24 
Colorado Experiment Station 
should not extend beyond the inside surface of the sides of the 
structure. The floor of the flume should be level in both directions 
and placed so that the floor line will be on the grade of the channel. 
The size of the gage wells is not important ; however they should be 
of sufficient size for cleaning purposes. If made of 2-by 12-inch 
plank and built as shown in the plan, the opening will be approxi- 
mately 8 by 10 inches. The depth should be sufficient to reach at 
least one-half foot below the floor of the flume and a bottom should 
be provided for both wells. When set in position, they should be 
vertical and close to the structure, with the tops of the wells at the 
same elevation. Covers for the wells may be provided if found 
necessary. 
ACKNOWLEDGMENT 
The authors wish to acknowledge the assistance and coopera- 
tion of the Jackson Ditch Company of La Porte, Colorado, in per- 
mitting the use of their diversion dam and head works in connec- 
tion with the experiments conducted at the Bellvue laboratory. 
SUMMARY 
The Venturi flume is intended to meet those conditions for 
which the standard weir or other measuring devices are not suited, 
the most important application being where sufficient head is not 
available for other types of measuring devices. 
The accuracy of the Venturi flume is sufficient to meet ordi- 
nary requirements and by actual computation it has been shown 
that, for all sizes of rectangular flumes investigated with discharges 
ranging from less than 1 second foot to nearly 400 second feet, 94 
per cent of all tests show an error in discharge of 5 per cent or less. 
A similar comparison for the V-notch flume shows that for 
discharges ranging from 0.1 to 10 second feet, 70 per cent of all the 
tests show an error of 2 per cent or less. 
In order to obtain the best results from the rectangular Ven- 
turi flume, it is recommended that four gage wells be installed, and 
that the mean reading be used in determining* the discharge. 
Where the installation of a flume is made with the intention of 
using a recording instrument, a special arrangement of float wells 
is necessary, and also' provision must be made for connecting these 
two wells with those on the opposite side of the flume. 
Frequent testing of the sensitiveness of the gage wells is advis- 
able. Cleaning of the wells of silt or sand should be done when 
