Geoscience Reference
In-Depth Information
18 log
12
R
b
k
s
C
h
=
(3.59)
where
R
b
is determined using Vanoni and Brooks' (1957) method.
Karim formula
Karim (1995) proposed the following formula to determine the Manning roughness
coefficient on a movable bed:
1.20
0.465
8.92
h
0.037
d
0.126
50
n
=
+
(3.60)
m
−
1
/
3
;
d
50
is in m; and
h
is the hydraulic depth, which is the flow
area divided by water surface width. The graphical relation between
where
n
is in s
·
and
U
∗
/ω
s
is
shown in Fig. 3.12. In the range of 0.15
<
U
∗
/ω
<
3.64,
is determined by
s
0.294
U
∗
ω
0.00316
U
∗
ω
2
0.0319
U
∗
ω
3
0.00272
U
∗
ω
4
h
=−
0.04
+
+
−
+
s
s
s
s
(3.61)
where
s
is the settling velocity of sediment particles with size
d
50
.
Eq. (3.61) was calibrated using experimental data reported by Guy
et al
. (1966) and
field data measured in the Missouri River.
ω
Figure 3.12
Relative roughness height as function of
U
∗
/ω
s
(Karim, 1995).
