SPILLWAYS FOR RESERVOIRS AND CANALS. 
29 
of a wide range of regulation of the water surface and floating trash 
had a tendency to enter and clog the neck of the valves. Screens 
fixed on their lower ends removed the difficulty. 
On the Sun River project there is a structure on the main canal, 
shown in figures 1 and 2, Plate XIV, and in cross-section in figure 10, 
which combines a storm culvert, sluice gate, and siphon spillway. 
The canal at the point of installation has a maximum capacity of 1,000 
FIG. 9. — Air-control valves to start and stop sipbonic action. Installed on siphon spill- 
ways of U. S. Reclamation Service near rhoe'nix and Yuma, Ariz. 
second-feet, and the siphon is designed to dispose of any water in 
excess of that amount up to 1,500 second-feet, because the combina- 
tion of the three siphons is calculated to discharge 500 second-feet. 
To provide for any possibility of silt deposit at this point, the three 
sluice gates, each 3 by 3 feet, operating under a head of 11 feet, will 
discharge about 500 second-feet and the culvert which conducts the 
flow to a natural drainage channel is designed for capacities of 900 
