3.2.3 Open flume inlet

Figure 8. Open flume inlet l/sec

where

Q = design discharge of the inlet, l/sec
B = width of the throat, cm
H = height of the designed full supply level in the feeder channel above the sill level of the inlet
C = discharge coefficient

Table 10 Values of Discharge Coefficient C for open Flume Inlet

B in cm	C
6 to 10	0.0160
10 to 15	0.0164
over 15	0.0166

Figure 9. Relationships of discharge to B and H

Length of the cistern:		lc = 0.82 H2, m
Depth of the cistern:		dc = 0.1 H2, m
	where	H2 = water depth in the pond, m
Depth of the glacis		dg = 0.5 H, m
	where	H = maximum water depth above the sill level of the inlet, m

Example 3

Design an open flume inlet for a discharge of 150 l/sec if the water depth in the feeder canal is 45 cm and 1.50 m in the pond.

Solution

The corresponding width of the throat to the water depth of 150 l/sec is defined from Figure 9.

then

B = 30 cm
d_g = 0.5×H = 0.5×0.45 = 0.23 m
l_c = 0.8×H₂ = 0.8×1.50 = 1.20 m
d_c = 0.1×H₂ = 0.1×1.50 = 0.15 m