318 Ground Water, Wells and Farm Drainage. 



steps are the same as those already described for the field 

 leveling, the results being recorded in a table calling for 

 two more columns when worked out than were needed in 

 the field work. These are indicated in the table below : 



Table showing Field Notes for determining depth of ditch and 

 grade of drain. 



In Fig. 137, which is a profile of the data in the table 

 showing the outlet of the drain at A, the first stake at O 

 and the second at 50, etc., up to 600, both the lines of 

 grade and the datum plane are shown. On each numbered 

 stake is given the depth of the ditch below the top of the 

 grade peg, and below the peg has been set the hight of the 

 bottom of the ditch above the datum plane. 



Since the outlet in this case is 7 feet above datum and 

 the surface at 600 feet is 11.36 feet the total fall is 

 11.36 feet -7 feet = 4.36. 



But if the depth of the ditch at the upper end is made 

 2.92 feet the available fall will then be 



4.36 feet 2.92 feet= 1.44. 

 Since the ditch is 12 times 50 feet long the fall will be 



--jjjj- = .12 feet per 50 feet. 



or .24 feet per 100 feet At each 50 foot station then the 

 bottom of the ditch above datum plane will be found by 



