Hydraulic Structures: Fourth Edition

WORKED EXAMPLES 357

Fig. 8.24 log(hz) versus logQ

2. Figure 8.21 suggests that the maximum stage before overtopping of
   banks occurs is 2.7 m (from the bed level). Allowing a reasonable
   groundwater table of 0.3 m below ground level, the maximum allow-
   able stage preventing overtopping and waterlogging is 1.7 m. There-
   fore the maximum water level upstream of the weir corresponding to
   this stage, h 1 1.7 0.61.1 m. Hence the discharge, Q, that can
   spill over the weir without flooding is 26.75 m^3 s^1 (from Fig. 8.24).
   Note the following:

QCdCvg1/2bh 1 3/2(weir formula) (ii)

Cvh 1 3/2H 1 3/2 (iii)

where

H 1 h 1 V^21 /2g (iv)

and

V 1 Q/[B(h 1 P)] (v)

Bbeing the mean width of the river in height (h 1 P).