK
Tominaga A, Nezu I (1991) Turbulent structure in compound open channel flows. Journal of Hydraulic Engineering 117(1), DOI: https://doi.org/10.1061/(ASCE)0733-9429(1991)117:1(21)
Versteeg HK, Malalasekera W (1995) An introduction to computational fluid dynamics, The finite volume method. Longman Scientific & Technical, Longman Group Limited, Harlow, UK, 75
Yang K, Cao S, Knight D (2007) Flow patterns in compound channels with vegetated floodplains. Journal of Hydraulic Engineering 133(2):148–159, DOI: https://doi.org/10.1061/(ASCE)0733-9429(2007)133:2(148)
Zhao F, Huai W (2016) Hydrodynamics of discontinuous rigid submerged vegetation patches in open-channel flow. Journal of Hydro-Environment Research 12:148–160, DOI: https://doi.org/10.1016/j.jher.2016.05.004
Acknowledgments
Authors acknowledge the Higher Education Commission, Pakistan for providing CFD facilities at University of Engineering and Technology, Taxila, Pakistan.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Asif, M., Ghani, U. & Pasha, G.A. Numerical Modelling of Flow Characteristics in an Asymmetric Trapezoidal Compound Channel with Vegetation Patches. KSCE J Civ Eng 24, 3659–3673 (2020). https://doi.org/10.1007/s12205-020-1435-x
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s12205-020-1435-x