Calculator
Formula used
- Trapezoidal (stage–area): V = (h/2) × (A₁ + A₂) for each interval, then sum all intervals.
- Prismoidal (stage–area): V = (h/6) × (A₁ + 4Aₘ + A₂). When mid‑area is unavailable, the calculator estimates Aₘ ≈ (A₁ + A₂)/2.
- Geometric basin (with side slopes): the water prism is treated as a frustum where V = (h/3) × (A_b + A_t + √(A_b A_t)).
- Allowances: net available applies losses as V_net = V_gross × (1 − (S+L)/100). adjusted required applies margins as V_adj = V_gross × (1 + (S+L+K)/100).
How to use this calculator
- Choose a calculation mode that matches your design stage.
- Select units and an output volume unit for reporting.
- For stage–area, enter ordered elevation and area rows from surveys. Use prismoidal with mid‑areas when available.
- For geometric basins, enter bottom dimensions, side slopes, and depths. Add dead storage and freeboard if your standard requires them.
- Set allowances for sediment, losses, and contingency.
- Press Calculate, then export results as CSV or PDF.
Example data table
Example contour areas at 1 m stage increments. Replace with your survey.
| Level | Elevation | Area | Comment |
|---|---|---|---|
| 1 | 100 | 0 | Bottom point / initial puddle |
| 2 | 101 | 120 | Early stage inundation |
| 3 | 102 | 240 | Mid stage area expansion |
| 4 | 103 | 360 | Near full storage stage |
| 5 | 104 | 480 | Design high water level |
Using trapezoidal integration across these rows yields a gross storage of
960 in the same volume base units.