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
The Draw/Assign Reaches command allows the user to manually draw/assign polylines on the Map View as reaches one after another until completed.
Follow the steps below to use the Draw/Assign Reaches command:
- From the Input ribbon menu, select the Routing Reaches dropdown menu and then choose the Draw/Assign Reaches command.
- The following dialog box(s) will be displayed.
- Draw Reaches:
- Assign Reaches:
- Draw Reaches:
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/Assign Reaches command and interact with the above dialog box(s).
Drawing Reach Polylines
The Draw Reach Polylines section is used to draw the reaches on the Map View using polylines. To draw reach polylines, follow the steps below:
- From the Draw Reach Polylines section, click the [Draw] button, and the dialog box will temporarily disappear. Use the Draw curvilinear polyline checkbox option to draw the polyline using curvilinear segments.
- 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.
- To draw the reaches 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.
- After completing the reach drawing, the Draw Reaches dialog box will be redisplayed, and the Reach polylines read-only field will be changed from Not Drawn to Drawn.
- The user can also reverse the direction of the drawn/assigned reach by clicking the [Reverse Direction] button.
Selecting Reach Polylines
The Select Reach Polylines section can be used to manually assign multiple polylines on the Map View as reaches. To assign reach polylines, follow the steps below:
- From the Select Reach Polylines section, click the [Pick] button and the dialog box will temporarily disappear.
- The status bar (shown under the Map View) will prompt you to select a reach polyline from the Map View. Click on the previously drawn reach polyline on the Map View to select it.
- Following the selection of a reach polyline, the Assign Reaches dialog box will be redisplayed, and the Reach polylines read-only field will be changed from Not Selected to 1 Selected.
This section is common to both the Draw Reaches and Assign Reaches dialog box and is used to specify the reach ID for each drawn/assigned 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:
- If a reach was drawn/assigned while the Reach ID radio button option was selected, the user can manually enter the reach ID in the corresponding field as shown below.
- Alternately, the user can enable the Auto-name reach ID radio button option to automatically name every newly drawn/assigned reach as per the user’s predefined naming formats as shown below.
The 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.
- After providing the Reach ID, press the [Enter] key or click 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/assigned reaches have already been named and created.
Assign Reach Slope, Downstream Invert Elevation, Flow Direction & Missing Junctions
This section is common to both the Draw Reaches and Assign Reaches dialog box and allows the user to assign an invert elevation to the reach using a terrain model. Define this section before drawing/assigning the reaches so that the invert elevations can be assigned.
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.
In the Assign Reaches dialog box, an additional Create junctions (if missing) at confluences checkbox option is provided. 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.