Culvert Capacity CalculatorHec10 Table of Contents for Capacity Charts for the Hydraulic Design of Highway Culverts List of FiguresList of Charts & Forms Cover Page : Capacity Charts for the Hydraulic Design of Highway Culverts Section 1 : HEC 10 Introduction Section 2 : HEC 10 Description of Capacity Charts A.Scope of Charts B.Composition of Charts C.Reading of Charts Section 3 : HEC 10 Requirements and Limitations for Use of Charts A.Requirements and Limitations B.Problems Not Meeting Above Requirements Section 4 : HEC 10 Special Uses of Capacity Charts Case 1 Paved invert corrugated metal pipe or pipearch culverts.Case 2 Fully paved corrugated metal pipe with headwall entrance.Case 3 Rectangular concrete box culverts of 5 ft. height or more.Case 4 Circular pipe sizes not included in the charts for concrete or corrugated metal pipe. Case 5 Oval concrete pipe sizes not on the charts.Case 6 Corrugated structural plate (2" x 6") pipearch sizes not on the charts. Case 7 Culvert slope zero (level invert).Case 8 Culverts with broken slopes.Case 9 The culvert L/100So exceeds the chart value. Section 5 : HEC 10 Design Considerations A.Magnitude and Frequency of Floods B.Design Floods C. Allowable Headwater D.Other Factors Section 6 : HEC 10 Design Data A. Hydrologic Data B.Topographic and Other Site Data C.Stream Channel Calculations D.Design Data Tabulation E. Multiple Barrel Culverts Section 7 : HEC 10 Culvert Capacity Charts Part I A. Concrete Box Culverts B.Circular Concrete Pipe Culverts C. Oval Concrete Pipe Culverts D. Oval Concrete Pipe Culverts Section 7 : HEC 10 Culvert Capacity Charts Part II E.Standard Circular Corrugated Metal Pipe Culverts F. Standard Corrugated Metal Pipe Arch Culverts G.Structural Plate Circular Corrugated Metal Pipe Culverts H. Structural Plate PipeArch Corrugated Culverts Appendix A : HEC 10 Hydraulic Principles and Compilation of Charts A1 Notation A2 Inlet Control Flow A3 Outlet Control Flow A4 Resistance Factors A5 Chart Curves A6 Interpolation for Headwater Appendix B : HEC 10 Accuracy of Chart Solutions B1 General Considerations B2 Effects of Relative Headwater Depths B3 Culverts on Level Grade Appendix C : HEC 10 Chart ListingList of Figures for Capacity Charts for the Hydraulic Design of Highway Culverts Back to Table of Contents Figure 1.Typical Culvert Capacity Charts Figure 2 Back to Table of Contents The headwater depth given by the charts is actually the difference in elevation between theC.Reading of ChartsThe capacity charts may be used for determining headwater or discharge of a given culvertFor purposes of illustrating how the charts are read, sections of charts are shown in Figure 1.Figure 1A contains curves for a 36inch pipe taken from Chart 19, and combines in one graphthe two separate sets of curves for a 36inch projecting entrance standard corrugated metalo of 50, and two outlet control curves withL/100So of 250 and 450.Additional curves for L/100So of 100, 200, 300 and 400 hare beenadded to the Chart 19 curves by linear interpolation. These additional curves are located bymeasurement along several discharge lines to divide the headwater depth range betweeno.The curves are shown to aid in illustrating theinterpolation procedure which is to be used in reading headwater from a culvert capacity charto ratio is different from the chart curve.Headwater depth is read from a capacity chart by entering at the design Q and following up theo value computed from the length and slope of theparticular culvert to be investigated.Headwater is read on the ordinate scale.Figure 1A isprepared to show how this is done. If L/100So is 50 or less, the culvert operates in inlet control,and headwater depth is read on the solid line inlet control curve.No lesser depth of headwatero values.If the L/100So happens to be that of one of thecurves shown, headwater depth would be read from that curve.For any L/100So value otherthan shown on the curves and within the chart limit, i.e., greater than 50 and less than 450,Figure 1.Typical Culvert Capacity ChartsFor example, consider a peak discharge rate of 50 cfs. For a 36inch culvert 78 ft.long on ao = 140), headwater depth will be 5.2 ft.Another culvert 166 ft.long at0.5% slope (L/100So = 330), will require a headwater depth of 6.3 ft.at the same dischargerate.It should be noted that the latter problem begins to get into the range of headwater depths(above 2D) where less reliable determinations of headwater can be made as discussed in"Composition of Charts", Section 2B.If the accuracy of the 6.3 ft.headwater depth is importantto the solution of the problem, this depth should be checked by procedures given in HEC No.5.The factors governing culvert size selection include the design discharge rate, a limitingorder to locate the capacity chart to be used.Figure 1B, which is a part of Chart 13 with anexpanded scale, is used to demonstrate culvert size selection. The type selected is a concreteFor a culvert length of 240 ft. and slope of 0.002 as shown in Figure 1B, a range of headwaterand discharges can be studied for the three sizes of grooveedged concrete pipe shown.Theo ratio is 1200, therefore headwaterdischarge values may be determined accuratelyalong the "1200 curve" up to the HW = 2D line. If the problem under consideration stated that(The "HW = 1.3D lines" shown on Figure 1B are limits below which the maximum L/100Soratios on the capacity chart may be extrapolated to 1.5 the value shown.In this case the curvesmay be extrapolated to L/100So of 1800 below HW = 1.3D as discussed in Section 4, Case 9.The 1.3D lines are not shown on the capacity charts.)A discharge rate of 120 cfs and an allowable headwater depth (AHW) of 6.0 ft.will be used toillustrate further the culvert selection procedure Inspection of Figure 1B or Chart 13 revealsthat Hec05 Table of Contents for HEC 5Hydraulic Charts for the Selection of Highway Culverts List of FiguresList of Tables List of Charts & Forms List of