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 1 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 

 (PI. II, fig. 2, p n . 8), and the joint heading spoken of on page 14 are 

 equipped in such a manner. 



