Calculator
Use single inputs or paste segment lines. Segment mode overrides single fields automatically.
Example data table
Example shows a single reach using meters.
| Length | Bottom width | Side slope | Design depth | Current depth | Allowance | Bulking | Loose volume (approx.) |
|---|---|---|---|---|---|---|---|
| 1200 m | 4.0 m | 1.5 : 1 | 2.0 m | 1.4 m | 5% | 1.25 | ≈ 4,725 m³ |
Formula used
- A(y) = b·y + m·y² (area from bed to depth y)
- t = max(0, D_design − D_current) (silt thickness)
- A_silt = A(D_design) − A(D_current)
- V_in-situ = A_silt · L
- V_adjusted = V_in-situ · (1 + allowance/100)
- V_loose = V_adjusted · bulking
How to use this calculator
- Choose units and enter canal length, bottom width, side slope, and depths.
- If the reach changes, paste segment lines to model variations.
- Set allowance for overcut and a bulking factor for loose handling.
- Click Calculate to view volumes and estimated truckloads.
- Download CSV or PDF for field reports and tender sheets.
Scope and survey inputs that drive accuracy
Desilting quantities are only as reliable as the survey section used. Measure bottom width, side slopes, and depths at representative chainages, then use segments when geometry changes. Record the same datum for “current” and “design” depths. If bank erosion is active, add a realistic allowance to reflect additional material that will be removed during trimming and clean-up.
Cross-section modeling for trapezoidal canals
This calculator models a trapezoidal section because it matches most lined and earthen canals. The wetted area to depth y is computed from bottom width and side slope, then the silt area is the difference between design and current areas. Multiplying by length yields in-situ volume. When a reach has transitions, the segmented input avoids averaging and reduces underestimation.
Allowances, bulking, and haul planning
Field production depends on swell (bulking) and operational losses. Bulking converts compacted in-place silt to loose volume for transport and stockpiling. Allowance accounts for overcut, side sloughing, and compliance cleaning. Use conservative bulking for silty clays and higher values for granular deposits. The truckload estimate helps plan dispatch, turnaround time, and disposal footprint.
Example data and interpretation
Example (single reach): length 1200 m, bottom width 4.0 m, side slope 1.5H:1V, design depth 2.0 m, current depth 1.4 m, allowance 5%, bulking 1.25, truck capacity 10 m³. The output indicates the in-situ silt volume, then adjusts for allowance and bulking to estimate loose volume and truckloads. If survey points vary, split into segments and compare each segment’s silt area.
Quality checks before issuing quantities
Verify that design depth is not less than current depth; otherwise, the silt thickness is zero for that section. Confirm units and apply the same slope convention (H per 1V). Review extreme results by checking segment lines and ensuring no negative widths or depths. For tender documents, attach the exported summary and keep the segment table as an auditable trail for revisions and claims.
FAQs
1) What does in-situ volume mean?
In-situ volume is the material volume in place before excavation. It reflects compacted silt within the canal prism, calculated from cross-section area difference multiplied by length.
2) When should I use segmented mode?
Use segments when bottom width, side slope, or depths change along the canal. Segmenting reduces averaging errors and produces a more defensible quantity for billing and planning.
3) Why can loose volume be much higher?
Loose volume includes bulking, which accounts for swell and voids after excavation. Wet, fine sediments often expand when disturbed, increasing haul and disposal requirements.
4) What allowance percentage is typical?
Allowance depends on access, trimming needs, and stability. Many projects use 3–10%. Use higher values where banks slough, vegetation removal is expected, or tolerances are strict.
5) How is side slope entered?
Enter side slope as horizontal to vertical (H:V). For example, 1.5 means 1.5H for every 1V. Keep the same convention across all segments.
6) Does the calculator handle over-deep areas?
Yes. If current depth exceeds design depth, the silt thickness becomes zero for that section, preventing negative volumes and keeping totals conservative.
7) What should I attach for approvals or tenders?
Export the CSV or PDF summary and include the segment table, survey notes, and assumptions for allowance and bulking. This improves traceability during reviews and variations.