8 
Colorado Experiment Station 
for counter- 
4- concrete wa/Zj 
‘re. 
- ^^ 
r 
Section ^Pi 
Figure 3. Details of Box for Dethridge Meter. 
The speed of the wheel varies with the flow of water in the 
ditch. If the wheel should fit the structure sO' as to leave practically 
no clearance, except to allow a free motion of the wheel, each revo¬ 
lution would deliver exactly the same volume of water regardless 
O'f the speed ol the wheel or depth of the water in the ditch. The 
clearance of one-fourth of an inch allows some water to slip by, 
and this slippage changes with the depth of water in the ditch, and 
the difference in the depth on the upstream and downstream sides 
of the wheel. The actual volume which passes the wheel is there¬ 
fore greater than the volume required to fill the space between the 
vanes and the drum, and the curves shown in the accompanying 
