Hi Julia -
Thanks for sending your data. When I bring the filled DEM into ArcGIS it appears to have a minimum value of 6e-317, which is strange (especially since this does not happen in QGIS). But then when I calculate statistics and symbolize it, the minimum value changes to 0 (just like it shows in QGIS), which is very different than the minimum of 180m in the unfilled DEM. So it’s a little confusing why there’s so much difference between the two minimum values - how did you do the Fill operation?
I’m also a bit concerned about the difference between the filled and unfilled DEM values - here’s a map of the difference, and you can see a very distinct striped pattern to it, which is suspect.
How did you resample the unfilled DEM to this coordinate system? Did you use the interpolation method of Bilinear or Cubic? If you used Nearest Neighbor, it often creates odd checkerboard patterns, so it’s better to use Bilinear or Cubic. If this isn’t the case, I’m a little concerned about the quality of the original DEM data.
Another thing that’s unusual is that your pixel size is not square in any of your inputs, including the original DEMs. This gets resampled by the model to a square cell size of 27.1m, which you can see in the output rasters. I wanted to try using the QGIS Wang & Liu Fill tool (which generally works well and we recommend) on the unfilled DEM, which also resampled the pixels to be square, and produced a filled elevation range of 188m - 911m, which seems more in line with what I’d expect (as different than a new minimum value of 0, as is in your filled DEM).
Still, if I look at the difference between the Wang & Liu filled DEM and unfilled DEM, it has that striped pattern, at least in what I’m guessing are the more flat lands:
And, it’s dramatically changing the hydrology patterns from the original DEM, which I’ve not seen happen before with this tool.
When I use this filled DEM with square pixels in SDR, it runs in about the same time as your original unfilled DEM (actually a few minutes faster). However, the defined streams are pretty bad, and take up a lot of the watershed:
Is this area very flat? Flat areas can produce this kind of stream pattern in SDR. It’s definitely hard to get good drainage patterns in very flat places, I just went through this in a large wetland in Bolivia, where I had to try 3 different DEMs to get one that worked well enough.
So I’m not sure what to say. Personally, I’d go back to the original DEM, evaluate it closely to make sure it doesn’t have any odd striped artifacts to begin with, then check how you resampled it, including the interpolation method and resampling to a square pixel size. You might want to try a different DEM too to see if that changes anything.