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I am using the GrassGIS r.stream.extract extension to delineate a stream network with the options 'mexp' (Montgomery exponent) and 'd8cut' (Use SFD above this threshold). It works perfect so far and is a great improvement over r.watershed. My problem is that if I use r.stream.basins afterwards I cannot extract half basins (left and right site of a river) as it was possible in r.watershed. I wonder if there is a tool with whom I can do that? r.stream.extract delivers a flow direction map and the stream network.

Best Regards

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What you refer to as half basins are often called hillslopes. I'm not aware of any tool in GRASS GIS that can extract these features from a stream network and a DEM, although it is possible that I have overlooked the correct tool. However, if you are open to using alternative open-source GIS then I can recommend the hillslopes tool in Whitebox GAT, for which I am a developer.

enter image description here

The tool takes a raster streams file and a D8 flow pointer grid as input and outputs a raster for which each cell is assigned to the unique hillslope draining either to a particular side of a stream segment or to a stream head. I've simply vectorized the raster polygons and streams file in the image above for visualization purposes.

enter image description here

If it turns out that you require a GRASS based solution, just let me know in a comment and I'll delete my answer, otherwise, I hope this helps to solve your problem.

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  • Excellent answer! I also cannot find a similar tool in GRASS. Regardless, I would keep this answer in as it provides a very clear solution for another software which could be of use to others.
    – Joseph
    Jan 14, 2015 at 15:45
  • It works perfect with my data from GRASS after I changed the flow direction map. Thank you very much and I will try to check out WhiteboxGIS a little more as soon as possible.
    – MonteCarlo
    Jan 14, 2015 at 17:20
  • @Joseph Thanks very much. I was a little surprised when I looked into it that there wasn't a similar tool in GRASS because that's where I thought I had got the idea many years ago to make the tool in what was then TAS. Oh well.
    – WhiteboxDev
    Jan 14, 2015 at 21:10
  • @MonteCarlo I'm glad that it worked. I'm sorry, I had thought about the fact that you'd probably need to redo your D8 flow pointer raster afterwards (since GRASS likely uses a different ordering scheme than Whitebox) but didn't remember to add it into the answer. Regardless, I'm glad that it was able to be of use to you.
    – WhiteboxDev
    Jan 14, 2015 at 21:12

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