Hydraulic Design of Highway Culverts - DOT On-Line Publications

Repeat the design process until an acceptable culvert configuration is determined. Once the
barrel is selected it must be fitted into the roadway cross section. The culvert barrel must have
adequate cover, the length should be close to the approximate length, and the headwalls and
wingwalls must be dimensioned.
If outlet control governs and the headwater depth (referenced to the inlet invert) is less than
1.2D, it is possible that the barrel flows partly full though its entire length. In this case, caution
should be used in applying the approximate method of setting the downstream elevation based
on the greater of tailwater or (dc + D)/2. If an accurate headwater is necessary, backwater
calculations should be used to check the result from the approximate method. If the headwater
depth falls below 0.75D, the approximate method should not be used.
If the selected culvert will not fit the site, return to the culvert design process and select another
culvert. If neither tapered inlets nor flow routing are to be applied, document the design. An
acceptable design should always be accompanied by a performance curve which displays
culvert behavior over a range of discharges. If tapered inlets are to be investigated, proceed to
Chapter VI.
If storage routing will be utilized, proceed to Chapter V.
Special culvert installations, such as culverts with safety grates, junctions, or bends are
discussed in Chapter VI. Unusual culvert configurations such as "broken-back" culverts,
siphons, and low head installations are also discussed.
5. Example Problems. The following example problems illustrate the use of the design
methods and charts for selected culvert configurations and hydraulic conditions. The problems
cover the following situations.
Problem No. 1: Circular pipe culvert, standard 68 by 13 cm (2-2/3 by 1/2) in CMP with beveled
edge and reinforced concrete pipe with groove end. No FALL.
Problem No. 2: Reinforced cast-in-place concrete box culvert with square edges and with
bevels. No FALL.
Problem No. 3: Elliptical pipe culvert with groove end and a FALL.
Problem No. 4: Analysis of an existing reinforced concrete box culvert with square edges.
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