Reservoir Storage Analyzer

Builds the elevation–area–volume table, draws the elevation–volume and elevation–area curves, and goes on from there to inundation maps, a volume-to-level lookup, depth rasters, and a way to make a DEM from contours.

All calculation is in metres, square metres and cubic metres. The saved table carries the volume in m³, 1,000 m³ and million m³, so the same file serves a design report and a map label.

How the volume is counted

• Flooded area is the set of cells below the water level that are connected to the lowest cell of the DEM. Isolated pits are not counted.
• Natural ground: volume = Σ (water level − ground) over the flooded area × cell area.
• Excavated: the bed is min(ground, base level); volume = Σ max(level − bed, 0) × cell area; soil removed = Σ max(ground − base level, 0) × cell area.

The tabs

• Curves and Table — the result of Calculate Storage: the two curves (whole-metre levels circled) and the table behind them. Save the table as CSV and the curve as PNG, PDF or SVG.
• Inundation Maps — one panel per water level on a hillshade, with depth shading, the flooded edge, background contours, scale bar, north arrow, a summary table and a footer. A4–A0, Letter, Tabloid or fit-to-content; PNG, PDF, TIFF, JPEG or SVG.
• Volume Lookup — the water level (and area) for volumes you give, read from the last calculation or a CSV this tool saved. Interpolated linearly between rows.
• Export Rasters — one GeoTIFF per level, clipped to the flooded area: water depth and/or bottom elevation. Summing depth × cell area reproduces the table's volume, which makes them useful for checking in other software.
• Contours to DEM — interpolates a DEM from elevation contour lines (linear, cubic, inverse distance or nearest), optionally clipped to a polygon in any CRS.
• Log — what each job did, and any warning.

1. Open KGA Irrigation Tools > Reservoir Storage Analyzer.
2. Choose the DEM — projected, in metres — and a boundary or split line if the DEM covers more than the reservoir.
3. Press DEM range to fill the levels, or type your own in Or levels.
4. Choose the surface: natural ground, or excavated to a base level.
5. Pick an output folder and press Calculate Storage. Press Stop to end the job at the next step.
6. Work through the tabs from there — maps, lookup, rasters — all using the same inputs.

• The lowest cell decides which water body is counted. A single stray low pixel outside the reservoir — a DEM artefact, a borrow pit — takes over, and the reservoir itself then reads as empty. Use a boundary polygon or split line so the lowest cell is inside the reservoir.
• A DEM with an undeclared NoData value (such as -9999) is flagged in the Log when the lowest cell is below −500 m. Set the NoData value first.
• The whole DEM is read into memory as 64-bit numbers: a very large raster needs a boundary or a coarser copy.
• A DEM made from contours is a model. Interpolating between lines flattens hill tops and pits, and the area outside the outermost contour takes the nearest contour's height — clip it to the reservoir.
• Levels cost one pass over the DEM each; more than 2,000 levels are refused.

Migrating from Storage Capacity Curve

The old tool took several DEMs in one run and wrote one chart per DEM with fixed axis settings. This one works on one DEM at a time and adds the surface option, maps, lookup and rasters. The CSV columns changed: Elevation_m is now Water_Level_m, Volume_1000m3 is unchanged in meaning, and Area_ha is the flooded area (connected to the lowest cell) rather than every cell under the level.