HEC-RAS River Analysis System Applications Guide CPD-70

US Army Corps of Engineers Hydrologic Engineering Cent er HEC-RAS HEC -R AS River Analysis System Applications Guide Version 3.1 November 2002 Approved for Public Release. Distribution Unlimited CPD-70 Table of Cont ent s Form Approved OMB No. 0704-0188 REPORT DOCUMENTATION PAGE Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the date needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503. 1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORT TYPE AND DATES COVERED November 2002 Computer Program Documentation 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS HEC-RAS, River Analysis System Applications Guide 6. AUTHOR(S) John C. Warner, Gary W. Brunner, Brent C. Wolfe, and Steven S. Piper 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER US ARMY CORPS OF ENGINEERS HYDROLOGIC ENGINEERING CENTER (HEC) 609 Second Street Davis, CA 95616-4687 CPD-70 10. SPONSORING / MONITORING AGENCY REPORT NUMBER 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 11. SUPPLEMENTARY NOTES 12a. DISTRIBUTION / AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Approved for Public Release. Distribution is unlimited. 13. ABSTRACT (Maximum 200 words) The U.S. Army Corps of Engineers’ River Analysis System (HEC-RAS) is software that allows you to perform onedimensional steady and unsteady flow river hydraulics calculations. HEC-RAS is an integrated system of software, designed for interactive use in a multi-tasking, multi-user network environment. The system is comprised of a graphical user interface (GUI), separate hydraulic analysis components, data storage and management capabilities, graphics and reporting facilities. The HEC-RAS system will ultimately contain three one-dimensional hydraulic analysis components for: (1) steady flow water surface profile computations; (2) unsteady flow simulation; and (3) movable boundary sediment transport computations. A key element is that all three components will use a common geometric data representation and common geometric and hydraulic computation routines. In addition to the three hydraulic analysis components, the system contains several hydraulic design features that can be invoked once the basic water surface profiles are computed. The current version of HEC-RAS supports Steady and Unsteady flow water surface profile calculations. New features and additional capabilities will be added in future releases. 14. SUBJECT TERMS 15. NUMBER OF water surface profiles, river hydraulics, steady and unsteady flow, computer program PAGES 344 16. PRICE CODE 17. SECURITY CLASSIFICATION OF REPORT 18. SECURITY CLASSIFICATION OF THIS PAGE 19. SECURITY CLASSIFICATION OF ABSTRACT 20. LIMITATION OF ABSTRACT UNCLASSIFIED UNCLASSIFIED UNCLASSIFIED UNLIMITED HEC-RAS River Analysis System Applications Guide Version 3.1 November 2002 US Army Corps of Engineers Institute for Water Resources Hydrologic Engineering Center 609 Second Street Davis, CA 95616 (530) 756-1104 (530) 756-8250 FAX www.hec.usace.army.mil Table of Cont ent s Table of Contents Table of Cont ent s ................................................................................................ i FOREWORD ............................................................................................................. I X I NTRODUCTI ON ........................................................................................................ XI HEC- RAS Docum ent at ion .................................................................................... xii Overview of t his Manual ..................................................................................... xii CH APTER 1 ......................................................................................................... 1 - 1 CRI TI CAL CREEK .................................................................................................... 1- 1 Purpose ......................................................................................................... 1- 1 Subcrit ical Flow Analysis ................................................................................... 1- 1 Geom et ric Dat a ............................................................................................ 1- 1 Flow Dat a .................................................................................................... 1- 3 St eady Flow Analysis ..................................................................................... 1- 4 Subcrit ical Flow Out put Review ....................................................................... 1- 5 Mixed Flow Analysis ........................................................................................ 1- 10 Modificat ion of Exist ing Geom et ry .................................................................. 1- 11 Flow Dat a ................................................................................................... 1- 13 Mixed Flow Analysis ..................................................................................... 1- 13 Review of Mixed Flow Out put ......................................................................... 1- 14 Sum m ary ...................................................................................................... 1- 15 CH APTER 2 ......................................................................................................... 2 - 1 BEAVER CREEK - SI NGLE BRI DGE ................................................................................ 2- 1 Purpose ......................................................................................................... 2- 1 Pressure/ Weir Flow Analysis.............................................................................. 2- 1 River Syst em Schem at ic ................................................................................ 2- 2 Cross Sect ion Geom et ric Dat a ........................................................................ 2- 3 Bridge Geom et ry Dat a ................................................................................... 2- 8 I neffect ive Flow Areas .................................................................................. 2- 12 Bridge Modeling Approach ............................................................................. 2- 14 St eady Flow Dat a......................................................................................... 2- 17 Pressure/ Weir Flow Sim ulat ion ....................................................................... 2- 19 Review of Pressure/ Weir Flow Out put ............................................................. 2- 20 Energy Met hod Analysis................................................................................... 2- 22 Energy Met hod Dat a and Sim ulat ion ............................................................... 2- 22 Review of Energy Met hod Out put ................................................................... 2- 23 Evaluat ion of Cross Sect ion Locat ions ................................................................ 2- 23 Expansion Reach Lengt h ............................................................................... 2- 23 Cont ract ion Reach Lengt h ............................................................................. 2- 26 Expansion Coefficient ................................................................................... 2- 27 Cont ract ion Coefficient ................................................................................. 2- 28 Model Calibrat ion ............................................................................................ 2- 29 Com parison of Energy and Pressure/ Weir Flow Met hods t o Observed Dat a .............. 2- 31 Sum m ary ...................................................................................................... 2- 33 CH APTER 3 ......................................................................................................... 3 - 1 SI NGLE CULVERT ( MULTI PLE I DENTI CAL BARRELS) ............................................................ 3- 1 Purpose ......................................................................................................... 3- 1 i Table of Cont ent s Geom et ric Dat a ............................................................................................... 3- 1 River Syst em Schem at ic ................................................................................ 3- 2 Cross Sect ion Geom et ry ................................................................................ 3- 2 Cross Sect ion Placem ent ................................................................................ 3- 4 Culvert Dat a ................................................................................................ 3- 9 St eady Flow Dat a ........................................................................................... 3- 15 Flow Dat a ................................................................................................... 3- 15 Boundary Condit ions .................................................................................... 3- 15 St eady Flow Analysis....................................................................................... 3- 16 Out put Analysis .............................................................................................. 3- 17 Expansion and Cont ract ion Reach Lengt h Evaluat ion ......................................... 3- 17 Channel Cont ract ion and Expansion Coefficient s ............................................... 3- 19 Wat er Surface Profiles .................................................................................. 3- 21 Sum m ary ...................................................................................................... 3- 27 CH APTER 4 ......................................................................................................... 4 - 1 MULTI PLE CULVERTS ............................................................................................... 4- 1 Purpose ......................................................................................................... 4- 1 Geom et ric Dat a ............................................................................................... 4- 1 River Syst em Schem at ic ................................................................................ 4- 2 Cross Sect ion Geom et ry ................................................................................ 4- 2 Expansion and Cont ract ion Reach Lengt hs ........................................................ 4- 3 Culvert Dat a ................................................................................................ 4- 3 I neffect ive Flow Areas ................................................................................... 4- 8 St eady Flow Dat a ............................................................................................ 4- 8 St eady Flow Analysis........................................................................................ 4- 9 Out put Analysis ............................................................................................... 4- 9 Expansion and Cont ract ion Reach Lengt hs ........................................................ 4- 9 Channel Expansion and Cont ract ion Coefficient s ............................................... 4- 12 Wat er Surface Profiles .................................................................................. 4- 13 Sum m ary ...................................................................................................... 4- 16 CH APTER 5 ......................................................................................................... 5 - 1 MULTI PLE OPENI NGS ............................................................................................... 5- 1 Purpose ......................................................................................................... 5- 1 River Syst em Geom et ric Dat a............................................................................ 5- 2 River Syst em Schem at ic ................................................................................ 