Frequency Analysis of Rainfall Intensities for Calcutta

From the record of the point rainfall data in Calcutta, India for 23 yr, a procedure is presented for arriving at the relationship between the average intensity of excessive rainfall, the corresponding duration the rain continued to fall at the average rate, and the frequency with which these combinations of intensity and duration of such storms occur. Well-known methods, such as probability, based on annual maximum events and partial duration series, and mathematical and graphical curve fitting based on frequency analysis are employed for developing the relationships. The developed intensity duration frequency relations are expressed in tabular and graphical forms, and as mathematical equations. The various methods do not give exactly identical results, and it depends on the designer's discretion to choose any of them for application in the design of a storm sewer system for the city. No particular method can be considered as the best for rainfall frequency determination.