I'm trying to generate the hydrological analysis using processing and I have already done some terrain processing using the DEM.

In this moment, I'm working in he channel network but, when I assign in the elevation (the DEM) and in the Initiation Grid (the catchment area) the program gives me error.

Here are the screen shots of what has been generated:

this is the configuration in the channel network

this is the error

  • Fast forward to 2018 and QGIS 3 - this issue is still there and it cannot be bypassed even if all inputs have the same grid extent/CRS. Probably a bug? Apr 28, 2018 at 13:55

5 Answers 5


I've struggled with the same problem for a while. Even when they were in the same CRS the elevation and catchment grids were out by a couple of meters. I think it has something to do with the raster resolution and pixel size. I was able to get around this error by setting the pixel size to a round number (eg 5) when interpolation of the Elevation layer when interpolating to create the DEM.


Since Chanel network is a SAGA-GIS algorithm it is vital to get some knowledge on how this application is handling the data.

In SAGA's environment most of the grid calculations are being made within the one/same Grid System. The Grid System is SAGA's way of grouping loaded grids - in a simple words it groups adjacent grids. By adjacent you should understand grids that have:

  • the same cell size,
  • the same resolution (height px / width px),
  • the same spatial extent (basically the same x,y coordinates of most-western, most-southern corner).

So, in order to run this tool you need to pre-process your data - use some clipping and/or resampling tools in order to get a proper (same Grid System) input data for Chanel network algorithm.


I had a similar issue and found out the same as jzol explained in his answer: for SAGA GIS algorithms, the grids have to match in both extent and cell size (by consequence, they also match in resolution/dimensions).

Even if it looks like your raster grids match, it is worth a look on their extent and cell size, because even slight differences can cause this error in SAGA tools.

I fixed this issue by using the tool Warp (reproject) from gdal, on QGIS 3.16, and choosing the other input raster as the extent for the resampled raster. I did not reproject the raster, as I only used Warp for resampling (do that by choosing the output CRS as the same CRS from the input).

If the problem lies in having different cell sizes, you can adjust the cell size of one of the rasters to match the cell size of the other one. You can also do that by using Warp (reproject).

I wrote a blog post in which I discuss this error, feel free to check it out: https://www.luisalucchese.com/post/saga-gis-error-catchment-area/


When I have seen that error it has often been because the coordinate systems do not match. Certain processing tools require input data sets to be in the same coordinate system to work properly, even if they otherwise appear to be correctly located onscreen.

That would be the first thing I check.


Giacomo had it right: QGIS SAGA Channel network error: Input layers do not have the same grid extent Alter extent of one of the layers to the other (in QGIS save layer as)... and the tool works.

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