Investigating the Flow Hydrodynamics in a Compound Channel with Layered Vegetated Floodplains

Muhammad Ahmad, Usman Ghani, Naveed Anjum, Ghufran Ahmed Pasha, Muhammad Kaleem Ullah, Afzal Ahmed


In natural rivers, vegetation grows on floodplains, generating complex velocity field within the compound channel. The efficient modelling of the flow hydraulics in a compound channel with vegetated floodplains is necessary to understand and determine the natural processes in rivers and streams. As the three dimensional (3D) flow features are difficult to capture through experimental investigation; therefore, the present numerical study was carried out to investigate the complex 3D flow structures with the vertically layered vegetation placed over the floodplains in a symmetric trapezoidal compound channel. The simulations were conducted using a Computational Fluid Dynamics (CFD) code FLUENT, whereas a Reynolds Averaged Navier-Stokes (RANS) technique based on Reynolds stress model (RSM) was implemented for turbulence closure. The numerical model successfully replicated the flow behavior and showed a good agreement with the experimental data. The present study concluded the presence of quite-S shaped velocity profile in the layered vegetated floodplains when the short vegetation was submerged during high flows or floods, whereas the velocity profile was uniform or almost logarithmic during low floods or when both short and tall vegetation remained emergent. The lateral exchange of mass and momentum was promoted due to the flow separation and instability along the junction of the floodplains and main channel. The flow velocities were significantly reduced in the floodplains due to resistance offered by the vegetation, which consequently resulted in an increased percentage i.e. 67-73%, of passing discharge through the main channel. In general, the spatial distribution of mean flow and turbulence characteristics was considerably affected near the floodplain and main channel interfaces. Moreover, this study indicated a positive flow response for the sediment deposition as well as for the nourishment of the aquatic organisms in the riparian environment.


Compound Channel; Vegetated Floodplains; Numerical Modelling; Flow Characteristics.


Takuya, U., Keiichi, K., and Kohji, M. "Experimental and numerical study on hydrodynamics of riparian vegetation". J. Hydrodyn, 26, (October 2014): 796-806. doi: 10.1016/S1001-6058(14)60088-3.

Bousmar, D., and Zech, Y. "Momentum transfer for practical flow computation in compound channels". J. Hydraul. Eng, 125, (July 1999): 696-706. doi: 10.1061/(ASCE)0733-9429(1999)125:7(696).

Unal, B., Mamak, M., Seckin, G., and Cobaner, M. "Comparison of an ANN approach with 1D and 2D methods for estimating discharge capacity of straight compound channels". Adv. Eng. Software, 41, (February 2010): 120-129. doi: 10.1016/j.advengsoft.2009.10.002.

Martin, L.A., and Myers, W.R.C. "Measurement of overbank flow in a compound river channel". Proc. Instn. Civ. Engrs, (September 1993). doi:10.1680/iwtme.1993.24584.

Ervine, D.A., Babaeyan-Koopaei, K., and Sellin, R.H.J. "Two-dimensional solution for straight and meandering overbank flows". J. Hydraul. Eng, 126, (September 2000): 653-669. doi: 10.1061/(ASCE)0733-9429(2000)126:9(653).

Sahu, M., Khatua, K.K., and Mahapatra, S.S. "A neural network approach for prediction of discharge in straight compound open channel flow". Flow Measure Instrum, 22, (2011): 438-446. doi: 10.1016/j.flowmeasinst.2011.06.009.

Knight, D.W., and Brown, F.A. "Resistance studies of overbank flow in rivers with sediment using the flood channel". J. Hydraulic Res, 39, (December 2001): 283-301. doi: 10.1080/00221680109499832.

Kisi, O., and Cigizoglu, H.K. "Comparison of different ANN techniques in river flow prediction". Civil Eng. Environ. Syst, 24, (August 2007): 211-231. doi: 10.1080/10286600600888565.

Al-Khatib, I.A., Abu-Hassan, H.M., and Abaza, K.A. "Development of empirical regression-based models for predicting mean velocities in asymmetric compound channels". Flow Measure Instrum, 33, (October 2013): 77-87. doi: 10.1016/j.flowmeasinst.2013.04.013.

Pasche, E., and Rouve, G. "Overbank flow with vegetatively roughened flood plains". J. Hydraul. Eng, 11, (September 1985): 1262-1278. doi: 10.1061/(ASCE)0733-9429(1985)111:9(1262).

Rameshwaran, P., and Shiono, K. "Quasi Two-Dimensional Model for Straight Overbank Flows Through Emergent". J.Hydraul. Res, 45, (2007): 302-315. doi: 10.1080/00221686.2007.9521765.

