Georeferencing Subbasins

When the GeoHECHMS software imports a model, it automatically places the subbasins on the Map View. However, if the original model was not spatially georeferenced, the subbasins will not align with any loaded background base map. While the software can operate without any issues in this situation, the user may prefer to have the subbasins georeferenced to the background base map. Therefore, it may become necessary to georeference the imported subbasins.

The Georeference Subbasins command is used to manually georeference each of the subbasins to the background base map displayed in the Map View. The process of georeferencing subbasins to the Map View can be a trial-and-error process—especially when the exact location of the original subbasins is not known. Using the Georeference Subbasins command, the georeferencing process can be accelerated.

Follow the steps below to georeference an existing subbasin:

1. From the Input ribbon menu, click on the Drainage Subbasins dropdown menu and then select the Georeference Subbasins command.
   
2. The Georeference Subbasins dialog box will be displayed.
   
3. Click the [Pick] button adjacent to the Subbasin ID dropdown combo box.
   
4. The Georeference Subbasins dialog box will temporarily disappear, and a prompt will be displayed on the status bar instructing the user what to do next.
5. Select subbasin on the Map View.
6. The Georeference Subbasins dialog box will be redisplayed, and the selected subbasin will be displayed in the Subbasin ID dropdown combo box.
   Alternatively, choose the subbasin from the dropdown combo box adjacent to the Subbasin ID entry.
   Note that if a subbasin has been preselected prior to running this command, the selected subbasin will be displayed in the Subbasin ID dropdown combo box.
7. Click the [Clear] button to cancel all the previous selections and redo the entire process.

Once the subbasin has been selected, the user can choose between the following options to georeference the subbasin.

Snap to Alignment Polyline/Polygon

If an existing river alignment centerline for the selected subbasin exists on the Map View, the Snap to Alignment Polyline/Polygon can be used to snap the HEC-HMS subbasin to the alignment polyline/polygon.

Follow the steps below to snap the subbasin to the selected alignment polyline or polygon:

1. Choose the Snap to Alignment Polyline/Polygon radio button option and click the [Pick] button adjacent to the Select alignment polyline/polygon read-only field.
   
2. The Georeference Subbasins dialog box will temporarily disappear, and a prompt will be displayed on the status bar instructing the user what to do next.
3. Select the alignment polyline or polygon on the Map View.
4. The Georeference Subbasins dialog box will be redisplayed, and the status of the Select alignment polyline/polygon read-only field will be changed from Not Selected to Selected.
5. Click the [Clear] button to cancel all the previous selections and redo the entire process.
6. Click the [Snap] button.
   
7. The software will snap the subbasin to the selected alignment polyline or polygon.

Draw on Map View

This section allows the user to draw the subbasin polygon on the Map View.

Follow the steps below to draw the storage area on the Map View:

1. Choose the Draw on Map View radio button option and click the [Draw] button. Alternatively, turn on the Create curvilinear polygon checkbox option to draw the polygon using curvilinear segments.
   
2. The Georeference Subbasins dialog box will temporarily disappear, and a prompt will be displayed on the status bar instructing the user what to do next.
3. Draw the subbasin polygon on the Map View.
4. When drawing the subbasin polygon, click on a starting location on the subbasin outline and click on locations where the subbasin outline changes direction. While drawing the subbasin on the Map View, a rubber banding line will be shown to indicate where the subbasin is being placed. Finally, click an ending location for the subbasin outline.
5. When finished, press the [Enter] key or right-click and choose Done from the displayed context menu.
   Note that only one subbasin can be drawn at a time, although the user can revise the drawn subbasin by reselecting the [Draw] button.
6. The Georeference Subbasins dialog box will be redisplayed.
7. The software will automatically snap the subbasin accordingly.

Additional Georeferencing Options

This section contains the Assign polygon area as subbasin drainage area checkbox option. The user can turn on this checkbox for assigning the polygon area as the subbasin’s drainage area. By default, this checkbox option is unchecked when the dialog box is displayed.