LAND DBAINAGE 



653 



The second formula determines the quantity of water 

 possible to remove, by multiplying the area of the cross 

 section of the tile by the velocity of flow. 



The third formula is used to determine the velocity of 

 flow of water in the outlet tile. 



In a small system, where the laterals are relatively 

 unimportant and where the soil is fairly close, the velocity 

 formula may be much simplified as follows : — 



dh 



1+ 54d 



The term i K is used only where the soil is so very 

 porous that the ready movement of the water through 

 the soil has an influence on the flow in the tile. 



Coefficients of drainage and their equivalents in cubic 

 feet per second of discharge are as follows : — 



Depth op Water in Inches Removed 

 IN Twenty-four Hours 



Cubic Feet to a Second op Dis- 



CHABGC 



Fraction 



Decimal 



To an Acre 



To a Square Mile 



1 



1 



4, 



i 



1 



1.00 

 0.75 

 0.50 

 0.25 



0.0420 

 0.0315 

 0.0210 

 0.0105 



26.9 



20.2 



13.4 



6.7 



From the above formula Elliott has calculated the 

 number of acres of land drained by outlet tiles of different 

 sizes and grades where the coelSicient is one-fourth of an 

 inch in twenty-four hours and where the main is 1000 

 feet in length : — 



