Culvert Outlet-Control Headwater Calculator

Calculate FHWA HDS-5 outlet-control headwater for circular and box culverts from tailwater, entrance, friction, and exit losses, with outlet velocity plus critical- and normal-depth results; check inlet control separately.

Inlet Loss Coefficients (Ke)

Inlet Type	Ke
Square edge with headwall	0.50
Groove end with headwall	0.20
Groove end projecting	0.20
Mitered to slope	0.70
Beveled edges	0.20
Side-tapered inlet	0.20
Slope-tapered inlet	0.20

Source: FHWA HDS-5, Appendix C, Table C.2

Manning's n Values for Culverts

Material	n
Concrete	0.012
Corrugated Metal (annular)	0.024
HDPE (smooth)	0.012
PVC (smooth)	0.010
Corrugated Metal (helical)	0.012-0.024
Stone Masonry	0.025-0.030

Source: FHWA HDS-5, Appendix B, Table B.1

Input Parameters

Flow Parameters

Design Discharge (Q)

cfs

Total flow through culvert

Tailwater Depth

Water depth above outlet invert

Culvert Geometry

Culvert Shape

Number of Barrels

Diameter (D)

Inside diameter

Culvert Length (L)

Total barrel length

Culvert Slope (S)

ft/ft

Longitudinal slope (rise/run)

Elevations

Inlet Invert Elevation

Invert elevation at culvert entrance

Hydraulic Properties

Culvert Material

Manning's n

Roughness coefficient

Inlet Type

Inlet Loss Coeff (Ke)

Entrance loss coefficient

Exit Loss Coeff (Ko)

Typically 1.0 for sudden expansion

Ready to Calculate

Enter culvert parameters and click Calculate to analyze outlet control hydraulics.

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