5- 2 Cross Sect ion Geom et ry ................................................................................ 5- 3 Placem ent of t he Cross Sect ions ..................................................................... 5- 3 Bridge Geom et ry ............................................................................................. 5- 3 Deck/ Roadway Dat a ...................................................................................... 5- 3 Piers and Abut m ent s ..................................................................................... 5- 5 Bridge Modeling Approach .............................................................................. 5- 5 Culvert Geom et ry ............................................................................................ 5- 6 Mult iple Openings ............................................................................................ 5- 7 St agnat ion Lim it s.......................................................................................... 5- 7 I neffect ive Flow Areas ................................................................................... 5- 9 Manning's n Values ...................................................................................... 5- 10 Cross Sect ion Locat ions ................................................................................... 5- 10 Expansion Reach Lengt h ............................................................................... 5- 11 Cont ract ion Reach Lengt h ............................................................................. 5- 13 Coefficient s of Expansion and Cont ract ion ....................................................... 5- 13 St eady Flow Analysis....................................................................................... 5- 14 ii Table of Cont ent s Mult iple Opening Out put Analysis ...................................................................... 5- 14 Cross Sect ion Placem ent Evaluat ion................................................................ 5- 15 Wat er Surface Profiles .................................................................................. 5- 15 Mult iple Opening Profile Table ........................................................................ 5- 16 Sum m ary ...................................................................................................... 5- 20 CH APTER 6 ......................................................................................................... 6 - 1 FLOODWAY D ETERMI NATI ON ...................................................................................... 6- 1 Purpose....................................................................................................... 6- 1 Floodplain Encroachm ent Analysis Procedure ....................................................... 6- 2 Base Flood Profile ............................................................................................ 6- 3 Met hod 5 Opt im izat ion Procedure....................................................................... 6- 4 Met hod 5 St eady Flow Dat a ............................................................................ 6- 4 Met hod 5 Encroachm ent Dat a ......................................................................... 6- 4 Met hod 5 Out put Review ................................................................................ 6- 6 Met hod 4 Encroachm ent Analysis - Trial 1 ........................................................... 6- 8 Met hod 4 St eady Flow Dat a - Trial 1 ................................................................ 6- 9 Met hod 4 Encroachm ent Dat a - Trial 1 ............................................................. 6- 9 Met hod 4 Out put - Trial 1 .............................................................................. 6- 10 Met hod 4 Encroachm ent Analysis - Trial 2 .......................................................... 6- 12 Met hod 4 St eady Flow Dat a - Trial 2 ............................................................... 6- 12 Met hod 4 Encroachm ent Dat a - Trial 2 ............................................................ 6- 12 Met hod 4 Out put - Trial 2 .............................................................................. 6- 13 Met hod 4 Encroachm ent Analysis - Trial 3 .......................................................... 6- 16 Met hod 1 Encroachm ent Analysis ...................................................................... 6- 18 Met hod 1 St eady Flow Dat a ........................................................................... 6- 18 Met hod 1 Encroachm ent Dat a ........................................................................ 6- 18 Met hod 1 Out put ......................................................................................... 6- 18 Sum m ary ...................................................................................................... 6- 20 CH APTER 7 ......................................................................................................... 7 - 1 MULTI PLE PLANS .................................................................................................... 7- 1 Purpose ......................................................................................................... 7- 1 Elem ent s of a Proj ect ....................................................................................... 7- 1 Elem ent s of a Plan ........................................................................................... 7- 2 Exist ing Condit ions Analysis .............................................................................. 7- 3 Exist ing Condit ions Geom et ry ......................................................................... 7- 3 St eady Flow Dat a.......................................................................................... 7- 5 Exist ing Condit ions Plan ................................................................................. 7- 6 Exist ing Condit ions Out put ............................................................................. 7- 7 Proposed Condit ions Analysis ............................................................................ 7- 8 Proposed Condit ions Geom et ric Dat a ............................................................... 7- 8 St eady Flow Dat a.......................................................................................... 7- 9 Proposed Condit ions Plan .............................................................................. 7- 10 Proposed Condit ions Out put .......................................................................... 7- 10 Com parison of Exist ing and Proposed Plans ........................................................ 7- 10 Profile Plot .................................................................................................. 7- 10 Cross Sect ion Plot s ...................................................................................... 7- 12 St andard Table ............................................................................................ 7- 13 Bridge Only Table ........................................................................................ 7- 14 X- Y- Z Perspect ive Plot .................................................................................. 7- 14 Sum m ary ...................................................................................................... 7- 15 CH APTER 8 ......................................................................................................... 8 - 1 iii Table of Cont ent s LOOPED NETWORK ................................................................................................. Purpose ......................................................................................................... Geom et ric Dat a ............................................................................................... River Syst em Schem at ic ................................................................................ Cross Sect ion Dat a........................................................................................ St ream Junct ion Dat a .................................................................................... St eady Flow Dat a ............................................................................................ Profile Dat a.................................................................................................. Boundary Condit ions ..................................................................................... St eady Flow Analysis........................................................................................ Analysis of Result s for I nit ial Flow Dist ribut ion ..................................................... St eady Flow Analysis wit h New Flow Dist ribut ion .................................................. Analysis of Result s for Final Flow Dist ribut ion....................................................... Sum m ary ....................................................................................................... 8- 1 8- 1 8- 1 8- 1 8- 2 8- 3 8- 4 8- 4 8- 5 8- 6 8- 6 8- 7 8- 8 8- 8 CH APTER 9 ......................................................................................................... 9 - 1 MI XED FLOW ANALYSI S ............................................................................................ 9- 1 Purpose ......................................................................................................... 9- 1 Geom et ric Dat a ............................................................................................... 9- 1 River Syst em Schem at ic ................................................................................ 9- 1 Cross Sect ion Dat a........................................................................................ 9- 2 Locat ion of t he Cross Sect ions ........................................................................ 9- 3 Bridge Dat a .................................................................................................... 9- 4 St eady Flow Dat a ............................................................................................ 9- 7 Profile Dat a.................................................................................................. 9- 7 Boundary Condit ions ..................................................................................... 9- 8 St eady Flow Analysis........................................................................................ 9- 9 Review of Out put for Energy Analysis ................................................................ 9- 10 Wat er Surface Profile.................................................................................... 9- 10 Wat er Surface Profiles for Subcrit ical and Supercrit ical Flow Analyses .................. 9- 13 Profile Table - Bridge Com parison .................................................................. 9- 14 Cross Sect ion Table - Bridge.......................................................................... 9- 15 Pressure/ Weir Analysis .................................................................................... 9- 16 Review of Out put for Pressure/ Weir Analysis ...................................................... 9- 18 Wat er Surface Profile.................................................................................... 9- 18 Expansion and Cont ract ion Reach Lengt hs ....................................................... 9- 19 Bridge Com parison Table .............................................................................. 9- 21 Bridge Det ailed Out put Table ......................................................................... 9- 21 X- Y- Z Perspect ive Plot .................................................................................. 9- 23 Sum m ary ...................................................................................................... 9- 23 CH APTER 1 0 ..................................................................................................... 1 0 - 1 STREAM JUNCTI ON ................................................................................................ 