212 NATURE AND PEOPERTIES OF SOILS 



111. Tile drains are the only reliable means of under- 

 drainage under all conditions. While stone drains ^ are 

 of value in certain cases, they must always be short and 

 are likely to clog. Besides, their drainage is slow and in- 

 efficient. On silty soil they do not long remain in service. 

 The operation of the tile drain is simple. The tile, generally 

 about twelve inches long with a diameter varying with the 

 water to be carried, are laid end to end in strings, on the 

 bottom of a trench of sufficient slope, a carefully protected 

 outlet being provided. The tile are then covered with earth, 

 straw or surface soil often being placed directly around the 

 tile to facilitate the entrance of the water. The superfluous 

 water enters the tile through the joints, mostly from the 

 sides. As a consequence, the tops of the joints may be cov- 

 ered with paper, cloth or even cemented in order to prevent 

 the entrance of silt or quick-sand. The function of a tile 

 drain system is twofold: (1) to collect the superfluous water 

 and (2) to discharge it quickly from the land. 



Where the land possesses considerable natural drainage, the 

 tile are laid along the depressions. This is spoken of as the 

 natural system of drainage in that the tile facilitate the quick 

 removal of the water from the places of natural accumulation. 

 Where the land is level or gently rolling, it often needs uni- 

 form drainage. A regular system must then be installed. 

 This may be either of the fisMone or gridiron style, or a 

 modification or combination of the two, natural drainage being 

 taken advantage of where possible. Where springs or seep- 

 age spots occur, cut-off systems must be devised. (See Figs. 

 38 and 39.) 



^ Stone drains are built by arranging stone in a properly located and 

 graded trench in such a manner as to provide a continuous channel 

 or throat from the upper end of the dram to the lower. One of the 

 safest modes of construction from the standpoint of clogging is to place 

 flat stone on edge m the trench with their faces parallel to the walls 

 of the ditch. The spaces between the stone provide for the movement 

 of the drainage water. 



