What is recurrence interval used for?
Recurrence intervals refer to the past occurrence of random events. Forecasting refers to the future likelihood of random events. These are often confused because the recurrence interval (calculated from past events) is used to gauge the future probability of an event.
Why is the calculation of a recurrence interval for floods important?
Your results for recurrence interval will tell you the probability that a flood of a particular magnitude will occur in any given year. If you calculate a recurrence interval of 3 for a flood event with a discharge of 3,000 cfs, it means that particular flood has a 1-in-3 chance of occurring in any given year.
What does a high recurrence interval mean?
The 100-year recurrence interval means that a flood of that magnitude has a one percent chance of occurring in any given year. In other words, the chances that a river will flow as high as the 100-year flood stage this year is 1 in 100.
What is the relationship between recurrence interval and discharge?
The relation between recurrence interval and annual peak discharge should become more “linear” when it is plotted as a semi-logarithmic graph. Use EXCEL to calculate the equation of a trend line through the data. This will be a logarithmic relation because it is a semi-logarithmic plot.
What is return period in insurance?
The estimated frequency of a catastrophic event reoccurring is usually expressed as the ‘Return Period. ‘ This refers to the average amount of time that passes between events of a similar magnitude in a given location; it can also be defined as the expected time, or average time, between two events of low probability.
What is the meaning of return period?
Return period describes the expected (mean) time (usually in years) between the exceedence of a particular extreme threshold. Return period is traditionally used to express the frequency of occurrence of an event, although it is often misunderstood as being a probability of occurrence.
What is the recurrence interval equation?
Use the formula: Recurrence Interval equals the number of years on record divided by the number of events. In the example, 100 years divided by five occurrences produces a recurrence interval of 20 years.
How does the return period or recurrence of a hazard event vary with the magnitude?
The magnitude of a natural hazard event varies in its frequency of occurrence over time in an inverse power relationship. In other words, the larger and the more energetic the event, the rarer it is in time.
Why is return period important?
Return period is useful for risk analysis (such as natural, inherent, or hydrologic risk of failure). When dealing with structure design expectations, the return period is useful in calculating the riskiness of the structure.
What is 50 year return period?
So in this case we could say that the reservoir is designed to a 1:50 year return period, sometimes expressed as a 2% or 0.02 chance. This means that it should not fail during an event which occurs on average once every 50 years.
How do you calculate return period?
Determining Return Periods for Rainfall
- Locate the contour lines on either side of your location.
- Estimate how far you are between the contours from the lower contour line.
- Calculate the difference in rainfall total between the two lines.
- Multiply the rainfall difference by the distance you calculated for your location.
