Civil Engineering MCQAE Level Civil Engineering
A flood with a return period of 50 years has a probability of being equaled or exceeded in any given year of:
HydrologyReturn Period ExceedanceMEDIUM
Choose the correct answer
A
50%
B
2% (= 1/50)
C
1%
D
0.02%
Correct Answer
B. 2% (= 1/50)
Why is this the answer?
Return period T (years) = 1 / P (annual exceedance probability). T = 50 years: P = 1/50 = 2% per year. Probability of at least one occurrence in n years: Pn = 1 - (1 - 1/T)^n. For T = 50, n = 50: Pn = 1 - (1 - 0.02)^50 = 1 - 0.364 = 0.636 = 63.6% chance of exceedance at least once in 50 years.
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