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Rainfall is the starting point for almost all stormwater simulations. The terms “rainfall”, “storms”, and “precipitation events” all have the same meaning in this tutorial. Rainfall data consists of a two column table containing a time step (usually in hours) and either total precipitation (in or mm) or intensity (in/hr or mm/hr).

Stormwater models use two types of rainfall data:

  • Design storms in which a total rainfall is assigned to a duration and temporal pattern. For a given location, duration, and total rainfall these storms are assigned a frequency, such as the 10-year and 24-hour rainfall.
  • Historical storms that are obtained from data collected in precipitation gauges. These storms are used to calibrate a model with observations of flow and water levels and assess the performance of collection system improvements.

The xp interface can utilize storms of any duration. A single data file can contain multiple storm events. Such These files consist of dry periods (rows with zero precipitation) between wet periods (rows with nonzero precipitation).

There are four methods of adding rainfall data to an xp model:

  • Starting a new file with a template
  • Merging global data from an existing model
  • Importing a rainfall data file
  • Manually adding data into a dialog

In this tutorial, the first method will be presented.

ObjectivesCreate a design storm from a template
Time0.25 hour
Data files



Each installation of xp contains template files (*.xpt) with standard data used to build models. This example demonstrates an application of the dimensionless storm temporal pattern for Sydney. As per the Australian Rainfall and Runoff manual, Sydney is in Zone 1.

  1. Launch the program. In the opening dialog, select Create from Template, and then click Continue.
  2. In Windows Explorer, navigate to your data folder, type in your file name and click Save.
  3. In Windows Explorer, navigate to the Getting Started folder and select the file ARR.xpt. Click Open. A message may be displayed that xpswmm or xpstorm is converting from an earlier database format. Click OK.
  4. Review the design storm in the Global Data
    1. From In the Configuration menu, select Global Data
    2. In the Data Base Type column, select (R) Rainfall. In the Record Name column, select Zone1 60min <30yr
    3. Click Edit

  5.  In the next dialog, select Constant Time Intervals.

  6. In the Rainfall section of the next dialog, click the Absolute Depth radio button and enter 47.3 mm in the multiplier Multiplier field. This is the depth of rainfall for 5 year – 60 minutes storm for Sydney. This is calculated using the IFD.exe as you did for the previous tutorial. 
  7. In the Time section, click the Time Interval and Minutes radio buttons. Enter in the box.

  8.  Click Graph to display a graph of intensity vs. time.

  9.  Click Close, and then click OK three times to return to the network view. The design storm is now available to assign to any subcatchment.

  10.  Add rainfall to runoff node:
    1. Set the active mode to Runoff (Rnf). 
    2. Double-click node N1 to open the Runoff Node dialog. 
    3. Double-click the Sub-Catchment 1 box. 
    4. In the Sub-Catchment data dialog, select Zone 1 60min <30yr as the Rainfall

    5. Click OK twice to return to the network view. 
    6. Save your model as Sydney Storm.xp.

  11. Solve the model. 
    1. On In the Analyze menu, select Solve or click on the Solve tool
    2. Right-click node N1 and select Review Results from the menu. 
    3. Confirm that the rainfall at N1 is the same as design storm specified in Step 6.

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  1. In the design storm, what is the:

    1. Duration?
    2. Average intensity?
    3. Time step?

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