GATE STRUCTURES FOR IRRIGATION CANALS. 7 



axle, to which the face is attached by arms centering at the axle. (PL 

 II, fig. 1.) In practice the face of the gates has been made of simple 

 planking nailed or bolted to ribs, or of sheet steel riveted to metal 

 ribs. There have been a few cases where the face was built of rein- 

 forced concrete. In Canada a very simple type of this shutter has a 

 perfectly flat face of planks attached to wooden arms. The practice 

 in this country is for the face to form the segment of a cylinder. The 

 arms of small gates may be made of wood, but the usual practice is 

 to make the arms of angle or channel iron, even where the face is 

 wood. The axles may be either sections of pipe or bars extending 

 completely across the openings, or pins extending through the side 

 walls adjoining the openings. Simple galvanized pipe makes a good 

 axle for economical construction if the conditions at the gate struc- 

 ture are such that there is no danger of debris catching on the axle 

 and bending it or washing it out. The more finished construction, 

 which does not tend to obstruct the channel, consists of a steel pin set 

 in a tube cast in the wall of the structure. 



There are two great advantages in this type of shutter. First, 

 friction is changed from sliding friction in the guideways, as usually 

 used for gate shutters, to axle friction, with a lever arm the length of 

 the gate arms. The second feature in favor of this gate lies in the 

 form of lift. The usual stem-gate lift requires that the point of 

 application be approximately twice the height of the opening above 

 the bottom of the gate in order to lift the shutter clear of the open- 

 ing. In nearly every case there is a waste of material in securing 

 the elevation for the lift. This argument does not apply to most 

 river gates, for the reason that the additional elevation is of benefit 

 and is necessary in some form to give a high bulkhead to prevent 

 flood water in the stream topping and destroying the structure. But 

 there is an advantage in the case of other gates where the height of 

 the levee is the controlling factor, and all the material above that 

 height is so much that does not add any benefits to the structure. 

 Since the cable or other form of lift, can be attached to the very bot- 

 tom of the radial gate, the winch may be set approximately on the 

 level of the gate top when the latter is closed and the cable wound 

 up by the winch, lifting the radial gate until the bottom is approxi- 

 mately level with the drum. As the radial gate requires no guides, 

 it extends up into the air without other support than the axle, and 

 there is no loss of material for lift standards, as is the case for most 

 stem lifts. 



The great factor against the radial gate always has been that the 

 only discharge through it was undershot, but there is no reason why 

 this should be, as the face does not need to be a single unit. It may 

 be made of two or more sections, the upper ones hinging on axles car- 



