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I am using qgis 2.14.17 with ubuntu16. Having as input data a DEM of the region and a river network. In the manual of qgis they suggest to use a toll of qgis: Catchment area (Parallel); I dont have this in my toolbox, anybody made the same experience and could tell me the reason for it and how to get it. It seems to offer the best solution for me. Tools which are available are from GRASS7 and TauDEM, the latter need much more data it seems. And I am not sure if I am able to create these just out of a DEM? The GRASS7 has one tool r.water.outlet: but here one has to put the outlet coordinates, which clearly I could get out of the river network, but the idea is that they are generated by delineating the watersheds.

Somebody has an idea how to solve it?

I managed now to get SAGA run in the toolbox, nevertheless would be great if somebody could help me with the qgis tool, since it should appear?!

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Assuming your QGIS 2.14.17 is equipped with SAGA 2.3.1 or 2.3.2, let me answer only the first question "where to find Catchment area (Parallel) in the QGIS Processing Toolbox?"

Try and find SAGA | Terrain Analysis - Hydrology | Catchment area

enter image description here

This tool uses parallel processing, so you would find it was called Catchment area (Parallel) in some older documents.

SAGA-wise, the tool has been renamed to Flow Accumulation (Top-Down) (from SAGA 2.1.3, I think). In the QGIS Processing Toolbox, it still keeps a plain name Catchment area, but this new name appears in the log while you are running the tool.

library path: C:\PROGRA~1\QGIS2~1.14\apps\saga-ltr\modules\
library name: ta_hydrology
library : Hydrology
tool : Flow Accumulation (Top-Down)
author : O.Conrad (c) 2001-2016, T.Grabs portions (c) 2010

In the meantime I am almost certain you will encounter an error Unknown option 'CAREA' using QGIS 2.14.17 (or even latest 2.14.19). If it occurs please try QGIS 2.18.13. (See this post Error in catchment area calculation by André Lourenço).

If successful, you will get something like this:

enter image description here

Usual workflow is to get this Catchment area first, next step is Channel network, and then Watershed basins.

If your River network is the same as Channel network (raster), you do not have to do this task. (I guess your river network might be vector...)

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    thanks again, I finally used SAGA (followed the workflow in youtube.com/watch?v=uSscn6ImRxU), here they start with: Fill sinks (Wang & Lui), calculate Strahler Order to find the freshold value for the tool: Channel Networl ad drainage basin (SAGA), finally to use the Upslope funcion of SAGA to find sub-catchment with given outlets (which was . of my final goals). And it worked fine with 2.14.17 – Nicole K. Oct 4 '17 at 21:01
  • @NicoleK. Thanks sharing the workflow! Great to know the way works with 2.14. – Kazuhito Oct 6 '17 at 9:57
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The GRASS option from the toolbox

  1. use the r.watershed with the DEM as input to obtain as output a drainage direction raster map and the accumulation raster map (Number of cells that drain through each cell).
  2. use the r.water.outlet with the drainage direction as input and a chosen point of the river taken from the acculation map
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    thanks, a lot to all of you, I also tried first r.watershed, but didnt get the results as I wanted, then I found another very nice tutorial from UNESCO online which uses QGIS and mainly the SAGA tools from the toolbox. You get the channel network and basins, as well explains how to get the sub-watershed of defined outlets, I can recommend it to everybody, it shows much more in the video (e.g. about plugins which are very helpful and other qgis tools): Catchment and steam delineation in qgis: youtube.com/watch?v=uSscn6ImRxU – Nicole K. Oct 4 '17 at 20:52

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