DRAINAGE 



81 



This may be computed by dividing the total quantity of 

 water on an acre, for a certain standard or depth, by the 

 number of seconds in 24 hours. For convenience, however, 

 the following table is included. 



Discharge per second per acre for different depths of run-off. 



Common fraction 



1 



15-16. 



7-8... 



13-16. 



3-4... 



11-16. 



5-8.., 



9-16. 



1-2... 



7-16.. 



3-8. . 



5-16. 



1-4... 



3-16. 



1-8.. 



1-16. 



Depth in inches. 

 Decimal 



Cu. ft. per sec. 

 per acre 



.000 



.0420 



.938 



.0394 



.875 



.0367 



.812 



.0341 



.750 



.0315 



.688 



.0289 



.625 



.0262 



.562 



.0230 



.500 



.0210 



.438 



.0184 



.375 



.0157 



.312 



.0131 



.250 



.0105 



.188 



.0079 



.125 



.0052 



.062 



.0026 



In applying the formula it is customary to assume a cer- 

 tain size of tile and then make the computation to determine 

 whether or not the tile will be sufficient. If too small, 

 another trial may be made with a larger tile. As an illus- 

 tration, suppose that the size of tile necessary to drain 80 

 acres is required, when the line is 1000 feet long and is laid 

 to a grade of 4-10 foot per 100 feet, assuming the drainage 

 standard or coefficient of \i inch. 



Referring to the formula, 



V = 48 



/ dh 

 1/ I + 54 d 



