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- 1. HEC-RAS for ManagersPresented byRaymond Walton, Ph.D., P.E,.D.WRE, F.ASCE06/04/13With thanks toDr. James L. MartinandFrom NRCS workshopby Reep, 2004
- 2. HEC-RAS for Managers - LectureBenefits and Learning Outcomes Understand why hydraulic information isimportant Learn basic hydraulic modeling terminology Develop basic understanding of HEC-RASand why it is useful Learn what is needed to use it Become aware of concerns for managers Identify resources available to help you useHEC-RAS Develop an appreciation for British Humour06/04/13
- 3. AgendaReview of basic definitions and terminologyProvide answers for the following questions: What is hydraulics? Why do we need models? What is HEC-RAS? What can you do with HEC-RAS? What is needed to use HEC-RAS? What concerns should I have about the use ofHEC-RAS? Where can I go for help with HEC-RAS?06/04/13
- 4. Hydraulic Information - It’sImportantNecessary for planning,flood risk reduction,design, environmentalimpact assessment andmitigation, restoration06/04/13 1a-4
- 5. Hydraulic ParametersVelocityDepthShearWidthAreaetc06/04/13
- 6. What is Hydraulics? Definition (Webster’s New World Dictionary) Hydraulics (hi-dro’liks), n.pl. “The branch of physics having to do with themechanical properties of water and other liquids andthe application of these properties in engineering” The branch of fluid mechanics whichaddresses fluid in motion (a.k.a., fluiddynamics), while hydrostatics addresses fluidat rest.06/04/13
- 7. Background – Areas of Hydraulics Pressure flow (e.g., closed conduits) Free surface flow (e.g., rivers andstreams) HEC-RAS is primarily devoted toaddressing free surface flow; however, itdoes have capabilities to consider culvertsand limited abilities to represent closedconduits06/04/13
- 8. Background – Hydraulic Parameters Characteristics that define the properties offlowing liquid. For free surface flow, primary parametersinclude: Depth Flow area Velocity06/04/13Hydraulic models calculatethese parameters
- 9. Background – Types of Flow Steady Flow – At any point, depth andvelocity remains constant with respect totime, such as a constant discharge in along straight canal.06/04/13
- 10. Background – Types of Flow06/04/13Unsteady flow – Depth and/or velocitychanges in magnitude or direction withrespect to time, such as a flood hydrographor a curve in a channel.
- 11. Background – Types of FlowUniform Flow At a given instance, depth and velocityremains constant with respect to distancealong a streamline (streamlines must bestraight and velocity is constant, such as ina canal) Slope of the water surface, channel bedand total head line are all the same.06/04/13
- 12. Background – Types of FlowNon Uniform (varied) Flow Examples: flow in a bend or at expansionsor contractions in the flow area.06/04/13
- 13. Basic Open ChannelFlow ConceptsSteady vs. UnsteadyUniform vs. VariedClassification of Open Channel FlowT1,T2T1T2
- 14. Background – Normal Deptha.k.a., Steady Uniform FlowCalculated using Manning’s equationQ = 1.486/n A R2/3S01/2Why is this important?06/04/13
- 15. Background – Critical DepthFlow RegimeFr = ratio of the inertia force over the gravitational forceClassification of Open Channel FlowgDVFr =Where:V = VelocityD = Hydraulic Depthg = acceleration of gravity(1)Fr < 1 The flow isSubcriticalFr = 1 The flow is atCritical depthFr > 1 The flow isSupercritical
- 16. Background – Critical DepthFlow Regime (Cont.) Wave propagationsWave CelerityClassification of Open Channel FlowgDc =FlowStill WaterSubcritical Critical Supercriticalc > V c = V c < V(2)
- 17. Equations for Basic ProfileCalculationsWater surface profiles are computed from one cross section to the nextby solving the Energy equation with an iterative procedure called thestandard step method.The Energy equation is written as follows:ehgVyzgVyz +++=++222111122222ααWhere: y1, y2 = Water depths cross sectionsz1, z2 = Elevation of bed above project datum (e.g., NAVD)V1, V2 = Average velocities (total discharge/total flow area)α1, α2 = Velocity weighting coefficientsg = Gravitational accelerationhe = Energy head loss
- 18. Background – Critical Depth Specific Energy is the total of the potential and kinematic energygVyE22α+= (5)Specific EnergyWhere:E = Specific energyy = Flow depthz = Height abovedatumα = Velocity weightingcoefficientsV = Velocityg = Gravitationalacceleration01234567891011121314151617180 5 10 15 20 25Specific Energy (ft)FlowDepth(ft)y2gV2
