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Draw Subbasins Command

In hydrology, a subbasin is used to represent the physical watershed. When precipitation is added as an input, the outflow from the subbasin element can be calculated by subtracting precipitation losses, transforming excess precipitation to stream flow at the subbasin outlet, and adding baseflow. In GeoHECHMS, the Draw Subbasins command allows the user to interactively draw polygons on the Map View as subbasins. After drawing subbasins, the user can name individual subbasin with a unique ID.

Follow the steps below to use Draw Subbasins command:

  1. From the Input ribbon menu, select the Drainage Subbasins menu item and then Draw Subbasins command.
  2. The Draw Subbasins dialog box will be displayed.

The following sections describe how to use the Draw Subbasins command and how to interact with the above dialog box.

Draw Subbasin Polygon

This option is used to draw the subbasins on the Map View using polygons. To draw a subbasin polygon, follow these steps:

  1. Click on the [Draw] button and the dialog box will temporarily disappear.
    Note that the user can press [Ctrl+B] to use the Draw Subbasins command directly on the Map View.
  2. To finish digitizing the subbasin polygon, the user can either press the [Enter] key or right-click and select Done from the displayed context menu. The user can press the [Esc] Key to abort the current draw command.
  3. After completing the subbasin drawing, the user is immediately returned to the Draw Subbasins dialog box, and the Subbasin polygon read-only field will be changed from Not Drawn to Drawn.
    Note that the user can turn on the Draw curvilinear polygon check box or can press the [Ctrl] key to enable the curvilinear segments while drawing the polygons.

Subbasin Specifications

This option is used to specify each drawn subbasin by providing each with an ID. The user can assign these IDs either manually or automatically by using some predefined formats.

Follow the steps below to assign subbasin IDs to the subbasins:

  1. If a subbasin has been drawn while the Subbasin ID option is enabled, the user can manually enter the Subbasin ID in the corresponding field as shown below.
  2. Alternately, the user can enable the Auto-name subbasin ID option in order to automatically name every newly drawn subbasins as per the user’s predefined naming formats as shown below.

    The different subbasin naming formats present in the Auto-name subbasin ID option are as follows:
    • Subbasin ID prefix: Turn on this option to add a prefix to the subbasin ID.
    • Subbasin ID digits: Use this option to prefix the number of zeros in the Next available subbasin ID.
    • Next available subbasin ID: Use this option to set the initial count number while assigning the Subbasin ID.
    • Subbasin ID increment: Use this option to add the increment in the Next available subbasin ID count.
    • Subbasin ID suffix: Turn on this option to add a suffix to the subbasin ID.
    • Subbasin ID preview: Use this option to see a preview of the subbasin naming scheme applied above.
  3. After providing the Subbasin ID, press the [Enter] key or click on the [Apply] button.
    Note that if the auto-name option is enabled and the user returns to the dialog box, the [Apply] button is disabled since the just drawn subbasins have already been named and created.
  4. The drawn subbasin will be displayed on the Map View.

About the Author Chris Maeder

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