42 THE HANDBOOK FOR PRACTICAL FARMERS 



than with the diameter directly. An eight-inch tile will carry 

 as much water as two six-inch tile on the same grade. 



Ordinarily, for large areas the outlet drain is of such size as 

 to discharge from the entire area of land tributary to the system 

 anj^vhere from one-quarter to as much as three-quarters of an 

 inch of water in twenty-four hours, depending on rainfall, sur- 

 face sloi^e and the occurrence of springs. The following table 

 will give some idea of the area of land that may be drained by 

 different sizes of tile laid on different grades: 



Number of Acres from Which One fourth Ixch of Water will be Eemoved in 

 Twenty-four IIoxjrs by Outlet Tile Drains of Different Diameters and 

 Different Lengths with Different Grades 



For small field laterals on grades of one foot or more per 

 hundred within the limits of length of one thousand feet, three- 

 inch tile may be used. The general inclination is away from the 

 smaller sizes, especially those below three inch. For more flat 

 grades and especially in fine sandy, silty and muck soils four 

 and five-inch tile should be the minimum size. 



For the submains and mains the tile should be correspond- 

 ingly larger according to the area of land served. For these 

 larger systems an experienced engineer is necessary to decide 

 on these important details. 



The outlet. — The outlet should be the first thing located on 

 a drainage system and the last part safeguarded. The outlet 

 tile drain should be properly buttressed to prevent washing 

 and caving, and the end protected by a grating or gate against 

 the entrance of small animals. 



