Hydraulic Design of Highway Culverts - DOT On-Line Publications

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Condition III-7-A represents the classic full flow condition, with both inlet and outlet submerged. The barrel is in pressure flow throughout its length. This condition is often assumed in calculations, but seldom actually exists. Condition III-7-B depicts the outlet submerged with the inlet unsubmerged. For this case, the headwater is shallow so that the inlet crown is exposed as the flow contracts into the culvert. Condition III-7-C shows the entrance submerged to such a degree that the culvert flows full throughout its entire length while the exit is unsubmerged. This is a rare condition. It requires an extremely high headwater to maintain full barrel flow with no tailwater. The outlet velocities are usually high under this condition. Condition III-7-D is more typical. The culvert entrance is submerged by the headwater and the outlet end flows freely with a low tailwater. For this condition, the barrel flows partly full over at least part of its length (subcritical flow) and the flow passes through critical depth just upstream of the outlet. Condition III-7-E is also typical, with neither the inlet nor the outlet end of the culvert submerged. The barrel flows partly full over its entire length, and the flow profile is subcritical. (2) Factors Influencing Outlet Control. All of the factors influencing the performance of a culvert in inlet control also influence culverts in outlet control. In addition, the barrel characteristics (roughness, area, shape, length, and slope) and the tailwater elevation affect culvert performance in outlet control (Table 1). The barrel roughness is a function of the material used to fabricate the barrel. Typical materials include concrete and corrugated metal. The roughness is represented by a hydraulic resistance coefficient such as the Manning’s n value. Typical Manning’s n values for culverts are presented in Table 4. Additional discussion on the sources and derivations of the Manning’s n values are contained in Appendix B. The barrel area and barrel shape are self-explanatory. The barrel length is the total culvert length from the entrance to the exit of the culvert. Because the design height of the barrel and the slope influence the actual length, an approximation of barrel length is usually necessary to begin the design process. The barrel slope is the actual slope of the culvert barrel. The barrel slope is often the same as the natural stream slope. However, when the culvert inlet is raised or lowered, the barrel slope is different from the stream slope. The tailwater elevation is based on the downstream water surface elevation. Backwater calculations from a downstream control, a normal depth approximation, or field observations are used to define the tailwater elevation. (3) Hydraulics of Outlet Control. Full flow in the culvert barrel, as depicted in Figure III-7-A, is the best type of flow for describing outlet control hydraulics. 32
Table 4--Manning’s n Values for Culverts.* Type of Culvert Roughness or Corrugation 33 Manning's n Reference Concrete Pipe Smooth 0.010-0.011 (64, 66, 67, 70) Concrete Boxes Smooth 0.012-0.015 (23) Spiral Rib Metal Pipe Smooth 0.012-0.013 (65, 69) Corrugated Metal Pipe, Pipe-Arch and Box (Annular and Helical corrugations -- see Figure B-3, Manning's n varies with barrel size) 68 by 13 mm 2-2/3 by 1/2 in Annular 68 by 13 mm 2-2/3 by 1/2 in Helical 150 by 25 mm 6 by 1 in Helical 125 by 25 mm 5 by 1 in 75 by 25 mm 3 by 1 in 150 by 50 mm 6 by 2 in Structural Plate 230 by 64 mm 9 by 2-1/2 in Structural Plate 0.022-0.027 0.011-0.023 0.022-0.025 0.025-0.026 0.027-0.028 0.033-0.035 0.033-0.037 (25) (25, 68) Corrugated Polyethylene Smooth 0.009-0.015 (71, 72) Corrugated Polyethylene Corrugated 0.018-0.025 (73, 74) Polyvinyl chloride (PVC) Smooth 0.009-0.011 (75, 76) *NOTE: The Manning's n values indicated in this table were obtained in the laboratory and are supported by the provided reference. Actual field values for culverts may vary depending on the effect of abrasion, corrosion, deflection, and joint conditions. (25) (25) (25) (25) (25)
Page 1: Publication No. FHWA-NHI-01-020 Sep
Page 4 and 5: Acknowledgements This document’s
Page 6 and 7: (Page intentionally blank) iv
Page 8 and 9: TABLE OF CONTENTS (Cont.) III. CULV
Page 10 and 11: TABLE OF CONTENTS (Cont.) F. Safety
Page 12 and 13: LIST OF FIGURES (Cont.) Figure III-
Page 14 and 15: LIST OF TABLES Table 1. Factors Inf
Page 16 and 17: ELhf ELhi ELho ELht ELO ELsf ELSO E
Page 18 and 19: GLOSSARY (Cont.) p Wetted perimeter
Page 20 and 21: (Page intentionally blank) xviii
Page 22 and 23: B. Overview of Culverts A culvert i
Page 24 and 25: Figure I-9--Side-tapered inlet Figu
Page 26 and 27: . Partly Full (Free Surface) Flow.
