Tutorial: Delineate multiple subcatchments

2. Digitize pour points

First we're going to digitize the pour points (points for which we want to delineate their contributing areas, i.e. catchments).

1. Start QGIS.

2. In the main menu go to Project | Open From | GeoPackage...

3. In the Load project from GeoPackage dialogue browse to the data_multiple_subcatchments.gpkg GeoPackage, choose the Multiple_Subcatchments project and click OK.

In the project you see the Rur catchment boundary, hydrography and filled DEM (filling a DEM is explained in the tutorial on stream and catchment delineation, which you need to apply to your own data before following the steps in this tutorial).

Now we're going to add a background map from which we can digitize some outlets. We'll use OpenStreetMap.

4. Install the QuickMapServices plugin. Go to the main menu and choose Plugins | Manage and Install Plugins...

5. Install the QuickMapServices plugin and click Close.

6. In the main menu go to Web | QuickMapServices | OSM Standard

7. Switch off the DEM and Hillshade by unchecking the box before the layer name in the Layers panel.

Rur with OSM

8. Zoom in to a location in the catchment where two tributaries join.

9. In the toolbar click to create a new temporary scratch layer.

10. In the New Temporary Scratch Layer dialogue give Pour point as Layer name, choose Point as Geometry type and select the projection of the project (EPSG: 32632). Keep the rest default.

11. Click OK to create the empty point vector layer.

We create this temporary scratch layer, because it is an intermediate step and we don't need to keep that layer.

Now we'll digitize the point in the river where the tributaries join.

12. Make sure editing is toggled on for the Pour point layer and click to add a point feature.

13. Place the feature on the point in the river on the map where the tributaries join.

14. Repeat this for a few other points for which you want to create the subcatchments.

15. Toggle off editing by clicking and click Save.

In the next section we're going to snap the digitized pour points to the hydrography.