FLOOD04208

• County: Statewide
• Basin: Statewide
• Title: Hydraulic Charts for the Selection of Highway Culverts
• Date: 12/1/1965
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Step 1:

Procedure for Selection of Cul.vert Size

List design data. (See suggested tabulation form, figure 7,
p. 5-18.)

a. Design discharge Q, in cfa., with average return period..
(i.e. Q25 or Q50 etc.)

b. Approximate length L of culvert, in feet.

c. Slope of culvert. (If grade is given in percent, convert
to slope in ft. per ft.)

d. Allowable headwater depth, in feet, which is the vertical
distance from the culvert invert (flow line) at the en-
trance to the water surface elevation permissible in the
headwater pool or approach channel upstream from the cul.-
vert.

e. Mean and maximum flood. velocities in natural stream.

f. Type of cul.vert for first trial selection, including bar-
rel material, barrel cross-sectional shape and entrance
type.

Step 2: Determine the first trial size cul.vert.

Since the procedure given is one of trial and error, the ini-
tial trial size can be determined in several ways:

a.

By arbitrary selection.

By using an approximating equation such as SL = A from
10
which the trial culvert dimensions are determined.

b.

c.

By using inlet control nomographs (Charts 1-7) for the
culvert type selected. If this method. is used an ~

must be assumed, say ~ = 1.5, and using the given Q a

trial size is determined.

If any trial size is too large in dimension because of limited
height of embankment or availability of size, multiple cul.-
verts may be used by dividing the discharge equally between
the number of barrels used. Raising the embankment height or
the use of pipe arch and box culverts with width greater than
height should be considered. Final selection shoul.d be based
on an economic analysis.

5-15