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IMPACT OF FLOODPLAIN VEGETATION ON THE
SHEAR LAYER AT THE INTERFACE IN 1D MODEL
FOR COMPOUND OPEN-CHANNEL FLOWS
SUNG-UK CHOI
∗
, MOONHYEONG PARK and HYEONGSIK KANG
School of Civil and Environmental Engineering
Yonsei University, Seoul 120-749, Korea
∗
schoi@yonsei.ac.kr
This paper investigates the impact of floodplain vegetation on the shear layer
in the one-dimensional (1D) apparent shear stress model for compound open-
channel flows. To obtain the mean flow and turbulence structures of the com-
pound channel flows, the three-dimensional (3D) Reynolds stress model is used.
The friction slope and interfacial eddy viscosity due to interfacial shear are eval-
uated and compared with values suggested previously. The impact of proposed
interfacial eddy viscosity on the backwater profiles for compound channel flows
with and without vegetation on the floodplains are also discussed.
1. Introduction
In general, the straightened wide rectangular channel could cause channel
instability, erosion and sedimentation problems, and reduce retention times.
Moreover, it can totally isolate the channel flora and fauna from the stream
corridor and reduce the natural development of biodiversity.
1
In such cases,
an irregular and meandering channel with vegetated floodplain may be an
effective low-cost solution.
Hydraulically, floodplain vegetation changes the resistance of the
streams, which can affect the flow structure seriously. The difference in
the streamwise mean velocities between the main channel and floodplain
creates a shear layer at the juncture. The shear layer is related with the twin
vortices at the juncture. Through this interface, momentum, and mass are
exchanged between the main channel and floodplain. Here, the momentum
exchange always exists although net flow carried by each portion remains
the same.
The objective of the present paper is to investigate the impact of flood-
plain vegetation on the interfacial shear layer in the one-dimensional (1D)
computation of compound channel flows. For this, a 1D model based on the
Apparent Shear stress Method (ASM) is developed. For compound channel
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