10- 1 Purpose ........................................................................................................ 10- 1 Geom et ric Dat a .............................................................................................. 10- 1 River Syst em Schem at ic ............................................................................... 10- 1 Cross Sect ion Placem ent ............................................................................... 10- 3 Cross Sect ion Dat a....................................................................................... 10- 4 St ream Junct ion Dat a - Energy Met hod ........................................................... 10- 5 St eady Flow Dat a ........................................................................................... 10- 6 St eady Flow Analysis ( St ream Junct ion Energy Met hod) ....................................... 10- 8 Review of Out put for St ream Junct ion Energy Analysis ......................................... 10- 8 Wat er Surface Profile.................................................................................... 10- 9 iv Table of Cont ent s St andard Table 2 ....................................................................................... 10- 10 St eady Flow Analysis ( St ream Junct ion Mom ent um Met hod) ............................... 10- 11 Review of Out put for St ream Junct ion Mom ent um Analysis ................................. 10- 12 Wat er Surface Profile.................................................................................. 10- 12 St andard Table 2 ....................................................................................... 10- 13 Com parison of Energy and Mom ent um Result s.................................................. 10- 14 Sum m ary .................................................................................................... 10- 16 CH APTER 1 1 ..................................................................................................... 1 1 - 1 BRI DGE SCOUR .................................................................................................... 11- 1 Purpose ........................................................................................................ 11- 1 Geom et ric Dat a .............................................................................................. 11- 2 St eady Flow Dat a ........................................................................................... 11- 3 St eady Flow Analysis....................................................................................... 11- 4 Hydraulic Design - Bridge Scour ....................................................................... 11- 5 Cont ract ion Scour ........................................................................................ 11- 6 Pier Scour ................................................................................................... 11- 8 Abut m ent Scour .......................................................................................... 11- 9 Tot al Bridge Scour ..................................................................................... 11- 10 Sum m ary .................................................................................................... 11- 12 CH APTER 1 2 ..................................................................................................... 1 2 - 1 I NLI NE STRUCTURE ................................................................................................ 12- 1 Purpose ........................................................................................................ 12- 1 Geom et ric Dat a .............................................................................................. 12- 1 Cross Sect ion Dat a....................................................................................... 12- 2 I nline St ruct ure ........................................................................................... 12- 2 Gat ed Spillways ........................................................................................... 12- 5 I neffect ive Flow Areas .................................................................................. 12- 7 Cross Sect ion Placem ent ............................................................................... 12- 8 St eady Flow Dat a ........................................................................................... 12- 9 Flow Profiles ............................................................................................... 12- 9 Boundary Condit ions .................................................................................. 12- 10 Gat e Openings .......................................................................................... 12- 11 St eady Flow Analysis..................................................................................... 12- 12 Out put Analysis ............................................................................................ 12- 13 Wat er Surface Profiles ................................................................................ 12- 13 I nline St ruct ure Det ailed Out put Table .......................................................... 12- 14 I nline St ruct ure Profile Sum m ary Table ......................................................... 12- 17 Sum m ary .................................................................................................... 12- 18 CH APTER 1 3 ..................................................................................................... 1 3 - 1 BOGUE CHI TTO - SI NGLE BRI DGE ( WSPRO) ................................................................. 13- 1 Purpose ........................................................................................................ 13- 1 Geom et ric Dat a .............................................................................................. 13- 2 River Syst em Schem at ic ............................................................................... 13- 2 Cross Sect ion Geom et ric Dat a ....................................................................... 13- 3 Cross Sect ion Placem ent ............................................................................... 13- 4 Bridge Geom et ry Dat a .................................................................................. 13- 7 I neffect ive Flow Areas ................................................................................ 13- 11 Bridge Modeling Approach ........................................................................... 13- 14 St eady Flow Dat a ......................................................................................... 13- 18 St eady Flow Analysis..................................................................................... 13- 20 Review of Out put .......................................................................................... 13- 21 v Table of Cont ent s Wat er Surface Profiles ................................................................................ 13- 21 Profile Tables ............................................................................................ 13- 22 Det ailed Out put Tables ............................................................................... 13- 25 Evaluat ion of Cross Sect ion Locat ions .............................................................. 13- 26 Expansion Reach Lengt h ............................................................................. 13- 27 Cont ract ion Reach Lengt h ........................................................................... 13- 28 Expansion and Cont ract ion Coefficient s ......................................................... 13- 29 Sum m ary .................................................................................................... 13- 29 CH APTER 1 4 ..................................................................................................... 1 4 - 1 I CE- COVERED RI VER .............................................................................................. 14- 1 Purpose ........................................................................................................ 14- 1 Open Wat er Analysis ....................................................................................... 14- 2 Open Wat er Geom et ry .................................................................................. 14- 2 St eady Flow Dat a......................................................................................... 14- 2 Open Wat er Plan.......................................................................................... 14- 3 Open Wat er Out put ...................................................................................... 14- 3 I ce Cover Analysis .......................................................................................... 14- 3 I ce Cover Geom et ry ..................................................................................... 14- 3 St eady Flow Dat a......................................................................................... 14- 4 I ce Cover Plan ............................................................................................. 14- 4 I ce Cover Out put ......................................................................................... 14- 4 I ce Jam Analysis............................................................................................. 14- 4 I ce Jam Geom et ry ....................................................................................... 14- 5 St eady Flow Dat a......................................................................................... 14- 6 I ce Jam Plan ............................................................................................... 14- 6 I ce Jam Out put ............................................................................................ 14- 6 Com parison of Open Wat er, I ce Cover, and I ce Jam Result s ................................. 14- 7 Profile Plot .................................................................................................. 14- 7 I ce Table .................................................................................................... 14- 8 CH APTER 1 5 ..................................................................................................... 1 5 - 1 SPLI T FLOW JUNCTI ON WI TH LATERAL W EI R/ SPI LLWAY ...................................................... 15- 1 Purpose ........................................................................................................ 15- 1 Geom et ric Dat a ........................................................................................... 15- 1 St ream Junct ion Dat a ................................................................................... 15- 2 Cross Sect ion Dat a....................................................................................... 15- 3 Lat eral St ruct ure ......................................................................................... 15- 3 Gat ed Spillway ............................................................................................ 15- 6 St eady Flow Dat a ........................................................................................... 15- 8 Flow Profiles ............................................................................................... 15- 8 Boundary Condit ions .................................................................................... 15- 9 Gat e Openings .......................................................................................... 15- 10 St eady Flow Analysis..................................................................................... 15- 11 Out put Analysis ............................................................................................ 15- 13 Wat er Surface Profiles ................................................................................ 15- 13 Lat eral St ruct ure Det ailed Out put Table ........................................................ 15- 14 Lat eral St ruct ure Profile Sum m ary Table ....................................................... 