The first step prior to further operations is to make sure that your DEM is free of depressions.

Otherwise you will get sinks in the middle of watercourses, which will impact contours and stream networks.

Note that in karst (cave) areas you need to be careful as there may be legitimate depressions.

There are two main approaches for removing depressions - Fill Sinks or Breach Depressions. The best one to use may depend on the landscape. Fill Sinks is the most common approach. However, for bushwalking areas, I have generally found that Breach Depressions works better. In particular, it tends to better carve out the path of streams through narrow canyons.

As of QGIS 3.30, none of the tools for doing this are provided in the core installation - you will need to install SAGA GIS, Whitebox Tools, or both. There are instructions for this on the Install Plugins.

My general preference is to use BreachDepressions from Whitebox Tools. It is simple and fast, and for typical bushwalking areas produces a good result.

There are various related tools in the Processing Toolbox that will do this, including:

• SAGA : Terrain Analysis - Hydrology : Fill Sinks
• SAGA : Terrain Analysis - Hydrology : Fill Sinks (Wang and Liu)
• SAGA : Terrain Analysis - Hydrology : Fill Sinks XXL (Wang and Liu)

The results from all will be similar, but the Wang and Liu versions should be faster.

There are other approaches that deepen channels rather than fill sinks in order to get a hydrologically sound drainage network. Within SAGA:

• SAGA : Terrain Analysis - Hydrology : Sink Removal

is one option

The other is Whitebox Tools BreachDepressions algorithm. Settings will depend again on the landscape, but a Maximum Breach Depth of 15-20m and a Flat Increment Value of 0.00001 have worked well so far.