1. Home
  2. Knowledge Base
  3. GeoHECHMS
  4. Draw and Assign Reaches Command

Draw and Assign Reaches Command

A reach is a section of a stream or river along which similar hydrologic routing conditions exist, such as discharge, depth, area, and slope.

In GeoHECHMS, reaches can be defined by either drawing or assigning polyline(s) on the Map View using the following commands:

  • Draw Reaches
  • Assign Reaches

Drawing Reaches

The Draw Reaches command allows the user to interactively draw polylines on the Map View as reaches.

Follow the steps below to use the Draw Reaches command:

  1. From the Input ribbon menu, select the Routing Reaches dropdown menu and then choose the Draw Reaches command.
    Draw Reaches ribbon menu command
  2. The Draw Reaches dialog box will be displayed.
    Draw Reaches dialog box

Note that pressing the [Ctrl+E] keys will run the Draw Reaches command directly on the Map View.

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

Drawing Reach Polylines

The Draw Reach Polylines section is used to draw the reaches on the Map View using polylines. To draw a reach polyline, follow the steps below:

  1. Click on the [Draw] button and the dialog box will temporarily disappear. Use the Draw curvilinear polyline checkbox option to draw the polyline using curvilinear segments.
    Draw Reaches dialog box - Draw Reach Polylines section
  2. The status bar (shown under the Map View) will prompt you to draw a reach on the Map View. Draw the reach polyline on the Map View. While drawing elements, the user can use the [Ctrl] key to switch between the curvilinear and the linear digitizing. Refer to this article in our knowledge base to learn more about drawing elements on the Map View.
    Drawing reach on Map ViewNotes:

    • To draw the reach more accurately, use the mouse roller wheel to zoom into a specific location.
    • The Snap Mode option can be enabled to cause the drawn reach to snap to the nearest HEC-HMS element.
  3. After drawing the reach, 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 draw command.
  4. After completing the reach drawing, the user is immediately returned to the Draw Reaches dialog box, and the Reach polylines read-only field will be changed from Not Drawn to Drawn.
    Draw Reaches dialog box - Reach polylines drawn
  5. The user can also reverse the direction of the drawn reach by clicking the [Reverse Direction] button.

Reach Specifications

This section is used to specify a reach ID for each drawn reach. The user can assign these IDs either manually or automatically using some predefined formats.

Follow the steps below to assign reach IDs to the reaches:

  1. If a reach has been drawn while the Reach ID option was enabled, the user can manually enter the reach ID in the corresponding field as shown below.
    Draw Reaches dialog box - Reach ID
  2. Alternately, the user can enable the Auto-name reach ID radio button option in order to automatically name every newly drawn reaches as per the user’s predefined naming formats as shown below.
    Draw Reaches dialog box - Auto-name reach IDThe different reach naming formats present in the Auto-name reach ID option are as follows:

    • Reach ID prefix: This option allows a prefix to be added to the start of the reach ID.
    • Reach ID digits: This option permits specification of a set number of digits to use for the reach ID. For example, using 3 digits causes the reach ID to be of the format 001, 002, etc.
    • Next available reach ID: This entry defines the next element ID number to be used.
    • Reach ID increment: This entry defines the increment to use when numbering elements. The default value is 1.
    • Reach ID suffix: This option allows a suffix to be added to the end of the reach ID.
    • Reach ID preview: This entry provides a preview of the reach naming specifications defined above.
  3. After providing the Reach ID, press the [Enter] key or click on the [Apply] button.
    Drawing reachNote 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 reaches have already been named and created.
  4. The drawn reach will be displayed on the Map View.

Assign Reach Slope, Downstream Invert Elevation, Flow Direction & Missing Junctions

This section of the dialog box allows the user to assign an invert elevation to the reach using a terrain model. Define this section before drawing the reaches so that the invert elevations can be assigned.
Terrain elevation source selection

To assign an invert elevation, the Terrain elevation source dropdown combo box supports the following surface types:

  • Elevation grids
  • LandXML data
  • TIN surfaces

The user can also apply an elevation offset to raise or lower the reach by the specified amount by checking the Apply elevation offset checkbox. On selecting this checkbox, the entry field next to it becomes available for entering an elevation offset value. A negative offset value will lower the reach by the specified amount.

Assigning Reaches

The Assign Reaches command is used to manually associate previously drawn polylines as reaches.

Follow the steps below to use the Assign Reaches command:

  1. From the Input ribbon menu, select the Routing Reaches dropdown menu and then choose the Assign Reaches command.
    Assign Reaches ribbon menu command
  2. The Assign Reaches dialog box will be displayed.
    Assign Reaches dialog box

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

Selecting Reach Polylines

The Select Reach Polylines section is used to select the previously drawn polylines from the Map View to assign them as reaches.

Follow the steps below to assign a reach polyline:

  1. Click the [Pick] button, and the dialog box will temporarily disappear.
    Assign Reaches dialog box - Select Reach Polylines section
  2. The status bar will prompt you to select the polyline on the Map View. Select the reach polyline on the Map View.
    Reach polyline selection on Map View
  3. After selecting the polyline, the user is immediately returned to the Assign Reaches dialog box. The Reach polylines read-only field will be changed from Not Selected to Selected.
    Assign Reaches dialog box - Reach polylines selected

Reach Specifications

This section is used to specify an ID for each selected reach polyline. The user can assign these IDs either manually or automatically by using some predefined formats.

Note that this section is similar to the Reach Specifications of the Draw Reaches dialog box. Hence, see the second subsection under Drawing Reaches to learn more about it.

Assign Reach Slope, Downstream Invert Elevation, Flow Direction & Missing Junctions

Note that the first three options of this section are similar to that of the Draw Reaches dialog box. Hence, refer to the third subsection of the Drawing Reaches section to learn more about it.

Additionally, a Create junctions (if missing) at confluences checkbox option is provided in this section. If the user assigns the reach polylines where the junction(s) are not available, then checking this checkbox option will automatically insert the junction(s) at the confluences.
Create junctions at confluences option

About the Author Chris Maeder

Was this article helpful?

Related Articles