drawing of an almost constant discharge over a wide range of water-
level fluctuations in the distribution channel. With the increase in
head the contraction of the jet increases, thus offsetting any increase
in the corresponding discharge. In order to cope with a much wider
range of water-level fluctuations, a double baffle plate orificed
module may be used. If the water-level fluctuations are beyond toler-
able limits for constant flow in the off-taking canal, auxiliary equip-
ment such as downstream and upstream level gates (Kraatz and
Mahajan, 1975) must be installed in the distribution system.Worked Example 9.3
Design an intake structure for a minor canal, using the following data:
Supply canal OfftakeUpstream DownstreamDischarge (m^3 s^1 ) 004.0 003.5 000.5
Bed level (m AOD) 120.00 119.94 119.86
FSL (m AOD) 120.96 120.84 120.36
Bed width (m) 008.0 007.0 002.0
Angle of offtake 0060°
Solution
The upstream full supply depth, D120.96 120.000.96 m. The water
depth in the offtake120.36 119.860.50 m. The working head
INTAKES 405
Fig. 9.30 Orifice-type rigid module (single-baffle layout)