Page 28 and 29: Table 1--Factors Influencing Culver
Page 30 and 31: D. Economics The hydraulic design o
Page 32 and 33: For gaged sites, statistical analys
Page 34 and 35: volume of the remaining runoff hydr
Page 36 and 37: Figure II-4--Flood hydrograph shape
Page 38 and 39: Figure II-6--Cross section location
Page 40 and 41: . Culvert Length. Important dimensi
Page 42 and 43: HYDROLOGY Peak Flow Check Flows Tab
Page 44 and 45: Figure III-1--Types of inlet contro
Page 46 and 47: Figure II-2--Flow contractions for
Page 48 and 49: The flow transition zone between th
Page 50 and 51: Figure III-6--Culvert with Inlet Su
Page 54 and 55: Outlet control flow conditions can
Page 56 and 57: 2 2 Vu Vd HW o + = TW + + HL (6) 2g
Page 58 and 59: This approximate method works best
Page 60 and 61: Figure III-12--Weir Crest Length De
Page 62 and 63: Critical depth is used when the tai
Page 64 and 65: 4. Add the culvert flow and the roa
Page 66 and 67: NOTE: If the nomographs are put int
Page 68 and 69: Figure III-19--Critical Depth Chart
Page 70 and 71: (1) If the Manning’s n value give
Page 72: Example Problem #1 (SI Units) A cul
Page 80 and 81: Example Problem #2 (SI Units) A new
Page 82 and 83: Example Problem #3 (SI Units) Desig
Page 84: Example Problem #4 (SI Units) An ex
Page 88 and 89: CHART 51A Figure III-21--Inlet Cont
Page 90 and 91: 2. Outlet Control. a. Partly Full F
Page 92 and 93: Backwater Calculations From hydraul
Page 95 and 96: English Units INLET CONTROL: AD 0.
Page 99 and 100: A. Introduction IV. TAPERED INLETS
Page 101 and 102: height by more than 10 percent (1.1
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A slope-tapered inlet has three pos
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The mitered face slope-tapered inle
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La is the approximate length of the
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E. Design Methods Figure IV-9--Tape
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a. Complete Design Data. Fill in th
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H 1 i. For FALL < D/4, use side-tap
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3. Example Problems a. Example Prob
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. Example Problem #1 (English Units
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103
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105
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c. Example Problem #2 (SI Units). F
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Conclusions: A side-tapered inlet a
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111
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G. Circular Pipe Culverts 1. Design
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Double barrel slope-tapered inlets
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117
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. Example Problem #3 (English Units
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121
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A. The Routing Concept V. STORAGE R
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C. Application to Culvert Design Fi
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Figure V-6--Peak Flow Reduction Bas
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I + I + ( 2s / ∆t − O) = ( 2s /
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Table 5--Inflow Hydrograph, Example
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Figure V-10—Culvert Design Form f
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Figure V-14--Storage vs. Outflow Re
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Table 5 --Inflow Hydrograph, Exampl
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Figure V-18--Culvert Design Form fo
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Figure V-22--Storage vs. Outflow Re
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A. Introduction VI. SPECIAL CONSIDE
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With minor modifications, the culve
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If headwater and flow consideration
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Figure VI-6--Subatmospheric Pressur
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Figure VI-7--Fish Baffles in Culver
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A popular method of providing for f
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passage of the peak flow. Methods f
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Figure VI-15--Sediment Deposition i
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1. Skewed Barrels. The alignment of
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Skewed inlets slightly reduce the h
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arrel for pipes or the flow per met
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Culvert shapes are as important in
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• Flood plain ordinances or other
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Figure VI-28--Guardrail Adjacent to
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Both of the above equations are emp
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Tables, charts, and formulas are av
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3. Endwalls and Wingwalls. Culvert
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2. Hydraulic Considerations. Long s
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conditions. Variations in the concr
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REFERENCES (www.fhwa.dot.gov/bridge
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28. "Design Approaches for Stormwat
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54. "Hydraulic Analysis of Pipe-Arc
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ADDITIONAL REFERENCES (In Alphabeti
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"Risk Analysis For Hydraulic Design
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A. Introduction APPENDIX A DESIGN M
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Chart No. 1 Shape and Material Circ
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NOTE: The rest of this Appendix A i
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Figure A-1--Dimensionless Performan
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developed for circular and elliptic
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APPENDIX B HYDRAULIC RESISTANCE OF
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D. Corrugated Metal Culverts The hy
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Curves are shown for 2-2/3 by 1/2 i
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F. Spiral Rib Pipe Spiral rib pipe
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APPENDIX C CULVERT DESIGN OPTIMIZAT
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C. Inlet Control Performance Curves
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Figure C-4--Optimization of Perform
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E. Tapered Inlet Face Control Perfo
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APPENDIX D DESIGN CHARTS, TABLES, A
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Chart Corrugated Metal Box Culverts
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Chart Circular Tapered Inlets 55A,
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Table 12--Entrance Loss Coefficient
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CHART 1B 225
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