CHAPTER XI 

 LAYING OUT THE DRAINAGE SYSTEM 



Definitions of Terms. Before beginning a discussion of 

 drainage systems it is well that the meaning of some of the 

 common terms used in connection therewith be explained. 



The discharge end of the tile line or main is called the 

 outlet, and the upper or upstream end is called the head. 

 The term lateral is used for the single tile line with no 

 branches. The main is the line of large tile that carries the 

 discharge from a number of laterals. If the discharges from 

 several laterals are received into a larger tile line before it 

 reaches the main, the line which receives the discharge from 

 the laterals is spoken of as the submain. It is customary to 

 designate the laterals and submains by number and the 

 mains by letter. 



Direction of Drains. As a rule, all drains should parallel 

 the slope of the surface. The surface of the ground water 

 is usually parallel to the surface of the ground and flows 

 down the slope. If tile be laid across the direction of the 

 slope, it will not receive any water from the ground below 

 the line, and in fact some water from above may flow past 

 the tile line. Rarely the lines may be laid across the slope 

 to intercept a seepage flow or to drain pockets in sub-surface 

 strata. 



Depth of Tile Drains. Except in very retentive soil 

 through which the water does not percolate rapidly, the tile 

 should be placed at a good depth. It takes little time for 

 the water to pass straight down to a tile, but it takes more 

 time for it to flow horizontally through the soil. By 



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