53:171 Water Resources Engineering
Problem #11
Flood Risk

You are called in on a legal case involving a levee you designed. Based on the design specifications (mandated by the owners) the levee protects against the 25-year flood.  Still, five years after it was built, the levee was overtopped.  The owners think they were ripped-off.  The judge (and jury) want to know the following:

1. What is the probability that the levee will fail in any given year?
2. What is the probability that the levee will not fail in five years?
3. What is the probability that the levee will fail in five years (at least one overtopping event)?
4. What would you (the engineer) consider to be the design life (in years) of the levee as constructed?  The judge and the owners agree that the risk of failure (at least one overtopping) should be no more than 1 in 4 (0.25) during its design life?
5. What design return period (in years) would you have selected for the levee if the allowable risk of failure during a 25-year design life were 1 in 4 (0.25)?