Outlet Velocity Calculator

Calculate outlet velocities from pipes and culverts to assess erosion potential. Determine scour depth, scour hole dimensions, and protection requirements using FHWA HEC-14 methodology.

Bed Material Critical Velocities

MaterialVc (ft/s)
Fine sand (0.06-0.25mm)0.5-1.0
Medium sand (0.25-0.5mm)1.0-1.5
Coarse sand (0.5-2mm)1.5-2.5
Fine gravel (2-6mm)2.5-4.0
Coarse gravel (6-60mm)4.0-7.0
Cobbles (60-250mm)7.0-12.0
Clay/silt (cohesive)2.0-5.0
Cohesive soil (mixed)3.0-6.0

Scour Potential Classification

Low (V/Vc < 0.8) No protection needed
Moderate (0.8-1.2) Minimal protection
High (1.2-2.0) Moderate protection
Severe (V/Vc > 2.0) Extensive protection

Input Parameters

Outlet Geometry

ft
ft

Depth of flow in pipe (not diameter)

Flow Parameters

cfs
ft

Downstream water depth

Longitudinal slope (ft/ft)

hours

For scour development

Bed Material

ft

Override material default if known

Ready to Calculate

Enter outlet geometry and flow parameters to calculate velocity and scour potential.

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

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