Outlet Velocity Calculator

Calculate pipe and culvert outlet velocity plus cohesionless-soil scour depth, width, length, and volume with FHWA HEC-14 Equation 5.1; use the separate outlet-protection tool for riprap design.

HEC-14 Equation 5.1

This calculator predicts depth, width, length, and volume of a culvert-outlet scour hole in cohesionless soil. It uses the full-flow hydraulic radius, grain-size gradation σ, peak-flow duration, culvert slope, and invert height above the bed.

Applicability

Equation 5.1 is not a cohesive-soil or riprap-sizing method. Review long-term channel degradation and field conditions separately. Use the dedicated outlet-protection calculator for HEC-14 Chapter 10 riprap design.

Input Parameters

Outlet Geometry

Outlet Shape

Pipe Diameter

Flow Depth at Outlet

Depth of flow in pipe (not diameter)

Flow Parameters

Design Discharge

cfs

Tailwater Depth

Applicability context; Eq. 5.1 has no continuous TW correction

Culvert Slope

Longitudinal slope (ft/ft)

Peak-flow Duration

min

HEC-14 recommends 30 min when unknown

Cohesionless-Soil Scour Inputs

Gradation σ = √(D84/D16)

Use sieve-analysis data; typical graded sand ≈ 1.87

Invert Height Above Bed

Vertical drop from outlet invert to receiving bed

Cohesive soils require HEC-14 Equations 5.2–5.4 and laboratory soil properties; they are outside this calculator's scope.

Ready to Calculate

Enter outlet geometry, flow, and cohesionless-soil parameters to calculate velocity and scour geometry.

For educational purposes only. Not a substitute for professional engineering judgment.