Graphing Recurrence Intervals (Continued)

There are two ways to present the horizontal axis of this graph: either in standard form where the curve is not straight, or as a logarithmic scale which converts the curve to a straight line. Use the button below the graph on the left to toggle back and from between the standard view, and the semilog one (one axis is log and the other linear.).

It's important to keep in mind that this curve is based on only 21 years of data! The standard graph extrapolates the trend of the curve out to 30 years, and the semilog one extrapolates (predicts) out to 100 years. This allows us to make predictions about the size of the 100 year flood. Be sure to understand that we are making a prediction about something that is based on only a small amount of observations. The 100 year flood may be larger or smaller than our prediction. Do you think it makes any sense to make a prediction about the size of a 500 year flooding event?

Use the graphs, drag on the curve (which will help you read the graph), and answer the questions below.

1. Suppose at sometime during the next 5 years, a flooding event of 5000 cfs occurs. What's its expected recurrence interval?
2. What is the expected magnitude of the 50 year flood?
3. What is the expected magnitude of the 100 year flooding event?
4. How often will the 100 year flood occur? (Trick question)

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