The next process to add is to fill the sinks in the DEM to get rid of depressions that trap the water flow.
1. In the Algorithms panel look for the SAGA Fill sinks (Wang & Liu) algorithm and double click.
2. In the Fill sinks (wang & liu) dialogue choose for DEM the algorithm output from the previous step. Because we need the filled DEM to be saved to disk we type Filled DEM for Filled DEM.
3. Click OK.
The model now looks like the figure below. Note that the output layer (Filled DEM) is in a green box. You can move the box below the last algorithm.
We can now proceed with implementing the next step.