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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3,10

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3,00

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2,90

0,16 020 0,24 0,28 0.32

A) DISCHARGE COEFFICIENT FOR
HWr IL, > 0.15

3.10
3.00
2.90
Cr 2,80
2,70
2,60

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2.0

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4,0

HW, ft.

B) DISCHARGE COEFFICIENT FOR
HWr/L,<f0.15

Cd" ktCr

1.00
0.90
0,80
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0.70
0.60

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0,50
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0,7

0,8

0,9

1.0

h,/HW,
C) SUBMERGENCE FACTOR

Figure III-lt--Discharge coefficients for roadway overtopping.

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The outlet control nomogrnphs in appcn-
dix D provide solutions for equation (5)
for entrance, friction, and cxit losscs
in full barrci flow, Using the approximatc
backwatcr method, the losscs (H) obtaincd
from thc nomographs can be npplicd for
the partly full flow conditions shown in
figures IlI-7 nnd llI-9. Thc lossc, arc
addcd to thc elcvation of the cxtcndcd
full flow hydraulic gradc linc at thr.
barrcl outlct in ordcr to obtain thc
headwatcr clevation. The cxtcndcd hy-
draulic gradc linc is sCI at the higher
of (de + D)/2 Of thc ta il wa tcr clcv't1:ion
at the culvcrt outlct. Again, thc approxi-
mation works best whcn the barrel flows
full ovcr at lcast part of it; length,

3. Roadway Overtopping. Overtop-
ping will begin whcn the headwater rises
to thc clcvation of the roadway. (figure
IH-IO) The overtopping will usually
occur at thc low point of a sag vertical
curvc on the roadway, The flow will be
similar to flow ovcr a broad crested
weir. Flow cocfficients for flow over-
topping roadway embankments are found in
HDS No. ), Hvdraulics of Brid~e Waterwavs
(21), as wcll as in the documentation of
HY -7, the Brid~e Waterwavs Analvsis Model
(22), Curvcs from reference (22) are
shown in figure III-II. Figure HI-II-A
is for dcep ovcrtopping, figure III-II-B
is for shallow overtopping, and figure
HI-) )-C is a corrcction factor for down-

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