How to use GRASS module to delineate watershed area？

Question

Update#1：I changed to work under qgis 1.8, I only input the DEM file and run the r.watershed module, and I got this：

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I have a DEM file of one specified region, and I take the following steps to get files that might be used：

1. Fill Sinks(this one I use SAGA module instead of GRASS)
2. r.fill.dir

After step 2, I want to get flow accumulation file, but I can not find this kind of module in GRASS, so I pass it and directly try the r.watershed module.

There are several input options in this module, like this：

I tried any of files I have as input files, but I can't get the output files through this module, and always got this error message：

The log below told me that the data source is invalid, and I go to check the sextante message log：

ERROR|Wed Jan 22 2014 12:38:01|Could not load model watersheds.model|ALGORITHM:saga:catchmentarea(parallel)

What should I do to successfully use the r.watershed module？

Thanks for giving me any suggestion!

Answer 1

Please do not use sink-filling for r.watershed, it is nor needed nor desired. r.watershed takes care by itself due to its internal least cost routing algorithm.

A minimalistic example:

r.watershed elev=dem basin=catchments thresh=10000

For a tutorial, see http://grasswiki.osgeo.org/wiki/Creating_watersheds