15- 15 Junct ions Profile Sum m ary Table .................................................................. 15- 16 St andard Profile Sum m ary Table .................................................................. 15- 17 Addit ional Adj ust m ent s.................................................................................. 15- 18 Junct ion Flow Split ..................................................................................... 15- 18 Lat eral St ruct ure Flow Split ......................................................................... 15- 18 vi Table of Cont ent s Sum m ary .................................................................................................... 15- 19 CH APTER 1 6 ..................................................................................................... 1 6 - 1 CHANNEL MODI FI CATI ON ......................................................................................... 16- 1 Purpose ........................................................................................................ 16- 1 Geom et ric Dat a .............................................................................................. 16- 1 Channel Modificat ion Dat a ............................................................................. 16- 1 Perform ing t he Channel Modificat ions ............................................................. 16- 4 Saving t he Channel Modificat ions ................................................................... 16- 4 St eady Flow Analysis....................................................................................... 16- 5 Com paring Exist ing and Modified Condit ions ....................................................... 16- 6 St eady Flow Analysis .................................................................................... 16- 6 Wat er Surface Profiles .................................................................................. 16- 7 Cross Sect ion Plot s ...................................................................................... 16- 8 X- Y- Z Perspect ive Plot ...................................................................................... 9 St andard Table ............................................................................................... 10 Sum m ary ......................................................................................................... 11 CH APTER 1 7 ..................................................................................................... 1 7 - 1 UNSTEADY FLOW APPLI CATI ON .................................................................................. 17- 1 Purpose ........................................................................................................ 17- 1 Geom et ric Dat a .............................................................................................. 17- 1 General Descript ion ...................................................................................... 17- 2 Creat ing St orage Areas................................................................................. 17- 4 Ent ering Dat a for a St orage Area ................................................................... 17- 6 Lat eral St ruct ure Connect ed t o a St orage Area ................................................. 17- 7 St orage Area Connect ions ............................................................................. 17- 9 Param et ers for Hydraulic Tables................................................................... 17- 11 Cross Sect ion Table Param et ers ................................................................... 17- 12 Unst eady Flow Dat a ...................................................................................... 17- 13 Boundary Condit ions .................................................................................. 17- 13 Upst ream Boundary Condit ion ..................................................................... 17- 14 Downst ream Boundary Condit ion ................................................................. 17- 16 I nit ial Condit ions ....................................................................................... 17- 16 Unst eady Flow Analysis ................................................................................. 17- 18 Sim ulat ion Tim e Window ............................................................................. 17- 18 Com put at ion Set t ings ................................................................................. 17- 19 Locat ion of St age and Flow Hydrographs ....................................................... 17- 19 Unst eady Flow Sim ulat ion .............................................................................. 17- 20 Geom et ry Pre- processor ( HTAB) .................................................................. 17- 20 Unst eady Flow Sim ulat ion and t he Post - Processor .......................................... 17- 22 Sum m ary .................................................................................................... 17- 27 REFERENCES ........................................................................................................ A- 1 vii Foreward Foreword The U.S. Arm y Corps of Engineers’ River Analysis Syst em ( HEC- RAS) is soft ware t hat allows you t o perform one- dim ensional st eady and unst eady flow river hydraulics calculat ions. The HEC- RAS soft ware supersedes t he HEC- 2 river hydraulics package, which was a one- dim ensional, st eady flow wat er surface profiles program . The HEC- RAS soft ware is a significant advancem ent over HEC- 2 in t erm s of bot h hydraulic engineering and com put er science. This soft ware is a product of t he Corps’ Civil Works Hydrologic Engineering Research and Developm ent Program . The first version of HEC- RAS ( version 1.0) was released in July of 1995. Since t hat t im e t here have been several releases of t his soft ware package, including versions: 1.1; 1.2; 2.0; 2.1; 2.2; 2.21; 3.0 and now version 3.1 in Sept em ber of 2002. The HEC- RAS soft ware was developed at t he Hydrologic Engineering Cent er ( HEC) , which is a division of t he I nst it ut e for Wat er Resources ( I WR) , U.S. Arm y Corps of Engineers. The soft ware was designed by Mr. Gary W. Brunner, leader of t he HEC- RAS developm ent t eam . The user int erface and graphics were program m ed by Mr. Mark R. Jensen. The st eady flow wat er surface profiles m odule and a large port ion of t he unst eady flow com put at ions m odules was program m ed by Mr. St even S. Piper. The unst eady flow equat ion solver was developed by Dr. Robert L. Barkau. The St able Channel Design Rout ines were program m ed by Mr. Chris R. Goodell. The rout ines t hat im port HEC- 2 and UNET dat a were developed by Ms. Joan Klipsch. The rout ines for m odeling ice cover and wide river ice j am s were developed by Mr. St even F. Daly of t he Cold Regions Research and Engineering Laborat ory ( CRREL) . Many of t he HEC st aff m ade cont ribut ions in t he developm ent of t his soft ware, including: Vern R. Bonner, Richard Hayes, John Pet ers, Al Mont alvo, and Michael Gee. Mr. Darryl Davis was t he direct or during t he developm ent of t his soft ware. This m anual was writ t en by John C. Warner, Gary W. Brunner, Brent C. Wolfe, and St even S. Piper. ix I nt roduct ion Introduction Welcom e t o t he Hydrologic Engineering Cent er's River Analysis Syst em ( HECRAS) . This soft ware allows you t o perform one- dim ensional st eady flow, unst eady flow, and sedim ent t ransport calculat ions ( The current version of HEC- RAS can only perform st eady flow calculat ions. Unst eady flow and sedim ent t ransport will be added in fut ure versions) . The HEC- RAS m odeling syst em was developed as a part of t he Hydrologic Engineering Cent er's " Next Generat ion" ( NexGen) of hydrologic engineering soft ware. The NexGen proj ect encom passes several aspect s of hydrologic engineering, including: rainfall- runoff analysis; river hydraulics; reservoir syst em sim ulat ion; flood dam age analysis; and real- t im e river forecast ing for reservoir operat ions. This int roduct ion discusses t he docum ent at ion for HEC- RAS and provides an overview of t his m anual. Con t e n t s • HEC- RAS Docum ent at ion • Overview of t his Manual xi I nt roduct ion HEC-RAS Documentation The HEC- RAS package includes several docum ent s. Each docum ent is designed t o help t he user learn t o use a part icular aspect of t he m odeling syst em . The docum ent at ion is arranged in t he following t hree cat egories: D ocum e n t a t ion D e scr ipt ion User's Manual This m anual is a guide t o using HEC- RAS. The m anual provides an int roduct ion and overview of t he m odeling syst em , inst allat ion inst ruct ions, how t o get st art ed, sim ple exam ples, det ailed descript ions of each of t he m aj or m odeling com ponent s, and how t o view graphical and t abular out put . Hydraulic Reference Manual This m anual describes t he t heory and dat a requirem ent s for t he hydraulic calculat ions perform ed by HEC- RAS. Equat ions are present ed along wit h t he assum pt ions used in t heir derivat ion. Discussions are provided on how t o est im at e m odel param et ers, as well as guidelines on various m odeling approaches. Applicat ions Guide This docum ent cont ains exam ples t hat dem onst rat e various aspect s of HEC- RAS. Each exam ple consist s of a problem st at em ent , dat a requirem ent s, general out line of solut ion st eps, displays of key input and out put screens, and discussions of im port ant m odeling aspect s. Overview of this Manual This Applicat ions Guide cont ains writ t en descript ions of 17 exam ples t hat dem onst rat e t he m ain feat ures of t he HEC- RAS program . The proj ect dat a files for t he exam ples are cont ained on t he HEC- RAS program dist ribut ion disket t es, and will be writ t en t o t he HEC\ RAS\ STEADY and HEC\ RAS\ UNSTEADY direct ories when t he program is inst alled. The discussions in t his m anual cont ain det ailed descript ions for t he dat a input and analysis of t he out put for each exam ple. The exam ples display and describe t he input and out put screens used t o ent er t he dat a and view t he out put . The user can act ivat e t he proj ect s wit hin t he HEC- RAS program when reviewing t he descript ions for t he exam ples in t his m anual. All of t he proj ect s have been com put ed, and t he user can review t he input and out put screens t hat are discussed as t hey appear in t his m anual. The user can use t he zoom feat ures and opt ions select ions ( plans, profiles, variables, reaches, et c.) t o obt ain clearer views of t he graphics, as well as viewing addit ional dat a screens t hat m ay be referenced t o in t he discussions. The exam ples are xii I nt roduct ion int ended as a guide for perform ing sim ilar analyses. This m anual is organized as follows: xiii I nt roduct ion Ex a m ple 1 , Cr it ica l Cr e e k , dem onst rat es t he procedure t o perform a basic flow analysis on a single river reach. This river reach is sit uat ed on a st eep slope, and t he analysis was perform ed in a m ixed flow regim e t o obt ain solut ions in bot h subcrit ical and supercrit ical flows. Addit ionally, t he exam ple describes t he procedure for cross sect ion int erpolat ion. xiv • Ex a m ple 2 , Be a ve r Cr e e k - Sin gle Br idge , illust rat es an analysis of a single river reach t hat cont ains a bridge crossing. The dat a ent ry for t he bridge and det erm inat ion for t he placem ent of t he cross sect ions are shown in det ail. The hydraulic calculat ions are perform ed wit h bot h t he energy and pressure/ weir flow m et hods for t he high flow event s. Addit ionally, t he m odel is calibrat ed wit h observed high flow dat a. • Ex a m ple 3 , Sin gle Culve r t ( M u lt iple I de n t ica l Ba r r e ls) , describes t he dat a ent ry and review of out put for a single culvert wit h t wo ident ical barrels. Addit ionally, a review for t he locat ions of t he cross sect ions in relat ion t o t he culvert is present ed. • Ex a m ple 4 , M u lt iple Cu lve r t s, is