Dear Behrouz Pirouz,

Thank you for your answer to my question.

Best regards,

Adekunle

Dear Adekunle, I would like to add a suggestion to Behrouz's answer: Among the various storm durations proposed in Behrouz's answer, you can focus more on a storm duration close to the concentration time of the water from the extreme point of your catchment to the runoff point (exit) of the catchment.

IDF method is relatively simple, but it is only a rough guide. There are many different formulas depending on the country, location and size of the drainage area under consideration. About the return period: we sometimes took the probability of exceedance p less than 1%, for example 0.5% or even 0.3% when designing the bridge structures. If p=0.3%, than ARI (the average recurrence interval) T=333 yr.

Dear Adekunle,

The maximum Intensity-Duration-Frequency (IDF) curve can be linked with the estimation of peak runoff if the area of catchment, its land cover and other characteristics remains unchanged over the time.

This is seldom possible in the natural processes. Further, linking development of IDF curves with the design of hydraulic structures for flood control is not possible because you need to convert the discrete signals of rainfall to continuous signal of discharge (depends upon the catchment reaction to rainfall). The value of discharges (observed) over the time are useful in design of hydraulic structure for flood control not the runoff.

Dear Contributors,

Thank you all for the response to my question.

Best regards,

Adekunle