- 19. Basic Open ChannelFlow Concepts Critical depth (Yc) is the depth associated with the minimum specificenergy Dependent on cross section geometry and flow.Specific Energy – Critical Depth01234567891011121314151617180 5 10 15 20 25Specific Energy (ft)WaterSurface(ft)Supercritical FlowSubcritical FlowYcSEminy2gV2
- 20. Background – Types of FlowGradually Varied Flow (GVF) Where changes in cross section take placevery gradually with distance along thechannel, acceleration effects are negligible Changes include geometry, obstructionsand balance between resisting forces andforce of gravity tending to accelerate theflow HEC-RAS calculates water surface profilesunder GVF conditions06/04/13
- 21. Background – Types of FlowRapidly Varied Flow (RVF) Examples: Waterfalls, hydraulic jumps andsteep channels (greater than 10 percentslope) HEC-RAS can not directly represent RVF06/04/13
- 22. Basic Open ChannelFlow ConceptsGradually Varied vs. Rapidly VariedClassification of Open Channel Flow
- 23. Hydraulic ComputerModels: Why do we care?Direct Measurements:hard, expensive,dangerousAnalytical: predictive06/04/13
- 24. BackgroundOne, Two and Three Dimensional Flow06/04/13X directionYdirectionZdirection
- 25. Background – 1 Dimensional FlowChanges in flow velocity are restricted to onlyone direction (X).Models readily availableWell understoodCommonly used06/04/13XDirection
- 26. Background – 2 Dimensional FlowChanges in flow velocity are restricted to onlytwo directions (X, Y)Better answers?Great visualization toolAccounts for momentum transferUse in confluences/complex areas06/04/13
- 27. Two-Dimensional ModelingXDirectionYDirection
- 28. Background – 3 Dimensional FlowChanges in flow velocity occur in threedirections (X,Y,Z)Data for calibration?When necessary?SophisticatedComputer intensive06/04/13
- 29. Background – What is a model?A mathematical representation(approximation) of physical processes.Useful for Characterization of existing conditions Evaluation of proposed conditions Estimation/mitigation of potential impacts06/04/13
- 30. Background – ModelingWisdom06/04/13“All models are wrong. Some are useful”George E.P. Box, UCL Mathematicianand Statistician (Un. Wisconsin)“Everything should be made as simple aspossible, but not simpler ” Albert Einstein"For every complex problem there isa simple solution, and it is wrong."H.L. Mencken
- 31. Background – More ModelingWisdom06/04/13“The model is never wrong. The modeleroften is”Ray Walton, UCL Mathematicianand (part-time) Statistician (Un. Florida)
- 32. What is HEC-RAS?US Army Corps ofEngineers’Hydraulic EngineeringCenterRiver Analysis System06/04/13
- 33. The HEC-RAS Modeling System1D River HydraulicsGraphical User InterfaceSteady & Unsteady FlowBridges, Culverts, Dams,weirs, levees, gates, etc…Data storage/managementGraphics, Tabular Output &ReportingGeoRas – ArcGISMore coming………06/04/13
- 34. History of HEC-RAS DevelopmentIn the beginning, there was HEC-2 and UNET andHEC-6, and ……1D Steady Flow Analysis FY 1992 - 1999 Produced Steady flow versions of HEC-RAS (Beta 1&2,Versions 1.0 - 1.2, 2.0 – 2.2)1D Unsteady Modeling for River Analysis FY 2000 – 2005 Versions 3.0 – 3.1.31D Steady and Unsteady Hydraulics. SedimentTransport and Water Quality Modeling, Version 4.0,March of 2008 Now up to Version 4.1.0 (2010)1D/2D/(3D?) Steady and Unsteady Hydraulics anddynamic groundwater, Version 5.0, stay tuned!!!06/04/13
- 35. HEC-RAS is software that allows theuser to perform one dimensionalsteady and unsteady flow riverhydraulics calculations.- Public domain and freely distributedby the Corps of Engineers- Support available from privatevendorsgo to:www.hec.usace.army.mil/software/hec-ras/06/04/13 1-36
- 36. What is HEC-RAS?Graphical User Interface (GUI) – Allowsefficient input of data and evaluation of outputData Storage and Management – Providesability to create, store and combine data filescontaining hydrologic, geometric, andhydraulic design data into uniquecombinations06/04/13
- 37. What Units Can HEC-RASUse?SI units (meters, seconds, etc.)Units from less-developed countries (e.g.,“U.S. Customary”)06/04/13
- 38. RAS Project Schematic•Existing•Proposed•Existing 10yr,100yr, & 500yr•10% Increase•Existing•Existing +10% Q•Proposed•Proposed +10%
- 39. Geometry Cross Section Spacing Structures Manning’s nFlows Calibration Data06/04/13
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- 47. Culverts06/04/13
- 48. Weirs or DamsTreated as in-linestructureCan be modeledusing elevation-control or time-controlCan be controlled withscripts06/04/13
