Hydraulic Design of Highway Culverts - DOT On-Line Publications

design a rectangular side-tapered inlet for a circular pipe culvert, use the design nomographs in
Appendix D for rectangular side-tapered inlets. Additional head can be provided on the throat
control section of a side-tapered inlet by constructing a depression upstream of the face section.
The depression designs are the same as for box culverts.
b. Slope-Tapered Inlets. Rectangular inlets are adapted to pipe culverts as shown in Figure IV-
13. The slope-tapered inlet is connected to the pipe culvert by use of a square to circular
transition. The design of the slope-tapered inlet is the same as for box culverts. There are two
throat sections, one square and one circular, but the circular throat section will control the flow
because the area is much smaller than the square throat section.
Figure IV-13--Slope-Tapered Inlet, Circular Pipe Culvert
2. Multiple Barrel Designs. Each barrel of the culvert must have an individual side-tapered
inlet with a non-rectangular face design. For rectangular side-tapered inlets with a square to
round transition, double barrel designs are the same as for box culverts. However, the center
wall at the transition must be flared to provide adequate space between the pipes for proper
backfill and compaction. The amount of flare required will depend on the size of the pipes and
the construction techniques used. No more than two circular barrels may be feed from the throat
section of a rectangular side-tapered inlet.
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