GATE STRUCTURES FOR IRRIGATION" CANALS. 39 
fied. The top of the gate guide rests against the top of a side post 
and* the brace is carried from the angle between the floor and the bot- 
tom of the post up to the gate guide and at right angles to the latter. 
The sheeting of the wings and cut-offs usually is set vertical and 
spiked or bolted through a waling strip. On small gates this sheet- 
ing is made of a single thickness. On large ones it is made triple 
thickness, each set of three boards being spiked together. The middle 
board is offset so as to form a tongue-and-groove joint. This " Wake- 
field " piling^ as it is called, may then be driven with a maul or light 
pile hammer. The lower end of each piling is slightly sharpened at 
the exposed edge. This causes it to crowd closely to the preceding 
pile and make a tight joint. 
The depth to which it was necessary to carry the cut-offs depends 
a great deal on the height to which the water is to be held up by the 
structure. If the water above and below the gate will be on approxi- 
mately the same level, say within 1 or 2 feet, then it is not necessary 
to go more than one-half the depth below grade that the side walls 
extend above grade, but if more than that amount of pressure is de- 
veloped the wings and cut-offs should extend as far below grade as the 
side walls do above. 
High side walls that are separated too far to carry caps as struts 
are braced diagonally from the floor at about the line of the first 
division wall. High "A" frames have several diagonal braces, with 
horizontal sashes to prevent buckling. 
The "A" frame catches trash easily and the water pounds vio- 
lently if under much pressure, but both these defects may be much 
remedied by sheeting all the "A" frames on both sides with light 
boards. If used as a simple lateral headgate or check the upper and 
lower wings and cut-offs are identical, but if there is a drop in the 
grade line at the structure the lower posts are carried to the bottom 
of the water cushion and sheeted horizontally on the earth side as 
shown in figure 9. 
DELIVERY GATES. 
The same general discussion applies to delivery gates as to lateral 
gates. In addition it is generally necessary to have some form of 
locking device. Many companies place a device such as this on all 
gates, but do not use it unless it is found that the consumer under the 
delivery gate is abusing the confidence placed in him. In deciding 
upon a locking device for a delivery gate the designer must know 
the system of delivery of water. Some companies allow the con- 
sumer to shut the gate after he has received what water he wishes 
for that particular irrigation. For such a consumer a lock must be 
used which permits the gate to be opened to a certain point, deter- 
mined by the position of the lock, but permits the gate shutter to 
