206 SOILS 



lake; tney lower its surface to the level of the bot- 

 tom of the tile at the points where each line of tile 

 runs. But the level of the water- table rises higher 

 between the lines of tile, as water cannot move as 

 freely through the soil as it does in the open. Thus 

 the surface of the water-table of a tile-drained 

 field is something like a series of crescents, the lines 

 of tiles being at the lowest points. 



The height to which the water-table rises be- 

 tween the lines of the tiles depends upon the 

 distance apart of the drains and the character 

 of the soil. The farther apart they are, the 

 higher the water rises between them. The more 

 sandy or porous the soil, the more nearly does 

 the water-table come to the level of the drains 

 over all the field. Thus, if under-drains are placed 

 four feet deep in a sandy soil, and a similar distance 

 in a clayey soil, the water-table of the former 

 might be lowered to an average level for the 

 field of three and one-half feet and the latter to 

 two and one-half feet. 



It must be clearly understood that under-drains 

 carry off only free water, never film water. Fur- 

 thermore, they remove no water from a soil unless 

 the water-table is above them. Water does not 

 run into them, it is squeezed in. For instance, if 

 a line of tile drains is placed four feet deep in a soil 

 in which the water- table is four feet six inches be- 

 low the surface in summer, none of this water 

 will get into the tiles until the water-table has 

 been raised to four feet, or over, as it might be 

 earlv in spring after heavy rains. 



Water enters tile drains through the joints and 

 also through the walls of the tiles. It is not 

 ^necessary, as many suppose, to leave a crevice be- 

 tween the tiles for the entrance of water. No 



