Bridge Scour Calculator

Calculate HEC-18 long-term, live-bed or clear-water contraction, pier, and abutment scour components, optional armoring checks, and resulting design scour elevations.

Bridge scour is a public-safety design calculation

Use hydraulic-model output for each subarea and have the analysis reviewed by a bridge hydraulics professional. This implementation intentionally stops short of pressure flow, cohesive time-rate scour, erodible rock, complex foundations, debris, and opaque empirical substitutes.

HEC-18 Inputs

FHWA Fifth Edition core equations

Scope of this combined analysis: free-surface live-bed, clear-water, and cohesive (Eqs. 6.6-6.9) contraction scour; the CSU/HEC-18, FDOT, coarse-bed, and maximum-potential cohesive pier methods (with the optional wide-pier, complex-pier, and erodible-rock pier families available through the API); and Froehlich, HIRE, or user-supplied-curve NCHRP abutment checks.

Datum and Long-Term Change

Existing Bed Elevation

Use one consistent project vertical datum

Long-Term Degradation

Supply from specific-gage, geomorphic, or sediment-continuity analysis; do not enter aggradation as negative scour

Contraction Scour

Transport Condition

Existing Contracted Depth (y₀)

Contracted Discharge (Q₂)

cfs

Contracted Width Less Piers (W₂)

Bed-Material D₅₀

Always enter grain diameter in millimetres

Upstream Main-Channel Depth (y₁)

Upstream Sediment-Transporting Flow (Q₁)

cfs

Upstream Bottom Width (W₁)

Bed-Material Transport Mode

Apply HEC-18 armoring check

Also calculate clear-water scour with Dm = 1.25D50 and use the smaller depth. A single material layer is represented.

Simple Pier Scour

Include simple-pier local scour

Select a documented HEC-18 equation family. Complex footing/pile-cap component superposition and debris are outside this calculator.

Pier Scour Method

Approach Flow Depth (y₁)

Approach Velocity (V₁)

ft/s

Pier Width Normal to Flow (a)

Pier Length (L)

Pier Nose

Bed Condition

Angle of Attack

deg

Entire pier length is exposed to the skewed flow

If unchecked, K₂ is held at 1.0. Use an effective exposed length where field flow is redirected or shielded.

Apply HEC-18 wide-pier correction

Eqs. 7.20/7.21 apply only for y/a < 0.8, a/D50 > 50, and subcritical flow.

Abutment Scour

Include abutment scour check

Automatic uses Froehlich at L/y ≤ 25 and HIRE at L/y > 25; NCHRP accepts an official design-curve factor.

Method

Abutment Shape

Approach Flow Depth

Approach Velocity

ft/s

Projected Embankment Length (L)

Length projected normal to flow; used for the L/y method applicability check

Active-Flow Obstructed Length (L-prime)

Froehlich active-flow length, often determined from a hydraulic-model stream tube

Embankment Angle to Flow

deg

Less than 90 points downstream; greater than 90 points upstream

The calculations provided by DrainageCalculators.com are for informational and educational purposes only. While we strive for accuracy, these tools do not substitute for professional engineering judgment or designs stamped by a licensed Professional Engineer (PE) where required by law. Users are solely responsible for verifying all calculations, confirming compliance with local codes and regulations, and determining the appropriateness of any methodology for their specific application. Critical infrastructure and public safety projects require review and certification by a licensed Professional Engineer.