118 



LAND DRAINAGE AND IRRIGATION 



desirable to have a gradual fall of three inches in 100 feet if pos- 

 sible. On flat areas, one and one-quarter inches, which is considered 

 the minimum grade, is frequently used. It is important to remem- 

 ber that the less the fall or gradient, the bigger should be the tile. 

 When a good fall is apparent, it is comparatively easy to lay 

 tile so that they will carry off the water properly. On level ground 

 however, much care should be exercised in securing sufficient fall. 



Fia. 52. Samples of drain tile and the necessary tools used in constructing systems of 

 tile drainage. (Wisconsin Station.) 



The level is the common instrument used in determining the 

 amount of fall. 



Some experienced tilers determine the grade by the flow of 

 the water in the trench before the tile are laid. 



Tile may be properly laid on a level area through the use of 

 grade lath (Fig. 53). For example, a line of tile 600 feet long 

 is to be laid, and it can be given a depth of four and one-half feet 

 at the outlet. To give this line a fall of two inches in 100 feet 

 the tile must be laid three and one-half feet deep at the upper end 

 of the line. Two stakes (a, 6) are driven about three and one-half 



