Environmental Engineering Reference
In-Depth Information
Table B.1.
Hydraulic regime types.
Type of regime
Classification parameter
u
∗
k
s
/
v
Smooth
u
∗
k
s
/
v <
5
Transition
5
< u
∗
k
s
/
v <
70
Rough
u
∗
k
s
/
v >
70
Depending on the bed condition the flow regimes in irrigation canals
can be determined as:
Plane bed
: for plane beds (no motion) the equivalent height
k
s
is related
to the largest particles of the bed material. Van Rijn (1982) described the
equivalent roughness height as
k
s
=
3
d
90
.
Assuming a uniform sediment size distribution in irrigation canals
(
d
90
≈
1.5
d
50
), the equivalent roughness height of the sediment for plane
beds can be represented by:
k
s
=
4
.
5
d
50
(B.2)
where:
d
50
=
median diameter of the sediment (m)
equivalent height roughness (m)
The parameter
u
∗
k
s
/
v
for a plane bed (bed without motion) follows from:
k
s
=
k
s
=
4.5
d
50
u
∗
=
critical Shield shear velocity (
u
∗
,cr
)
Values of this parameter for various sediment diameters and for a
plane bed are shown in Table B.2. The flow regimes that belong to the
condition of a plane bed are the regimes smooth and transition.
Table B.2.
u
∗
k
s
/
v
parameter for plane bed (no motion).
d
50
(mm)
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
u
∗
(cr)
k
s
/
v
2.8
5.1
8.2
11.5
14.9
18.5
21.3
25.8
30.6
35.7
Bed forms
: for higher velocities, the occurrence of bed forms changes
the bed roughness. The effective roughness or the total equivalent height
follows from van Rijn (1984c):
k
s
+
k
s
k
s
=
(B.3)
where:
k
s
=
total equivalent height (m)
k
s
=
equivalent height related to the grain (m)
k
s
=
equivalent height related to the bed form (m)
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