Question

Identify the true statement.

A. Two 100-year floods cannot occur in the same year (or in consecutive years).
B. The size of a flood and its recurrence interval are inversely related; the larger the flood, the shorter its recurrence interval.
C. A 200-year flood has a recurrence interval of, on the average, once every 200 years.
D. An annual probability of 4% means that there's a 1 in 4 chance that a flood of some given size will happen in any given year.

Answer 1

The true statement is C: A 200-year flood has a recurrence interval of, on average, once every 200 years. This correctly describes the average interval at which such a flood might occur, based on probability.

Step-by-step explanation:

The question is asking to identify the true statement about flood recurrence intervals and their probability of occurrence. The correct option is C: A 200-year flood has a recurrence interval of, on the average, once every 200 years. This means that there is a 0.5% chance each year that a flood of this size will occur.

It does not preclude multiple occurrences within shorter periods, nor does it guarantee an event will happen exactly every 200 years. However, it simply conveys the average frequency over a long time.

Option A is incorrect because two floods with a recurrence interval of 100 years can occur within the same or consecutive years; recurrence intervals express probability, not strict scheduling.

Similarly, Option B is false because the size of a flood and its recurrence interval are directly related, not inversely; larger floods tend to have longer recurrence intervals.

Option D also presents a misunderstanding of probability, as an annual probability of 4% corresponds to a 1 in 25 chance, not 1 in 4, of a flood of a given size happening in any given year.