Sun, X., and Shiono, K. "Flow Resistance of One-Line Emergent Vegetation along the Floodplain Edge of a Compound Open Channel". Journal of Adv. Water Resour, 32, (March 2009): 430-438. doi: 10.1016/j.advwatres.2008.12.004.

Carling, P.A., Cao, Z., and Holland, et al. "Turbulent flow across a natural compound channel". Water Resour. Res, 38, (December 2002). doi: 10.1029/2001WR000902.

Van Prooijen, B.C., Battjes, J.A., and Uijttewaal, W.S.J. "Momentum exchange in straight uniform compound channel flow".J.Hydraul. Eng, 131, (March 2005): 175-183. doi: 10.1061/(ASCE)0733-9429(2005)131:3(175).

Pradhan, S., and Khatua, K.K. "An Improved Approach for Flow Prediction in Compound Open Channel Flow of Uniform Roughness". International Conference on Hydraulics, Water Resources, Coastal and Environmental Engineering, MANIT Bhopal, (2014).

Koftis, T., and Prinos, P. "Reynolds stress modelling of flow in compound channels with vegetated floodplains". J. Appl. Water Eng. Res, (July 2016). doi: 10.1080/23249676.2016.1209437.

Anjum, N., and Tanaka, N. "Hydrodynamics of longitudinally discontinuous, vertically double layered and partially covered rigid vegetation patches in open channel flow". River Res. Appl, 36, no. 1 (November 2019). doi: 10.1002/rra.3546.

Yang, K., Cao, S., and Knight, D.W. "Flow Patterns in Compound Channels with Vegetated Floodplains". J. Hydraul. Eng, 133, (February 2007). doi: 10.1061/(ASCE)0733-9429(2007)133:2(148).

Juez, C., Hassan, M.A., and Franca, M.J. "The origin of fine sediment determines the observations of suspended sediment fluxes under unsteady flow conditions". Water Resour. Res, 54, (July 2018): 5654-5669. doi: 10.1029/2018WR022982.

Juez, C., Thalmann, M., Schleiss, A.J., and Franca, M.J. "Morphological resilience to flow fluctuations of fine sediment deposits in bank lateral cavities". Adv. Water Resour, 115, (May 2018): 44-59. doi: 10.1016/j.advwatres.2018.03.004.

Liu, D., Diplas, P., Hodges, C.C., and Fairbanks, J.D. "Hydrodynamics of flow through double layer rigid vegetation". Geomorphology, 116, (April 2010): 286–296. doi: 10.1016/j.geomorph.2009.11.024.

Anjum, N., Ghani, U., Pasha, G.A., Latif, A., Sultan, T., and Ali, S. "To investigate the flow structure of discontinuous vegetation patches of two vertically different layers in an open channel". Water, 10, (January 2018). doi: 10.3390/w10010075.

Nadaoka, K., and Yagi, H. "Shallow-water turbulence modeling and horizontal large-eddy computation of river flow". J. Hydraul. Eng, 124, (May 1998): 493-500. doi: 10.1061/(ASCE)0733-9429(1998)124:5(493).

Su, X., and Li, C.W. "Large Eddy simulation of free surface turbulent flow in partly vegetated open channels". Int. J. Numer. Methods Fluids, 39, (July 2002): 919-937. doi: 10.1002/fld.352.

Jahra, F., Kawahara, Y., Hasegawa, F., and Yamamoto, H. "Flow–vegetation interaction in a compound open channel with emergent vegetation". Int. J. River Basin Manage, 9, (December 2011): 247-256. doi: 10.1080/15715124.2011.642379.

Kang, H., and Choi, S.K. "Turbulence modeling of compound open-channel flows with and without vegetation on the floodplain using the Reynolds stress model". Adv. Water Resour, 29, (November 2006): 1650-1664. doi: 10.1016/j.advwatres.2005.12.004.

Anjum, N., and Tanaka, N. "Study on the flow structure around discontinued vertically layered vegetation in an open channel". J. Hydrodyn, (April 2019). doi: 10.1007/s42241-019-0040-2.

Anjum, N., and Tanaka, N. "Numerical modeling of the turbulent flow structure through vertically double layer vegetation". J JpSoc Civil Eng, Ser. B1(Hydraulic Engineering), 75, (2019): 487-492.

Souliotis, D., and Prinos, P. "Effect of a vegetation patch on turbulent channel flow". J. Hydraul. Res, 49, (May 2011): 157–167. doi: 10.1080/00221686.2011.557258.

Zhao, H., Yan, J., Yuan, S., Liu, J., and Zheng, J. "Effects of Submerged Vegetation Density on Turbulent Flow Characteristics in an Open Channel". Water, 11, (October 2019): 2154. doi: 10.3390/w11102154.

