Geoscience Reference
In-Depth Information
0.8
0.6
0.4
shear layer
0.2
0
1
2
3
4
5
y/H
Fig. 1.
3D simulation result of secondary current vectors.
Figure 1 shows the simulated secondary flow vectors and vortical struc-
ture. In the figure, a pair of counter-rotating vortices is found at the juncture
between main channel and floodplain. In order to evaluate the friction slope
due to interfacial shear
S
s
, we define the shear layer along the interfacial
line of twin vortices at the juncture in Fig. 1. The friction slope due to
interfacial shear is evaluated by
sin
θ
u
w
d
s,
1
gA
i
1
gA
i
u
θs
u
θn
d
s
=
S
s
=
·
u
v
−
cos
θ
·
(4)
s
s
where
u
θs
and
u
θn
are the fluctuating velocity components tangent and
normal to the interfacial line, respectively.
4. Results and Discussions
Figure 2 shows the friction slope due to interfacial shear layer for various
flow depth ratios. It can be found that the general trend observed in our
study is the same as that observed in Refs. 3 or 5. Specifically, the friction
slope by the present study lies between their results. Figure 3 shows the
interfacial eddy viscosity estimated by the present study for various flow
depth ratios. The values are of the same order of magnitude as the maximum
value (= 0
.
0001) assumed by Yen
et al.
,
3
but slightly larger than their value.
A backwater computation is performed using Fig. 3. For the com-
putation, such channel data are used as
B
m
=0
.
28 m,
B
f
=0
.
32 m,
H
m
−
H
f
=0
.
18 m,
S
0
=0
.
00025, and the roughness coecients in main
channel and floodplain
n
m
=0
.
014 and
n
f
=0
.
027, respectively. The dis-
charge of
Q
=0
.
15 m
3
/s and flow depth of
H
m
=1
.
422 m are imposed at
the upstream and downstream boundaries, respectively. Figure 4 shows the
computed discharge carried by the floodplain along the distance from the
