Cross-drainage systems: Culverts Gupta, Chapter 14, pp 722-731

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Cross-drainage systems CulvertsGupta, Chapter
14, pp 722-731

• Purpose
• Design objective
• Design parameters
• Design Procedure
• Regime Classification
• Examples

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PURPOSE

• Pass natural stream flows or runoff under
  roadways
• Outlet for detention basins

Crossing below dam at Douthat State Park, Virginia
Box culverts will protect streams crossed by the
new road from Route 50. Photo courtesy of George
Golden, Smithsonian Office of Physical Plant
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Culvert Types
Section Views (Looking Downstream)
box culvert (typ. unsubmerged)
circular culvert (typ. submerged)
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Design Objective
road
culvert

• Design culvert (D,So) to pass flood of given
  return period (10 or 100-year event).
• Design Q
• Rational method
• TR-55 method
• USGS Regression method, pp. 393-394.

drainage area
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Design Parameters (Profile)
headwater/inlet
road deck
lw
V1
outlet/tailwater
L, So
H
1
2
4
Q
D
h4
3
z
datum
intlet invert El.
outlet invert El.
Aoarea of culvert barrel A3area of section of
flow at outlet lWtyp. one stream width
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Design Procedure

• Estimate Qdesign for drainage area design
  return period.
• Select culvert shape, material and trial size, D
  and calculate H/D.
• Design for desired culvert flow type (Table 14.5)
  select discharge formula.
• Unsubmerged flow conditions (e.g. box culverts
  supporting roadways)
• Calculate dc dn and classify slope as Mild or
  Steep
• Compare dn, dc and tailwater depth h4 and
  classify flow type dn ltdc h4ltdc S2 profile,
  inlet control with dc as control depth, TYPE 1
• dn gtdc h4 ltdc M2 profile, outlet control with
  dc as control depth, TYPE 2
• dn gtdc h4 gtdc M2 profile or M1(h4 gt dn),
  outlet control with h4 as control depth, TYPE 3
• Submerged flow conditions (most culverts)
• If culvert submerged at inlet and outlet outlet
  control, TYPE 4
• If culvert unsubmerged at outlet use Figs. 14.6
  14.7
• Compute ratios L/D, r/D or w/D, So (and
  29n2H/Ro4/3 for rough pipes), where r is the
  radius of rounding and w is the effective bevel.
• For concrete pipes, use Fig. 14.6
• For rough pipes, use Fig. 14.7.
• Plot the point So, L/D.
• If the point plots to the right of the curve it
  is outlet control, TYPE 5
• If the point plots to the left of the curve it is
  inlet control, TYPE 6
• Calculate Qtrial and compare with Qdesign.
  Iterate until they equal.

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Regime Classification Unsubmerged, 1-3
Table 14.5, p. 724.
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Regime Classification Submerged, 4-6
Table 14.5, p. 725.
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Criteria for Types 5 6 Submerged (H/D gt 1.2)
Conditions for Smooth (Concrete) Culverts
r radius of rounding
W effective bevel
Figure 14.6, p. 727.
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Criteria for Types 5 6 Submerged (H/D gt 1.2)
Conditions for Rough (Corrugated) Culverts
Figure 14.7, p. 728-729.
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USDOT Federal Highway Administration Design
References Culvert Design Model

• Hydraulic Design of Highway Culverts
• http//www.fhwa.dot.gov/bridge/hds5SI.pdf
• Hydraulic Charts for the Selection of Highway
  Culverts
• http//www.fhwa.dot.gov/bridge/hec05.pdf
• FHWA HY8 Culvert Analysis Computer Program, v6.1
• http//www.fhwa.dot.gov/bridge/hyddescr.htmhy_8_c
  ulvert_analysis

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