A 100-year flood is

Concept:Return period (T): It is defined as the average time interval after which a flood of given discharge is equaled or exceeded.Mathematically, \({\bf{T}} = \frac{1}{{\bf{p}}}\)Where,p = probability of occurrence or exceedance of an event.A 100-year flood is a flood that has a 1% chance of occurring in any given year. A 100-year flood is called that because, on average, it will occur about once every 100 YEARS.A 100-year flood can HAPPEN two years in a row or not at all over a 100-year SPAN. If a 100-year flood happened last year, there would still be a 1/100 chance that it would happen this year too.It is used in the Design of Hydroelectric Power Plants, WATER Supply, etc.