Subbasins define the drainage area polygons that produce runoff to the other elements in the stormwater model. In the GeoSTORM software, the Subbasin Data command allows users to add new subbasins, edit subbasin data, and display the associated output results of a project.
The user can create or assign new subbasins using the Draw Subbasins or Assign Subbasins commands. Refer to this article in our knowledge base to learn more about these commands.
This article describes how to use the Subbasin Data command in the GeoSTORM software.
Follow the steps below to view or modify the subbasin data:
- From the Input ribbon menu, click the Drainage Subbasins dropdown menu and select the Subbasin Data command.
- The Subbasin Data dialog box will be displayed.
The following sections describe how to interact with the Subbasin Data dialog box.
Defining Subbasin Data
The Subbasin Data dialog box contains the following options to select and define subbasin data:
- Select Subbasin Section
- Subbasin Specifications Data Panel Selector:
- General Specifications Data Panel
- LID Specifications Data Panel
Selecting Subbasin
The Select Subbasin section allows the user to select the subbasin for defining the subbasin data. The user can create a new subbasin, copy existing subbasin data to a new subbasin, and delete a subbasin. In addition, the user can navigate between subbasins and enter a description detailing the defined subbasins.
The following entries are provided in this section:
- Subbasin ID
This dropdown combo box lists all the subbasins defined in the current scenario of the project. Click on the edit option (i.e., the pencil icon) to edit the subbasin ID. The user can navigate between the previous and next subbasin using the Up and Down arrow buttons. Alternatively, the user can click the […] button to select the subbasin from the Map View. Note that the Up and Down arrow buttons will be disabled (i.e., grayed out) if the current scenario contains a single subbasin.
- Description
This optional field allows the user to enter additional information that describes the selected subbasin.
- New
The [New] button allows the user to create a new subbasin on the Map View. The ID of every newly created subbasin must be unique.
- Copy
The [Copy] button allows the user to copy an existing subbasin along with its associated data to a new subbasin. The software automatically provides a unique ID to the copied subbasin.
- Delete
The [Delete] button allows the user to delete the selected subbasin from the current scenario.
- Less/More
The [<Less] and [More>] buttons at the Select Subbasin section header allow the user to collapse or expand the Computed Results section.
Defining Subbasin Specifications
The Subbasin Specifications dropdown selector contains General Specifications and LID Specifications entries. Selecting these entries displays corresponding data panels to define general and low-impact design (LID) specifications for the subbasins defined in the current scenario of the project.
Defining General Specifications Based on Hydrology Method
In the Subbasin Data dialog box, the contents of the General Specifications data panel change based on the hydrology and infiltration methods selected in the Scenario Manager dialog box, as shown below.
In addition, selecting different hydrology methods enables and disables the infiltration methods. The table below shows the infiltration methods available depending on the hydrology method selected.
| Hydrology Method | Available Infiltration Method |
|---|---|
| EPA SWMM | • Green Ampt • Horton • Modified Green Ampt • Modified Horton • SCS Curve Number |
| Modified Rational | All methods are disabled |
| DeKalb Rational | All methods are disabled |
| Rational Method | All methods are disabled |
| SCS TR-20/TR-55 | All methods are disabled |
EPA SWMM Hydrology Method
The combination of different infiltration methods with the selected EPA SWMM hydrology method changes the contents of the General Specifications data panel.
Refer to this article in our knowledge base to learn how the EPA SWMM hydrology method, along with different infiltration methods, changes the contents of the General Specifications data panel.
Modified Rational Hydrology Method
The following General Specifications data panel is displayed when the Modified Rational is selected as the hydrology method.
General Specifications
This section allows the user to define the general parameters of the defined subbasin.
The following parameters are available in this section.
- Drainage area
This entry field defines the area of the selected subbasin. The user can click the […] button to measure the subbasin area from the Map View. Clicking the [Recalc] button will cause the software to recalculate the area of the digitized subbasin. Similarly, the [Recalc All] button will cause the software to recalculate the area of all the digitized subbasins.
