KUTTER'S FORMULA 183 



of Q from the grade and size of pipe, " Colby's Sewer Com- 

 puter " is of value. Based on Kutter's formula, with w = .oi3, 

 the logarithms of the grades, discharges, and diameters are 

 laid off on the rule and runner, so that by proper setting of 

 grade and diameter the discharge can be at once read off. 

 No velocity is given, although the runner could have addi- 

 tional divisions for this purpose. The rule is shown in Fig. 46. 



PROBLEMS 



65. Determine numerically the difference in the value of C between 

 values of # = .013 and # = .015; for values of 5 between .005 and .0005, and 

 for values of R between ^ = .125 and ^ = 1.25. 



If a diagram is based on a value of # = .013, by what per cent would v 

 be increased or diminished for n = .015. 



66. For ordinary range of values used in sewer work show numerically 

 how much variation in s would affect the value of c. 



67. Compute average values of C for ordinary sizes of pipes, and for 

 ordinary range of s, with ^ = .013. 



68. Given an open ditch section, of side slopes 2 horizontal to i vertical 

 with bottom an arc of 18" radius tangent to the sides, determine the 

 depth of flow, on a grade of .005 per cent, to carry 35 cubic feet per 

 second. Ditch is lined and n may be taken at .015. 



69. Find the size of a trough whose width is double its depth that 

 will deliver 180 cubic feet per minute. Assume the slope to be 2 feet in 

 1000 feet and the coefficient of roughness, n, to be .013. 



70. An outfall flume is to discharge 40 cubic feet of sewage per 

 second. It is to be built of plank (n = .01 1) on a slope of i in 3000. What 

 should be the dimensions to give the minimum amount of lumber. 



71. If a 36-inch brick sewer has a coefficient of roughness = .oi5 

 and a 36-inch pipe sewer one of .013, compute the grades in the two cases 

 necessary to give velocities of 2 feet per second. If the sewer were a mile 

 long, how much deeper in the ground would the brick sewer be? 



