CANAL CONSTRUCTION. 57 



or silt to lodge. The gate is turned open to its full capac- 

 ity and stands nearly at right angles to its position when 

 shut. As soon as the flood has receded and the water in 

 the canal has lowered to its normal stage, the gate low- 

 ers accordingly, when the weight is moved forward a'.id 

 receives its former power and closes the gate. 



The forces acting through the system of levers 

 as arranged, and holding the gate shut when the water 

 in the canal is at normal hight, or not exceeding the 

 hight to which the gate has been adjusted, are reduced 

 in the same proportion as the water pressure against the 

 gate is reduced when opened. Between each set of gates 

 is placed a beam or cap lengthwise of the waste way, 

 supported on posts to which are fastened the boxings 

 in which the main axle revolves. This axle is made 

 from timber six inches square, banded at each end, and 

 also has a steel or iron rod one and one-fourth inches 

 in diameter passing through the center, with ends pro- 

 jecting and resting in the boxing. The levers 3 and 4 

 are bolted to the main axle. Between levers 4 is placed 

 and fastened with bolts a set of X braces to prevent the 

 levers from becoming displaced by wind or other causes, 

 thus making the structure firm and rigid. 



Ditch Outlets. The outlets or culverts through 

 the canal banks to the main lateral should be set before 

 the bank is built and with reference to the supply lat- 

 erals. The size of the outlet will be governed by the 

 amount of water to be delivered to the lateral. The out- 

 lets may be made of plank or vitrified sewer pipe, the 

 latter being especially good but in most cases not so 

 readily obtainable. The earth should be well tamped 

 about the box or pipe in order to make a water-tight 

 joint. 



Regarding gates, these should bo set at the inner 

 end of the outlets, and a plank wall built from the top of 

 the bank leading out over the water to a point over the 



