Apr. 33,1917 
The Venturi Flume 
117 
the device. Since the velocity increases throughout the converging sec¬ 
tion, all material carried into the flume also will be carried out, and this 
self-cleaning feature is of considerable practical importance. When the 
depth of water is low, floating trash might lodge in the throat of the 
V-notch Venturi flume, which is of small cross section, but it would cause 
an accumulation of water in the upstream channel until the wetted cross 
section at the throat would be sufficient to allow the obstruction to pass. 
It must be borne in mind that a Venturi flume of whatever form must 
not be placed below canal grade, for this would give a standing-water 
condition which would alter the calibration of the device, and it would 
also allow sand and silt to accumulate within the structure at low veloc¬ 
ities. It is important also that the width of the channel of approach be 
not greatly in excess of the greatest width of the flume, as this permits a 
silt bank to be deposited at either side wing of the. flume. 
A desirable phase of this device is the practical connection which it 
may make with the ditch banks. At the ends of the structure, wings 
may be placed at an angle of 90° to the axis of the structure to make 
the connection with the ditch banks, or the ends of the structure may be 
joined directly to the ditch lining. 
Another practical feature in connection with the Venturi flume is the 
small loss of head required for purposes of measuring the flow. Table I 
shows for the V-notch flume the lost head for the different discharges 
obtained with different depths of water. The head at the upstream gage 
is called H a , the head at the throat gage is called H bt and the difference 
between these heads (H a — H b ) is called H*. Under usual conditions of 
operation the lost head will be negligible. 
Table I. —Loss in head (in feet) in V-notch Venturi flume for different heads at the two gages 
Hm 
Hd^OrCS 
i/d—o.io 
Hd=* 0.15 
Hd** 0.20 
Hd^o.as 
//<I“0.30 
Q in 
sec¬ 
ond- 
feet. 
Loss 
in 
head 
in 
feet. 
Q in 
sec¬ 
ond- 
feet. 
Loss 
in 
head 
in 
feet. 
Q in 
sec¬ 
ond- 
feet. 
Loss 
in 
head 
in 
feet. 
Q in 
sec¬ 
ond- 
feet. 
Loss 
in 
head 
in 
feet. 
Qin 
sec¬ 
ond- 
feet. 
Loss 
in 
head 
in 
feet. 
Q in 
sec- 
ond- 
feet. 
Loss 
in 
head 
in 
feet 
0.4. 
0.10 
o- 06 
0.11 
0.08 
.6. 
. 26 
.05 
• 3 ° 
.07 
.8. 
•49 
.04 
. 60 
.06 
0.62 
0.15 
i.o... 
.81 
•03 
1.00 
.06 
1.09 
• 23 
1.12 
0.24 
1.2. 
X. 20 
•03 
1*52 
.06 
1.63 
. 11 
1. 76 
• J 7 
1. 79 
0.29 
1*4. 
I. ?! 
•03 
2.17 
•05 
2.42 
. 10 
2. 56 
.14 
2.63 
• 21 
2.67 
0.31 
1.6. 
2-33 
•03 
2. 96 
•os 
3-31 
.09 
3-52 
. 12 
3 - 6 $ 
• 27 
3-74 
.33 
RECTANGULAR VENTURI FLUME 
The original idea was to invent a device which would replace the ordi¬ 
nary rating flume, such as is used in irrigation canals. It was thought 
that the flume might be converted into a self-contained measuring device 
by placing a restricted section in the flume, which would cause a loss of 
