TYPES OF DRAINS 



173 



as require a main drain to carry off large quantities of 

 water. Several closed drains may open into a main open 

 ditch. 



Many types of closed drains are in operation. The 

 main requirement is to preserve through the subsoil an 

 open channel that will carry off percolating waters. A 



FIG. 23. MACHINE FOR MAKING DRAINS IN HEAVY SOIL WITHOUT 

 THE USE OF TILE. 



ditch is dug and some material that will maintain the 

 channel open placed in it. Rocks, brush, straw, timber, 

 and tile are all used. 



In certain heavy gumbo soils a special device known as 

 a gopher machine, shown in Fig. 23, makes a hole through 

 the soil that does not require filling. In this device a tor- 

 pedo about 8 inches in diameter is attached to a subsoiling 

 point, which is held in the ground by a heavy wheeled 

 frame. The depth at which the torpedo is pulled through 