a con t inu a t ion of Ex a m ple 3 , wit h t he addit ion of a second culvert at t he sam e cross sect ion. The second culvert also cont ains t wo ident ical barrels, and t his exam ple describes t he review of t he out put for m ult iple culvert s. • Ex a m ple 5 , M u lt iple Ope n in gs, present s t he analysis of a river reach t hat cont ains a culvert opening ( single culvert wit h m ult iple ident ical barrels) , a m ain bridge opening, and a relief bridge opening all occurring at t he sam e cross sect ion. The user should be fam iliar wit h individual bridge and culvert analyses before reviewing t his exam ple. • Ex a m ple 6 , Floodw a y D e t e r m ina t ion, illust rat es several of t he m et hods for floodplain encroachm ent analysis. An exam ple procedure for t he floodplain encroachm ent analysis is perform ed. The user should be aware of t he sit e specific guidelines for a floodplain encroachm ent analysis t o det erm ine which m et hods and t he appropriat e procedures t o perform . • Ex a m ple 7 , M u lt iple Pla n s, describes t he file m anagem ent syst em used by t he HEC- RAS program . The concept s of working wit h proj ect s and plans t o organize geom et ry, flow, and ot her files are described. Then, an applicat ion is perform ed t o show a t ypical procedure for organizing a proj ect t hat cont ains m ult iple plans. • Ex a m ple 8 , Loope d N e t w or k , dem onst rat es t he analysis of a river syst em t hat cont ains a loop. The loop is a split in t he m ain channel t hat form s t wo st ream s which j oin back t oget her. The exam ple focuses on t he procedure for balancing of t he flows around t he loop. • Ex a m ple 9 , M ix e d Flow An a lysis, describes t he use of a m ixed flow regim e t o analyze a river reach cont aining a bridge crossing. The bridge crossing const rict s t he m ain channel supercrit ical flow, creat ing a subcrit ical backwat er effect , requiring t he use of t he m ixed flow regim e for t he analysis. Result s by subcrit ical and supercrit ical flow regim e analyses are present ed t o show inconsist encies t hat developed, and t o provide guidance when t o perform a m ixed flow analysis. • Ex a m ple 1 0 , St r e a m Junct ion , dem onst rat es t he analysis of a river syst em t hat cont ains a j unct ion. This exam ple illust rat es a flow com bining of t wo subcrit ical st ream s, and bot h t he energy and m om ent um m et hods are used for t wo separat e analyses. I nt roduct ion • Ex a m ple 1 1 , Br idge Scou r , present s t he det erm inat ion of a bridge scour analysis. The user should be fam iliar wit h t he procedures for m odeling bridges before reviewing t his exam ple. The scour equat ions and procedures are based upon t he m et hods out lined in Hydraulic Engineering Circular No. 18 ( FHWA 1995) . • Ex a m ple 1 2 , I n lin e W e ir a nd Ga t e d Spillw a y, dem onst rat es t he analysis of a river reach t hat cont ains an inline weir and a gat ed spillway. Procedures for ent ering t he dat a t o provide flexibilit y for t he flow analysis are provided. • Ex a m ple 1 3 , Bogu e Ch it t o - Single Br idge ( W SPRO) , perform s an analysis of a river reach t hat cont ains a bridge crossing. The exam ple is sim ilar t o Exam ple 2, however, all of t he wat er surface profiles are low flow and are com put ed using t he WSPRO ( FHWA, 1990) rout ines t hat have been adapt ed t o t he HEC- RAS m et hodology of cross sect ion locat ions around and t hrough a bridge. • Ex a m ple 1 4 , I ce - Cove r e d Rive r, is an exam ple of how t o m odel an ice covered river as well as a river ice- j am . • Ex a m ple 1 5 , Split Flow Ju n ct ion W it h La t e r a l W e ir a n d Spillw a y, is an exam ple of how t o perform a split flow opt im izat ion wit h t he st eady flow analysis port ion of t he soft ware. This exam ple has a split of flow at a j unct ion, as well as a lat eral weir. • Ex a m ple 1 6 , Cha nne l M odifica t ion . This exam ple dem onst rat es how t o use t he channel m odificat ion feat ure wit hin t he HEC- RAS Geom et ric Dat a Edit or. Channel m odificat ions are perform ed, and exist ing and m odified condit ions geom et ry and out put are com pared. • Ex a m ple 1 7 , Un st e a dy Flow Applica t ion. This exam ple dem onst rat es how t o perform an unst eady flow analysis wit h HEC- RAS. Discussions include: ent ering st orage area inform at ion; hydraulic connect ions; unst eady flow dat a ( boundary condit ions and init ial condit ions) ; perform ing t he com put at ions; and reviewing t he unst eady flow result s. • Appe ndix A cont ains a list of references. xv Exam ple 1 Crit ical Creek CH APT ER 1 Critical Creek Purpose Crit ical Creek is a st eep river com prised of one reach ent it led " Upper Reach." The purpose of t his exam ple is t o dem onst rat e t he procedure for perform ing a basic flow analysis on a single river reach. Addit ionally, t he exam ple will dem onst rat e t he need for addit ional cross sect ions for a m ore accurat e est im at e of t he energy losses and wat er surface elevat ions. Subcritical Flow Analysis From t he m ain window, select File and t hen Ope n Pr oj e ct . Select t he proj ect labeled " Crit ical Creek - Exam ple 1." This will open t he proj ect and act ivat e t he following files: Plan: " Exist ing Condit ions Run" Geom et ry: " Base Geom et ry Dat a" Flow: " 100 Year Profile" Geometric Data From t he m ain program window, select Edit and t hen Ge om e t r ic D a t a . This will act ivat e t he Ge om e t r ic D a t a Edit or and display t he river syst em schem at ic, as shown in Figure 1.1. As shown in t he figure, t he river nam e was ent ered as " Crit ical Creek," and t he reach nam e was " Upper Reach." The reach was defined wit h 12 cross sect ions num bered 12 t o 1, wit h cross sect ion 12 being t he m ost upst ream cross sect ion. These cross- sect ion ident ifiers are only used by t he program for placem ent of t he cross sect ions in a num erical order, wit h t he highest num ber being t he m ost upst ream sect ion. The cross sect ion dat a were ent ered in t he Cr oss Se ct ion D a t a Edit or , which is act ivat ed by select ing t he Cr oss Se ct ion icon on t he Ge om e t r ic D a t a Edit or ( as out lined in Chapt er 6 of t he Use r 's M a n u a l) . Most of t he 12 cross sect ions cont ain at least 50 pairs of X- Y coordinat es, so t he cross sect ion dat a will not be shown here for brevit y. The dist ances bet ween t he cross sect ions are as shown in Figure 1.2 ( The reach lengt hs for cross sect ion 12 can be seen by using t he scroll bars in t he window.) . This sum m ary t able 1-1 Exam ple 2 Beaver Creek- Single Bridge can be viewed by select ing Ta ble s and t hen Re a ch Le n gt h s on t he Ge om e t r ic D a t a Edit or . Figure 1-1: River System Schematic for Critical Creek 1-2 Exam ple 1 Crit ical Creek Figure 1-2: Reach Lengths For Critical Creek From t he geom et ric dat a, it can be seen t hat m ost of t he cross sect ions are spaced approxim at ely 500 feet apart . The change in elevat ion from cross sect ion 12 t o cross- sect ion 1 is approxim at ely 56 feet along t he river reach of 5700 feet . This yields a slope of approxim at ely 0.01 ft / ft , which can be considered as a fairly st eep slope. The rem aining geom et ric dat a consist s of Manning’s n values of 0.10, 0.04, and 0.10 in t he left overbank ( LOB) , m ain channel, and right overbank ( ROB) , respect ively. Also, t he coefficient s of cont ract ion and expansion are 0.10 and 0.30, respect ively. Aft er all t he geom et ric dat a was ent ered, it was saved as t he file " Base Geom et ry Dat a." Flow Data To ent er t he st eady flow dat a, from t he m ain program window Edit and t hen St e a dy Flow D a t a were select ed. This act ivat ed t he St e a dy Flow D a t a Edit or , as shown in Figure 1.3. For t his st eady flow analysis, t he one percent chance flow profile was analyzed. A flow of 9000 cfs was used at t he upst ream end of t he reach at sect ion 12 and a flow change t o 9500 cfs was used at sect ion 8 t o account for a t ribut ary inflow int o t he m ain river reach. This flow change locat ion was ent ered by select ing t he river, reach, river st at ion, and t hen pressing t he Add A Flow Cha n ge Loca t ion but t on. Then, t he t able in t he cent ral port ion of t he edit or added t he row for river st at ion 8. Finally, t he profile nam e was changed from t he default heading of " PF# 1" t o " 100 yr." The change t o t he profile label was m ade by select ing Edit Pr ofile N a m e s from t he Opt ion s m enu and t yping in t he new nam e. 1-3 Exam ple 2 Beaver Creek- Single Bridge Figure 1-3: Steady Flow Data Editor Next , t he Re a ch Bou nda r y Condit ion s but t on locat ed at t he t op of t he St e a dy Flow D a t a Edit or was select ed. The reach was analyzed for subcrit ical flow wit h a downst ream norm al dept h boundary condit ion of S = 0.01 ft / ft . This value was est im at ed as t he average slope of t he channel near t he downst ream boundary. For a subcrit ical flow analysis, boundary condit ions m ust be set at t he downst ream end( s) of t he river syst em . Aft er all of t he flow dat a was ent ered, it was saved as t he file " 100 Year Profile." Steady Flow Analysis To perform t he st eady flow analysis, from t he m ain program window Run and t hen St e a dy Flow Ana lysis were select ed. This act ivat ed t he St e a dy Flow Ana lysis W in dow as shown in Figure 1.4. Before perform ing t he st eady flow analysis, Opt ions and t hen Cr it ica l D e pt h Ou t pu t Opt ion were select ed. The opt ion Cr it ica l Alw a ys Ca lcu la t e d was chosen t o have crit ical dept h calculat ed at all locat ions. This will enable t he crit ical dept h t o be plot t ed at all locat ions on t he profile when t he result s are analyzed. Next , t he Flow Re gim e was select ed as " Subcrit ical" . The geom et ry file was select ed as " Base Geom et ry Dat a," and t he flow file was select ed as " 100 Year Profile" . The plan was t hen saved as " Exist ing Condit ions" , wit h a short I D of " Exist Cond" . Finally, t he st eady flow analysis was perform ed by select ing COM PUTE from t he St e a dy Flow Ana lysis window. 1-4 Exam ple 1 Crit ical Creek Figure 1-4: Steady Flow Analysis Window Subcritical Flow Output Review As an init ial view of t he st eady flow analysis out put , from t he m ain program window Vie w and t hen W a t e r Sur fa ce Pr ofile s were select ed. This act ivat ed t he wat er surface profile as shown in Figure 1.5. From t he Opt ion s m enu, t he Va r ia ble s of wat er surface, energy, and crit ical dept h, were chosen t o be plot t ed. Figure 1-5: Profile Plot for Critical Creek From t his profile, it can be seen t hat t he wat er surface appears t o approach or is equal t o t he crit ical dept h at several locat ions. For exam ple, from sect ion 12 t hrough 8, t he wat er surface appears t o coincide wit h t he crit ical dept h. This im plies t hat t he program m ay have had som e difficult y in 1-5 Exam ple 2 Beaver Creek- Single Bridge det erm ining a subcrit ical flow value in t his region, or perhaps t he act ual value of t he flow dept h is in t he supercrit ical flow regim e. To invest igat e t his furt her, a closer review of t he out put needs t o be perform ed. This can be accom plished by reviewing t he out put at each of t he cross sect ions in eit her graphical or t abular form , and by viewing t he sum m ary of Er r or s, W a r n in gs a n d N ot e s. First , a review of t he out put at each cross sect ion will be perform ed. From t he m ain program window, select Vie w , D e t a ile d Out put Ta ble s, Type , and t hen Cr oss Se ct ion . Select ion of cross sect ion 12 should result in t he display as shown in Figure 1.6. At t he bot t om of t he t able is a box t hat displays any errors, warnings, or not es t hat are specific t o t hat cross sect ion. For t his exam ple, t here are several warning m essages at cross sect ion 12. The first warning is t hat t he velocit y head has changed by m ore t han 0.5 feet and t hat t his m ay indicat e t he need for addit ional cross sect ions. To explain t his m essage, it is im port ant t o rem em ber t hat for a subcrit ical flow analysis, t he program st art s at t he downst ream end of t he reach and works upst ream . Aft er t he program com put ed t he wat er surface elevat ion for t he 11t h cross sect ion, it m oved t o t he 12t h cross sect ion. When t he pr ogram com put ed t he wat er surface elevat ion for t he 12t h cross sect ion, t he difference in t he velocit y head from t he 11t h t o t he 12t h cross sect ion was great er t han 0.5 feet . This im plies t hat t here was a significant change in t he average velocit y from sect ion 11 t o sect ion 12. This change in velocit y could be reflect ing t he fact t hat t he shape of t he cross sect ion is changing dram at ically and causing t he flow area t o be cont ract ing or expanding, or t hat a significant change in slope occurred. I n order t o m odel t his change m ore effect ively, addit ional cross sect ions should be supplied in t he region of t he cont ract ion or expansion. This will allow t he program t o bet t er calculat e t he energy losses in t his region and com put e a m ore accurat e wat er surface profile. 