FLOOD01360

• County: Statewide
• Title: Hydraulic Design of Highway Culverts
• Date: 9/1/1998
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

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CIRCULAR

BOX (RECTANGULAR)

ELliPTICAL

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PIPE ARCH

METAL BOX

ARCH

Figure I-4--Commonly used culvert shapes.

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Figure I-S--Precast concrete box culvert
(American Concrete Pipe Association).

The hydraulic capacity of a culvert
may be improved by appropriate inlet selec-
tion. Since the natural channel is usu-
ally wider than the culvert barrel, thc
culvert inlet edge represents a flow
contraction and may be the primary flow

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control. The provision of a more gradual
flow transition will lessen the energy
loss and thus create a more hydraulically
efficient inlet condition. (figure 1-8)
Beveled edges are therefore more efficient
than square edges. Side-tapered and
slope-tapered inlets, commonly referred
to as improved inlets, further reduce
the flow con traction. Depressed inlets,
such as slope-tapered inlets, increase the
effective head on the flow control sec-
tion, thereby further increasing the
culvert efficiency. Figures 1-9 and
1-10 depict a side-tapered and a slope-
tapered inlet respectively.

C. Culvert Hvdraulics.

A complete theoretical analysis of
the hydraulics of a particular culvert
installation is time-consuming and dif-
ficult. Flow conditions vary from culvert
to culvert and they also vary over time
for any given culvert. The barrel of
the culvert may flow full or partly full
depending upon upstream and downstream
conditions, barrel characteristics, and
inlet geometry.

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