GATE STRUCTURES FOR IRRIGATION CANALS. 59 
but no influence from the waste would be felt by the water at the 
other side of the canal. 
Concerning the operation of these gates the chief engineer of the 
company states that the ducts do not clog so long as they are operated 
continuously, but if completely closed for a period, the openings may 
become clogged with sand and trash and must be cleaned out with a 
trash hook (shown on top of the check gate in the photograph) be- 
fore they will start carrying off the sand. He adds that the gates do 
not remove all of the sand from the canal, but do materially assist in 
keeping the canal clear. 
The complete structure, comprising both the sand and the check 
gates, contain 135 cubic yards of plain concrete and 95 cubic yards 
of reinforced concrete. The total cost was $5,388.60, divided as 
follows, the detail items not being obtainable : 
Excavation, concrete work, back filling $4,160.08 
Structural steel for radial gates 953. 52 
Hoisting device for radial gates 275.00 
Total cost 5, 388. 60 
WASTE GATES. 
USES OF WASTE GATES. 
The waste gate is used on canal systems for two distinct purposes : 
First, it may be simply a safety valve, carrying off excess water which 
enters the canal during storms or which is turned back into the canal 
unexpectedly by consumers. Second, it may be located near the head 
of the canal with a view of running excess water from the river, 
relieving the pressure on the headgate in times of flood, and reducing 
maintenance charges by using the large volume of water to develop 
a high velocity in the upper reaches of the canal, scouring out sedi- 
ment. It then becomes a combination of waste and sand gate. In 
fact, it is very often a hard matter to differentiate between a waste 
gate and a sand gate. A refinement of the second use is found on 
systems'which are running water to the full capacity of the canal and 
the rough adjustments at the river gate would allow such fluctua- 
tion in the volume in the canal that the banks would be endangered 
part of the time and the canal not run to capacity at other times. 
The check below the waste gate on such a system acts as a secondary 
headgate and the discharge through the check is adjusted to supply 
the canal to capacity, while excess water is wasted out the gate in the 
bank adjoining the secondary headgate, the upper headgate being set 
to discharge more water than would be done if the secondary gate 
did not exist. The main canal of the Turlock irrigation district 
(PL II, fig. 2, p. 8), and the joint heading spoken of on page 14 are 
equipped in such a manner. 
