222 IRRIGATION. 



kind is shown at fig. 103. A dam made of piles and rock 

 is shown at fig. 104. 



This form of dam is suitable for river beds in which 

 piles can be easily driven, such as those consisting of 

 quicksand, mud or soft earth, upon which a structure not 

 founded upon piles would be neither substantial nor per- 

 manent. It is made by driving, across the river, three 

 rows of piles, of graduated lengths, as shown in the en- 

 graving. These are connected by stringers, solidly bolted 

 to them, and the framework is stiffened, where necessary, 

 by girts and braces. Cap pieces of flattened timber are 

 bolted on to the top, and the whole frame is filled in with 

 rock, and then planked over. The face may be filled in 

 with fine brush, and earth, to a proper slope. Dams of 

 this kind may be made of great lengths, where the fall 

 is not more than 10 or 12 feet, and resist the most severe 

 freshets. 



In taking the water from the stream, it is necessary to 

 consult the laws which control the motions of liquids, 

 else counter-currents or eddies may be established, which 

 will wear away, or undermine the dam, or sluice. The 

 dam should slope away at an angle toward the sluice, so 

 that the current of the stream may be easily diverted in- 

 to the canal without reflux, or regurgitation. To further 

 this end the dam may be placed diagonally across the 

 stream, or partly so, and the floor of the dam should be 

 carried so far up the stream as to cover the entrance to 

 the canal, and a few feet into it, so that the bed may be 

 protected from washing by the current. 



PUMPS. The use of steam pumps in irrigation, will 

 probably be found profitable within a few years, when 

 the valley lands that are easily and cheaply irrigated, are 

 supplied with water. The surplus then running to waste 

 will eventually be raised to the higher lands, by whatever 

 power may be cheapest. In many localities there are 

 no valley lands, but the banks of the streams are abrupt, 



