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I am using QGIS 3.22.1 for this task.

I have points with X, Y, Z of river bed. I have two sets, first is top of the mud and second is bottom of the mud-gravel layer. My goal is to calculate difference between these two DEMs. My process was this:

  1. Made two DEMs from points
  2. Raster to vector both
  3. Intersection of these polygons
  4. Then mask layer (I have points in C shape, so I needed to remove excess areas)
  5. Clip both DEM with mask layer
  6. Raster calculator (top DEM - bottom DEM)
  7. Raster zonal statistics
  8. In attribute table of statistics - calculate new column "Volume" = ("m2"*"sum")
  9. Basic statistics for fields - "Volume"

After this procedure I have an HTML file with "sum" which shows number "67366.96377954601". This is not possible. Area of DEM is 7600 m2. This means that there is 8,85 m of mud. This is not true. Difference DEM shows values from -0,19 m to 2,74 m.

Do you have any suggestions? What am I doing wrong?

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  • 3
    Which software are you working with?
    – Erik
    Commented Jun 12, 2023 at 14:07
  • 1
    Thank you for reply, I am using QGIS 3.22.1.
    – Nightfather
    Commented Jun 12, 2023 at 14:27
  • 2
    You can check out this answer here: gis.stackexchange.com/questions/277572/volume-of-a-raster?rq=1
    – Padmanabha
    Commented Jun 12, 2023 at 14:32
  • 1
    QGIS allows you to calculate volumes directly from raster DEM, no need to convert stuff (check the link Padmanabha posted).
    – Erik
    Commented Jun 12, 2023 at 14:36
  • Great! Thank you very much. Now i have valid volume of 5549 m3.
    – Nightfather
    Commented Jun 12, 2023 at 14:41

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