Equations Cover Page : HEC 5Hydraulic Charts for the Selection of Highway Culverts Part I : HEC 5 Hydraulic Charts for the Selection of Highway Culverts Introduction Culvert Hydraulics Culverts Flowing with Inlet Control Culverts Flowing with Outlet Control Computing Depth of Tailwater Velocity of Culvert Flow Performance Curves Inlets and Culvert Capacity Part II : HEC 5 Hydraulic Charts for the Selection of Highway Culverts Procedure for Selection of Culvert Size InletControl Nomographs (Charts 1 through 7) Instructions for Use Part III : HEC 5 Hydraulic Charts for the Selection of Highway Culverts OutletControl Nomographs (Charts 8 through 14) Instructions for Use Appendix A : HEC 5 Performance Curves Appendix B : HEC 5 Hydraulic Charts for the Selection of Highway Culverts Appendix C : HEC 5 Illustrative Problems Referencesconventional or commonly used culverts flowing with inlet control.In all culvert design, headwater or depth of ponding at the entrance to a culvert is an importantthe culvert invert at the entrance to the energy line of the headwater pool (depth + velocityHeadwaterdischarge relationships for the various types of circular and pipearch culvertsThese research data were analyzed and nomographs for determining culvert capacity for inletnomographs, Charts 1 through 6, give headwaterdischarge relationships for most conventionalculverts flowing with inlet control through a range of headwater depths and discharges.Chart 7,discussed in Part I, is included in this revised edition to stress the importance of improving themethod given for the part full flow condition, Figure 2D, gives a solution for headwater depththat decreases in accuracy as the headwater decreases.The head H (Figure 2A) or energy required to pass a given quantity of water through a culvertflowing in outlet control with the barrel flowing full throughout its length is made up of threev, an entrance loss He, and a friction loss Hf.This energy is obtained from ponding ofwater at the entrance and expressed in equation formH = Hv + He + Hf(1)The velocity head Hv equals where V is the mean or average velocity in the culvert barrel.(The mean velocity is the discharge Q, in cfs, divided by the crosssectional area A, in sq. ft., ofThe entrance loss He depends upon the geometry of the inlet edge.This loss is expressed as acoefficient ke times the barrel velocity head or He = ke. The entrance loss coefficients kefor various types of entrances when the flow is in outlet control are given in Appendix B, Table1.The friction loss Hf is the energy required to overcome the roughness of the culvert barrel.Hfcan be expressed in several ways.Since most highway engineers are familiar with Manning's nwheren= Manning's friction factor (see nomographs and Part II for values)L= length of culvert barrel (ft)V= mean velocity of flow in culvert barrel (ft/sec)g= acceleration of gravity, 32.2 (ft/sec2)R= hydraulic radius or (ft)whereA= area of flow for full crosssection (sq.ft)WP= wetted perimeter (ft)Figure 5Computing Depth of TailwaterIn culverts flowing with outlet control, tailwater can be an important factor in computing both theMuch engineering judgment and experience is needed to evaluate possible tailwater conditionsAn approximation of the depth of flow in a natural stream (outlet channel) can be made byTable 2, in Appendix B.If the water surface in the outlet channel is established by downstreamcontrols, other means must be found to determine the tailwater elevation.Sometimes thisVelocity of Culvert FlowA culvert, because of its hydraulic characteristics, increases the velocity of flow over that in theEnergy dissipators for channel flow have been investigated in the laboratory and many haveparticularly important to culvert performance in inletcontrol flow.A comparison of several typesof commonly used inlets can be made by referring to Chart 2 and Chart 5.The type of inlet hassome effect on capacity in outlet control but generally the edge geometry is less important thanin inlet control.(See reference 6.)As shown by the inlet control nomograph on Chart 5, the capacity of a thin edge projectingmetal pipe can be increased by incorporating the thin edge in a headwall.The capacity of thethe construction of Chart 7, an inlet control nomograph for the performance of a beveled inleton a circular culvert. A sketch on the nomograph shows the dimensions of two possible bevels.e equals 0.25 forcorrugated metal barrels and 0.2 for concrete barrels.Figure 6 shows a photograph of a bevel constructed in the headwall of a corrugated metal pipe.Photo  Courtesy of Oregon State Highway DepartmentFigure 6Go to Part IIPart II : HEC 5Hydraulic Charts for the Selection of Highway CulvertsGo to Part IIIProcedure for Selection of Culvert SizeStep 1:List design data.(See suggested tabulation form, Figure 7.)Design discharge Q, in cfs., with average return period.(i.e. Q25 or Q50 etc.). Approximate length L of culvert, in feet.b. Slope of culvert.(If grade is given in percent, convert to slope in ft.per ft.)c. Allowable headwater depth, in feet, which is the vertical distance from the culvert invert (flow line) atthe entrance to the water surface elevation permissible in the headwater pool or approach channelupstream from the culvert.d. Mean and maximum flood velocities in natural stream.e. Type of culvert for first trial selection, including barrel material, barrel crosssectional shape andentrance type.f. Step 2:Determine the first trial size culvert.Since the procedure given is one of trial and error, the initial trial size can be determined in several ways:By arbitrary selection.. By using an approximating equation such as Q/10 = A from which the trial culvert Tags: culvert capacity calculator,capacity of box culverts,box culvert calculator,culvert inlet control,arch pipe capacity,culvert water velocity,culvert water capacity,culvert water storage,culvert waterproofing 
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