DRAINAGE 



203 



of the ditch uniform in grade, or fall, toward the outlet is 

 the only difficult part of constructing a tile drain. Where 

 water gently oozes out into the ditch from the surround- 

 ing soil and runs toward the outlet, it can be used by 

 the experienced man as a guide in grading the bottom of 

 the ditch. The eye soon learns to judge by the rippling 

 of the water in the bottom of the ditch whether or not 

 the grade is uniform. If the stream lies smooth and 

 sluggish in one place 

 and flows rapidly in 

 another, the tile hoe 

 is used to make the 

 ditch deeper at the 

 upper portions of the 

 rapids, and thus the 

 grade is made so even 

 that the water runs 

 with a uniform speed 

 throughout the entire 

 length of that part of 

 the drain which is 

 being constructed on 

 a given grade. Where 

 the grade changes, as 

 in changing the grade 

 below a given station 

 to another grade 

 above, the eye must 

 be trained to adjust 

 the new grade to the 

 flow of water. If the 

 depth of the ditch at 

 the separate stations 

 has been placed on stakes, by measuring down when the 

 new station is reached the grade can be corrected, as 

 each stake is approached, so as to keep it at that depth 



Fig. 93. Method of spading out successive courses in 

 opening a ditch for tiles. 



