Create a Rainfall IDF Analysis

Rainfall IDF (Intensity-Duration-Frequency) Analysis is useful when you want to compare rainfall data to historical values. Like all reports in FlowWorks, data for IDF analysis is updated as frequently as new data is received – for IDF analysis, this enables users to watch as a storm develops in real time.

1. Open the IDF Analysis Tool

  1. Click Analyze in the main toolbar. A drop-down menu appears.
  2. Click Rainfall IDF.

2. Choose the Channel and date range to analyze

  1. Select the Rainfall Site; then choose the Rainfall Channel you wish to analyze.
  2. Select an IDF Curve, using the drop-down list.
    Usually, an IDF curve will be automatically selected when you choose the Rainfall Site. You can change the IDF Curve to something else, if available.
  3. Set a date range using the Select Start Date and Select End Date fields.
  4. (Optional) Hone-in your date range by setting the hour and minute.

3. Click Generate IDF Analysis

Your IDF graph will appear in a separate window, showing an IDF plot for the Channel you've selected.

Your web-browser must be configured to accept popup windows from FlowWorks, in order to view the IDF graph output. If your graph does not appear in a separate tab, please ensure that your browser settings have popup windows enabled.

Interpreting the Results

Referring to the example below: The colored lines on the graph represent the historical IDF information for the site. This information is obtained from either the National Oceanic and Atmospheric Administration, or Environment Canada. You can also supply your own rainfall data if you have more detailed local records.

The red line shows the data for the storm you previously selected (known as the ‘current period’), overlaid on top of the historical values. If the red line crosses over the historical values for any given rainfall duration, it indicates that a historically significant value has been exceeded by the current period at that duration.


The graph shows an example of the current period exceeding a ten-year historical line (blue line), at the 30 minute duration point. This graph indicates that for that particular time duration, the current period had a 10-year historical event.

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