Calculator inputs
Example data table
Sample inputs and outputs using the plan area method.
| Plan area (m²) | Existing depth (m) | Design depth (m) | Overdepth (m) | Dredge depth (m) | In-situ volume (m³) | Siltation (%) | Bulking (%) | Loose volume (m³) |
|---|---|---|---|---|---|---|---|---|
| 150,000 | 10.00 | 14.00 | 0.30 | 4.30 | 645,000 | 5.0 | 15.0 | 778,838 |
Formulas used
- Plan area method: V = A × d, where d = (Design − Existing) + Overdepth.
- Cross-section area (trapezoid): A = b·d + m·d² (m is side slope H:V per side).
- Average End Area volume: V = Σ ((Aᵢ + Aᵢ₊₁)/2) × Lᵢ.
- Siltation allowance: Vₛ = V × (1 + S/100).
- Loose volume: Vₗ = Vₛ × (1 + B/100).
- Compacted disposal volume: V𝚌 = Vₗ × (1 − C/100).
- Mass estimate: M = Vₛ × ρ (tonnes), where ρ is in-situ density (t/m³).
How to use this calculator
- Choose a method: plan area for quick estimates, cross-sections for detail.
- Enter overdepth, bulking, and optional siltation and compaction factors.
- Provide either plan area and depths, or section geometry and spacing.
- Click Calculate to view results immediately above the form.
- Use Download CSV or Download PDF for records.
For tendering and payment, align inputs with survey tolerances and measurement rules.
Harbor dredging volume planning notes
1) Why volume estimates drive cost
Dredging budgets are commonly built around measured or estimated cubic meters, production rates, and disposal logistics. This calculator separates in‑situ excavation volume from loose transport volume so you can forecast barge or truck cycles, fuel, and disposal footprint with consistent assumptions. For early studies, retain inputs and dates so later survey reconciliation is straightforward.
2) Choosing the right method for your data
Use the plan area method when you have a reliable dredge footprint and an average depth change from surveys. For more detailed geometry, the cross‑section method applies Average End Area between consecutive sections, which typically improves accuracy when the channel widens, shoals, or transitions near berths. Where possible, base depths on recent multibeam surveys and checked soundings.
3) Overdepth and siltation allowances
Overdepth is often added to account for equipment tolerance and local acceptance criteria. Small increases in overdepth can create large volume changes on large footprints, so record the basis used. A siltation allowance (for example, 0–10%) is a practical contingency when maintenance intervals and seasonal sediment loads are known.
4) Bulking and compaction: converting to transport and disposal volumes
Bulking converts in‑place material to loose volume after excavation and handling. Many fine to mixed sediments are modeled with bulking in the 10–30% range, but site testing and local experience should govern. If placement compacts at the disposal area, the compaction percentage reduces the loose volume to an estimated compacted footprint for containment or reclamation planning.
5) Density and mass for environmental and logistics reporting
In‑situ density (t/m³) converts volume to an estimated mass, supporting permit reporting, dewatering planning, and payload checks. Density varies with grain size and moisture; keep it consistent with geotechnical data and the measurement rules used for payment. Always document survey dates, datum, and any excluded obstructions.
FAQs
1) What is the difference between in‑situ and loose volume?
In‑situ volume is the material volume in its natural, undisturbed state. Loose volume is the expanded volume after excavation and handling, estimated using the bulking factor for transport planning.
2) When should I use the cross‑sections method?
Use cross‑sections when width or depth varies along the alignment, or when you have surveyed sections at known chainages. Average End Area usually outperforms a single average depth for irregular channels.
3) How does overdepth affect the result?
Overdepth adds directly to dredge depth. Because volume scales with area and depth (or section area and length), even 0.10 m can add thousands of cubic meters on large footprints.
4) What bulking factor should I choose?
Choose bulking from lab tests, local experience, or contract guidance. Fine sediments often bulk more than dense sands, and handling method matters. Start conservative, then refine after sampling.
5) Why include a siltation allowance?
It covers expected infill between survey, mobilization, and completion. This helps align estimates with maintenance cycles, seasonal sediment loads, and procurement contingencies without altering base survey inputs.
6) How is mass (tonnes) computed?
Mass is estimated by multiplying the volume including siltation by the in‑situ density (t/m³). Use a density consistent with geotechnical data and the reporting or payment method specified in your project documents.
7) Can I use this for payment quantities?
It is suitable for planning and tender estimates. For payment, confirm the contract measurement basis (pre/post‑dredge surveys, templates, tolerances, and exclusions) and validate assumptions with the supervising engineer and applicable specifications.