Subbasin Data Command

Subbasins define the drainage area polygons that produce runoff to the other elements in the model. In GeoHECHMS, the Subbasin Data command allows users to add new subbasin and edit subbasin data in a project.

Follow the steps below to view or modify the subbasin data:

From the Input ribbon menu, select the Subbasin Data command.
Alternatively, the user can either double-click on the subbasin polygon from the Map View or choose the Subbasin Data command from the Drainage Subbasins dropdown menu of the Input ribbon menu.
The Subbasin Data dialog box will be displayed.

The following sections describe the Subbasin Data command and how to interact with the above dialog box.

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 subbasin.
Select Subbasin section

The following options are provided in this section:

Subbasin ID
This dropdown combo box lists all the subbasins that are defined in the project. The user can select the desired subbasin from the dropdown combo box. Click the pencil icon to edit the subbasin ID.

The user can navigate between the previous and next subbasins 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) when the model contains only a single subbasin.
Description
This text field allows the user to enter additional information to describe the selected subbasin.
New
The [New] button allows the user to create a new subbasin. On clicking this button, the dialog box will temporarily disappear. A prompt will be displayed on the status bar directing the user to draw a new subbasin on the Map View. Once finished, press the [Enter] key, or right-click and select Done from the displayed context menu. While drawing a subbasin, the user can press the [Esc] key to abort the creation of a new subbasin, which returns the dialog box to its previous state.

The dialog box will be redisplayed. Next, enter the subbasin name in the Subbasin ID entry field and click the [Accept Changes] button. The software checks that the defined ID is unique. If not, a warning dialog box is displayed, and the user is then returned to the Subbasin ID field to change the ID.
Copy
The [Copy] button allows the user to copy existing subbasin data to a new subbasin. When this command is executed, the software automatically provides a unique default name for the duplicated subbasin. The cursor is then placed into the Subbasin ID. The user can go with the default name or enter a different valid and unique ID before moving on to add any other data.
Delete
The [Delete] button allows the user to delete a selected subbasin and its associated data from the project.

Subbasin Specifications

The following sections describe the subbasin. Click on the dropdown selector at the Subbasin Specifications entry to display the various data panels that define the subbasin data.
Subbasin Specifications dropdown entry

General Specifications

This panel allows the user to define the infiltration, runoff, baseflow, surface storage, and canopy methods to be used for the current subbasin.
General Specifications panel

Note that the infiltration, runoff, baseflow, surface storage, and canopy methods are defined for the project in the Scenario Manager, which will be displayed automatically in the corresponding dropdown entries. However, the user can change the desired method for the selected subbasin from this dialog box. Refer to this article in our knowledge base to learn how to use the Scenario Manager dialog box.

The following options are provided in this data panel:

Infiltration (loss) method
This dropdown combo box allows the user to select the infiltration method for the selected subbasin. Infiltration methods are used to calculate precipitation loss due to infiltration. It is impossible to precisely predict infiltration in heterogeneous soil over commonly used modeling scales, such as hundreds to thousands of square miles. The dropdown combo box provides the following infiltration methods:
1. None
2. Deficit and Constant
3. Exponential
4. Green and Ampt
5. Initial and Constant
6. Layered Green and Ampt
7. SCS Curve Number
8. Smith Parlange
9. Soil Moisture Accounting Loss
  
  Refer to this article in our knowledge base to learn about various infiltration methods and how to use them to compute surface runoff.
Runoff (transform) method
This dropdown combo box allows the user to select the runoff method for the selected subbasin. Runoff (transform) methods are used to transform the excess precipitation (after the losses have been subtracted) into surface runoff (direct runoff). The dropdown combo box provides the following runoff methods:
1. None
2. Clark Unit Hydrograph
3. Kinematic Wave
4. SCS Unit Hydrograph
5. Snyder Unit Hydrograph
6. User-Specified S-Graph
7. User-Specified Unit Hydrograph
  
  Refer to this article in our knowledge base to learn about various runoff methods and how to use them to compute surface runoff.
Baseflow method
This dropdown combo box allows the user to select the baseflow method for the selected subbasin. Baseflow methods are used to represent contributions to subbasin runoff due to excess groundwater. Baseflow is comprised of runoff that infiltrates into the ground, flows down gradient or slope, and then reaches back on the land surface and flows back into small channels. The smaller channels merge into a larger channel, then into the stream and river and so on. The dropdown combo box provides the following runoff methods:
1. None
2. Bounded Recession
3. Linear Reservoir
4. Monthly Constant
5. Nonlinear Boussinesq
6. Recession
  
