2.0

Table Of Contents
Calculating Culvert Size and Shape
481
Items you need to size a culvert:
n
Tailwater (depth of water measured above the outlet invert)
n
Length of culvert
n
Diameter
n
Flow
n
Mannings n
n
Roadway elevation (used to check for roadway overtopping)
n
Inlet elevation
n
Outlet elevation
n
Culvert entrance conditions
You can use the Culvert Calculator command to design circular and box
culverts. You can include roadway overtopping in the calculations, and you can
base the calculations on inlet, outlet, or optimum control. The Culvert
Calculator uses Mannings n coefficients to define the culvert friction factors.
NOTE
For more information about the input and output variables, see the Federal
Highway Administration (FHWA) Hydraulic Design Series #5 publication,
Hydraulic Design of Highway Culverts.
The following illustration shows culvert values:
Culvert values