96 IRRIGATION FARMING. 



mate is made on the basis of coal costing $5 a ton, and 

 an average engine of 50-horse power. If the water is 

 pumped during the whole year the cost will be re- 

 duced to two-thirds of this amount. With a depres- 

 sion having natural sides in place, and where not more 

 than one- fourth of the circumference would have to be 

 construdled, the cost would be proportionately less. 



Damming a Stream. — The chief cause of failure 

 in dams of all kinds is the faulty constru(5lion of the 

 foundation. Dams .should be made of timber or stone. 

 For a safe and simple form of timber dam the founda- 

 tion should be rock or a hard-pan of gravel, and the 

 mudsills on the lower tier should be bedded in broken 

 rock, pounded down firmly with a fifteen-pound sledge. 

 The sills are saddled, and the cross- ties laid upon them 

 are notched to rest upon the saddles, and two-inch pins 

 should be put through both of the logs. Where the 

 foundation is shelving rock, one-and-a-half inch iron 

 pins should be put down into the rock at least a foot, 

 to prevent sliding. But the sliding force is almost 

 neutralized in this form of dam by the weight of water 

 which lies upon the sheeting. 



The tiers of timber are built up, saddled, and 

 notched. A plank sheeting is put down to the solid 

 foundation above the first sill, and the end is spiked 

 with eightpenny spikes firmly. The sheeting is filled 

 to the foundation as close as possible, and hydraulic 

 cement concrete is bedded in front of it to make a tight 

 joint. No leaks will ever trouble a dam founded in 

 this way. The rafters should be strong enough to 

 bear any weight of water which the stream may carry 

 doubled. If the highest flood known is five or ten 



