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 Eiver 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 siphonic action. Installed on siphon spill- 

 ways of U. S. Reclamation Service near rhoenix 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 



