Cross-drainage systems: Culverts Gupta, Chapter 14, pp 722-731 Purpose Design objective Design parameters Design Procedure Regime Classification Examples

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

Culvert Types Section Views (Looking Downstream) box culvert (typ. unsubmerged) circular culvert (typ. submerged)

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

Design Parameters (Profile) headwater/inlet lw road deck V1 L, So outlet/tailwater H 1 2 Q 4 D z 3 h4 intlet invert El. datum outlet invert El. Ao=area of culvert barrel; A3=area of section of flow at outlet lW=typ. one stream width

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 <dc; h4<dc : S2 profile, inlet control with dc as control depth, TYPE 1 dn >dc; h4 <dc : M2 profile, outlet control with dc as control depth, TYPE 2 dn >dc; h4 >dc : M2 profile or M1(h4 > 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.

Regime Classification: Unsubmerged, 1-3 Table 14.5, p. 724.

Regime Classification: Submerged, 4-6 Table 14.5, p. 725.

Criteria for Types 5 & 6: Submerged (H/D > 1 Criteria for Types 5 & 6: Submerged (H/D > 1.2) Conditions for Smooth (Concrete) Culverts r = radius of rounding W = effective bevel Figure 14.6, p. 727.

Criteria for Types 5 & 6: Submerged (H/D > 1 Criteria for Types 5 & 6: Submerged (H/D > 1.2) Conditions for Rough (Corrugated) Culverts Figure 14.7, p. 728-729.

Hydraulic Design of Highway Culverts 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.htm#hy_8_culvert_analysis