1-6 Exam ple 1 Crit ical Creek Figure 1-6: Cross Section Table For River Station 12 The second warning at cross sect ion 12 st at es t hat t he energy loss was great er t han 1.0 feet bet ween t he current cross sect ion ( # 12) and t he previous cross sect ion ( # 11) . This warning also indicat es t he possible need for addit ional cross sect ions. This is due t o t he fact t hat t he rat e of energy loss is usually not linear. However, t he program uses, as a default , an average conveyance equat ion t o det erm ine t he energy losses. Therefore, if t he cross sect ions are t oo far apart , an appropriat e energy loss will not be det erm ined bet ween t he t wo cross sect ions. ( The user m ay select alt ernat e m et hods t o com put e t he average frict ion slope. Furt her discussion of user specified frict ion loss form ulat ion is discussed in Chapt er 4 of t he H ydr a u lic Re fe r e n ce M a n ua l.) A review of ot her cross sect ions reveals t he sam e and addit ional warnings. To review t he errors, not es, and warnings for all of t he cross sect ions, select Sum m a r y Er r or s, W a r n in gs, a nd N ot e s from t he Vie w m enu on t he m ain program window. A port ion of t he sum m ary t able is shown in Figure 1.7. 1-7 Exam ple 2 Beaver Creek- Single Bridge Figure 1-7: Summary of Warnings and Notes for Critical Creek The addit ional warnings and not es t hat are list ed in t he sum m ary t able are described as follows. 1-8 • Warning - The energy equat ion could not be balanced wit hin t he specified num ber of it erat ions. The program used crit ical dept h for t he wat er surface and cont inued on wit h t he calculat ions. This warning im plies t hat during t he com put at ion of t he upst ream wat er surface elevat ion, t he program could not com put e enough energy losses t o provide for a subcrit ical flow dept h at t he upst ream cross sect ion. Therefore, t he program default ed t o crit ical dept h and cont inued on wit h t he analysis. • Warning - Divided flow com put ed for t his cross- sect ion. Aft er t he flow dept h was calculat ed for t he cross sect ion, t he program det erm ined t hat t he flow was occurring in m ore t han one port ion of t he cross sect ion. For exam ple, t his warning occurred at river st at ion # 10 and t he plot of t his cross sect ion is shown in Figure 1.8. From t he figure, it can be seen t hat at approxim at ely an X- coordinat e of 800, t here exist s a large vert ical land m ass. During t his out put analysis, it m ust be det erm ined whet her or not t he wat er can act ually be flowing on bot h sides of t he land m ass at t his flow rat e. Since t he m ain channel is on t he right side of t he cent ral land m ass, could t he wat er be flowing on t he left side or should all of t he flow be cont ained t o t he right side of t he land m ass? By default , t he program will consider t hat t he wat er can flow on bot h sides of t he land m ass. I f t his is not correct , t hen t he m odeler needs t o t ake addit ional act ion. Exam ple 1 Crit ical Creek Figure 1-8: Cross Section 10, Showing Divided Flow Addit ional act ion can be one of t wo procedures. First , if t he exist ing scenario is not feasible, t hen t he wat er on t he left side m ay be considered as an ineffect ive flow area, where t he wat er is account ed for volum et rically but it is not considered in t he conveyance det erm inat ion unt il a m axim um elevat ion is reached. Secondly, if all of t he flow should be occurring only on t he right side of t he land m ass, t hen t he land m ass could be considered as a levee. By defining t he cent ral vert ical land m ass as a levee, t he program will not perm it a flow ont o t he left side of t he levee unt il t he flow dept h overt ops t he levee. For furt her discussion on ineffect ive flow areas and levees, refer t o Chapt er 6 of t he Use r ’s M a n ua l and Chapt er 3 of t he H ydr a u lic Re fe r e n ce M a n ua l. • Warning - During t he st andard st ep it erat ions, when t he assum ed wat er surface was set equal t o crit ical dept h, t he calculat ed wat er surface cam e back below crit ical dept h. This indicat es t hat t here is not a valid subcrit ical answer. The program default ed t o crit ical dept h. This warning is issued when a subcrit ical flow analysis is being perform ed but t he program could not det erm ine a subcrit ical flow dept h at t he specified cross sect ion. As t he program is at t em pt ing t o det erm ine t he upst ream dept h, it is using an it erat ive t echnique t o solve t he energy equat ion. During t he it erat ions, t he program t ried crit ical dept h as a possible solut ion, which result ed in a flow dept h less t han crit ical. Since t his is not possible in a subcrit ical analysis, t he program default ed t o using crit ical dept h at t his cross sect ion and cont inued on wit h t he analysis. This error is oft en associat ed wit h t oo long of a reach lengt h bet ween cross sect ions or m isrepresent at ion of t he effect ive flow area of t he cross sect ion. • Warning - The parabolic search m et hod failed t o converge on crit ical dept h. The program will t ry t he cross sect ion slice/ secant m et hod t o find 1-9 Exam ple 2 Beaver Creek- Single Bridge crit ical dept h. This m essage appears if t he program was required t o calculat e t he crit ical dept h and had difficult y in det erm ining t he crit ical dept h at t he cross sect ion. The program has t wo m et hods for det erm ining crit ical dept h: a parabolic m et hod and a secant m et hod. The parabolic m et hod is t he default m et hod ( t his can be changed by t he user) because t his m et hod is fast er and m ost cross sect ions have only one m inim um energy point . However, for cross sect ions wit h large, flat over banks, t here can exist m ore t han one m inim um energy point . For furt her discussion, refer t o t he sect ion Crit ical Dept h Det erm inat ion in Chapt er 2 of t he Hydraulic Reference Manual. • Not e - Mult iple crit ical dept hs were found at t his locat ion. The crit ical dept h wit h t he lowest , valid, wat er surface was used. This not e appears when t he program was required t o det erm ine t he crit ical dept h and accom panies t he use of t he secant m et hod in t he det erm inat ion of t he crit ical dept h ( as described in t he previous warning m essage) . This not e prom pt s t he user t o exam ine closer t he crit ical dept h t hat was det erm ined t o ensure t hat t he program supplied a valid answer. For furt her discussion, refer t o t he sect ion Crit ical Dept h Det erm inat ion in Chapt er 2 of t he Hydraulic Reference Manual. • Warning - The conveyance rat io ( upst ream conveyance divided by downst ream conveyance) is less t han 0.7 or great er t han 1.4. This m ay indicat e t he need for addit ional cross sect ions. The conveyance of t he cross sect ion, K, is defined by: K= 1.486 AR 2 / 3 n ( 1- 1) I f t he n values for t wo subsequent cross sect ions are approxim at ely t he sam e, it can be seen t hat t he rat io of t he t wo conveyances is prim arily a funct ion of t he cross sect ional area. I f t his rat io differs by m ore t han 30% , t hen t his warning will be issued. This warning im plies t hat t he cross sect ional areas are changing dram at ically bet ween t he t wo sect ions and addit ional cross sect ions should be supplied for t he program t o be able t o m ore accurat ely com put e t he wat er surface elevat ion. I n sum m ary, t hese warnings and not es are int ended t o inform t he user t hat pot ent ial problem s m ay exist at t he specified cross sect ions. I t is im port ant t o not e t hat t he user does not have t o elim inat e all t he warning m essages. However, it is up t o t he user t o det erm ine whet her or not t hese warnings require addit ional act ion for t he analysis. Mixed Flow Analysis Upon reviewing t he profile plot and t he sum m ary of errors, warnings, and not es from t he subcrit ical flow analysis, it was det erm ined t hat addit ional cross- sect ion inform at ion was required. Addit ionally, since t he program default ed t o crit ical dept h at various locat ions along t he river reach and could not provide a subcrit ical answer at several locat ions, a subsequent analysis in t he m ixed flow regim e was perform ed. A m ixed flow analysis will provide result s in bot h t he subcrit ical and supercrit ical flow regim es. 1-10 Exam ple 1 Crit ical Creek Modification of Existing Geometry Before perform ing t he m ixed flow regim e analysis, t he exist ing geom et ry was m odified by adding addit ional cross sect ions. To obt ain t he addit ional cross sect ion inform at ion, t he m odeler should use surveyed cross sect ion dat a whenever possible. I f t his dat a are not available, t hen t he cross sect ion int erpolat ion m et hod wit hin t he HEC- RAS program can be used. However, t his m et hod is not int ended t o be a replacem ent for act ual field dat a. The m odeler should review all int erpolat ed cross sect ions because t hey are based on a linear t ransit ion bet ween t he input sect ions. Whenever possible, use t opographic m aps for assist ance in evaluat ing whet her or not t he int erpolat ed cross sect ions are adequat e. The m odeler is referred t o t he discussions in Chapt er 6 of t he Use r ’s M a nua l and Chapt er 4 of t he H ydr a u lic Re fe r e n ce M a n u a l for addit ional inform at ion on cross sect ion int erpolat ion. To obt ain addit ional cross sect ions for t his exam ple, t he int erpolat ion rout ines were used. From t he Ge om e t r ic D a t a Edit or , Tools and t hen XS I n t e r pola t ion was select ed. The init ial t ype of int erpolat ion was W it h in a Re a ch . The int erpolat ion was st art ed at cross sect ion 12 and ended at cross sect ion 1. The m axim um dist ance was set t o be 150 feet ( This value can be changed lat er by t he m odeler t o develop any num ber of cross sect ions desired.) . Finally, I n t e r pola t e XS’s was select ed. When t he com put at ions were com plet ed, t he window was closed. At t his point , t he m odeler can view each cross- sect ion individually or t he int erpolat ed sect ions can be viewed bet ween t he original sect ions. The lat t er opt ion is accom plished by select ing Tools, XS I n t e r pola t ion, and t hen Be t w e e n 2 Xs’s. The up and down arrows are used t o t oggle up and down t he river reach, while viewing t he int erpolat ed cross sect ions. When t he upper river st at ion is select ed t o be 11 ( t he lower st at ion will aut om at ically be 10) , t he int erpolat ion shown in Figure 1.9 should appear. 