I am trying to follow along with this exercise using my own DEM.

I have done the first step, creating the catchment area, with no trouble. When I try to run the Channel network algorithm, however, I get the error message “Input layers do not have the same grid extent.”

I don’t see anywhere to specify a change in extent or cell size, so I’m puzzled about why the extents are different at all. And then if they are different, how can I get them to be the same? I’ve tried using the raster layer clipping to make new layers from the DEM and the catchment area to the same extent, but this gave me the same error.

I did try running the Channel network and drainage basins algorithm, and this worked but the channels seemed to be incomplete − it looked like only the top two order channels were there, with nothing below these.

I’m using QGIS 2.6.0 on Windows 8.1.

I’ve been using TauDEM to do this work since I haven’t resolved the issue described above.

  • Update: I’ve been using TauDEM to do this work since I haven’t resolved the issue described above.
    – Graham vdR
    Commented Dec 8, 2014 at 21:33
  • I've had the same trouble with "Channel networks". I even changed my DEM to match the extents and resolution of the "catchment area" output - which were slightly different (why?). (I hope this was a legal move.... I am a beginner.) I did this by saving the DEM with new extents/resolution, then importing. I'm using SAGA 2.08 (v. 2.10 or 2.12 give problems with the "fill sinks"- placing the outputs in far away places - so I had reverted to v.2.08) within QGIS 2.6. Sorry to add this in the "Answer" section. As a new user, I'm not permitted to "comment."
    – user46458
    Commented Feb 13, 2015 at 7:07
  • In the end, I found that the problem was in having inconsistent CRS.
    – user46458
    Commented Feb 24, 2015 at 7:24
  • This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post. Commented Feb 24, 2015 at 7:56

2 Answers 2


To make two grids to have the same grid system, open SAGA GUI and load your both (or more grids).Then open the tool "Resampling". Choose one grid as input grid and grid system. You will be able to select the other grid system as target grid system. After that both grids will be in the same grid system. Please notice that the resampling may modify the values of the processed grid.


I had the same issue some time ago, and found out eventually that my grids were actually slightly off centered, even if it did not look like they were.

I solved it by using gdal Warp (reproject) tool on QGIS 3.16 without reprojecting the raster. I used it just to resample one of the rasters to match the exact grid of the other one. The grids also need to have the same cell size, which can also be adjusted in Warp (reproject) tool.

I wrote a blog post about it, where you can find a larger explanation: https://www.luisalucchese.com/post/saga-gis-error-catchment-area/

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