Environmental Engineering Reference
In-Depth Information
k
sl
k
sl
h
k
sb
B
R
k
sl
k
sb
k
sl
h
B
h
Figure 5.13. Non-wide
rectangular canal schematised
as a wide canal.
B
*
Replacing the de Chézy coefficients in the equation (5.44) by a function
of the surface roughness and water depth gives:
2
18 log
12
R
k
sl
hR
RS
f
+
18 log
12
R
k
sb
BR
RS
f
Q
=
(5.45)
Expressing the discharge in terms of the equivalent surface roughness
gives:
18 log
12
R
k
se
(
B
2
h
)
R
RS
f
Q
=
+
(5.46)
Equating both equations and rearranging the terms gives:
2log
k
sl
+
(
B/h
)log
k
sb
log
k
se
=
(5.47)
2
+
(
B/h
)
Expressed in terms of the Manning's coefficient results in:
B
h
2
+
n
e
=
(5.48)
1
n
b
2
n
l
+
B
h
Méndez (1998) has tested this method for rectangular canals with a
selected set of laboratory data from Krüger (1988). The selection cri-
teria for the data were similar to those used for the trapezoidal canals
and the comparison of the prediction method for the equivalent roughness
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