114 



IRRIGATION. 



cut a drain (see fig. 48) from each of them, leading to a 

 common channel, and deep enough to reach the subterra 

 nean sources from whence the overflow comes. The main 

 channel is made to discharge at a point 

 required either into a cistern or into an 

 irrigating ditch. The method of mak 

 ing the drains need not be costly. If 

 stone is at hand, and flat long pieces 

 can be easily procured, the drains may 

 be made by placing long narrow stones 

 against the sides of the ditch, at the bot 

 tom, and covering them with shorter 

 pieces placed crosswise. Small fragments 

 maybe thrown upon these and earth up 

 on them. This is shown at fig. 49. If 

 round stones only can be procured, the 

 drain may be made as shown in figs. 50 and 51. The 

 depth of the drain, should not be more than is neces 

 sary to reach the main stream, as for every foot deeper 

 than that, so much head at the outlet is lost, and so much 

 less land can be watered. In digging the drains, for the 



Fig. 49. 



FIAT STONE DRAIN 



Fig. 50. BOUND STONE DRAINS. Fig. 51. 



same reason, no greater fall should be given than is need 

 ed. Six inches in 100 feet is ample fall to keep the drains 

 clear from sediment, and more would probably result in 

 washing out portions of the drains at the sides or bot 

 toms. A very useful level for laying out the drains may 



