478 



Irrigation and Drainage 



Referring to 157, which is a profile of the data in 

 the table, A is the outlet of the drain ; the first stake 

 set is marked 0, the second 50, etc., up to 600, the 

 numbers expressing the number of feet from the out- 

 let. The datum plane is chosen 10 feet below the 



50 100 150 * p 



300 350 *00 450 500 550 600 







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Fig. 157. Determining grade line and depth of ditch. 



surface of the ground, at station 0, and the ground 

 here is 3 feet above the bottom of the drain, which 

 leaves the outlet 7 feet above datum, as stated in the 

 table, which is also the elevation of the grade line at 

 this place. 



Referring to the table, in the column of elevations 

 it will be seen that the surface of the ground at 600 

 feet from the outlet is 11.36 feet above datum plane, 

 while the outlet is 7 feet above, making a total fall of 



11.36 7 = 4.36 feet. 

 Jf it is decided to give the drain a fall of .24 foot, 



