TILE DRAINS MUST HAVE FALL 117 



Covered Drains. — The only way to eliminate the objections to 

 many small open ditches is to use covered drains, among which 

 may be mentioned tile drains, cobblestone drains, rock drains and 

 pole drains (Fig. 51). Cobblestone, rock and pole drains are not 

 commonly used, except in certain localities where these materials 

 are available. They are usually of short duration, because 

 they become easily clogged. The universal covered or under- 

 drain is tile, and because of its importance, it shall be given 

 special consideration. 



TILE DEAINAGE 



Drain Tile. — ^Drain tile are pipes usually of circular form from 

 one to two feet long and varying in diameter from three to thirty 

 inches (inside measurements). Most drain tile are made of 

 burnt clay; some are made of cement. When well made, tile are 

 very durable. Clay tile have been in operation on a farm in New 

 York since 1837; and in France some have been in use 200 years 

 and more. 



How Tile Are Laid. — (Fig. 52). Drain tile are laid end to end 

 in narrow trenches and covered. A drain constructed by placing 

 tile end to end in a trench is called a "line of tile " It is quite 

 necessary that they be laid deep enough to escape tillage tools, 

 to give deep underdrainage, and to escape freezing, if possible. 

 In clay the usual depth is three feet, in sandy soils four and one- 

 half feet. Occasionally conditions do not permit their being laid 

 more than about two or two and one-half feet deep. In peat and 

 muck soils tile should be laid especially deep (four and one-half 

 feet and more), because these soils settle rapidly after they are 

 tile drained. On some marshes the settling of the peat brought 

 the tile so near the surface that they had to be taken up and 

 laid deeper. 



The size of the tile to use depends upon the amount of water to 

 be removed. It is a safe rule to follow not to use smaller than five- 

 men Tjiie. 



The digging of a trench for a line of tile is always begun at 

 the outlet, and it is generally necessary to lay the tile as soon as 

 the bottom of the trench is made ready, although it is better to 

 finish the trench and start laying the tile at the upper end, or head. 



Tile Drains Must Have Fall. — Every line of tile should be so 

 laid that water entering it at any point will flow to the outlet. 

 This descent or fall of a line of tile is called the "gradient.'^ It is 



