GATE STRUCTURES FOR IRRIGATION CANALS. 15 



wide by 9^ feet high, set in suitable piers at the head of the joint 

 canal, which shapes up after a transition section about 20 feet long 

 into a concrete-lined channel 10.33 feet in total depth, 13.5 feet wide 

 on the bottom, with side slopes of -J horizontal to 1 vertical. The 

 designed ultimate capacity of the canal will not be reached until 

 some time in the future when the lower bank is raised and lined 

 about 2 feet higher. 



It is expected that the larger portion of silt will be prevented from 

 entering the canal by the sluice-way trough in front of the river open- 

 ings. The water will be further cleared of sand by the covered ducts 

 below the gravity dam. The floor across the channel in a line 16-J 

 feet above the lower gate piers slants down 2-J feet in 4 feet, while 

 curved ribs carrying reinforced-concrete slab covers form ducts for 

 carrying the sand out through the waste gate into the canyon. 



The underlying ideas in these headworks are as follows: The ve- 

 locity of the water through the structure is raised from 5 to 9 feet 

 per second, with as little commotion as possible, by lowering the floor 

 and curving the outside wall and lower ends of the piers so as to in- 

 terfere no more than is necessary with parallel filaments of water. 

 The wall is curved on the formula of a cubic parabola. The canal is 

 protected from the entry of flood water by the high gravity section 

 at the dam. The automatic spillway, waste gate, and sand sluice 

 permit the removal of excess water and such sand as passes the upper 

 sluice way. The lower gates accurately determine the quantity of 

 water finally entering the canal. 



In all portions of the headworks : depths, widths, and shapes were 

 adjusted as carefully as practicable to prevent losses of head. Assum- 

 ing the water level in the river to be the crest of the dam at eleva- 

 tion 350 feet, 1,500 second-feet of water enters at a velocity of 5 feet 

 per second, the bottom of the head-wall openings being at elevation 

 311. Five feet above the lower gates this elevation has lowered 1.42 

 feet at the river side and one-half foot less on the bank side. The 

 floor now falls rapidly to a uniform elevation of 338.59 feet. The 

 velocity has increased to 9 feet per second. The floor from the upper 

 gates falls 0.T1 foot in a distance of 35 feet. 



The upper sand sluiceway designed to catch sancl, bowlders, etc., 

 is at present regulated by stop logs, but it is the plan eventually to 

 install an ordinary vertical sluice gate. 



The contract price for concrete work in this heading runs from $14 

 to $15 per cubic yard on the basis of payment in bonds worth 80 

 cents, or less than $12 per cubic yard on a cash basis. The total cost 

 will be about $40,000 in bonds. The structure was completed in No- 

 vember, 1912. The floors are made of a 1:3:6 mixture of cement, 

 sand, and gravel, while most of the balance of the structure is made 

 a 1 : 2A : 5 mixture. 



