CHARACTERISTICS OF FLOW THROUGH RIGID, EMERGENT AND SPARSE VEGETATION

Authors

  • Suraya Sharil Department of Civil and Structural Engineering, Engineering Faculty and Build Environment, UKM, 43600, Bangi, Selangor, Malaysia
  • Wan Hanna Melini Wan Mohtar Department of Civil and Structural Engineering, Engineering Faculty and Build Environment, UKM, 43600, Bangi, Selangor, Malaysia
  • Siti Fatin Mohd Razali Department of Civil and Structural Engineering, Engineering Faculty and Build Environment, UKM, 43600, Bangi, Selangor, Malaysia

DOI:

https://doi.org/10.11113/jt.v78.6506

Keywords:

Emergent vegetation, mean velocity, transverse velocity, turbulence intensity, turbulent kinetic energy

Abstract

This paper looks into the flow profiles in terms of longitudinal and transverse velocities, turbulence intensity and turbulent kinetic energy in relation to the vegetation density, flow depth and stem Reynolds number. An experimental study was conducted in a fully vegetated flume, whereby a control volume was selected for detailed velocity measurement using Acoustic Doppler Velocimeter (ADV). This research considered 0.97%, 3.90% and 7.80% vegetation density or solid volume fractions (SVF) which are categorised as sparse in the lab work. Series of experiments were conducted in uniform flow condition with stem Reynolds number, Red ranging between 1300 and 3000. Experimental results managed to capture the wake area (velocity deficit; < 1) and fast flow region (velocity enhance; > 1). The boundary between the wake area and fast flow region is reflected by the highest magnitude of the normalised longitudinal turbulence intensity and turbulent kinetic energy. Positive normalised transverse velocity represents the flow diversion away from the vegetation and the negative normalised transverse velocity indicates flux towards the centre of the wake. Both turbulence intensity and turbulent kinetic energy display no observable relation with the flow depth. This is probably because the characteristic length for turbulent flow through vegetation is the stem diameter.  

References

Douglas, J. F., Gasiorek, J. M., and Swaffield, J. A. 1979. Fluid Mechanics. Longman, UK.

Nepf, H. M., Sullivan, J. A., Zavistoski, R. A. 1997. A Model For Diffusion Within Emergent Vegetation. Limnology and Oceanography. 42(8): 1735-1745.

Nepf, H. M. 2004. Vegetated Flow Dynamics. In S. Fagherazzi, M. Marani, and L. Blum [eds]. Ecogeomorphology Of Tidal Marshes. Coastal Estuar. Monogr. 137-164.

Zavistoski, R. A. 1994. Hydrodynamics Effects of Surface Piercing Plants. MSc Thesis. Massachusetts Institute of Technology.

Liu, D. 2008. Flow through Rigid Vegetation Hydrodynamics. MSc Thesis. Virginia Polytechnic Institute and State University.

Buckman, L. 2013. Hydrodynamics of Partially Vegetated Channels: Stem Drag Forces and Application to an in-stream Wetland Concept for Tropical, Urban Drainage Systems. MSc Thesis. National University of Singapore and Delft University of Technology.

White, B. L. and Nepf, H. M. 2003 Scalar Transport In Random Cylinder Arrays At Moderate Reynolds Number. Journal of Fluid Mechanics. 487: 43.

Gerard. 1978. Gerrard, J. H. 1978. The Wakes Of Cylindrical Bluff Bodies At Low Reynolds Number. Philosophical Transactions of the Royal Society of London. A(288): 351-382.

Li and Shen, Li, R., and Shen, H. W. 1973. Effect Of Tall Vegetation On Flow And Sediment. Journal of the Hydraulics Division. 99(HY5). 793-814.

Zong, L. 2011. Interactions Among Flow, Sediments Deposition And Aquatic Vegetation In A Channel. MSc Thesis. Massachusetts Institute of Technology.

Toth, L. G., Parpala, L., Balogh, C. and Tatrai, I. and Baranyai, E. 2011. Zooplankton Community Response To Enhanced Turbulence Generated By Water Level Decrease In Lake Balaton, The Largest Shallow Lake In Central Europe. Limnol. Oceanogr. 56(6): 2211-2222.

Stoesser, T., Kim, S. J. and Diplas, P. 2010. Turbulent Flow through Idealized Emergent Vegetation. Journal of Hydraulic Engineering. 136(12): 1003-1017.

Malki, R. 2009. The Influence of Saltmarsh Vegetation Canopies on Hydrodynamics in the Iintertidal Zone. PhD Thesis. Cardiff University.

Shucksmith, J. D. 2008. Impact of Vegetation in Open Channels on Flow Resistance and Solute Mixing. PhD Thesis. University of Sheffield.

Nepf, H. M. 2012. Flow and Transport in Regions with Aquatic Vegetation. Annual Review of Fluid Mechanic. 44: 123-142.

Tanino, Y. Nepf, H. M. 2008. Lateral Dispersion In Random Cylinders Arrays At High Reynolds Number. J. Fluid Mech. 600: 339-371.

Nepf, H. M. 1999. Drag, Turbulence And Diffusion In Flow Through Emergent Vegetation. Water Resources Research 35(2): 479-489.

Downloads

Published

2016-09-29

Issue

Section

Science and Engineering

How to Cite

CHARACTERISTICS OF FLOW THROUGH RIGID, EMERGENT AND SPARSE VEGETATION. (2016). Jurnal Teknologi, 78(10). https://doi.org/10.11113/jt.v78.6506