82 



SOILS AND FERTILIZERS 



103. Arrangement of drains. — In laying out a system 

 of drains certain rules must be regarded. A main drain 

 usually follows a depression in the land, rising with the 



natural grade, or 

 if that does not 

 give a sufficient 

 rise, becoming 

 shallower as it 

 ascends. Some- 

 times this will be 

 sufficient to re- 

 move the surplus 

 water, but more 

 often lateral 

 drains will be nec- 

 essary. These are 

 of smaller tile and 

 are usually paral- 

 lel to each other 

 and from twenty 

 to a hundred feet 

 apart. This ar- 

 rangement is 

 called the herring 

 bone system. 

 (See Fig. 15.) 

 There may also be 

 submains branch- 

 ing off of the main 

 drain, and laterals 

 running into the submains. This is known as the gridiron 

 system. (See Fig. 15.) Sometimes the laterals are run 

 across the slope, but usually it is better to run them down. 

 A lateral should not enter a main drain at a right angle, 



Fig. 15. — The upper drawing illustrates the her- 

 ring bone system of laying tile drains. The lower 

 represents the gridiron system. 



