Culvert Outlet Control Calculator

Calculate outlet control hydraulics for culverts including headwater depth, outlet velocity, critical depth, normal depth, and head loss breakdown. Uses FHWA HDS-5 methodology for circular and box culverts.

Inlet Loss Coefficients (Ke)

Inlet TypeKe
Square edge with headwall0.50
Groove end with headwall0.20
Groove end projecting0.25
Mitered to slope0.70
Beveled edges0.25
Side-tapered inlet0.20
Slope-tapered inlet0.15

Source: FHWA HDS-5, Table 4-1

Manning's n Values for Culverts

Materialn
Concrete0.012
Corrugated Metal (annular)0.024
HDPE (smooth)0.012
PVC (smooth)0.010
Corrugated Metal (helical)0.012-0.024
Stone Masonry0.025-0.030

Source: FHWA HDS-5, Table 3-3

Input Parameters

Flow Parameters

cfs

Total flow through culvert

ft

Water depth above outlet invert

Culvert Geometry

ft

Inside diameter

ft

Total barrel length

ft/ft

Longitudinal slope (rise/run)

Elevations

ft

Invert elevation at culvert entrance

Hydraulic Properties

Roughness coefficient

Entrance loss coefficient

Typically 1.0 for sudden expansion

Ready to Calculate

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

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