6.5 Basin delineation

The next step involves delineating your river basin. Note that this step is only required if the routing module has been selected from the Modules tab. An overview of the Basin delineation tab is shown in Figure 19. Before you can delineate your basin, you need to have an outlets.shp shapefile, representing the outlet(s) of your basin(s). If you do not have this file, then you can create it using QGIS and following the steps below:

1. Create a new shapefile layer by clicking the New Shapefile Layer button (Figure 20).

2. Make sure you select Point as Type in the window that pops-up (Figure 21) and that you select the correct CRS (see Section 3.2.2).

3. Click Ok.

4. Give it the name outlets.shp and save it somewhere on your hard disk. It is recommended to save this file under the processed model data folder you have set in Section 3.2.1. After saving this layer it will appear in the QGIS map canvas (Figure 22).

5. Now start editing this layer by clicking the Toggle Editing button (Figure 23). Make sure that the outlets layer is selected before clicking this button.

6. Now start adding the outlets by clicking the Add Feature button (Figure 24).

7. Make sure you can accurately determine the location of your river network. This can be done by looking at the accuflux layer and choosing an appropriate color layout. Now start adding one or more outlets to this layer by clicking on the desired locations of your river network (Figure 25). Each time you click a location you need to enter a value. Start with 1, and continue numbering until the number of outlets you desire.

8. Figure 26 shows an example of having 3 outlets added to the outlets.shp layer. The attribute table can be shown by right clicking on this layer and then Open Attribute Table.

9. If you are finished with adding outlets you can click again on the Toggle Editing button (Figure 23). Next click Save to save your edits to the outlets.shp layer. Now you are finished with creating an outlet(s) layer shapefile.

Figure 19: Overview of the Basin delineation tab.

Figure 20: Creating a new shapefile layer.

Figure 21: Setting the properties of the new Shapefile Layer.

Figure 22: outlets.shp layer in the layers overview.

Figure 23: Editing a layer in QGIS.

Figure 24: Adding features in QGIS

Figure 25: Adding outlets to the outlets.shp layer in QGIS

Figure 26: Example of 3 outlets that have been added to the outlets.shp layer.

Now select the outlets.shp file by clicking the Select outlet(s) shapefile button (Figure 19). Your GUI now may look like Figure 27.

Figure 27: Overview of the Basin delineation tab with the outlet(s) shapefile selected.

There are now two additional options available for delineating your basin:

• Clip to basin mask: all SPHY model input maps will be clipped to the extent of your delineated basin. This results in smaller input map sizes and reduced model runtime.

• Create sub-basins: sub-basins will be createdfor outlets that are located inside the basin outline of your most downstream outlet.

Select or de-select these options, and click Delineate basin to start the basin delineation. Basin delineation may take a while, and during delineation several maps will be removed and added to the QGIS map canvas. After delineation has been completed the GUI may look something similar like Figure 28.

Note that the Delineate basin button has become inactive if you have selected the Clip to basin mask option. This means you only can redo basin delineation after going back to the Modules tab and click the Create initial maps button again. Or you may start over with the Area selection tab if you are not happy with the results of the delineated basin(s).

Figure 28: Basin delineation finished.