138 ENGINEERING FOR LAND DRAINAGE. 



and apply the formula, being careful to consider the 

 physical conditions of the area for which the computa- 

 tion is made. Substitute the proper numbers in formula 

 7 and find the value of v\ multiply the value of v by 

 the area of the tile as lound in Table 2 to find value of 

 Q. The result will be the quantity of water in cubic 

 feet per second which the tile will discharge. Divide 

 this number by the number in Table 5, which expresses 

 the quantity of rainfall per acre which it is desired to 

 remove per second in twenty-four hours. The result 

 will be the number of acres which the given drain will 

 afford an outlet for. 



Table 5. 



TABLE OF CUBIC FEET PER SECOND WHICH MUST BE DIS- 

 CHARGED PROM A DRAIN TO RELIEVE ONE ACRE OF LAND 

 OP VARIOUS DEPTHS OP WATER IN 24 HOURS 



.0420 cu. ft I inch per acre 



.0315 *' - f - 



.0210 '* "• \ '' 



.0140 '' '' I ** 



.0105 '* '* i '' 



.0052 ** '' \ '' 



Example. — How many acres will a 6 mch tile drain, 1000 feet long, 

 laid on a grade of 3 inches per 100 feet and 3 feet deep at the upper 

 end, computing on the J-inch standard ? 



d-= .5; 



Formula (7): z/ = 48 j/ .— ^^, / = 2.5 + i-S = 4; 



+ SAd I j^ 24^ -. 1027. 



= .00194 



1027 

 4S y' ,00194 = ^'iJC^ t= V, 



Q =z av •= 2,112 X .1964 = .41479, 



.41470 



Acres = -l-~^^^ = 39.5. 

 .0105 ^ ^ 



