Abstract
An idealized parallel flow caused by a lateral bed roughness difference due to the partial vegetation across a channel is investigated. Similar to the flow in a compound channel, there are mixing layers adjacent to the interface between the vegetation and the non-vegetation lanes, and a lateral momentum exchange occurs between the slow-moving water in the former lane and the fast-moving water in the latter lane. Under a uniform flow condition, the three-dimensional (3D) instantaneous velocities of two cases with different discharges and water depths are measured with a 16MHz acoustic Doppler velocimeter (micro ADV). The longitudinal variation of the streamwise velocity and the vertical variation of the Reynolds stress are analyzed. A quadrant analysis is carried out to investigate the outward and inward interaction, ejection, and sweep phenomenon caused by the vegetation variation across the channel. The results show that the flow characteristics in the vegetation lane are similar to those in an open channel fully covered with submerged vegetation, and the flow characteristics in the smooth non-vegetation lane are similar to those in a free open channel. For the cases studied here, the width of the mixing region is about 10% of the channel width, and the mixing region is mainly on the non-vegetation half.
Similar content being viewed by others
References
Wang, W. J., Huai, W. X., Zeng, Y. H., and Zhou, J. F. Analytical solution of velocity distri-bution for flow through submerged large deflection flexible vegetation. Applied Mathematics and Mechanics (English Edition), 36(1), 107–120 (2015) DOI 10.1007/s10483-015-1897-9
Folkard, A. M. Flow regimes in gaps within stands of flexible vegetation: laboratory flume simu-lations. Environmental Fluid Mechanics, 11, 289–306 (2011)
Stephenson, D. and Kolovopoulos, P. Effects of momentum transfer in compound channels. Journal of Hydraulic Engineering, 116, 1512–1522 (1990)
Tominaga, A. and Nezu, I. Turbulent structure in compound open-channel flows. Journal of Hydraulic Engineering, 117, 21–41 (1991)
Wang, Z. Q. and Cheng, N. S. Time-mean structure of secondary flows in open channel with longitudinal bed forms. Advances in Water Resources, 29, 1634–1649 (2006)
Spooner, J. and Shiono, K. Modelling of meandering channels for overbank flow. Proceedings of the Institution of Civil Engineers, Water & Maritime Engineering, 156, 225–233 (2003)
Shiono, K. and Feng, T. Turbulence Measurements of dye concentration and effects of secondary flow on distribution in open channel flows. Journal of Hydraulic Engineering, 129, 373–384 (2003)
Van Prooijen, B., Battjes, J., and Uijttewaal, W. Momentum exchange in straight uniform com-pound channel flow. Journal of Hydraulic Engineering, 131, 175–183 (2005)
Vermaas, D. A., Uijttewaal, W. S. J., and Hoitink, A. J. F. Lateral transfer of streamwise mo-mentum caused by a roughness transition across a shallow channel. Water Resources Research, 47, 1–12 (2011)
Darby, S. E. Effect of riparian vegetation on flow resistance and flood potential. Journal of Hydraulic Engineering, 125, 443–454 (1999)
White, B. L. and Nepf, H. M. A vortex-based model of velocity and shear stress in a partially vegetated shallow channel. Water Resources Research, 44, 1–15 (2008)
Pasche, E. and Rouve, G. Overbank flow with vegetatively roughened flood plains. Journal of Hydraulic Engineering, 111, 1262–1278 (1985)
Shiono, K. and Knight, D. W. Turbulent open-channel flows with variable depth across the chan-nel. Journal of Fluid Mechanics, 222, 617–646 (1991)
Voulgaris, G. and Trowbridge, J. H. Evaluation of the acoustic Doppler velocimeter (ADV) for turbulence measurement. Journal of Atmospheric and Oceanic Technology, 15, 272–289 (1998)
Knight, D. W. and Shiono, K. Turbulence measurements in a shear layer region of a compound channel. Journal of Hydraulic Research, 28, 175–196 (1990)
Ghisalberti, M. and Nepf, H. The structure of the shear layer in flows over rigid and flexible canopies. Environmental Fluid Mechanics, 6, 277–301 (2006)
Author information
Authors and Affiliations
Corresponding author
Additional information
Project supported by the National Natural Science Foundation of China (Nos. 51379154, 51479145, and 51439007) and the Program for New Century Excellent Talents in University of China (No.NCET-11-0393)
Rights and permissions
About this article
Cite this article
Zeng, Y., Huai, W. & Zhao, M. Flow characteristics of rectangular open channels with compound vegetation roughness. Appl. Math. Mech.-Engl. Ed. 37, 341–348 (2016). https://doi.org/10.1007/s10483-016-2035-6
Received:
Revised:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10483-016-2035-6
Keywords
- vegetated flow
- lateral momentum exchange
- acoustic Doppler velocimeter (ADV)
- mixing layer
- quadrant analysis