| Category | Height (m) | Storage (m3) |
| Small | 5.0 < height < 15 | 0.05 × 106 < volume < 1.0 × 106 |
| Medium | 15 < height < 30 | 1.0 × 106 < volume < 50 × 106 |
| Large | height > 30 | volume > 50 × 106 |