Environmental Engineering Reference
In-Depth Information
Total energy line
∆
H
h
1
H
1
H
2
h
2
control section
P
1:6
Figure 4.8. Typical rectangular
flume (Wahl, 2005).
converging
transition
approach canal
throat
diverging transition
For
H
=
h
d
(design head), the equation reduces to:
2
.
20
B
c
h
3
/
2
Q
=
(4.33)
where:
Q
discharge (m
3
/s)
=
C
=
0.75 (for the design head above the crest)
B
c
=
crest width (m)
H
=
total head above the crest (m)
Flumes consist of an approach canal, a converging transition, usually
a throat and a diverging transition (see Figure 4.8). A flume is formed
either by narrowing the width or by narrowing the width and raising the
bed; in both cases it is called a flume. When only the bed is raised then it
is called a weir (Clemmens et al., 2001). Examples of flumes are Parshall,
Venturi, long-throated (RBC flume) and cut-throat flumes.
The discharge equation is identical to that of a broad-crested weir
(equation).
mh
c
)
2
g
(
H
1
−
Q
=
C
d
(
B
s
h
c
+
h
c
)
(4.34)
where:
Q
=
discharge (m
3
/s)
C
d
=
discharge coefficient
B
s
=
bottom width of the sill at the throat (m)
H
1
=
upstream energy head (m)
h
c
=
critical depth in the throat (m)
m
=
side slope (1 vertical : m horizontal)
The discharge coefficient
C
d
depends upon the size and shape of the
flume and for each flume type head discharge relationships are avail-
able (Bos, 1989; Bureau of Reclamation, 2001). Flumes may have two
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