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.
In Australia, the whole country is divided into eight rainfall zone storms as per the Australian Rainfall and Runoff 1987 guidelines (ARR):
Design Rainfall Temporal Pattern Zones for Australia – Source: ARR 1987, BOM
The rainfall intensity and the pattern are varied depending upon the zone, return period, and duration. This example demonstrates adding a design storm for Brisbane, Queensland, Australia for a storm with 100 ARI and 1 hr duration.
Note: The process below involves a significant amount of setup time for generating rainfall inputs. xpertcare clients can contact Innovyze support for access to the Australian Rainfall files for a specific location in an .xpx format ready for import. Please email firstname.lastname@example.org with the coordinates, zone, and location name to log a ticket with your request.
Part 1 - Adding a Design Storm with File Merge
- Launch the program. Open the file Single_Design_Storm.xp.
- Merge global databases:
- In the File menu, select Merge.
- In the Merge Database dialog, select only Merge Global Databases.
- Click File.
- In Windows Explorer, navigate to the Samples folder and select ARR_Zone3_Storms.xp. Click Open.
- Create a new Global Data record:
- In the Configuration menu, select Global Data.
- Select (R) Rainfall from the Data Base Type panel.
- Highlight Zone3 60min >30 Yr as the record name and click Duplicate (Note that we will simulate the design storm for ARR Zone 3 with 100 years ARI and 1 hour duration). A new record Zone3 60min >30 Yr.1 will be created.
- Type in the name Brisbane100Yr_1Hr and then click Rename.
- Click Edit.
- In the (R) Rainfall dialog, click Constant Time Intervals .
Now you will see the temporal pattern for a design storm in zone 3 with 100 year return period and 1 hour duration. Note that this is a dimensionless pattern and sums up to one.The next step is to determine the average intensity of the design rainfall event. Click OK three times and return to the main window.
Calculation of average intensity:
Go to Tools > Launch Application > IFD.exe.
Enter all the parameters in the dialog. You will get this data from Australian Rainfall and Runoff Manual or alternatively from the Rainfall IFD Data System.
Open the website of Australian Bureau of Meteorology and click the Create an IFD Tab. Enter the Latitude and Longitude of the location. Click the Submit button and finally select the IFD table option. You will see the IFD coefficients for the area in the bottom-left of the IFD Table tab. Click the images below to see the full-sized version.
Source: http://www.bom.gov.au/hydro/has/cdirswebx/cdirswebx.shtml - Australian Bureau of Meteorology web site.
Now, enter the highlighted red data into the dialog below.
Click the Save Data button and save the file as Bris.ifd.
Now the IFD data for Brisbane has been saved, click the Load Data button and open the saved Bris.ifd file.
Finally, click the Solve button and you will see the average intensity of the design storm has been calculated as 103.98 mm/hr. The absolute rainfall depth for the design storm will be 103.98 mm/hr x 1 hr = 103.98 mm. Enter this value in the rainfall dialog shown above and click the graph button.
Add rainfall to runoff node:
Double-click Node1 to open the Runoff Node dialog. Click the Sub-Catchment 1 box.
In the Sub-Catchment dialog, select Brisbane100Yr_1Hr as the Rainfall.
Click OK to return to the network view.
Save your model as Brisbane_Design_Storm.xp.
Go to Configuration > Job Control > Runoff.
- Select the Time Control button.
- Select Use Simulation Start Time for Rainfall Event.
Solve the model:
In the Analyze menu, click Solve.
Right-click Node 1 and select Review Results from the menu.
Part 2 – Using Global Storms
Now you will create four design storms and simulate together using the Global Storms option. This will be a very helpful tool when analyzing a system for different design storms. The four design storms are the following:
Return Period (Years)
Average Intensity (mm/hr)
Absolute Depth (mm) (Multiplier)
Note that these intensities are estimated using the ifd.exe utility, as you did previously.
- Open the file Single_Design_Storm.xp.
- Import the global storms’ temporal pattern:
- Go to the File menu, select Import/Export Data > Import XPX/EPA Data.
- Click Select under the XPX Format File and browse for the file Australian Temporal Patterns.xpx in the templates folder and open it.
- Click Import and you will see a generic warning message and click OK .
Now all the design rainfall temporal patterns for Australia have been imported to the model. In the next step, you will see how to set up multiple design storms.
- In the Configuration menu, select Job Control > Runoff.
- Click Global Storms.
- Click Insert Storm four times.
- Enter the data as shown in the figure below. Make sure that both boxes are checked. Note that the rainfall patterns you selected are imported by the XPX file previously. The multipliers are absolute depths calculated by the ifd.exe.
- Click OK twice to return to the network view.
- Save your file as Multi_Design_Storm.xp.
- Solve the model:
- In the Analyze menu, select Solve. Note the calculation is performed four times – once for each storm.
- Right-click Node 1 and select Review Result from the menu.
- For each Global Storm, what is the:
- Maximum intensity?
- Time step?
Part 3 – Design Storms for Malaysian Catchments
In Malaysia, the rainfall temporal patterns for the West and East coasts are the same for durations less than 180 minutes. For durations of 180 and 360 minutes, the patterns are different.
Importing temporal patterns for design rainfalls for Malaysia:
Open the file Single_Design_Storm.xp and Save As KL_Design_Storm.xp.
Go to the File menu, click Import/Export Data and select Import XPX/EPA Data.
Under the XPX Format File option, click Select and browse for the file Malaysia_Temporal_Pattern.xpx in the templates folder and open it.
Click the Import button and disregard the generic warning message and then click OK.
Go to Configuration menu and select Global Data.
- Select (R) Rainfall from the Data Base Type panel. Here you will see the imported temporal pattern using the XPX file import.
- Click the record EWCPM 60min and then click the Duplicate button.
Click EWCPM 60min.1 and type in KL_100Yr_60min and then click Rename. Note that this is the rainfall temporal pattern for Kuala Lumpur with 100 year ARI and 2 hours duration. Click OK.
Calculating average rainfall intensity.
Click Launch Application under the Tools menu.
Click the Load Data button, browse for the file Kuala Lumpur.ifd and open it. The Return Period, Duration, and Catchment Area will be populated as shown below.
Click the Solve button. Now you will see that the average rainfall intensity calculated as 65.39 mm/hr.
Running the model.
Go to Configuration > Global Data.
- Select (R) Rainfall from the Data Base Type panel, and select the KL_100Yr_60min storm.
- Click Constant Time Intervals.
Enter the multiplier as 65.39 for Rainfall (65.39 mm/hr x 1 hr).
Click the Graph button and review the design rainfall.
Click Close and then click OK and return to the main window.
Double-click Node1 and change the catchment area to 2000 Ha and width as 4500 m.
Open the Sub-Catchment 1 dialog. Change the rainfall as shown below:
Click OK twice and return to main window.
Change the duration of 6 hours by editing the Time Control in Configuration > Job Control > Runoff.
Select Use Simulation Start Time for Rainfall Event, and then click OK.
In the Results menu, click Solve.
Click Node 1 and right-click Review Results.