48 SEWER DESIGN 



in two years and once a year to storms as frequent as five 'times 

 a year. The equations of Mr. Bruyn-Kops are shown in the 

 following table: 



TABLE V 



TABLE SHOWING EQUATIONS FOR RAINFALL CURVES FOR STORMS 

 OF VARIOUS FREQUENCY SAVANNAH, GA. 



Maximum storms y = - 



Storms occurring once in two years 



Storms occurring once a year y = ~ 





Storms occurring twice a year y = 



QS- 



Storms occurring three times a year y = 



x+ig 



Storms occurring four times a year y = ~ 

 Storms occurring five times a year y = 



Fig. 12, from an article * by C. E. Gregory of the firm of 

 Hering & Gregory, on " Rainfall and Run-off in Storm Water 

 Sewers," shows some of the curves above referred to together 

 with one by Edwin Duryea,f and three prepared by himself 

 from various records of high intensity storms. His equations 



are y = , y ~~\ an d y = ~^ for the curves numbered 4, 9, and 



8 respectively. The last is particularly selected as applicable 

 to winter storms, the intensity of which is shown to be less than 

 storms at other seasons of the year. By this diagram, it is 

 seen that if the curves numbered 2, 10, and 3 are eliminated 

 as giving excessive values for ordinary engineering practice; 

 the others are similar both as to form and position on the diagram 

 and the fact is thus emphasized that the curve must indicate 

 to the best judgment of the engineer, not only the existing 

 relation between the duration of the storm and its intensity, 

 but also the frequency of the storms considered. 



* Trans. Am. Soc. C. E., Vol. LVIII, p. 458. 

 t West. Soc. C. E., Vol. IV, p. 73. 



