Q. How to determine the frequency of flood?

Flood frequency may be estimated preferably from flood records, if available, for a number of years or they may be based on rainfall records.

Where records are available for a period more than 50 years, the design flood for 50 year frequency should be determined using statistical method.

Where records are available extending over a period near about 50 years, the design flood should be the 50 years flood determined from the probability curve prepared on the basis of recorded flood during the period.