How can I apply a rainfall depth or intensity to a dimensionless curve to create a storm event?

Applies To 
Product(s): SewerGEMS, CivilStorm, StormCAD, PondPack, SewerCAD
Version(s): CONNECT Edition, V8i
Area:  Layout and Model Input
Original Author: Mark Pachlhofer, Bentley Technical Support Group


How can I apply a rainfall depth to a dimensionless curve such as the standard SCS 24 hour distribitions, to create a storm event?


1) Create a new Time-Depth or Time-Intensity entry by right clicking on the folder and choosing, New > Time-Depth (or New > Time-Intensity)

2) Single left click on the new time-depth or time-intensity curve that you created and look to the right side of the window under the Storm Event Input tab. Click on the drop down arrow next to the new button and choose "Add return event from dimensionless curve...".

3) This will open the engineering library and you can then go in and select the dimensionless curve you want to use, such as the SCS Type II 24 hour. This defines how the total rainfall is distributed over time.

If you need to create a custom distribution first, you can do so under Components > Engineering libraries. If you are not sure which distribution to use, contact your local reviewing agency. In some cases the required distributions may come from NOAA Atlas 14 (see article here).

Note that some distributions are only dimensionless depth (where the time is fixed such as 24 hours for the SCS types since they were built for 24 hour storms) and others are dimensionless time and depth (where you can apply any total duration and any total depth to the dimensionless shape in order to create the hyetograph).

4) In the "Generate Storm Event" window that appears next, provide a label, return frequency, total depth, etc and click OK. Your time-depth or time-intensity event will be constructed based on the entered depth and dimensionless distribution. 

Storm Tracking

Starting with the CONNECT Edition Update 1, when using Time-Depth or Time-Intensity storm data, the source of the dimensionless rainfall curves is now documented in the Storm Data dialog. This will include information on if the storm is from a dimensionless curve, and if so, which dimensionless curve library and rainfall curve was used. This makes it easier for you to understand the source of your storm events.

If the storm was not created from a dimensionless curve, the fields for Dimensional Rainfall Curve Library and Dimensionless Rainfall Curve will be blank. If you open an existing model from an older version of the product with existing rainfall data, these fields will be listed as Unavailable, even if they were generated from a dimensionless curve library.

NOTE: as of October 2019, the above update does not apply to PondPack. Furthermore, for storms that were constructed from a dimensionless distribution, that distribution name (for example "SCS Type II 24hr") is not currently exposed in Report Builder. The modeler will need to ensure that the distribution type is included as part of the storm name if they would like it to appear in reports.

See Also

How to create a custom rainfall distribution

How to incorporate NOAA Atlas 14 rainfall distributions

Where does the data for the bul70-71 and bas70-71 dimensionless rainfall curve come from?