THE NATURAL SYSTEM 



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sible to remove the capillary, or the useful water, by tiling; it is 

 only the free or harmful water that is drained out. Tile may 

 drain somewhat deeper than the depth they are laid. The capil- 

 lary rise of water may cause the water-table to drop below the tile. 

 Drainage during the wet period may cause the water-table to drop 

 lower during the dry period than it would if no water had been 

 removed. The deeper root development encouraged by early 

 drainage compensates for this apparent loss. 



Systems of Tile Drainage. A tile system simply means the 

 arrangement of the lines of tile designed to drain any particular 

 area. Usually tile systems are made up of " mains," "laterals" 



FIG. 55. The gridiron or parallel system of tile drainage. Troublesome outlets are 

 avoided by having several laterals discharge into a single main. A line of tile is located at 

 the edge of the high land to cut off seepage. (Wisconsin Station.) 



and "sub-mains " (Fig. 54). A main carries and discharges the 

 water from an entire system. A lateral is a single branch drain 

 into which no other line of tile discharges. One or several laterals 

 may discharge into a "sub-main" which, in turn, empties into 

 a main. } 



The water of the areas to be drained and the slope of the land 

 necessarily call for different systems of tile drainage, of which 

 four are generally recognized the "natural" system, the "grid- 

 iron" or "parallel" system, the "herringbone" system and a 

 "combination" of two or all three of these systems. 



1. The Natural System. When an irregular area is to be 

 drained, the laterals and sub-mains have varying directions, and 

 they must necessarily join the main in an irregular manner (Fig. 

 54). This is called the "natural" system. 



