April 19 Daily Question: Rate of Return for a Flood Event

NCEES Civil PE Specification V.C.: Storm Characteristics

Problem

Municipal records show a flood devastated a rural town 40 years ago. Risk assessors employed by the town have determined that the probability a flood of the same magnitude will not occur over the next 20 years is 80%. In nearly how many years would you anticipate a similar flood event to occur from present?

Select an Answer:

CORRECT 😃

INCORRECT 😟

Average:

42.2%

Solution

The probability that an event will not occur in N years is defined by the following equation:

$$ R=\left(1-p\right)^N $$

$$ where\ p=annual\ probability $$

Given the findings of the risk assessors, we are able to solve for the yearly probability of the event:

$$ 0.80=\left(1-p\right)^{20} $$

$$ p=0.011 $$

Calculate the return period based on the annual probability:

$$ T=\frac{1}{p}=90\ yr $$

Calculate the number of years from today when the flood can be expected occur: