28 BULLETIN 831, U. S. DEPARTMENT OF AGRICULTURE. 
with the flaring outlet. In each unit the inlet is well submerged, with 
its upper end 5.5 feet below the water surface. The inlet is 3.5 feet 
high and 6 feet wide, protected by a vertical screen with f-inch bars 
spaced 4 inches center to center. The over-all efficiency was tested 
using the formula Q = kAV 2 gH and gave a coefficient of discharge 
of 0.65. These siphons are not provided with water seals on their 
outlet ends, but have free discharge. The whole structure, gate in- 
cluded, was placed in a length of 90 feet and the cost was one-third 
that estimated for the overflow type of spillway. 
UNITED STATES RECLAMATION SERVICE SIPHONS. 
The United States Reclamation Service has located a siphon about 
12 miles below the heading of the Yuma Project, where the main 
canal leaves the foot of the mesa and turns southward toward Yuma. 
At this point there is a drop of about 12 feet in water level, bringing 
the canal to the level of the lower valley. It is intended to develop 
power here to be delivered to a point below Yuma and used for 
pumping water from the main canal through a lift of about 80 feet 
to the top of the mesa, for the irrigation of some 30,000 to 40,000 
acres of land. A battery of 5 siphons has been installed. They can 
be adjusted to discharge at different levels and all employed when 
the canal is running full, the combined theoretical discharge being 
1,488 second-feet. They have been tested operating as a battery at 
efficiencies ranging from 68 to 70 per cent and in combinations from 
64 to 80 per cent. The area of the smallest or throat section, which 
was used in the computations, is 11.35 square feet, and at the outlet 
end 21 square feet. In the tests for efficiency the actual drop between 
water surfaces was 11.87 feet, which was certainly all the head avail- 
able for producing velocity, but the partial vacuum registered by 
the mercury gage showed an equivalent of 15.60 feet of water. 
This was noted as indicating that the siphon was acting in a man- 
ner similar to a compound diverging tube under pressure and having 
a discharge coefficient greater than one and which may even have 
been greater than two. It also indicated that the draft tube should 
flare, which was the case in this instance. The observed depth over 
the lip of throat necessary to start siphonic action was 0.35, 0.40, 
0.35, 0.15, 0.35, and 0.40 foot respectively for the siphons as listed 
above and with 5.35 feet of water over the lip of the outlet, and they 
ran uniformly one-tenth foot higher in each case with the outlet sealed 
with 6 feet of water. They are of reinforced concrete and cost about 
$23,000 complete. The regulation of siphonic action is by means of a 
specially designed sliding air valve shown in figure 9. This same 
design is used on the installations at the Salt River project near 
Phoenix, iVriz. The operation of these control valves was satisfac- 
tory, except that there was not enough vertical movement to permit 
