io 
Colorado Experiment Station 
Table 3 shows some interesting points. The discharge for each square 
inch of opening increases as the size of the opening is increased. For a 
constant depth of orifice the discharge per square inch of opening is the 
greatest for a width of 1 inch, decreases as the width is increased for a 
few inches, or approximately until the orifice is square for the larger 
sizes of orifices, and then increases as the width is increased. The num¬ 
ber of Statute Inches to one second-foot varies from 42.9 to 35.5, but 
for the sizes of orifices commonly used, for measuring water to the indi¬ 
vidual irrigator, it is probable the value would be from 3 6 to 37, and as 
low as 35 might be obtained for wider orifices. The discharges given in 
table 3 are probably the least quantities that can be obtained for orifices 
of that type, because they were thin-edged, the velocity of approach was 
negligible, and the contractions were complete. 
The discharge through full contraction, thin-edged, free-flow orifices 
having a depth or vertical dimension of 6 inches and a head of 5 inches 
above the top of the orifice, is represented by the formula, 
0.06 
Q = 0.16.9b—0.06 +- 
1 + 0.015 b 26 
in which Q is in second-feet, and b is the breadth or horizontal dimension 
of the orifice in inches. 
Uncompahgre Orifice.—The type of orifice shown in figures 1 and 2 
has been used for years on some of the canal systems now included in 
the Uncompahgre project of the U. S. Reclamation Service, and they con¬ 
form to the Colorado Inch law in all respects as long as a 5-inch depth 
of water is maintained over the top of the orifice. The side of the box 
in which the orfice is placed is made 5 inches higher than the top of the 
orifice for a length of 5 feet, which acts as a spillway to regulate the 
head, but it is occasionally necessary to run a greater or less amount of 
water for short periods. When necessary to deliver 90 or 75 per cent of 
the full head temporarily the depth of water in the box will decrease as 
the depth decreases in the ditch, which saves changing the size of all of 
the orifices and they act somewhat as proportional dividers of the flow 
because all of the boxes on a ditch are set under almost identical condi¬ 
tions. When the supply of water in the ditch is greater than normal, the 
boxes act as spill-boxes. Mr. F. D. Pyle, manager of the Uncompahgre 
Project, has added a heavy galvanized iron orifice plate to the original 
device. The orifice is 6 inches deep and is provided with a slide which 
moves horizontally. Holes punched through the orifice plate and slide 
allow the slide to be set for each 0.05 second-foot up to 2 second feet 
and a padlock placed through the hole prevents the size of the orifice 
being tampered with after it is set by the ditch rider. Graduations on 
the side of the orifice indicate its discharge when operating as a weir. 
The discharges through the Uncompahgre orifice under various con¬ 
ditions are given in table 4. Although the original water-rights are ex¬ 
pressed in inches, the water is delivered in second-feet. By comparing 
tables 3 and 4 it will be seen that the discharge is greater through the 
