THE DRAINAGE OF FARM SOILS 223 



Wheeler makes the following estimate of the 

 relative capacity of different sizes of tiles: 



A 2^-in. tile will carry 1 \ times as much water as a 2-in. tile 

 " 3 " " " " 2 " " " " " " " " " 



i - 



An 8 " " " " 25 " " " " " "" " " 



Chamberlain gives these rules for estimating the 

 size of mains: When the fall is not more than 3 

 inches in 100 feet the diameter of the tiles should be 

 squared and the result divided by 4. Thus a 

 3-inch main will drain 2J acres; a 4-inch main, 

 4 acres; a 5-inch main, 6J acres; and so on. When 

 the fall is greater than 3 inches, square the diameter 

 and divide by 3. In this case a 3-inch main will 

 drain 3 acres; a 4-inch main, 5^ acres; a 5-inch 

 main, 8^ acres ; a 6-inch main, 12 acres, etc. These 

 rules have been found to be quite reliable on 

 ordinary soils. 



On heavy soils the different sizes will drain 

 more than the area given, as water moves through 

 them more slowly. Elliott says, "For drains 

 not more than 500 feet long a 2-inch tile will 

 drain 2 acres. Lines more than 500 feet long 

 should not be laid of 2-inch tiles. A 3-inch tile will 

 drain 5 acres and should not be of greater length 

 than 1,000 feet. A 4-inch tile will drain 12 acres; 

 a 5-inch tile, 20; a 6-inch, 40; and a 7-inch tile, 60 

 acres." The capacity of tiles is thus seen to vary 

 widely in the judgment of experts. The size of 

 the main increases as it proceeds toward the 

 outlet and receives the drainage of the larger 

 area. 



