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 



^^ ^^ ^ ^ ^ procure( ^ 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 



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 



