85
Theory
For an underflow gate with free discharge:
0
d
y
g
2
A
C
Q
=
where:
Q
= Volume flowrate
(m
3
s
-1
)
= Volume/time (using volumetric tank)
C
d
= Overall coefficient of discharge
(Dimensionless)
A
= Area of the opening
(m
2
)
= b breadth x height of gate opening y
a
y
0
= Upstream depth of flow
(m)
g
= Gravitational constant
(ms
-2
)
Note:
If the downstream side is submerged then y
o
is replaced with (y
o
-y
1
) in the above
equation.
Equipment Set Up
Clamp the radial gate assembly securely to the sides of the channel then level the flume.
Adjust the screw on the top of the gate to create a small gap between the bottom of the
gate and the bed of the channel. Gradually open the flow control valve and allow the flow
to stabilise without the water flowing over the gate.
Procedure
With the flow constant, measure and note the values of Q, y
g
and y
0
. Raise the gate in
increments, measuring and noting the values of Q, y
g
and y
0
for each step.
The procedure should be repeated with a varying flow and constant y
0
thus obtaining a
further set of results.
Stop logs can be added at the discharge end of the channel to submerge the discharge side
of the gate. Measurements should include the downstream level in the flume.
