40 



DESIGN 



The determining conditions are, the kind of soil, slope of 

 the land and elevation of the water-table. The thorough- 

 ness of drainage is another feature. Waring's rule is 

 frequently used in the design. 



The mains are of porous tile up to 4 inches in diameter 

 and above that of vitrified sewer pipe. If the line dis- 

 charges into an open channel, the detail at the outlet is 



Vitrified Sewer 

 Method of Providing Underdrainagef&r Damp or Swampy 

 Soil. Surface Water should be Removed bu Inlets and 

 Catch Basins along Upper Sides of Paths and Drioea. 



FIG. 12. 



very important. To prevent injury and dislocation to the 

 line, the use of a 12-foot length of cast-iron pipe is recom- 

 mended. This pipe does not have to be perfect. A piece 

 of " seconds " can be used to good advantage. 



Tile drains become clogged in a few years, especially 

 when in the neighborhood of willows and other trees which 

 absorb much water. But the drainage process still con- 

 tinues in some measure, due to increased porosity of the 



