298 ENGINEERING ON THE FARM 



will crack the tile and possibly destroy it because of the 

 expansion of the ice. Soft or porous tile which absorbs a 

 large percentage of water may be destroyed by freezing and 

 thawing a number of times, but hard tile is not destroyed 

 in this manner. Continuous dripping of water in cold tile 

 may fill it with ice without bursting it, or where the earth 

 is well packed around the tile it may crack from freezing and 

 not collapse. It cannot be assumed that because a tile drain 

 is in good working condition it has not been affected by freez- 

 ing. Tile drains in cold climates, with good outlets and laid 

 to grade, will not be injured when laid above the frost line. 

 Roots of trees. Roots of trees and plants are sometimes 

 the cause of annoyance in tile drains, and there are many con- 

 flicting opinions in regard to the injury done by them. Where 

 water ceases to flow in the tile as soon as the surrounding 

 land dries out, there is little danger of obstruction, as the 

 dry tile offers no attraction to the roots ; but if the tile carries 

 water far into the dry season, the roots will go into it in 

 search of water. While a wet-land tree, as well as some 

 others, may grow along a tile without forming an obstruc- 

 tion, for the reason that there is plenty of water in the 

 soil at the time the tile is running, wet-land trees, espe- 

 cially willows, should be regarded with suspicion when near 

 a tile drain. If it is not desirable to destroy the trees, the 

 joints of the tile should be carefully cemented past the point 

 where small roots can be found in the ground. 



OTHER METHODS OF DRAINAGE 



Levees. Lands along a stream which are lower than the 

 ordinary high-water plane of the stream can be made pro- 

 ductive only by being protected from overflow. Where the 

 overflow is due to an insufficient or an obstructed channel, 

 relief may be had by means of a new channel of a size that 

 will carry the water below the ground surface. Where it 

 is practicable to construct such a channel, it is the only 

 method that should be used. If a great area of overflowed 



