We frequently use design storms to evaluate existing and proposed stormwater management systems. Design storms vary by geographic location and are typically designated by duration and frequency such as the 10year - 24hour storm. We are encouraged to consult local regulations and design manuals to obtain the appropriate design storms for their systems.

It is a common practice to evaluate the performance of systems against multiple design storms. The Global Storms tool in the user interface allows us to analyze several storms simultaneously and to compare results on a single graph.

Creating a design storm event has two steps involved:

  • Selecting the average rainfall intensity for the storm event depends upon the return period and duration.
  • Selecting the appropriate temporal pattern depends upon the location.

Rainfall intensities are provided by the Bureau of Meteorology (BOM) for different durations and recurrence intervals for all locations around Australia based on a 2 km2 GRID.

The rainfall intensities are multiplied by the temporal patterns to give design storms. Twelve temporal zones are used to describe the rainfall storm patterns across Australia based on Australian Rainfall and Runoff Guidelines 2016 (ARR16).

Temporal Pattern Regions – Source: ARR 2016 Book 2 Chapter 5

Each zone provides 10 storm patterns per standard duration for each recurrence interval range as described in ARR16. The 10 patterns are referred to as an ensemble.

Temporal Pattern Ranges – Source: ARR 2016 Book 2 Chapter 5

This example demonstrates adding design storm ensembles for Brisbane, Queensland, Australia for the 1% AEP 1, 2 and 3 hour durations.

Adding a Design Storm with File Merge

  1. Launch the program. Open the file Single_Design_Storm.xp.

  2. Create the storms using the ARR Storm Generator.  Go to Configuration > Job Control > Runoff, and select Global Storms on the dialog.

  3. Select the ARR Storm Generator button at the bottom-left corner of the dialog. By default, the storm generator will access the same file location as the project (.xp) file.  Any previously created storm files will be displayed for editing.

  4. We do not currently have any previously created files available in the window, so select New to create a new set of storms. The AEPs and Durations lists should be empty. 

  5. To populate the storm data (AEPs and Durations), select ARR Data at the top-right corner of the dialog.

  6. Use the scroll wheel on the mouse to zoom and pan to find the Brisbane Airport.  Click the Airport to populate the Latitude (-27.381) and Longitude (153.123) of the desired location.  Alternatively, you could type these in manually. Select Download. The Data Files status should change to ‘Downloaded’ once successful. Click OK.

    Note: If no internet connection is available or there is an issue with either the BOM or ARR Data Hub websites, files can be downloaded and the Add from File action can be used to generate rainfall data manually. 

  7. The available AEP and Duration lists should now be populated.  Clear the Select All box at the top of both lists to deselect all. Then select the desired events (1% AEP, 1 hour, 2 hour and 3 hour).
  8. Click View Summary Report to check the storms that will be added to the model.  There should be 30 (one ensemble for each of the three durations). If you are happy with the summary report, click OK.

  9. You should now see the newly created zip file displayed in the window.  This file contains all the data files used to create the storms.  Select the new file, use the Add to Existing on import option and select Import. This will add the 30 new storms to the global storms window and close the window.

  10. Now that we have added our storms, we can check the Time Control in the Runoff Job Control to ensure we run the model long enough. Select the Time Control button and update the Simulation End to 3 hrs and 30 min. Select the Simulation Start Time for Rainfall Event. Click OK twice to exit the Job Control dialog.

  11. Save the model.
  12. Solve the model using the Analyse > Solve or Solve Manager, if available.
  13. Right-click Node 1 and select Review Results from the menu.  Check the hydrographs look okay and are as you expected. Close the results view.

  14. Now, we will use the Ensemble Statistics Utility to analyse the results.  With Node 1 still selected, go to Results > Ensemble Statistics Utility.  A table of statistics for the three ensembles should appear.  Here you can see the mean ensemble results and the corresponding storm that gave the closest result to the mean.

  15. These statistics can be viewed graphically by selecting the Box and Whisker button. Select the ‘Show Mean Marks’ button on the top of the dialog and select Mean from the display drop down.  The value shown in the Green text at the top of the box plot shows the maximum of the three Mean results for the three ensembles.