FLOOD01242

• County: Statewide
• Community: State of Colorado
• Stream Name: All
• Title: Hydraulic Design of Improved Inlets for Culverts
• Date: 9/1/1981
• Prepared For: USDOT
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

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III. Box Culvert Improved Inlet Design

Bevel-Edged Inlets

Four inlet control charts for culverts with beveled edges
are included in this Circular: Chart 8 for 900 headwalls (same
as 900 wingwalls), Chart 9 for skewed headwalls, Chart 10 for
wingwalls with flare angles of 18 to 45 degrees, and Chart 13
for circular pipe culverts with beveled rings. Instructions
for the use of nomographs are given in REC No.5. Note that
Charts 8 through 10 apply only to bevels having either a 330
angle (1.5:1) or a 450 angle (1:1). For example, the minimum bevel
dimension for an 8 ft. x 6 ft. box culvert designed using Chart 8
for a 1:1 bevel, or 450 angle, would be d = 6 ft. x 1/2 in/ft =
3 in. and b = 8 ft. x 1/2 in/ft = 4 in. Therefore, the top bevel
would have a minimum height of 3 in. , and the side bevel would be
4 in. in width. Similar computations would show that for a 1.5:1
or 33.70 angle, d would be 6 in. and b would be 8 in.

The design charts in this Circular are based on research
results from culvert models with barrel width, B, to depth, D,
ratios of from 0.5:1 to 2:1.

Multibarrel Installations

For installations with more than one barrel, the nomographs
are used in the same manner as for a single barrel, except that
the bevels must be sized on the basis of the total clear opening
rather than on individual barrel size. For example, in a double
8 ft. by 8 ft. box culvert, the top bevel is proportioned based
on the height, 8 ft., and the side bevels proportioned based on
the clear width, 16 feet. This results in a d dimension, for the
top bevel of 4 in. for the 1:1 bevel, and 8 in. for the 1.5:1
bevel and a b dimension for the side bevels of 8 in. for the 1:1
bevel and 16 in. for the 1.5:1 bevel. The ratio of the inlet face
area to the barrel area remains the same as for a single barrel
culvert.

For multibarrel installations exceeding a 3:1 width to
depth ratio, the side bevels become excessively large when pro-
portioned on the basis of the total clear width. For these struc-
tures , it is reconnnended that the side bevel be sized in proportion
to the total clear width, B , or three times the height, whichever
is smaller. The top bevel dimension should always be based on the
culvert height. Until further research information becomes
available, the design charts in this Circular may be used to
estimate the hydraulic performance of these installations.

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