GATE STRUCTURES FOR IRRIGATION CANALS. 15 
wide by 9J 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 2J 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 heaclworks 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 
341. 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 0.71 foot in a distance of 35 feet. 
The upper sand sluiceway designed to catch sand, 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 carsh 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 : 2| : 5 mixture. 
