Hydraulic Design of Highway Culverts - DOT On-Line Publications

CHART 52A
Figure III-22--Inlet Control Curves - High and Low Profile
Structural Plate Arches (SI Units)
The curves in these figures are for four different inlet edge conditions: thin edge projecting,
mitered, square-edge, and 45-degree bevels. The horizontal axis of the chart is flow rate divided
by the area times the square root of barrel height (Q/AD 0.5 ) and the vertical axis is headwater
depth divided by barrel height (HW/D). Figure III-21 will provide adequate results for any
conduit with curved surfaces, including pipe-arches and underpasses. Figure III-22 is used for
conduits similar to arches with flat bottoms.
To use the figures, perform the following steps:
a. From manufacturers' information, select a barrel size, shape and inlet edge configuration.
Obtain the area, A, and the interior height, D, for the selected barrel.
b. Calculate AD 0.5.
c. Divide the design flow rate, Q, by AD 0.5.
d. Enter the appropriate design chart with Q/AD 0.5 , and for the selected edge condition, read
HW/D.
e. Multiply HW/D by D to obtain the face control headwater, HW.
f. If it is desired to take credit for the approach velocity (Vu) in the calculations, deduct the
approach velocity head (Vu 2 /2g) from HW to obtain the face control headwater, HWf. If Vu is
neglected, set HWf equal to HW.
g. If the inlet control headwater is higher than the design headwater, or if the conduit is
oversized, select another conduit size and/or inlet edge condition and return to step a.
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