- Downstream connection
This read-only entry field defines the downstream element that the selected subbasin drains to. The user can click the […] button to select the subbasin downstream connection from the Map View.
The following elements can be selected:
- Manhole
- Routing Junction
- Storage Area
- Subbasin (only when using EPA SWMM hydrology method)
- Terminal Outfall
The user can click the [Clear] button to remove the downstream element connection.
Modified Rational Method Specifications
The parameters in this section are important for running the analysis using the modified rational method.
Note that the header of this section changes based on the selected hydrology method. For example, if the user selects Rational Method as the hydrology method, the header of this section changes to Rational Method Specifications. Similarly, for the DeKalb Rational hydrology method, the header of this section changes to DeKalb Rational Method Specifications.
The following parameters are available in this section:
- Runoff coefficient
This entry field defines the runoff coefficient for the defined subbasin. Clicking the […] button displays a Runoff Coefficients lookup table dialog box, as shown below.
- Time of concentration
This entry field defines the time of concentration for the defined subbasin.
Computational Results
After successfully computing the analysis, this section provides a summary of the computational results for the defined subbasin.
The following results are provided in this section:
- Peak runoff rate
This read-only field displays the peak runoff rate that occurred from the subbasin during the storm event.
- Rainfall intensity
This read-only field displays the rainfall intensity applied to the subbasin during the storm event.
- Total runoff
This read-only field displays the total runoff volume from the subbasin during the storm event.
DeKalb Rational Hydrology Method
The following General Specifications data panel is displayed when DeKalb Rational is selected as the hydrology method.
The contents of the dialog box for the DeKalb Rational hydrology method are similar to those for the Modified Rational hydrology method. Refer to the Modified Rational Hydrology Method section of this article for more information.
Rational Method Hydrology Method
The following General Specifications data panel is displayed when the Rational Method is selected as the hydrology method.
The contents of this dialog box for the Rational Method hydrology method are similar to those for the Modified Rational hydrology method. Refer to the Modified Rational section of this article for more information.
SCS TR-20/TR-55 Hydrology Method
The following General Specifications data panel is displayed when the SCS TR-20/TR-55 is selected as the hydrology method.
General Specifications
This section allows the user to define the general parameters of the defined subbasin.
The following parameters are available in this section:
- Drainage area
This entry field is similar to the Drainage area entry field available in the General Specifications section for the Modified Rational hydrology method.
- Downstream connection
This entry field is similar to the Downstream connection entry field available in the General Specifications section for the Modified Rational hydrology method.
- Runoff (flow) adjustment ratio
This entry field defines an adjustment ratio for calibrating the runoff from the selected subbasin. The default value for this entry is 1.000, meaning that there is no adjustment.
SCS Hydrology Method Specifications
This section allows the user to define the SCS hydrology method parameters for the defined subbasin.
The following parameters are available in this section:
- Curve number
This entry field defines the curve number for the defined subbasin. Clicking the […] button will display a SCS Curve Number lookup table dialog box as shown below.
- Impervious surface area
This entry field defines the percent impervious surface area for the selected subbasin.
- Time of concentration
This entry field is similar to the Time of concentration entry field available in the Modified Rational Method Specifications section for the Modified Rational hydrology method.
Computational Results
After successfully computing the analysis, this section allows the user to see a summary of the computational results for the defined subbasin.
Note that the Detailed Results section provides additional analysis results computed for the defined subbasin.
Defining LID Specifications
The LID Specifications data panel of the Subbasin Data dialog box allows the user to define general specifications for Low Impact Design (LID) elements within the selected subbasin. Note that this data panel is only enabled when EPA SWMM is selected as the hydrology method.
Refer to this article in our knowledge base to learn more about the LID Specifications data panel of the Subbasin Data dialog box.