I have tried to calculate the Specific Catchment Area in QGis from Specific Catchment Area and Flow Width Tool available through Saga. However, I got just SCA product with valour 0. I got a reasonable product with Flow width.

Can anyone help me?

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    – PolyGeo
    Commented Jul 31, 2018 at 1:58
  • Eduardo's description is precise. Because this tool is so simple, believe me, there is nothing much to add. If you give DEM then it will return Flow width. If you give DEM + Catchment Area, it will return Flow width + SCA.
    – Kazuhito
    Commented Aug 1, 2018 at 14:51
  • Thank you Kazuhito, I got some results, however, I am not sure which file I should use in Total Catchment Area. I have read some discussion I saw that Total Catchment Area could be provided through Catchment Area or Flow Accumulation (through Saga tools available in Qgis). Initially, I thought that it was the catchment area rasterized (filled polygon or only the limit of catchment). Please if anyone may give details about what is the file associated with Total Catchment Area. Commented Aug 2, 2018 at 17:28
  • Sorry Eduardo it seems I have missed your message. Yes, you are right; A raster layer Catchment area (aka Flow accumulation) is the one you need.
    – Kazuhito
    Commented Aug 10, 2018 at 21:09

1 Answer 1


Flow width and Specific catchment area tool in QGIS processing toolbox returns only Flow width if you do not give it a Total Catchment Area (TCA) layer as an input.

It is possibly misleading that the tool still produces a blank layer (all zeros), and I can understand your dismay at it.

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