Effects of Rigid Vegetation on the Turbulence Characteristics in Sediment-Laden Flows

Shengqi Lu^*, Jieren Chen

State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing, China.

DOI: 10.4236/jamp.2014.212126                

Abstract

The effects of rigid vegetation on the turbulence characteristics were experimentally studied in the interior water flume. An ADV was used to determine the three dimensional turbulent velocities in clear water flow without vegetation, sediment-laden flow without vegetation, sediment-laden flow with submerged vegetation and sediment-laden flow with non-submerged vegetation. By experimental and theoretical analysis, the effects of rigid vegetation on the distribution of averaged velocities, turbulence intensities and Reynolds stress were summarized. In sediment-laden flow with submerged vegetation, the averaged stream wise velocities above the top of vegetation fit well with the log distribution low. The three-dimensional turbulence intensities increase from the bottom until they reach the maximum at the top of the vegetation. The method to calculate the shear velocity with the maximum of the Reynolds stress is recommended. In sediment-laden flow with non-submerged vegetation, the turbulence problems cannot be explained by theory of bed shear flow. The average velocities, turbulence intensities and Reynolds stress approximate uniformly distributed along vertical direction.

Keywords

Rigid Vegetation, Turbulence Characteristics, Sediment-Laden Flow, Experimental Study

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	Kouwen, N., Li, R.M. and Simons, D.B. (1981) Flow Resistance in Vegetated Waterways. Transactions of ASCE, 24, 684-698. http://dx.doi.org/10.13031/2013.34321
[2]	Gourlay, M.R. (1970) Discussion of “Flow Resistance in Vegetated Channels” by Kouwen, N. et al. Journal of the Irrigation and Drainage Division, 96, 351-357.
[3]	Ei-Hakim, O. and Salama, M.M. (1992) Velocity Distribution inside and above Branched Flexible Roughness. Journal of the Irrigation and Drainage Engineering, 118, 914-927. http://dx.doi.org/10.1061/(ASCE)0733-9437(1992)118:6(914)
[4]	Carollo, F.G., Ferro, V. and Termini, D. (2002) Flow Velocity Measurements in Vegetated Channels. Journal of Hydraulic Engineering, 128, 664-673. http://dx.doi.org/10.1061/(ASCE)0733-9429(2002)128:7(664)
[5]	J?rvel?, J. (2005) Effect of Submerged Flexible Vegetation on Flow Structure and Resistance. Journal of Hydrology, 307, 233-241. http://dx.doi.org/10.1016/j.jhydrol.2004.10.013
[6]	Huang, B.-S., Lai, G.-W., Qiu, J. and Wan, P. (1999) Experimental Research on Influence of Vegetated Floodplains upon Flood Carrying Capacity of River. Journal of Hydrodynamics, Series A, 14, 468-474.
[7]	Shi, Y.-Z., Huang, B.-S. and Zhou, Z. (2003) Calculation of Length of Flow Coming into Main Channel in Flood Plain Planted with Trees. Hydro-Science and Engineering, 4, 53-56.
[8]	Shi, Z. (1997) Velocity Profile of Unidirectional Steady Current in a Salt Marsh Canopy. Journal of Sediment Research, 3, 82-88.
[9]	Yan, J., Zhou, Z. and Qiu, X.-Y. (2004) Transportation Characteristics of Bed Load Sediment of Upper Reaches End before Vegetation Dam. Journal of Xinjiang Agricultural University, 27, 67-72.
[10]	Ni, H.-G. and Gu, F.-F. (2005) Roughness Coefficient of Non-Submerged Reed. Journal of Hydrodynamics, Series A, 20, 167-173.
[11]	Tang, H.-W., Yan, J., Xiao, Y. and Lu, S.-Q. (2007) Manning’s Roughness Coefficient of Vegetated Channels. Shuili Xuebao, 38, 1347-1353.
[12]	Yan, J., Tang, H.-W., Xiao, Y., Li, K.-J. and Tian, Z.-J. (2011) Experimental Study on Influence of Boundary on Location of Maximum Velocity in Open Channel Flows. Water Science and Engineering, 4, 185-191.
[13]	Lu, S.-Q., Tang, H.-W. and Yan, J. (2007) Comparison of the Turbulence Parameters in Vegetated Flow and Non-Vegetated Flow. Advances in Science and Technology of Water Resources, 27, 64-68.
[14]	Wang, X.K., Shao, X.J. and Wang, G.Q. (2004) River Mechanics. Science Press, Beijing, 65-73.
[15]	Nezu, I. and Nakagawa, H. (1993) Turbulence in Open-Channel Flows. Balkema, Rotterdam, 12-28.