442 Irrigation and Drainage 



intermediate line of tiles is placed at D, then the 

 highest levels of the ground water would be found at 

 E and F, farther below the surface, leaving the field 

 better drained. It is very important that this prin- 

 ciple be thoroughly grasped, because so many local 

 conditions affect the depth and distance apart at 

 which drains should be placed that no specific figures 

 can be safely followed in all cases. It is generally 

 true that in loose, loamy soils, and especially if under- 

 laid by sand, good drainage will be secured with 

 drains 100 feet apart and 3% feet deep. On heavier 

 soils, they must be closer, and on more open ones 

 they may be farther apart. 



In regard to depths of drains, it should be under- 

 stood that the deeper they are placed the better work 

 they do as a rule. If one soil has had its non- 

 capillary pores 'emptied to a depth of 4 feet, and 

 another one only to a depth of 2 feet, the capacity 

 of the former to store a heavy rain without over- 

 saturation will evidently be greater than that of the 

 latter, and hence the shallow drained fields will oftenest 

 become over -wet in wet seasons. But the cost of 

 digging 4 feet is much greater than 2% feet, the 

 expense increasing faster than in proportion to the 

 depth. 



In cold climates the tiles must be placed as deep as 

 2 feet, to prevent their destruction by frost. Tiles 

 are laid at a depth of 18 inches, but the practice is 

 not only unsafe so far as destruction of the tiles is 

 concerned, but not half the advantage can then be 

 secured which they are capable of giving if laid deeper. 



