Flooding Along The Brazos River Near Simonton, Texas
The N Maximum Annual Discharge data were ranked with the largest discharge having rank M = 1 and the smallest rank M =77 (in this case).
The Recurrence Interval (RI) is the average interval, in years, between occurrences of two discharges of equal (or greater) magnitude. This relationship, known as the Weibull equation, can be written:
where N and M are defined as above.
The Annual Exceedence Probability (P) is the probability (expressed as a percentage) that a flood of that magnitude or greater will occur in a given year and is given by:
For the problem as stated, the numerator of the Weibull equation (RI = (N+1)/M ) has a value of:
[Click on the blank and the cursor should appear. Type in the answer and hit return. If you entered a wrong value the correct value will appear in red]
[Remember that there are 77 years of data in the complete set - therefore N = 77]
The largest value of M in this abreviated data set (the ranking of a particular event) is :
Click on the blank on the left and center a value. Hit the tab key and enter the other value. Click on the operation that you want to preform.
Year | Maximum Annual Discharge (cfm) | Rank | Recurrence Internal | Exceedence Probability |
---|---|---|---|---|
1929 | 123,000 cfm | 1 | 78 | 1.28% |
1957 | 119,000 cfm | |||
1941 | 117,000 cfm | 3 | ||
1965 | 98,900 cfm | 4 | ||
1992 | 94,000 cfm |