- 49. Gates06/04/13Variety of gate typesCan be modeledusing elevation-control or time-controlCan be controlled withscripts
- 50. GIS InterfaceInterface with GIS software for efficientdata input and output display andevaluation - Identify areas of floodinundationHEC-GeoRASMore GIS tools06/04/13
- 51. Hydraulic Design Functions Bridge scour Uniform Flow Stable channeldesign Sediment transportcapacity Sediment ImpactAssessment(SIAM)06/04/13
- 52. Sediment Transport and Budgets06/04/13
- 53. Water Quality (including temperature)06/04/13
- 54. GraphicalTabularProfileSection06/04/13
- 55. 06/04/13
- 56. From NRCS workshop by Reep, 200406/04/13
- 57. From NRCS workshop by Reep,200406/04/13
- 58. From NRCS workshop by Reep, 200406/04/13
- 59. 06/04/13
- 60. 06/04/13
- 61. 06/04/13
- 62. What concerns should Managershave about HEC-RAS?1-Dimensional Model Appropriate application ofmodel?Recognize andUnderstand Limitations Flow is gradually varied withdistance Dominant flows in x direction Applicable to channel slopesless than 1:10H06/04/13
- 63. Know what it can do – HEC-RASCapabilitiesBridge Hydraulics -extensiveCulverts (9 types)Multiple Opening (bridges &culverts)Inline Structures – gates & weirsLat. Structures – gates, levees,weirs, culverts, and rating curvesStorage/ponding areasHydraulic connections betweenstorage areasPump StationsFloating iceLeveesExtensive data import and exportGIS ConnectionsSteady flow profilesUnsteady flow simulationsFEMA floodway encroachmentsSplit flow optimizationSediment Transport Capacityand Bridge ScourDam and Levee BreachingNavigation Dam OperationsChannel ModificationsMixed Flow regimeExtensive Calibration FeaturesGeometric Features: Analysis Features:06/04/13
- 64. Water Surface Profile PlotsCross SectionsRating curvesStage and flow hydrographsGeneralized profile plot of anyvariable (I.e velocity)3D view of river systemGraphical Animations250+ output variables at everycross section per profileDetailed output tables for XSand all structuresSummary output tablesUser define outputExtensive Manuals User’s Manual Hydraulic Reference Manual Applications GuideOnline Help SystemExample Data SetsGraphical Output: Tabular Output:Documentation:06/04/13Know what it can do – HEC-RASCapabilities (continued)
- 65. What concerns should Managershave about HEC-RAS?(continued)Input Data Remember: Garbage In, Garbage Out (GIGO) Need enough to get the job done (spacing) Data can be expensive to collect Look for existing data sources Pay attention to datums LiDAR data can be inaccurate Use model to guide data collection06/04/13
- 66. What concerns should Managershave about HEC-RAS? (continued)Calibration/Validation What is calibration? When is it “calibrated”? What is validation? What if data for calibration/validation areunavailable?06/04/13
- 67. What concerns should Managershave about HEC-RAS? (continued)Rigid bed assumption Hydraulic calculations are all made with arigid bed assumption Hydraulic roughness can change withbedform (dunes, gravel bars, debris) Bedforms can change with sediment inputand temperature (seasonality) Sediment transport / Unstable channels Lateral channel migration not considered06/04/13
- 68. What concerns should Managershave about HEC-RAS? (continued)Sensitivity of results Conduct a sensitivity analysis/riskassessment Look at accuracy of involved input data Topography/geometry Hydrology Hydraulic roughness Structures/Modeling techniques Look at accuracy of output application Mapping accuracy06/04/13
- 69. What concerns should Managershave about HEC-RAS? (continued)Any idiot can use itNeed qualified users Qualifications, Training andExperienceProvide QA/QC Appropriate application Input, Output06/04/13
- 70. What is so great about HEC-RAS?Public Domain/Free/Widely usedSupported by Corps of EngineersContinuing Improvement 2-D capabilities being developed Expected by end of 2012Graphical AbilitiesGood DocumentationTraining Available06/04/13
- 71. HEC-RAS - Documentation User’s Manual: provides an introduction and overview ofthe modeling system, installation instructions, how to getstarted, a simple example, detailed descriptions of each of themajor modeling components, and how to view graphical andtabular output Hydraulic Reference Manual: describes the theoryand data requirements for hydraulic calculations Applications Guide: contains a series of examples thatdemonstrate various aspects of HEC-RAS.06/04/13
- 72. The HEC-RAS software is anengineering tool.Not a replacement for soundengineering.06/04/13
- 73. Questions?Questions?06/04/13

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