Which method should I use for bridge pier scour calculation?

HEC-18 is the FHWA standard; Froehlich is simpler. The AI recommendation averages both for safety. For historical context, check the classical methods in this post.

What is the effect of angle of attack on scour depth?

Larger angles increase scour depth significantly. K2 factor increases from 1.0 (0 degrees) to 1.5 (20 degrees or more).

Can I use this calculator for tidal bridges?

Yes, but use peak ebb/flood velocity and adjust for salinity. Consider using the Melville method for sensitivity checks.

How can I reduce bridge pier scour?

Use riprap around the pier, increase pier width, or add guide banks. See our riprap design tool for more details.

Ultimate Bridge Pier Scour Calculator – HEC-18, Froehlich & Classical Methods | 2D Viz, Batch, PDF

Ultimate Bridge Pier Scour Calculator

HEC‑18 · Froehlich · Lacey · Laursen · Melville · 2D Pier‑Flow Viz · Batch (CSV/ZIP) · PDF Report · History · Unit Toggle

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📐 1. Why Bridge Pier Scour Matters

Scour – the removal of sediment around bridge foundations – is the #1 cause of bridge failures. This calculator implements the FHWA HEC‑18 (Richardson & Davis) and Froehlich (1988) methods, plus classical empirical formulas (Lacey, Laursen, Melville) for preliminary design and cross‑checking. The AI blended recommendation gives you a safe design value.

📌 K1 (shape), K2 (angle), K3 (bed condition) are automatically applied. For skewed flow >10°, scour increases significantly.

🚀 2. Live Scour Calculator (HEC‑18 & Froehlich)

Flow depth y₁ m

Upstream approach depth

Velocity V₁ m/s

Approach velocity

Pier width a m

Projected width normal to flow

Pier length L m

Used for Froehlich angle correction

Angle of attack (deg)

Flow skew relative to pier axis

Pier shape (K1)

Bed condition (K3)

Output unit

Company Logo URL (optional)

Company Name

Batch Processing (ZIP → PDFs)

🌊 3. Pier & Flow Visualization

📐 4. Alternative Empirical Formulas (Classical)

Use these for cross‑checking and preliminary design:

Lacey's Formula: S = 0.47 × (Q/f)^1/3 (alluvial rivers)
Laursen (Live‑Bed): d_s/y = 1.35 × (b/y)^0.3 × Fr^0.7
Melville's Method: d_s = K_y · K_I · K_d · K_s · K_a · y (predecessor to HEC‑18)

🔍 Always use HEC‑18 / Froehlich for final design. Classical methods are for sensitivity checks.

📊 5. Method Comparison & History

📘 6. How to Use – Step by Step

Enter flow depth (y₁), velocity (V₁), pier width (a) and length (L).
Set angle of attack, pier shape (K1) and bed condition (K3).
Choose output unit (m, ft, in).
Click “Compute” – HEC‑18 and Froehlich results plus AI recommendation appear.
The 2D canvas shows pier, flow, and horseshoe vortex with scour depth.
Bar chart compares both methods; history stores last 20 calculations.
Batch ZIP: Upload a ZIP of CSV files (columns: y1,V1,a,angle,K1,K3) – each CSV becomes a PDF.
PDF report includes company branding and the 2D sketch.

❓ 7. Frequently Asked Questions

❓ HEC‑18 vs Froehlich – which is better?

HEC‑18 is the FHWA standard for bridge design. Froehlich is a simpler energy‑based method. The tool gives both and an AI average for conservative design.

❓ How does angle of attack affect scour?

K2 increases from 1.0 (0°) to 1.5 (≥20°). Even a 10° skew increases scour by ~30%.

❓ Can this be used for tidal bridges?

Yes, use peak ebb/flood velocities. Salinity affects sediment but the equations are valid for both fresh and salt water.

❓ How to reduce scour?

Use riprap around the pier, increase pier width, add guide banks, or use a larger foundation depth. See our riprap tool for design.

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🌐 8. Standards & References

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🌉 Bridge Pier Scour Calculator – HEC-18 & Froehlich (Free)