The Venturi Flume 
17 
to the water surface in the throat well. The index of the clamp 
will then give the difference in head as read on the fixed scale. This 
means of determining the readings is very advantageous as the 
tape and plumb bob can be carried about in one’s pocket. 
In order to have a continuous record of the depths of water 
passing through the flume, some type of recording instrument is 
required. The need of an instrument of this kind has been felt for 
some time, but not until recently has one been designed and built. 
This model instrument, built at the hydraulic laboratory at Fort 
Collins, is, in its general form, similar to the usual single stage 
recording instruments, but in addition to recording a single gage 
height, it also records the difference between two gage heights. An 
eight day chart is used where the depth scale is two inches to the 
foot, which permits the readings to be made to hundredths of a foot. 
The installation of such an instrument to record the gage heights 
is a simple and inexpensive operation. The gage wells should be 
large enough to accommodate a ten inch float, and the upper and 
throat gage wells should be placed side by side. The instrument 
should be mounted on a suitable support, in such a position as to 
permit the floats to freely actuate the recorder, and at such a height 
as to be convenient and easy to manipulate. A wooden box, hinged 
at one side and provided with hasp and lock, should be provided 
for field installation to protect the instrument. 
Plate II shows the installation of this type of register in con- 
junction with the V-notch Venturi flume. If it is intended that a 
recording instrument be installed, special arrangement of the posi- 
tion of wells is necessary. The present design of the Venturi flume 
recording instrument requires that the two wells be in close proxim- 
ity and separated by a thin partition wall, common to both wells. 
To successfully install this instrument will further require that some 
means of communicating the heads from the opposite side of the 
flume to the float wells be provided. A pipe of moderate dimension 
• should be placed beneath the floor of the flume and connected to 
each pair of wells. As a practical means of testing the pipe con- 
nections, or tubes, it is suggested that the wells be filled with water 
by means of a bucket and the rate of drop in the water surface 
observed. 
It is of considerable practical importance to know what con- 
ditions will obtain after the Venturi flume has been installed in 
the canal. The loss of head or difference in the elevation of the 
