Tutorial: Stream and Catchment Delineation

6. Fill Sinks and Calculate Flow Direction

Raw, unprocessed DEMs have artifacts such as depressions. Artifacts are a result of the DEM acquisition process and must be removed before a DEM can be used for hydrological analysis, like catchment and stream delineation or hydrological modelling. There are several algorithms for filling sinks. Here we'll use the lddcreate tool from the PCRaster Tools plugin. This tool fills the sinks and creates a flow direction map (also called local drain direction map) at the same time. The resulting flow direction raster can be used in the next steps.

First we'll install the PCRaster Tools plugin. Then we'll convert the DEM in PCRaster format (.map, which is a GDAL supported raster format). Next we'll fill the sinks and derive the flow direction with the lddcreate tool. Finally, we'll style the flow direction map.