CHAPTER XL 

 OPEN DRAINS. 



Successful tile drainage necessitates the construc- 

 tion of open ditches, unless the mains are so situated as 

 to discharge into natural streams. When the area is too 

 great to be drained by a tile main whose cost will be 

 within profitable limits, then an open ditch should be 

 used. It is sometimes difficult to determine when an 

 open ditch should take the place of tile drain. Usually 

 where the cost of the two is about equal the tile should 

 be used provided the outlet for the tract will be just as 

 efficient. However, this is a question that must be de- 

 cided in the light of such facts and considerations as 

 pertain to each individual case, and in accordance with 

 sound theory and safe practice. 



It is proposed to discuss this matter in such a practi- 

 cal way that what is said may be of use to the young 

 engineer in laying out and constructing large open 

 ditches for drainage purposes, not in a guess-work sort 

 of a way, but according to the best knowledge and prac- 

 tice now existing. 



Grade for Open Ditches. 



The total fall across a tract has been fixed by nature, 

 but it is the work of the engineer to determine whether 

 or not nature has provided enough for his purpose, and 

 to adapt the size, form, and cross-section of the ditch 



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