Calculate Lake or Crater Water Volume from a Drone DTM in QGIS

After a drone survey of a reservoir or crater, you often need to estimate water storage volume. This script computes it directly in QGIS from your DTM raster and a boundary polygon — no external tools needed.

Here’s a real farm pond survey mid-construction — the kind of site this script is built for:

What it does

The calculate_lake_volume.py script takes a polygon layer defining the lake or crater boundary and a DTM raster. It samples the DTM elevations inside the polygon and compares them against a reference surface derived from the polygon’s own boundary edges. The difference gives the depth at each pixel.

Output:

• Volume in cubic metres, litres, and acre-feet — written to a text report
• A depth raster ({lake_name}_volume_map.tif) styled red → green, showing how deep each pixel is relative to the reference surface

What you need

• QGIS 3.28 or newer
• numpy, rasterio (bundled with QGIS)
• A polygon layer defining the lake boundary — set as the active layer
• A DTM raster loaded into QGIS with “dtm” in the layer name
• The calculate_lake_volume.py script from the Terrain Analysis Pack

The DTM this script reads, as coloured hillshade — the excavated pond basin is clearly visible as the lower (purple) area:

Steps

1. Load your DTM raster into QGIS. Make sure the layer name contains “dtm”.
2. Load the boundary polygon layer and click it to make it the active layer.
3. Check (tick) the DTM raster in the Layers panel.
4. Open Plugins → Python Console → Show Editor.
5. Paste the script and click Run.

The depth raster is saved in the DTM’s directory and added to your project. The text report goes to 2.Session/Insights/ in the project directory structure (inferred from the DTM file path, created automatically if it doesn’t exist yet) — falling back to the DTM’s directory only if that folder can’t be created.

Here’s the depth raster on a real pond survey, styled red (shallow edge) to green (deepest point, ~4 m below the reference surface):

What the reference surface is

The script builds a reference surface by interpolating the DTM elevation values along the polygon boundary. This represents what the ground level would be if the lake were drained — essentially, the shoreline elevation. The volume is the space between that surface and the actual DTM values inside the polygon.

Configurable parameters

The script is self-contained and needs no changes for standard use. The polygon name is used to name the output files.

Related scripts

• generate_contour_level_polygon.py — answers a related but different question: not “how much water,” but “how far would it extend at a given level.” Useful for mapping flood extent or fill area at a target elevation from the same DTM.

Get the script

calculate_lake_volume.py is part of the Terrain Analysis Pack — five terrain analysis scripts for QGIS at $35 USD.