Hydraulic Design of Highway Culverts - DOT On-Line Publications

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Elevation versus discharge data can be computed from culvert data and the roadway geometry. Discharge values for the selected culvert and overtopping flows are tabulated with reference to elevation. The combined discharge is utilized in the formulation of a performance curve as depicted in Figure V-5. 2. Initial Culvert Sizing. Despite the consideration of storage routing, the selection of an appropriate culvert size for a given set of hydrologic and site conditions is the design objective. However, in order to perform the storage routing calculations, a culvert must first be selected. Storage routing calculations will then be required to verify the selected size. It is desirable to make a good first estimate of culvert size to minimize the number of routing calculations performed. The selection of a tentative culvert size requires an estimate of peak flow reduction based on upstream storage capacity. A triangular inflow hydrograph may be formulated based on studies of runoff hydrographs by the SCS. (12) The formulation of the inflow hydrograph requires an estimate of peak inflow rate (Qp) and the time-to-peak parameter (tp). These data items are established using appropriate hydrologic techniques. Next, the available storage below the established design headwater elevation must be estimated based on relief upstream of the culvert location. From the routing concept, a relationship exists between peak inflow, storage (S), and peak outflow (Qr) or the reduced peak. Figure V-6 graphically displays this relationship, assuming a triangular outflow hydrograph. 126 Figure V-4--Elevation versus storage curve Figure V-5--Performance curve The storage volume is represented by the area between the inflow and outflow hydrographs in Figure V-6. This area is determined by taking the difference in areas between two triangles with a common base (28). The resulting expression can be written: s p p p r = 1/ 2 ( 2. 67 t Q ) − 1/ 2( 2. 67 t Q ) (17)
Figure V-6--Peak Flow Reduction Based on Available Storage Rearranging and simplifying the equation provides a quick, direct solution for the reduced outflow based on the storage available. s Qr = Qp − (18) 1. 33 t p By expressing the volumes in cubic meters (cubic feet), the time-to-peak in minutes and the inflow peak in cubic meters per second (cubic feet per second); the reduced outflow in cubic meters per second (cubic feet per second) can be expressed as: s Qr = Qp − (19) 80 t p A culvert, or culverts, may now be selected based on passing this reduced discharge at the design headwater elevation. At least two alternative culvert selections should be chosen, one larger and one smaller than the required capacity. A full routing calculation is necessary to verify the performance of the selected culvert. D. Storage Indication Method The storage indication routing method is outlined in the following steps. The Storage Routing Form shown in Figure V-7 is designed to facilitate the routing process. Space is provided to calculate the appropriate peak flow reduction due to routing and to document the method used to generate the inflow hydrograph. Tables are provided for the elevation-discharge relationship, the elevation-storage relationship, the storage-outflow relationship, and the storage-indication routing calculations. A reproducible copy of the Storage Routing Form is provided in Appendix D. 127
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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
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Outlet control flow conditions can
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2 2 Vu Vd HW o + = TW + + HL (6) 2g
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This approximate method works best
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Figure III-12--Weir Crest Length De
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Critical depth is used when the tai
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4. Add the culvert flow and the roa
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NOTE: If the nomographs are put int
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Figure III-19--Critical Depth Chart
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(1) If the Manning’s n value give
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Example Problem #1 (SI Units) A cul
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Example Problem #2 (SI Units) A new
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Example Problem #3 (SI Units) Desig
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Example Problem #4 (SI Units) An ex
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CHART 51A Figure III-21--Inlet Cont
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2. Outlet Control. a. Partly Full F
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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 and 104: A slope-tapered inlet has three pos
Page 105 and 106: The mitered face slope-tapered inle
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: C. Application to Culvert Design Fi
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
Page 155 and 156: Figure V-14--Storage vs. Outflow Re
Page 157 and 158: Table 5 --Inflow Hydrograph, Exampl
Page 159 and 160: Figure V-18--Culvert Design Form fo
Page 161 and 162: Figure V-22--Storage vs. Outflow Re
Page 163 and 164: A. Introduction VI. SPECIAL CONSIDE
Page 165 and 166: With minor modifications, the culve
Page 167 and 168: If headwater and flow consideration
Page 169 and 170: Figure VI-6--Subatmospheric Pressur
Page 171 and 172: Figure VI-7--Fish Baffles in Culver
Page 173 and 174: A popular method of providing for f
Page 175 and 176: passage of the peak flow. Methods f
Page 177 and 178: Figure VI-15--Sediment Deposition i
Page 179 and 180: 1. Skewed Barrels. The alignment of
Page 181 and 182: Skewed inlets slightly reduce the h
Page 183 and 184: arrel for pipes or the flow per met
Page 185 and 186: Culvert shapes are as important in
Page 187 and 188: • Flood plain ordinances or other
Page 189 and 190: Figure VI-28--Guardrail Adjacent to
Page 191 and 192: Both of the above equations are emp
Page 193 and 194: Tables, charts, and formulas are av
Page 195 and 196: 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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