Bedload Transport Calculator for Construction Channels

Inputs

Example Data Table

Use project measurements or hydraulic modeling for inputs.

Formula Used

Bed shear stress (wide-channel approximation):

τ = ρ g R S where R ≈ depth for wide channels.

Shields parameter:

θ = τ / [(ρs − ρ) g d]

Dimensionless bedload rate:

• MPM: Φ = 8 (θ − θc)^(3/2) for θ > θc
• Einstein-Brown (simplified): Φ = 40 (θ − θc)^(5/2) for θ > θc

Unit bedload transport:

qb = Φ √[(s − 1) g d^3], with s = ρs/ρ.

Totals and conversions:

• Total (bulk) rate: Qb = qb × width
• Solids rate (approx.): Qs = Qb (1 − n)
• Mass rate: Ms = Qs ρs

How to Use This Calculator

1. Pick a method based on your material and project guidance.
2. Enter channel width, depth, and energy slope from hydraulics.
3. Provide representative median grain size and sediment density.
4. Adjust critical Shields θc if you have calibration data.
5. Set porosity to estimate solids fraction in the transported load.
6. Click Calculate to view results above the form.
7. Use CSV/PDF buttons to export the most recent computation.

Professional Guide to Bedload Transport in Construction

1) Why bedload matters on job sites

Bedload is the coarse fraction that rolls, slides, or hops along the bed. In temporary diversions, cofferdams, and bridge approach channels, it controls bed elevation change and exposure of foundations. A few millimeters of aggradation per hour can bury filters, while modest degradation can undermine toe keys, riprap, or buried utilities.

2) Linking hydraulics to shear stress

The calculator estimates boundary forcing with τ = ρ g R S. For wide channels, R ≈ depth, so small depth or slope errors can noticeably shift τ. For example, increasing slope from 0.0010 to 0.0015 raises τ by 50% at the same depth, often pushing flows from “no motion” into active transport.

3) Using Shields parameter for initiation

Shields parameter θ = τ / [(ρs−ρ) g d] normalizes shear against particle weight. Typical critical values θc ≈ 0.03–0.06 are common for sands to gravels under steady flow. When θ < θc, transport is near zero; when θ > θc, transport grows rapidly and becomes sensitive to small hydraulic changes.

4) Grain size selection and field sampling

Choose d50 from sieve or pebble-count data that represent the active bed layer, not bank material. Coarse beds may armor, making surface d50 larger than subsurface d50. If you expect armoring, run scenarios with a higher d50 and a slightly higher θc to bracket uncertainty during construction dewatering or staged flow releases.

5) Comparing common transport relations

This tool offers two widely used forms through the dimensionless transport rate Φ. The MPM option (Φ = 8(θ−θc)^(3/2)) is often applied for coarse sediment beds. The simplified Einstein-Brown option increases sensitivity (Φ ∝ (θ−θc)^(5/2)), useful for exploring higher-transport regimes and conservative checks.

6) Converting to practical rates for planning

The unit bedload rate qb is expanded to a total bulk rate Qb = qb × width. A porosity adjustment estimates solids volume Qs = Qb(1−n). With n = 0.40, solids are 60% of bulk. The calculator also reports m³/day and t/day to support hauling, spoil management, and sediment-trap sizing.

7) Construction-focused checks and limits

Use energy slope consistent with your hydraulic model and verify units carefully. Uniform-flow shear stress may underrepresent bends, contractions, and local accelerations near culverts or temporary crossings. For short events, compare daily totals with available storage and confirm whether predicted movement exceeds maintenance thresholds for excavation, dredging, or rock protection.

8) Reporting and defensible documentation

Export results as CSV for design files and as a PDF summary for submittals. Include your chosen method, θc basis, and the assumed porosity. Document the input source (survey, model, or monitoring) and run multiple scenarios around depth and slope. Clear reporting helps justify temporary works, environmental controls, and contingency plans.

FAQs

1) What does the calculator output represent?

It estimates bedload transport rate for the chosen method, reporting unit rate (per width), bulk volumetric rate, solids volumetric rate using porosity, and mass-based daily totals.

2) Which method should I choose?

Use MPM for coarse beds and routine checks. Use the simplified Einstein-Brown option to explore higher sensitivity and provide a conservative comparison when uncertainty in hydraulics or sediment properties is high.

3) Why is porosity included?

Bulk bedload volume contains voids. Porosity converts bulk volume to solids volume by multiplying by (1−n). This supports spoil estimation, disposal volume, and mass conversion for trucking plans.

4) What if my channel is not wide?

Select the manual hydraulic radius option and enter R from your cross-section. This helps when depth is not a good proxy for hydraulic radius, such as narrow trapezoidal or box sections.

5) Why do small changes in slope or depth matter?

Shear stress scales with R and S, and transport scales with a power of (θ−θc). Near threshold conditions, modest hydraulic changes can shift predictions from zero transport to active motion.

6) Can I use this for fine silts and clays?

Use caution. The relationships here are intended for noncohesive sands and gravels. Cohesive beds require different erosion frameworks, including critical shear and time-dependent detachment.

7) How should I document results for submittals?

Export PDF and include input sources, selected θc, method choice, and scenario ranges. Add notes about site conditions, model assumptions, and any field calibration or monitoring data used.

Practical Notes

• Bedload equations are sensitive to grain size and slope; confirm field ranges.
• Uniform-flow shear stress may differ from complex structures or bends.
• Use conservative assumptions for temporary works and diversion channels.
• Compare multiple methods to bracket uncertainty for design decisions.