Physical Oceanography, Vol. 19, No. 1, 2009
EXPERIMENTAL AND FIELD RESEARCH
LONGITUDINAL DISPERSION IN WAVE-CURRENT-VEGETATION FLOW
B. Y. F. Tam,
C. Y. Song,
Y. P. Chen,
The flow, turbulence, and longitudinal dispersion in wave-current flow through submerged vege-
tation are experimentally examined. Laboratory experiments are carried out by superimposing
progressive waves on a steady flow through simulated submerged vegetation. The resultant
wave-current-vegetation interaction shows strong interface shear with increase in the velocity
due to the wave-induced drift. The increase in turbulence in the region of vegetation is found to
be about twice higher than in the no-wave case due to the additional mixing by wave motions.
Solute experiments are conducted to quantify the wave-current-vegetation longitudinal disper-
sion coefficient (WCVLDC) by the routing method and by defining length and velocity scales for
the wave-current-vegetation flow.
An empirical expression for the WCVLDC is proposed.
though the increase in vertical diffusivity is observed as compared with bare-bed channels, the
shear effect is stronger, which increases the value of the WCVLDC.
The study can be a guide-
line to understand the combined hydrodynamics of waves, current, and vegetation and quantify
the longitudinal dispersion therein.
The understanding of transport and mixing processes (such as advection and diffusion) is important to veri-
fy the acceptable limit of pollutants released into open channel systems. Parallel with these processes, short-pe-
riod surface waves often exist due to the ubiquity of wind shear and contribute to the process of mixing of pollu-
tants . Another agent of influence is the common vegetation growth on the channel bed, which hydrodynami-
cally enhances turbulence and the associated processes of mixing [2–4]. The resultant flow is the combination of
waves, steady current, and the action of vegetation which generally exists in nature. The knowledge of the com-
bined hydrodynamics of waves, current, and vegetation is practical in understanding the particulate sediment
transport , vertical momentum transfer , and distortion of plant morphology [7, 8]. In the present paper, the
flow, turbulence, and longitudinal dispersion in the combined wave-current-vegetation flow field are experimen-
tally examined. The depthwise velocity profiles and turbulence have been measured by conducting dye studies
and an empirical expression is proposed for the longitudinal dispersion coefficient of the wave-current-vegeta-
tion flow (WCVLDC). The results of our studies will improve the understanding of hydrodynamics and mixing
of pollutants in the combined wave-current-vegetation flow. The paper is organized as follows. Section 1 pro-
vides introduction followed by a brief literature survey of wave-current and current-vegetation studies presented
Hong Kong Polytechnic University, Hong Kong.
Beijing IS & T University, Beijing, China.
Tianjin University, Tianjin, China.
Published in Morskoi Gidrofizicheskii Zhurnal, No.
50–67, January–February, 2009. Original article submitted June 7, 2007;
revision submitted July 15, 2007.
0928-5105/09/1901–0045 © 2009 Springer Science+Business Media, Inc. 45