Hydraulic Design of Highway Culverts - DOT On-Line Publications

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The slope-tapered inlet combines an efficient throat section with additional head on the throat. The face section does not benefit from the FALL between the face and throat; therefore, the face sections of these inlets are larger than the face sections of equivalent depressed sidetapered inlets. The required face size can be reduced by the use of bevels or other favorable edge configurations. The vertical face slope-tapered inlet design is shown in Figure IV-4 and the mitered face design is shown in Figure IV-5. Figure IV-5--Slope-Tapered Inlet with Mitered Face 84
The mitered face slope-tapered inlet design is more complicated than the vertical face design. A hypothetical face section is located downstream of the weir crest formed where the extension of the fill slope meets the stream bed. The face section is defined by a perpendicular line extending to the FALL slope from the top edge of the inlet, neglecting bevels. The slope-tapered inlet is the most complex inlet improvement recommended in this manual. Construction difficulties are inherent, but the benefits in increased performance can be great. With proper design, a slope-tapered inlet passes more flow at a given headwater elevation than any other configuration. Slope-tapered inlets can be applied to both box culverts and circular pipe culverts. For the latter application, a square to round transition is normally used to connect the rectangular slopetapered inlet to the circular pipe. C. Hydraulics 1. Inlet Control. Tapered inlets have several possible control sections including the face, the bend (for slope-tapered inlets), and the throat. In addition, a depressed side-tapered inlet has a possible control section at the crest upstream of the depression. Each of these inlet control sections has an individual performance curve. The headwater depth for each control section is referenced to the invert of the section. One method of determining the overall inlet control performance curve is to calculate performance curves for each potential control section, and then select the segment of each curve which defines the minimum overall culvert performance (Figure IV-6). Figure IV-6—Inlet control performance curves (schematic) If the dimensional criteria of this publication are followed, the crest and the bend sections will not function as control sections over the normal range of headwaters and discharges. The crest of the depression may function as a control section for very low flows and headwaters but this is generally not of importance in design. Figure IV-6 depicts performance curves for each of the potential inlet control sections and the overall inlet control performance curves. The design procedures for tapered inlets include checks on crest lengths for both depressed sidetapered inlets and slope-tapered inlets with mitered faces. As long as) the actual crest length exceeds a certain minimum value, there is no need to construct a crest performance curve. Also, if the bend section is located a minimum distance of D/2 upstream of the throat section, the bend will not control and the bend section performance curve does not need to be calculated. 85
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Publication No. FHWA-NHI-01-020 Sep
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Acknowledgements This document’s
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TABLE OF CONTENTS (Cont.) III. CULV
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TABLE OF CONTENTS (Cont.) F. Safety
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LIST OF FIGURES (Cont.) Figure III-
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LIST OF TABLES Table 1. Factors Inf
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ELhf ELhi ELho ELht ELO ELsf ELSO E
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GLOSSARY (Cont.) p Wetted perimeter
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B. Overview of Culverts A culvert i
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Figure I-9--Side-tapered inlet Figu
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. Partly Full (Free Surface) Flow.
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Table 1--Factors Influencing Culver
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D. Economics The hydraulic design o
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For gaged sites, statistical analys
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volume of the remaining runoff hydr
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Figure II-4--Flood hydrograph shape
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Figure II-6--Cross section location
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. Culvert Length. Important dimensi
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HYDROLOGY Peak Flow Check Flows Tab
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Figure III-1--Types of inlet contro
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Figure II-2--Flow contractions for
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The flow transition zone between th
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Figure III-6--Culvert with Inlet Su
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Condition III-7-A represents the cl
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
Page 103: A slope-tapered inlet has three pos
Page 107 and 108: La is the approximate length of the
Page 109 and 110: E. Design Methods Figure IV-9--Tape
Page 111 and 112: a. Complete Design Data. Fill in th
Page 113 and 114: H 1 i. For FALL < D/4, use side-tap
Page 115: 3. Example Problems a. Example Prob
Page 121 and 122: . Example Problem #1 (English Units
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Page 125 and 126: 105
Page 127 and 128: c. Example Problem #2 (SI Units). F
Page 129 and 130: Conclusions: A side-tapered inlet a
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Page 133 and 134: G. Circular Pipe Culverts 1. Design
Page 135 and 136: Double barrel slope-tapered inlets
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Page 139 and 140: . Example Problem #3 (English Units
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Page 143 and 144: A. The Routing Concept V. STORAGE R
Page 145 and 146: C. Application to Culvert Design Fi
Page 147 and 148: Figure V-6--Peak Flow Reduction Bas
Page 149 and 150: I + I + ( 2s / ∆t − O) = ( 2s /
Page 151 and 152: Table 5--Inflow Hydrograph, Example
Page 153 and 154: 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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