Yan, P., Tian, Y., Lei, X., Fu, Q., Li, T., and Li, J. "Effect of the Number of Leaves in Submerged Aquatic Plants on Stream Flow Dynamics". Water, 11, (2019): 1448. doi: 10.3390/w11071448.

Yu, Z., Wang, D., and Liu, X. "Impact of Vegetation Density on the Wake Structure". Water, 11, (July 2019): 1266. doi: 10.3390/w11061266.

Zhao, F., and Huai, W. "Hydrodynamics of discontinuous rigid submerged vegetation patches in open-channel flow". J Hydro-Environ. Res, 12, (September 2016): 148–160. doi: 10.1016/j.jher.2016.05.004.

Versteeg, H.K., and Malalasekera, W. "An introduction to computational fluid dynamics, The finite volume method". 2nd edition, Pearson Education Publishers, London, (2007).

Tsujimoto, T., Shimizu, Y., Kitamura, T., and Okada, T. "Turbulent open-channel flow over bed covered by rigid vegetation". J. Hydrosci. Hydraul. Eng, 10, (1992): 13–25.

Nepf, H.M., and Vivoni, E.R. "Flow structure in depth-limited, vegetated flow". J. Geophys. Res, 105, (December 2000): 547–557. doi: 10.1029/2000JC900145.

Anjum, N., and Tanaka, N. "Experimental study on flow analysis and energy loss around discontinued vertically layered vegetation". Environ Fluid Mech, (November 2019). doi: 10.1007/s10652-019-09723-8.

Finnigan, J. "Turbulence in plant canopies". Ann. Rev. Fluid Mech, 32, (January 2000): 519–571. doi: 10.1146/annurev.fluid.32.1.519.

Ghisalberti, M., and Nepf, H. "The structure of the shear layer in flows over rigid and flexible canopies". Environ. Fluid Mech, 6, (June 2006): 277–301. doi: 10.1007/s10652-006-0002-4.

Huai, W., Zhang, J., Wang, W. J., and Katul, G.G. "Turbulence structure in open channel flow with partially covered artificial emergent vegetation". J. Hydrol, 573, (June 2019): 180–193. doi: 10.1016/j.jhydrol.2019.03.071.

Tang, X., Rahimi, H., Singh, P., Wei, Z., Wang, Y., Zhao, Y., and Lu, Q. "Experimental study of open‐channel flow with partial double‐layered vegetation". The 1st international symposium on water resource and environmental management (WREM 2018), Kunming, China, Volume 81, (2019).

Yan, X.F., Wai, W.G.O., and Li, C.W. "Characteristics of flow structure of free‐surface flow in a partly obstructed open channel with vegetation patch". Environ. Fluid Mech, 16, (April 2016): 807-832. doi: 10.1007/s10652-016-9453-4.

Caroppi, G., Vastila, K., Jarvela, J., Rowinski, P.M., and Giugni, M. "Turbulence at water‐vegetation interface in open channel flow: Experiments with natural‐like plants". Adv. Water Resour, 127, (December 2019): 180-191. doi: 10.1016/j.advwatres.2019.03.013.

Folkard, A.M., and Gascoigne, J.C. "Hydrodynamics of discontinuous mussel beds: Laboratory flume simulations". J. Sea Res, 62, (November 2009): 250-257. doi: 10.1016/j.seares.2009.06.001.

Widdows, J., and Navarro, J.M. "Influence of current speed on clearance rate, algal cell depletion in the water column and resuspension of biodeposits of cockles (Cerastodermaedule)". J. Exp. Mar. Biol. Ecol, 343, (March 2007): 44-51. doi: 10.1016/j.jembe.2006.11.011.

Tsujimoto, Tetsuro. “Fluvial Processes in Streams with Vegetation.” Journal of Hydraulic Research 37, no. 6 (November 1999): 789–803. doi:10.1080/00221689909498512.

Gurnell, A.M., Thompson, K., Goodson, J., and Moggridge, H. "Propagule deposition along river margins: Liking hydrology and ecology". J. Ecol, 96, (February 2008): 553-565. doi: 10.1111/j.1365-2745.2008.01358.x.

Ghani, U., Anjum, N., Pasha, G.A., and Ahmad, M. "Numerical investigation of the flow characteristics through discontinuous and layered vegetation patches of finite width in an open channel". Environ. Fluid Mech, 19, (April 2019): 1469-1495. doi: 10.1007/s10652-019-09669-x.

Anjum, N., and Tanaka, N. "Numerical investigation of velocity distribution of turbulent flow through vertically double-layered vegetation". Water Sci. Eng, 12, no. 4 (December 2019). doi: 10.1016/j.wse.2019.11.001.

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DOI: 10.28991/cej-2020-03091513


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