1-11 Exam ple 2 Beaver Creek- Single Bridge Figure 1-9: Cross Section Interpolation Based on Default Master Cords As shown in Figure 1.9, t he int erpolat ion was adequat e for t he right overbank and t he m ain channel. However, t he int erpolat ion in t he left overbank failed t o connect t he t wo exist ing high ground areas. These t wo high ground areas could be represent ing a levee or som e nat ural exist ing feat ure. Therefore, Del I nt erp was select ed t o delet e t he int erpolat ion. ( This only delet ed t he int erpolat ion bet ween cross sect ions 11 and 10.) Then, t he t wo high point s and t he low point s of t he high ground areas were connect ed wit h user supplied m ast er cords. This was accom plished by select ing t he Mast er Cord but t on and connect ing t he point s where t he m ast er cords should be locat ed. Finally, a m axim um dist ance of 150 feet was ent ered bet ween cross sect ions and I nt erpolat e was select ed. The final int erpolat ion appeared as is shown in Figure 1.10. The m odeler should now go t hrough all of t he int erpolat ed cross sect ions and det erm ine t hat t he int erpolat ion procedure adequat ely produced cross sect ions t hat depict t he act ual geom et ry. When com plet ed, t he geom et ric dat a was saved as t he new file nam e " Base Geom et ry + I nt erpolat ed." This allowed t he original dat a t o be unalt ered and available for fut ure reference. 1-12 Exam ple 1 Crit ical Creek Figure 1-10: Final Interpolated With Additional Master Cords Flow Data At t his point , wit h t he addit ional cross sect ions, t he m odeler can perform a flow analysis wit h subcrit ical flow as was perform ed previously and com pare t he result s wit h t he previously obt ained dat a. However, for t he purposes of t his exam ple, an upst ream boundary condit ion was added and t hen a m ixed flow regim e analysis was perform ed. Since a m ixed flow analysis ( subcrit ical and supercrit ical flow possibilit ies) was select ed, an upst ream boundary condit ion was required. From t he m ain program window, Edit and t hen St e a dy Flow D a t a were select ed. Then t he Bou nda r y Con dit ion s but t on was chosen and a norm al dept h boundary condit ion was ent ered at t he upst ream end of t he reach. A slope of 0.01 ft / ft as t he approxim at e slope of t he channel at sect ion 12 was used. Finally, t he flow dat a was saved as a new file nam e. This will allow t he m odeler t o recall t he original dat a when necessary. For t his exam ple, t he new flow dat a file was called " 100 YR Profile - Up and Down Bndry." t hat includes t he changes previously m ent ioned. Mixed Flow Analysis To perform t he m ixed flow analysis, from t he m ain program window Run and St e a dy Flow An a lysis were select ed. The flow regim e was select ed t o be " Mixed," t he geom et ry file was chosen as " Base Geom et ry + I nt erpolat ed," and t he st eady flow file as " 100 YR Profile - Up and Down Bndry." The Short 1-13 Exam ple 2 Beaver Creek- Single Bridge I D was ent ered as " Modified Geo," and t hen File and Save Plan As were select ed and a new nam e for t his plan was ent ered as " Modified Geom et ry Condit ions" . This plan will t hen associat e t he geom et ry, flow dat a, and out put file for t he changes t hat were m ade. Finally, COMPUTE was select ed t o perform t he st eady flow analysis. Review of Mixed Flow Output As before, t he m odeler needs t o review all of t he out put , which includes t he profile as well as t he channel cross sect ions bot h graphically and in t abular form . Also, t he list of errors, warning, and not es should be reviewed. The m odeler t hen needs t o det erm ine whet her addit ional act ion needs t o be t aken t o perform a subsequent analysis. For exam ple, addit ional cross sect ions m ay st ill need t o be provided bet ween sect ions in t he reach. The m odeler m ay also consider t o use addit ional flow profiles during t he next analysis. The m odeler should review all of t he out put dat a and m ake changes where t hey are deem ed appropriat e. For t his analysis, t he result ing profile plot is shown in Figure 1.11. From t his figure, it can be seen t hat t he flow dept hs occur in bot h t he subcrit ical and supercrit ical flow regim es. ( The user can use t he zoom feat ure under t he Opt ion s m enu in t he program . This can im ply t hat t he geom et ry of t he river reach and t he select ed flows are producing subcrit ical and supercrit ical flow result s for t he reach. Figure 1-11: Profile Plot for Critical Creek – Mixed Flow Analysis To invest igat e t his furt her, t he result s will be viewed in t abular form . From t he m ain program window, Vie w , Pr ofile Sum m a r y Ta ble s, St d. Ta ble s, and t hen St a n da r d Ta ble 1 were select ed. This t able for t he m ixed flow 1-14 Exam ple 1 Crit ical Creek analysis is shown as Figure 1.12. The t able colum ns show t he default set t ings of river, reach, river st at ion, t ot al flow, m inim um channel elevat ion, wat er surface elevat ion, et c. The m eanings of t he headings are described in a box at t he bot t om of t he t able. By select ing a cell in any colum n, t he definit ion of t he heading will appear in t he box for t hat colum n. From t he St a n da r d Ta ble 1 , t he wat er surface elevat ions and crit ical wat er surface elevat ions can be com pared. The values at river st at ion 11.2* show t hat t he flow is supercrit ical at t his cross sect ion since t he wat er surface is at an elevat ion of 1811.29 ft and t he crit ical wat er surface elevat ion is 1811.46 ft . Addit ionally, it can be seen t hat t he flow at river st at ion 11.0 is subcrit ical. ( Not e: t he ast erisks ( * ) denot e t hat t he cross sect ions were int erpolat ed.) By select ing t he Cr oss Se ct ion t ype t able ( as perform ed for Figure 1.6) , and t oggling t o river st at ion 11.0, a not e appears at t he bot t om of t he t able indicat ing t hat a hydraulic j um p occurred bet ween t his cross sect ion and t he previous upst ream cross sect ion. These result s are showing t hat t he flow is bot h subcrit ical and supercrit ical in t his reach. The user can cont inue t his process of reviewing t he warnings, not es, profile plot , profile t ables, and cross sect ion t ables t o det erm ine if addit ional cross sect ions are required. Figure 1-12: Standard Table 1 for Mixed Flow Analysis – Critical Creek Summary I nit ially, t he river reach was analyzed using t he exist ing geom et ric dat a and a subcrit ical flow regim e. Upon analysis of t he result s, it was det erm ined t hat addit ional cross- sect ion dat a were needed and t hat t here m ight be supercrit ical flow wit hin t he reach. Addit ional cross sect ions were t hen added by int erpolat ion and t he reach was subsequent ly analyzed using t he m ixed flow regim e m et hod. Review of t he m ixed flow analysis out put showed t he exist ence of bot h subcrit ical and supercrit ical flow wit hin t he reach. This 1-15 Exam ple 2 Beaver Creek- Single Bridge exhibit s t hat t he river reach is set on a slope t hat will produce a wat er surface around t he crit ical dept h for t he given flow and cross sect ion dat a. Therefore, a com plet ely subcrit ical or supercrit ical profile is not possible. 1-16 Exam ple 2 Beaver Creek- Single Bridge CH APT ER 2 Beaver Creek - Single Bridge Purpose This exam ple dem onst rat es t he use of HEC- RAS t o analyze a river reach t hat cont ains a single bridge crossing. For t his exam ple, t he bridge is com posed of t ypical geom et ry and was locat ed perpendicular t o t he direct ion of flow in t he m ain channel. The st ream for t his exam ple is a sect ion of Beaver Creek locat ed near Kent wood, Louisiana. The bridge crossing is locat ed along St at e Highway 1049, near t he m iddle of t he river reach. The field dat a for t his exam ple were obt ained from t he Unit ed St at es Geological Survey ( USGS) Hydrologic At las No. HA- 601. This at las is one part of a series developed t o provide dat a t o support hydraulic m odeling of flow at highway crossings in com plex hydrologic and geographic set t ings. The bridge, cross sect ion geom et ry, and high wat er flow dat a were used t o evaluat e t he flood flow of 14000 cfs t hat occurred on May 22, 1974, along wit h analysis of t wo addit ional flow values of 10000 cfs and 5000 cfs. I t should be not ed t hat m odelers t ypically do not have access t o high wat er m arks and act ual field flow m easurem ent s at bridges during t he peak event s. However, for t his exam ple, t he flood st age wat er dept h values were com pared t o t he out put from t he m odel. For t his analysis, t he wat er surface profiles were det erm ined by first using t he pressure/ weir flow m et hod and t hen t he energy m et hod. Next , an evaluat ion of t he bridge cont ract ion and expansion reach lengt hs was perform ed and result ed in t he necessit y t o reposit ion t he locat ion of cert ain cross sect ions. Aft er t hese adj ust m ent s were m ade, t he m odel was t hen calibrat ed wit h t he observed wat er surface elevat ion dat a. Finally, a com parison of t he pressure/ weir flow m et hod t o t he energy m et hod was m ade. Pressure/Weir Flow Analysis From t he m ain program window, select File and t hen Open Proj ect . Select t he proj ect labeled " Single Bridge - Exam ple 2.” This will open t he proj ect and act ivat e t he following files: Plan : " Pressure/ Weir Met hod” Geom et ry : " Beaver Cr. + Bridge - P/ W” Flow : " Beaver Cr. - 3 Flows” 2-1 Exam ple 2 Beaver Creek- Single Bridge To perform t he pressure/ weir flow analysis, t he following dat a were ent ered: • River Syst em Schem at ic • Cross Sect ion Geom et ric Dat a • Bridge Geom et ry Dat a • I neffect ive Flow Areas • Bridge Modeling Approach • St eady Flow Dat a Aft er t he input of t his dat a, t he pressure/ weir flow m et hod was used t o det erm ine t he result ing wat er surface elevat ions for t he select ed flow values. River System Schematic From t he m ain program window, select Edit and t hen Ge om e t r ic D a t a . This will act ivat e t he Ge om e t r ic D a t a Edit or and t he screen will display t he river syst em schem at ic for t he Beaver Creek reach, as shown in Figure 2.1. The river nam e was ent ered as " Beaver Creek” and t he reach nam e was " Kent wood.” Figure 2-1: River System Schematic for Beaver Creek 2-2 Exam ple 2 Beaver Creek- Single Bridge The reach was init ially defined wit h 14 cross sect ions beginning at river m ile 5.00 as t he downst ream river st at ion and river m ile 5.99 as t he upst ream river st at ion. The cross sect ions wit h an ast erisk ( * ) were added by int erpolat ion for t he purposes of t his exam ple. When t he bridge was added, it was placed at river m ile 5.40 t o place it at t he appropriat e locat ion. On t he river schem at ic, som e of t he cross sect ion labels m ay not appear due t o overlapping of t he labels. I f t his occurs, t he labels can be seen by zoom ing in on t he locat ion of t he closely spaced cross sect ions. Cross Section Geometric Data The cross sect ion geom et ric dat a consist s of t he: X- Y coordinat es, reach lengt hs, Manning’s n values, locat ion of levees, and cont ract ion and expansion coefficient s. Each of t hese river st at ion geom et ric dat a com ponent s are described in t he following sect ions. X- Y Coor din a t e s. To view t he cross sect ion geom et ry dat a, from t he Ge om e t r ic D a t a Edit or select t he Cr oss Se ct ion icon. This will act ivat e t he Cr oss Se ct ion D a t a Edit or as shown in Figure 2.2 for river m ile 5.99. As shown in Figure 2.2, t he X- Y coordinat es were ent ered in t he t able on t he left side of t he edit or. The addit ional com ponent s of t he cross sect ion geom et ry are described in t he following sect ions. Figure 2-2: Cross Section Data Editor For River Station 5.99 2-3 Exam ple 2 Beaver Creek- Single Bridge Re a ch Le ngt h s. The dist ances bet ween t he cross sect ions are ent ered as t he downst ream reach lengt hs in t he Cr oss Se ct ion D a t a Edit or. To view t he sum m ary of t he reach lengt hs, t he t able as shown in Figure 2.3 can be act ivat ed by select ing Ta ble s and t hen Re a ch Le n gt h s from t he Ge om e t r ic D a t a Edit or . The reach lengt hs were obt ained by m easuring t he dist ances on t he USGS at las. To det erm ine t he m ain channel dist ances, it was init ially assum ed t hat during t he peak event , t he m aj or act ive port ion of t he flow will follow t he course of t he m ain channel. I f, aft er t he analysis, it is det erm ined t hat t he m aj or port ion of t he act ive flow is not following t he m ain channel course, t