132 ENGINEERING FOR LAND DRAINAGE. 



experimental tests that the existing formulas for the 

 flow of water through pipes are with some allowances 

 more applicable to tile drains than at first would be 

 thought possible. The art of using a formula success- 

 fully is in bringing to it in proper form the data which 

 should be used and in making the proper assumptions 

 which should precede the application of any formula. 



The following formula has been found to be simple 

 and of easy application and has been verified by use of 

 a current meter upon the discharge from lines of tile in 

 which the grade of the drain and the quality of work- 

 manship in its construction were known : 



For velocity ^ = 48./-^^ . (7)* 



For discharge Q = 48a'y / t g.> • (^) 



where v = velocity in feet per second ; 

 d = diameter of tile in feet; 

 /= total fall in length of drain in feet; 

 / = length of drain in feet ; 

 a = area of tile in feet ; 

 Q = discharge in cubic feet per second. 



All measurements to be taken in feet. 



Application of the Formula. 



This formula will give quite correctly the velocity 



and discharge from lines of tile drains which are laid in 



a first-class manner, within certain limitations as to size 



and length, which will hereafter be considered. In ap- 



* Known as Poncelet's formula. 



