2 PURPOSE Pass natural stream flows or runoff under roadways Outlet for detention basinsCrossing below dam at Douthat State Park, VirginiaBox culverts will protect streams crossed by the new road from Route 50. Photo courtesy of George Golden, Smithsonian Office of Physical Plant
4 Design Objective road culvert Design culvert (D,So) to pass flood of given return period (10 or 100-year event).Design QRational methodTR-55 methodUSGS Regression method, ppdrainagearea
5 Design Parameters (Profile) headwater/inletlwroad deckV1L, Sooutlet/tailwaterH12Q4Dz3h4intlet invert El.datumoutlet invert El.Ao=area of culvert barrel; A3=area of section of flow at outletlW=typ. one stream width
6 Design ProcedureEstimate 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 SteepCompare dn, dc and tailwater depth h4 and classify flow type: dn <dc; h4<dc : S2 profile, inlet control with dc as control depth, TYPE 1dn >dc; h4 <dc : M2 profile, outlet control with dc as control depth, TYPE 2dn >dc; h4 >dc : M2 profile or M1(h4 > dn), outlet control with h4 as control depth, TYPE 3Submerged flow conditions (most culverts)If culvert submerged at inlet and outlet: outlet control, TYPE 4If culvert unsubmerged at outlet use Figs & 14.7Compute 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. 14.6For rough pipes, use FigPlot the point So, L/D.If the point plots to the right of the curve it is outlet control, TYPE 5If the point plots to the left of the curve it is inlet control, TYPE 6Calculate Qtrial and compare with Qdesign. Iterate until they equal.
7 Regime Classification: Unsubmerged, 1-3 Table 14.5, p. 724.
8 Regime Classification: Submerged, 4-6 Table 14.5, p. 725.
9 Criteria for Types 5 & 6: Submerged (H/D > 1 Criteria for Types 5 & 6: Submerged (H/D > 1.2) Conditions for Smooth (Concrete) Culvertsr = radius of roundingW = effective bevelFigure 14.6, p. 727.
10 Criteria for Types 5 & 6: Submerged (H/D > 1 Criteria for Types 5 & 6: Submerged (H/D > 1.2) Conditions for Rough (Corrugated) CulvertsFigure 14.7, p
11 Hydraulic Design of Highway Culverts USDOT Federal Highway Administration Design References & Culvert Design ModelHydraulic Design of Highway CulvertsHydraulic Charts for the Selection of Highway CulvertsFHWA HY8 Culvert Analysis Computer Program, v6.1
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