164 ENGINEERING FOR LAND DRAINAGE. 



use of the different standards for the quantity of water 

 that it is desired to remove. For example, if the tract 

 through which the ditch passes is rolHng, so that the 

 lateral drainage is brought to the main ditch more 

 rapidly than is indicated by the fall of the main, there 

 is a greater run-off in a given time, and hence the 

 higher rate of discharge must be used in computing the 

 number of acres that a ditch will serve. A more elab- 

 orate hydraulic formula more correct theoretically 

 would require a greater refinement of data than can 

 usually be obtained for such work within reasonable 

 cost limits 



(i) 



i/51.81 



^ X 3 = 2.81, 

 19.56 ^ ' 



145.6 

 Q = 145A A = — -- = 6931. 



.021 



(2) 





V = 



^ V^^^ X 2.25 



21.70 ^ 



2.56, 





Q = 



= 162.4, 



A 



162.4 

 .021 



= 7733- 





V 



(3) 



= 3-i8, 







^ 25.82 ^ 3 - 





Q = 



= 277.8, 



A 

 (4) 



277.8 

 .021 



= 13223. 



a/ 192 



38.62 ^ '-5 ^73, 



Q = 524, ^ = .6i"t = ^5000. 



