Combining the above gives
1
2
C^2 d[(b/B)(h 1 /(h 1 P))]^2 C^2 v Cv2/3 1 0. (vi)
The solution of this equation – tabular or graphical (Water
Resources Board, 1970) – gives
Cv1.175.
The discharge so computed has a return period of about 25 years, which
is quite acceptable for the stated land use upstream of the structure.
Similar calculations indicate that a flood flow of around 73 m^3 s^1 with
a return period of 175 years clearly floods the upstream land (the water
level above the sill is around 2 m). Hence the presence of the proposed
structure will not cause any major flooding problems.
The modular flow equation can be used to construct the stage–
discharge curve. The following table lists the data points:
358 RIVER ENGINEERING
Fig. 8.25 Design curves
Q vs H 1 ;P0.7 m
Q vs H 1 ;P0.6 m
Q vs 1.33H 1 ;P0.7 m
Q vs 1.33H 2 ;P0.6 m
