How to Calculate Dredging Quantity?

2026-04-21 14:19:51     Category：Technical Resources     Browse number：149     Release time：2026-04-21 14:19:51

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How to Calculate Dredging Quantity? Standard Calculation Steps 

This article is fully based on Design Code for Dredging and Reclamation Works JTS181-5-2012, providing the standard calculation method for engineering design, budget, construction and approval. 

JTS 181-5-2012 is the Design Code for Dredging and Reclamation Works issued by the Ministry of Transport of the People’s Republic of China. It is a mandatory industrial standard for port and waterway engineering, effective since January 1, 2013. It specifies survey, design, equipment selection, quantity calculation, environmental protection and construction requirements for dredging and reclamation projects, and is the core code for design, budget, construction and approval.

1. Composition of Total Dredging Quantity (Code Requirement)

Total Dredging Quantity = Design Section Quantity + Calculated Over-depth & Over-width Quantity + Siltation Quantity During Construction

All values shall be calculated in natural compacted volume, without considering the swell factor.

2. Step 1: Determine Key Parameters (Look up in Code)

2.1 Calculated Over-depth and Over-width (By Dredger Type)

2.2 Design Slope Ratio (By Soil Type)

Sludge / Flowing mud: 1:8 ~ 1:50

Silty soil: 1:3 ~ 1:8

Cohesive soil: 1:1.5 ~ 1:3

Loose sand: 1:5 ~ 1:10

Dense sand: 1:2 ~ 1:5

Rock: 1:0.75 ~ 1:2.5

2.3 Siltation Quantity

For areas with heavy siltation, calculate by:

Historical maintenance dredging data

Empirical formulas

Similar project references

Model tests (complex marine areas)

3. Step 2: Draw the Calculation Section

Define 4 key dimensions for the section:

Design bottom width (B)

Design depth (H)

Calculated over-width (ΔB)

Calculated over-depth (ΔH)

Slope ratio (1:m)

Calculate the cross-sectional area after drawing the section.

4. Step 3: Choose Calculation Method (3 Recommended Methods)

4.1 Cross-section Area Method (Most Accurate & Common)

Applicable for channels, foundation trenches, regular dredging areas.

Formula:

V = (A₀+A₁)/2 × L₁ + (A₁+A₂)/2 × L₂ + …

Explanation:

The symbol … means you need to calculate the volume of all segments between every two adjacent cross-sections using the same formula, then add all results together to get total volume.

Symbols explanation:

V = total dredging volume (m³)

A₀, A₁, A₂ = cross-sectional areas of each section (m²)

L₁, L₂ = distance between two sections (m)

4.2 Average Water Depth Method (Simple & Fast)

Applicable for flat terrain and large-area dredging.

Formula:

V = Calculated bottom width × Average dredging thickness × Length + Slope quantity

Explanation:

Calculate the volume of the flat bottom part first, then add the volume of both side slopes.

4.3 Grid Method (Used in Software)

Applicable for CAD and earthwork software.

Formula:

V = Σ△V

△V = △A × [(H₂₁+H₂₂+H₂₃+H₂₄) − (H₁₁+H₁₂+H₁₃+H₁₄)] ÷ 4

Explanation:

Σ means sum all grid volumes

△V = volume of one grid

△A = area of one grid

H₂ = design water depth

H₁ = original water depth

5. Step 4: Calculate by Soil Type and by Section (Code Mandatory)

Calculate separately by soil grade (sludge, silty soil, clay, sand, rock)

Segment at turns, width changes, depth changes and soil boundaries

Calculate foundation trenches, channels and basins individually

6. Step 5: Add Siltation Quantity

Final Quantity = Design Section Quantity + Over-depth & Over-width Quantity + Siltation Quantity

Maintenance dredging: Add annual siltation quantity

Capital dredging: Add siltation quantity during construction

Sudden siltation areas: Add extra sudden siltation quantity

7. 1-Minute Quick Calculation Flow

Check dredger type → Get over-depth & over-width

Check soil type → Get slope ratio

Draw section → Calculate section area

Calculate design quantity (cross-section / average depth method)

Add over-depth & over-width quantity

Add siltation quantity

Get total dredging quantity



FAQs:

Q:  Why do we need to add over-depth and over-width in dredging calculation?

A:  Over-depth and over-width are set according to JTS181-5-2012 to compensate for construction deviation of dredgers, ensuring the designed depth and width can be achieved.

Q:  Which method is the most accurate for dredging quantity calculation?

A:  The cross-section area method is the most accurate and widely used in channels, basins and foundation trenches, as required by the design code.