68 



SEWER DESIGN 



the rate of rainfall be taken at 2 inches, then the percentage 

 for Gary is only 9^ , while in Baltimore it is 95 and in St. Louis 

 it is 70. With such variation in values, it seems hopeless to 



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extend efforts on perfecting details of any one factor while the 

 combined factors give such widely different results. 



A proper solution of the problem calls for a careful study 

 of the district to be drained, with careful attention to the soil, 

 the shape, the slope, the relative amount of impervious area, 

 all uncertain and not susceptible of mathematical expression. 