  Refer to this article in our knowledge base to learn about various baseflow methods and how to use them to compute surface runoff.
Surface storage method
This dropdown combo box allows the user to select the surface storage method for the selected subbasin. Surface storage methods are used to compute precipitation losses due to local depressions in the ground surface, cracks and crevices in parking lots or roofs. The surface component is included to represent the ground surface where water may accumulate in surface depression storage. Selecting a surface method is optional and generally only used for continuous simulation applications. The dropdown combo box provides the following runoff methods:
1. None
2. Simple Storage
  
  Refer to this article in our knowledge base to learn about various surface storage methods and how to use them to compute surface runoff.
Canopy method
This dropdown combo box allows the user to select the canopy method for the selected subbasin. The canopy component represents the presence of plants in the landscape. The dropdown combo box provides the following runoff methods:
1. None
2. Simple Canopy
  
  Refer to this article in our knowledge base to learn about various canopy methods and how to use them to compute surface runoff.
Drainage area
This entry field defines the area of the selected subbasin. The user can either enter the value manually or click the […] button to measure the subbasin area from the Map View. Clicking on the […] button allows the user to draw a measurement polyline representing the outline of the subbasin area. However, initially the software will assign the area from the defined subbasin polygon. If the user graphically edits the subbasin polygon boundary, then the drainage area value automatically updates based upon the Recompute dimensions on element edits checkbox setting in the Options backstage page. Refer to this article in our knowledge base to learn about the Options backstage page.

Clicking on the [Recalc] button causes the software to automatically update this field value with the corresponding subbasin polygon area. Similarly, the [Recalc All] button causes the software to update the subbasin areas for all subbasin polygon areas.
Downstream connection
This entry field defines the downstream element that the selected subbasin drains to. Clicking on the […] button allows the user to select the downstream element from the Map View. The following elements can be selected:
1. Diversion
2. Junction
3. Reach
4. Reservoir
5. Sink
  
  Note that a subbasin cannot connect to another subbasin.
Runoff (flow) adjustment ratio
This spin control entry field allows the user to specify an adjustment ratio for calibrating the runoff from the selected subbasin. By default, the software uses a value of 1.00, meaning that there is no adjustment. However, the user can enter a different value ranging from 0 to 1.

Computational Results

This section allows the user to see the analysis results for the current subbasin that was computed by HEC-HMS.
Computational Results section

DSS Data

This section includes an external DSS file for referencing the HEC-HMS computational results. It allows the user to easily copy the references and paste them into GeoHECRAS.
DSS Data section

DSS file name: This entry defines the external DSS file to be used for reading the data.
Data path: This entry denotes the data path within the DSS data file which contains the paired data.

Baseflow Data

The Baseflow Data panel is used to enter the data for the selected baseflow method for the defined subbasins. This panel is displayed when the Baseflow Data option is selected in the Subbasin Specifications dropdown combo box. Note that the Baseflow Data panel content changes based upon the baseflow method selected in the General Specifications section.
Baseflow Data panel

Refer to this article in our knowledge base to learn more about this panel.

Canopy Data

The Canopy Data panel is used to enter data for the selected canopy method for the defined subbasins. This panel is displayed when the Canopy Data option is selected in the Subbasin Specifications dropdown combo box. Note that the Canopy Data panel content changes based upon the canopy method selected in the General Specifications section.
Canopy Data panel

Refer to this article in our knowledge base to learn more about this panel.

Infiltration (Loss) Data

The Infiltration (Loss) Data panel is used to enter data for the selected infiltration method for the defined subbasins. This panel is displayed when the Infiltration (Loss) Data option is selected in the Subbasin Specifications dropdown combo box. Note that the Infiltration (Loss) Data panel content changes based upon the infiltration (loss) method selected in the General Specifications section.
Infiltration (Loss) Data panel

Refer to this article in our knowledge base to learn more about this panel.

Runoff (Transform) Data

The Runoff (Transform) Data panel is used to enter data for the selected runoff method for the defined subbasins. This panel is displayed when the Runoff (Transform) Data option is selected in the Subbasin Specifications dropdown combo box. Note that the Runoff (Transform) Data panel content changes based upon the runoff (transform) method selected in the General Specifications section.
Runoff (Transform) Data panel

Refer to this article in our knowledge base to learn more about this panel.

Surface Storage Data

The Surface Storage Data panel is used to enter data for the selected surface storage method for the defined subbasins. This panel is displayed when the Surface Storage Data option is selected in the Subbasin Specifications dropdown combo box. Note that the Surface Storage Data panel content changes based upon the surface storage method selected in the General Specifications section.
Surface Storage Data panel