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Georeferencing River Reaches
When the software imports a model, it automatically places the river reach, junctions, and cross sections on the Map View. However, if the original model was not spatially georeferenced, the river reach (and associated junctions and cross sections) will not align with any loaded background base map. While the software can operate without any issues in this situation, it is preferable to have the river data georeferenced to the background base map. Therefore, it might become necessary to georeference the imported river reach.
The Georeference River Reaches command in GeoHECRAS is used to manually georeference each of the river reaches to the background base map displayed in the Map View. The process of georeferencing a river reach to the Map View can be a trial and error process—especially when the exact location of the original river reach is not known. Using the Georeference River Reaches command, the georeferencing process can be accelerated.
Follow the steps below to georeference an existing river reach:
- From the Input ribbon menu, click on the River Reaches dropdown menu and then select the Georeference River Reaches command.
- The Georeference River Reaches dialog box will be displayed.
The following sections describe how to georeference an existing river reach and interact with the above dialog box.
Selecting River Reach
This section allows the user to select the river reach to be georeferenced.
Note that if a river reach has been preselected from the Map View before running this command, then the selected river and reach will be displayed in the River and Reach dropdown combo boxes.
If the model contains a single river and reach, then it will automatically be selected in the River and Reach dropdown combo boxes. If the model contains multiple rivers and reaches, then the user can select the desired river and reach from the River and Reach dropdown combo boxes.
Alternatively, the user can click the [Pick] button to select the river reach from the Map View. Clicking on the [Pick] button causes the dialog box to temporarily disappear and the user will be prompted to select the river reach from the Map View. After selecting a river reach, the dialog box will be redisplayed with the river reach shown as selected. The selected river reach is highlighted on the Map View. To abort the selection process, press the [Esc] key or right-click and select Cancel from the displayed context menu.
After selecting the river reach, the user can select one of the following georeference options:
- Snap to Alignment Centerline
- Slide along Alignment Centerline
- Draw on Map View
Snap to Alignment Centerline
If an existing river alignment centerline for the selected river reach exists on the Map View, the Snap to Alignment Centerline can be used to snap the HEC-RAS river reach to the alignment centerline. Select the Snap to Alignment Centerline radio button option to enable this section.
- Pick near upstream end
Clicking the [Pick] button adjacent to this read-only entry allows the user to pick a point from the Map View near the upstream end of the river alignment centerline.On clicking the [Pick] button, the dialog box will temporarily disappear and the user will be prompted to select an upstream point on the river centerline. After selecting the point, the user will be returned to the dialog box and the Pick near upstream end entry changes from Not Selected to Selected. In addition, a temporary highlighted point is shown on the river centerline to show the selected location. To abort the selection process, press the [Esc] key or right-click and choose Cancel from the displayed context menu. - Pick near downstream end
Clicking the [Pick] button adjacent to this read-only entry allows the user to pick a point from the Map View near the downstream end of the river alignment centerline. On clicking the [Pick] button, the dialog box will temporarily disappear and the user will be prompted to select a downstream point on the river centerline. After selecting the point, the user will be returned to the dialog box and the Pick near downstream end entry will change from Not Selected to Selected. In addition, a temporary highlighted point is shown on the river centerline to show the selected location. To abort the selection process, press the [Esc] key or right-click and choose Cancel from the displayed context menu.
After selecting the upstream and downstream end of the river reach, click the [Snap] button and the river reach will get snapped to the alignment centerline.
Note that the [Snap] button can only be enabled when the upstream and downstream end of the river reach has been selected. In addition, a preview of the snapped river reach is shown on the river alignment centerline, which allows the user to reselect the pick points or cancel the selection process.
The user can turn on the Scale to fit checkbox option to scale the river reach to fit within the alignment centerline.
If the upstream and downstream points do not overlay the same continuous alignment centerline, then the following informational message will be displayed.
Slide along Alignment Centerline
If the HEC-RAS river reach has been snapped to an alignment centerline on the Map View, but is not precisely located where it should be, the Slide along Alignment Centerline option can be used. This option allows the user to slide the HEC-RAS river reach along an underlying river alignment centerline, as well as shrink or stretch the river reach to fit between two known locations. Select the Slide along Alignment Centerline radio button option to enable this section.
Click the [Slide] button to manually slide river reach along the underlying alignment centerline. Clicking the [Slide] button makes the dialog box temporarily disappear and prompts the user to click on the river reach and drag it along the underlying river centerline. Once finished, press the [Enter] key or right-click and select Done from the displayed context menu. To abort the operation, press the [Esc] key and the moved river reach will return to its original location.
While dragging (sliding) the river reach along the river alignment centerline, the user would not be allowed to move the river reach beyond the end of the centerline.
Note that if the endpoints of the HEC-RAS river reach do not overlay the same continuous centerline, then the following informational message will be displayed.
Draw on Map View
This section allows the user to draw the river reach on the Map View. Select the Draw on Map View radio button option to enable this section.
Clicking the [Draw] button temporarily removes the dialog box and prompts the user to draw the river reach on the Map View in an upstream to downstream direction. Once the river reach drawing is finished, press the [Enter] key or right-click and select Done from the displayed context menu. The river reach will automatically snap to the drawn alignment polyline. To abort the operation, press the [Esc] key and the snapped river reach will return to its previous location.
The user can turn on the Create curvilinear polyline checkbox option to draw the polyline using a curvilinear segment. Refer to this article in our knowledge base to learn more about element digitizing on the Map View.
The user can select the Maintain existing reach alignment for segments outside of the drawn reach checkbox option to maintain the existing reach alignment for segments outside of the drawn reach.
Reach Length Handling
This section allows the user to select the method that should be used to reference the total length of the river reach.
The following radio button options are provided:
- Use actual river reach length (total channel flow length)
On selecting this option, the software will automatically extend or shorten the downstream end of the river reach to match the total channel flow length. - Use digitized length (schematic layout)
On selecting this option, the software uses the user’s digitized river reach as the river reach, even if the actual river reach length is greater or less than what the user has digitized. The benefit of this option is that the user can create a schematic layout of the river reach to fit perhaps poorly created HEC-RAS data models to fit a map.
Other Options
The Update cross section geometric layout checkbox option allows the user to update the cross section geometric layout. By default, this option is checked. If unchecked, then the river reach cross sections will not be moved from their current position.
Note that checking the Maintain existing reach alignment for segments outside of drawn reach checkbox option will automatically uncheck the Update cross section geometric layout checkbox.
