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I have a set of streams (currently a shapefile (line)) which I need to delineate the watersheds for. I have attempted to use various QGIS tools, however, each tool I have tried is for delineation of an entire region (i.e. DEM) rather than a few streams contained in a vector file.

My question is this: does anyone know of a tool designed to use vector files as an input (along with a filled dem) to generate watershed basin areas only for the lines in the file?

If more information is needed, please let me know and I will provide it and/or edit this post accordingly.

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  • gis.stackexchange.com/a/348154/120129...I wrote this script specifically for these cases, if you can use it, it should help you solve your problem... – Cyril Mikhalchenko Feb 20 '20 at 20:04
  • @CyrilM's suggestion will generate voronoi diagrams around the streams, which will look like watersheds. But they won't be actual, accurate watersheds, because watershed boundaries depend on elevation. You need elevation data to generate real watershed boundaries. – csk Feb 20 '20 at 20:06
  • @csk, you're really right, if we're talking about the exact model of the watersheds :-)...if we're talking about an approximate one, then... – Cyril Mikhalchenko Feb 20 '20 at 20:10
  • @bob-bob the watershed needs a point more than a line, so if you have a line for a streach of a stream, you need to choose a point of the line, the higher or the lower along the river? it will depend of your purpposes, but my guess is that the lowest point is the one you are looking for. – Marco Feb 24 '20 at 8:09
  • I know how r.water.outlet works, which I think it could fit your needs, but it is true that it needs a previous step of calculating the flow directions for a larger area and it will require that the stream lines (your lines) are actually on the accumulation path – Marco Feb 24 '20 at 8:15

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