Hydraulic Design of Highway Culverts - DOT On-Line Publications

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HYDROLOGY Peak Flow Check Flows Table 3--Data Requirements for Culvert Design. DATA SOURCE Hydrographs (if storage routing is utilized) SITE DATA Culvert Location Waterway Data Cross Sections Longitudinal Slope Resistance Tailwater Field Upstream storage Roadway Data Cross Section Profile Culvert Length Design Headwater Critical points on roadway Surrounding buildings or structures Regulatory Constraints Arbitrary Constraints Stream gage analysis or calculated using Rational formula, SCS Method, regression equations, etc. Same as for peak flow From stream gage information or synthetic development methods such as SCS, Method, Snyder Method, or computer models Based on site characteristics including natural stream section, slope, and alignment Field survey or topographic maps Field survey or topographic maps Observation, photographs, or calculation methods Field survey, maps Field survey, maps Roadway plans Roadway plans Roadway plans Roadway plans Aerial photographs, surveys, or topographic maps Floodplain and flood insurance regulations for stream reach of interest State or local regulations for culvert installations 22
A. Culvert Flow III. CULVERT DESIGN 1. General. An exact theoretical analysis of culvert flow is extremely complex because the flow is usually nonuniform with regions of both gradually varying and rapidly varying flow. An exact analysis involves backwater and drawdown calculations, energy and momentum balance, and application of the results of hydraulic model studies. For example, the U.S. Geological Survey has defined 18 different culvert flow types based on inlet and outlet submergence, the flow regime in the barrel, and the downstream brink depth. (20) Often, hydraulic jumps form inside or downstream of the culvert barrel. In addition, the flow types change in a given culvert as the flow rate and tailwater elevations change. In order to systematically analyze culvert flow, the procedures of this publication have been developed, wherein the various types of flow are classified and analyzed on the basis of control section. A control section is a location where there is a unique relationship between the flow rate and the upstream water surface elevation. Many different flow conditions exist over time, but at a given time the flow is either governed by the inlet geometry (inlet control); or by a combination of the culvert inlet configuration, the characteristics of the barrel, and the tailwater (outlet control). Control may oscillate from inlet to outlet; however, in this publication, the concept of "minimum performance" applies. That is, while the culvert may operate more efficiently at times (more flow for a given headwater level), it will never operate at a lower level of performance than calculated. The culvert design method presented in this publication is based on the use of design charts and nomographs. These charts and nomographs are, in turn, based on data from numerous hydraulic tests and on theoretical calculations. At each step of the process, some error is introduced. For example, there is scatter in the test data and the selection of a best fit design equation involves some error. Also, the correlation between the design equations and the design nomographs is not exact. Reproduction of the design charts introduces additional error. Therefore, it should be assumed that the results of the procedure are accurate to within plus or minus ten percent, in terms of head. Additional information on the precision of the design charts is provided in Appendix A. Table 1 in Chapter 1 shows the factors which must be considered in culvert design for inlet and outlet control. In inlet control, only the inlet area, the edge configuration, and the shape influence the culvert performance for a given headwater elevation. The headwater elevation is calculated with respect to the inlet invert, and the tailwater elevation has no influence on performance. In outlet control, all of the factors listed in Table 1 affect culvert performance. Headwater elevation is calculated with respect to the outlet invert, and the difference between headwater and tailwater elevation represents the energy which conveys the flow through the culvert. 2. Types of Control. A general description of the characteristics of inlet and outlet control flow is given below. A culvert flowing in inlet control has shallow, high velocity flow categorized as "supercritical." For supercritical flow, the control section is at the upstream end of the barrel (the inlet). Conversely, a culvert flowing in outlet control will have relatively deep, lower velocity flow termed "subcritical" flow. For subcritical flow the control is at the downstream end of the culvert (the outlet). The tailwater depth is either critical depth at the culvert outlet or the downstream channel depth, whichever is higher. In a given culvert, the type of flow is dependent on all of the factors listed in Table 1. 23
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 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 52 and 53: 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
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Backwater Calculations From hydraul
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English Units INLET CONTROL: AD 0.
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A. Introduction IV. TAPERED INLETS
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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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