Hydraulic Design of Highway Culverts - DOT On-Line Publications

The following steps outline the design process for culverts with tapered inlets. Steps 1 and 2 are
the same for all culverts, with and without tapered inlets.
1. Preliminary Culvert Sizing. Estimate the culvert barrel size to begin calculations.
2. Culvert Barrel Design. Complete the Culvert Design Form (Figure III-17). These
calculations yield the required FALL at the culvert entrance. For the inlet control calculations,
the appropriate inlet control nomograph is used for the tapered inlet throat. The required FALL is
upstream of the inlet face section for side-tapered inlets and is between the face section and
throat section for slope tapered inlets. The Culvert Design Form should be completed for all
barrels of interest. Plot outlet control performance curves for the barrels of interest and inlet
control performance curves for the faces of culverts with nonenlarged inlets and for the throats
of tapered inlets.
3. Tapered Inlet Design. Use the Tapered Inlet Design Form (Figure IV-9) for selecting the
type of tapered inlet to be used and determining its dimensions. If a slope-tapered inlet with
mitered face is selected, use the special design form shown in Figure IV-10. A separate form is
provided for the mitered inlet because of its dimensional complexity.
To use the Tapered Inlet Design Form (Figure IV-9) or the design form for a slope-tapered inlet
with mitered face (Figure IV-10), perform the following steps:
Figure IV-10--Design Form-Slope-Tapered Inlet with Mitered Face
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