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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PROFILE OF ROAD

Figure II-B.--Road profile - valley section.

way overtopping elevation, Another cri-
teria might be the flood damage elevation
of an upstream building. Possible loss
of life and the importance of the highway
are likewise considered. While all of
these facton pertain to risk analysis,
a detailed risk analysis is generally
not performed.

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b. Rel!ulatorv Constraints. The
requirements of the National Flood Insur-
ance Program are a major con5ideration
in culvert design. Most communities are
now participating in this program. The
limitation on flood plain construction
as it affects the base (IOO-year) flood
elevation is of primary importance.
Depending upon the culvert location,
existing flood way encroachments, and
whether there is a specified flood way,
the allowable water surface elevation
increase varies from 0 to I foot (0.3m).
Regardless of the return period utilized

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in the culvert design for the particular
roadway, the 100-year return period flood
must be checked to ascertain the effects
of the culvert on the base flood eleva-
tion. (19)

c. Arbitrarv Constraints. Some
state or local agencies place arbitrary
constraints on the design headwater pro-
duced by a culvert. For example, the
headwater depth may not be allowed to
exceed the barrel height or some multiple
of the barrel height. Although these
constraints will severely limit the flex-
ibility inherent in culvert design, they
must be followed unless the controlling
agency can be convinced to relax the
restrictions or grant an exemption.

C. Summarv of Data Needs.

Table 3 summarizes the various data
needed for culvert design.

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