hen t he m ain channel flow dist ances will need t o be adj ust ed. I n ot her words, if t he m aj or port ion of t he act ive flow is " cut t ing across” t he m eanders of t he m ain channel, t hen t hese reach lengt hs will need t o be reevaluat ed. Figure 2-3: Reach Lengths Summary Table The reach lengt hs det erm ine t he placem ent of t he cross sect ions. The placem ent of t he cross sect ions relat ive t o t he locat ion of t he bridge is crucial for accurat e predict ion of expansion and cont ract ion losses. The bridge rout ine ut ilizes four cross sect ions t o det erm ine t he energy losses t hrough t he bridge. ( Addit ionally t he program will int erpret t wo cross sect ions inside of t he bridge by superim posing t he bridge dat a ont o bot h t he im m ediat e downst ream and upst ream cross sect ions from t he bridge.) The following is a brief sum m ary for t he init ial est im at ion of t he placem ent of t he four cross sect ions. The m odeler should review t he discussion in Chapt er 6 of t he Use r ’s M a n u a l and Chapt er 5 of t he H ydr a ulic Re fe r e nce M a nu a l for furt her det ail. 2-4 Exam ple 2 Beaver Creek- Single Bridge First Cross Sect ion. I deally, t he first cross sect ion should be locat ed sufficient ly downst ream from t he bridge so t hat t he flow is not affect ed by t he st ruct ure ( ie, t he flow has fully expanded) . This dist ance should generally be det erm ined by field invest igat ion during high flows and will vary depending on t he degree of const rict ion, t he shape of t he const rict ion, t he m agnit ude of t he flow, and t he velocit y of t he flow. I n order t o provide bet t er guidance t o det erm ine t he locat ion of t he fully expanded cross sect ion, a st udy was perform ed by t he Hydrologic Engineering Cent er [ HEC- 1995] . This st udy focused on det erm ining t he expansion reach lengt h, t he cont ract ion reach lengt h, and t he expansion and cont ract ion energy loss coefficient s. For t his exam ple, cross sect ion num ber 5.29 was init ially considered as t he cross sect ion of fully expanded flow. This cross sect ion was det erm ined by field invest igat ions as t he approxim at e locat ion of fully expanded flow during t he high flow event . Aft er t he pressure/ weir flow analysis was perform ed, t he locat ion of t his cross sect ion was evaluat ed using t he procedures as out lined in t he recent HEC st udy [ HEC- 1995] . The procedures required flow param et ers at t he init ially chosen locat ion t o evaluat e t he locat ion of t he cross sect ion. These procedures will be described aft er t he pressure/ weir flow analysis is perform ed near t he end of t his exam ple. Second Cross Sect ion. The second cross sect ion used by t he program t o det erm ine t he energy losses t hrough t he bridge is locat ed a short dist ance downst ream of t he st ruct ure. This sect ion should be very close t o t he bridge, and reflect t he effect ive flow area on t he downst ream side of t he bridge. For t his exam ple, a roadway em bankm ent sloped gradually from t he roadway decking on bot h sides of t he roadway. Cross sect ion 5.39 was locat ed at t he t oe of t he roadway em bankm ent and was used t o represent t he effect ive flow area on t he downst ream side of t he bridge opening. The program will superim pose t he bridge geom et ry ont o t his cross sect ion t o develop a cross sect ion inside t he bridge at t he downst ream end. Third Cross Sect ion. The t hird cross sect ion is locat ed a short dist ance upst ream from t he bridge and should reflect t he lengt h required for t he abrupt accelerat ion and cont ract ion of t he flow t hat occurs in t he im m ediat e area of t he opening. As for t he previous cross sect ion, t his cross sect ion should also exhibit t he effect ive flow areas on t he upst ream side of t he bridge. For t his exam ple, cross sect ion 5.41 was locat ed at t he t oe of t he roadway em bankm ent on t he upst ream side of t he bridge. Sim ilar t o t he previous cross sect ion, t he program will superim pose t he bridge geom et ry ont o t his cross sect ion t o develop a cross sect ion inside t he bridge at t he upst ream end. Fourt h Cross Sect ion. The fourt h cross sect ion is locat ed upst ream from t he bridge where t he flow lines are parallel and t he cross sect ion exhibit s fully effect ive flow. For t his exam ple, cross sect ion 5.44 was init ially used as t his sect ion where t he flow lines were parallel. Aft er t he pressure/ weir flow analysis, t he locat ion of t his cross sect ion was evaluat ed using t he procedures as out lined in t he HEC st udy [ HEC- 1995] . This evaluat ion will be present ed in t he discussion near t he end of t his exam ple. M a n n in g’s n Va lu e s. The Manning’s n values were obt ained from t he field dat a displayed on t he USGS at las. For som e of t he cross sect ions, t he Manning’s n values changed along t he widt h of t he overbank areas and t he 2-5 Exam ple 2 Beaver Creek- Single Bridge horizont al variat ion in n values opt ion was select ed, such as for cross sect ion 5.99. This opt ion was perform ed from t he Cr oss Se ct ion D a t a Edit or by select ing Opt ions and H or izon t a l Va r ia t ion in n Va lue s. This caused a new colum n t o appear under t he Cross Sect ion X- Y Coordinat es heading ( as shown in Figure 2.2) . For cross sect ion 5.99, t he n values changed at t he Xcoordinat es of 518 ( in t he left overbank) , 866 ( t he m ain channel left bank st at ion) , and 948 ( t he m ain channel right bank st at ion) . This can be seen by scrolling down in t he coordinat es window of t he cross sect ion edit or. The overbank areas have densely wooded areas, which creat ed t he necessit y for t he variat ion in n values. The final dat a are shown in t he cross sect ion plot in Figure 2.4. Figure 2-4: Cross Section 5.99: Horizontal n Variation and Levee Options Le ve e s. As can be seen in t he plot of cross sect ion 5.99 in Figure 2.4, t here exist s a large area t o t he left of t he m ain channel t hat is lower in elevat ion t han t he invert of t he m ain channel. During t he analysis, t he program will consider t he wat er t o be able t o go anywhere in t he cross sect ion. The m odeler m ust det erm ine whet her or not t he lower area t o t he left of t he m ain channel can init ially convey flow. I f t he area cannot convey flow unt il t he m ain channel fills up and t hen overt ops, t hen t he levee opt ion should be used. For t his exam ple, a left levee was est ablished at t he left m ain channel bank st at ion for river st at ion 5.99. This prevent s wat er from being placed t o t he left of t he levee unt il t he elevat ion of t he levee is reached. The elevat ion select ed for t his levee was t he elevat ion of t he left side of t he m ain channel. To insert t he levee, Opt ion s and t hen Le ve e s were select ed from t he Cr oss Se ct ion D a t a Edit or. This result ed in t he display shown in Figure 2.5. The 2-6 Exam ple 2 Beaver Creek- Single Bridge values for t his exam ple were st at ion 866 and elevat ion 214.8 for a left levee. As can be seen in Figure 2.4, t he levee is displayed as a sm all square locat ed at t he LOB st at ion. Addit ionally, a not e appears ident ifying t he select ion of a levee for t he specific cross sect ion at t he bot t om of t he Cr oss Se ct ion D a t a Edit or . This not e can be seen in t he box at t he bot t om of Figure 2.2. Levee opt ions were select ed for ot her cross sect ions in addit ion t o cross sect ion 5.99. I n each case, t he m odeler needs t o view each cross- sect ion and det erm ine whet her t he levee opt ion needs t o be ut ilized. Figure 2-5: Levee Option for Cross Section 5.99 Con t r a ct ion / Ex pa nsion Coe fficie n t s. The cont ract ion and expansion coefficient s are used by t he program t o det erm ine t he t ransit ion energy losses bet ween t wo adj acent cross sect ions. From t he dat a provided by t he recent HEC st udy [ HEC- 1995] , gradual t ransit ion cont ract ion and expansion coefficient s are 0.1 and 0.3, and t ypical bridge cont ract ion and expansion coefficient s are 0.3 and 0.5, respect ively. For sit uat ions near bridges where abrupt changes are occurring, t he coefficient s m ay t ake larger values of 0.5 and 0.8 for cont ract ions and expansions, respect ively. A list ing of t he select ed values for t his river reach can be viewed by select ing Ta ble s and t hen Coe fficie n t s from t he Ge om e t r ic D a t a Edit or. This t able is shown in Figure 2.6 and displays t he values select ed for t he river cross sect ions. Typical gradual t ransit ion values were select ed for st at ions away from t he bridge. However, near t he bridge sect ion, t he coefficient s were increased t o 0.3 and 0.5 t o represent great er energy losses. For addit ional discussion concerning cont ract ion and expansion coefficient s at bridges, refer t o Chapt er 5 of t he H ydr a u lic Re fe r e n ce M a n u a l. 2-7 Exam ple 2 Beaver Creek- Single Bridge Figure 2-6: Coefficients For Beaver Creek This com plet ed t he input for t he cross sect ion geom et ric dat a. Next , t he bridge geom et ry dat a was ent ered as out lined in t he proceeding sect ion. Bridge Geometry Data To ent er t he bridge geom et ry dat a, t he Br idge / Culve r t icon was select ed from t he Ge om e t r ic D a t a Edit or . This act ivat ed t he Br idge / Cu lve r t D a t a Edit or . The river and reach were select ed as " Beaver Creek” and " Kent wood” ( t he only reach for t his exam ple) . Then, Opt ion s, and Add a Br idge or Cu lve r t were select ed and river st at ion 5.4 was ent ered as t he locat ion for t he bridge. Th e Br idge / Cu lve r t D a t a Edit or t hen displayed t he upst ream ( river st at ion 5.41) and downst ream ( river st at ion 5.39) cross sect ions. A descript ion was t hen ent ered as " Bridge # 1.” The following sect ion provides a brief sum m ary of t he input for t he bridge geom et ry including t he bridge deck/ roadway and t hen t he bridge piers. Br idge D e ck a nd Roa dw a y Ge om e t r y. From t he Br idge / Cu lve r t D a t a Edit or , t he D e ck / Roa dw a y icon was select ed and t his act ivat ed t he D e ck / Roa dw a y D a t a Edit or , as shown in Figure 2.7. 2-8 Exam ple 2 Beaver Creek- Single Bridge Figure 2-7: Bridge/Deck and Roadway Data Editor The first input at t he t op of t he edit or is t he dist ance from t he upst ream side of t he bridge deck t o t he cross sect ion im m ediat ely upst ream from t he bridge ( cross sect ion 5.41) . This dist ance was det erm ined t o be 30 feet from t he USGS at las. I n t he next field, t he bridge deck widt h of 40 feet was ent ered. Finally, a weir flow coefficient of 2.6 was select ed for t he analysis. ( Addit ional discussion of t he weir flow coefficient will be present ed in t he calibrat ion sect ion.) The cent ral sect ion of t he D e ck / Roa dw a y Edit or is com prised of colum ns for input of t he st at ion, high cord elevat ion, and low cord elevat ion for bot h t he upst ream and downst ream sides of t he bridge deck. The dat a are ent ered from left t o right in cross sect ion st at ioning and t he area bet ween t he high and low cord is t he bridge st ruct ure. The st at ioning of t he upst ream side of t he deck was based on t he st at ioning of t he cross sect ion locat ed im m ediat ely upst ream . Likewise, t he st at ioning of t he downst ream side of t he deck was based on t he st at ioning of t he cross sect ion placed im m ediat ely downst ream . I f bot h t he upst ream and downst ream dat a are ident ical, t he user needs only t o input t he upst ream dat a and t hen select Copy Up t o D ow n t o ent er t he downst ream dat a. As a final not e, t he low cord elevat ions t hat are concurrent wit h t he ground elevat ion were ent ered as a value lower t han t he ground elevat ion. The program will aut om at ically clip off and rem ove t he deck/ roadway area below t he ground. For exam ple, at st at ion 0, a low cord elevat ion of 200 feet was ent ered. However, t he act ual ground elevat ion at t his point is approxim at ely 216 feet . Therefore, t he program will aut om at ically rem ove t he area of t he 2-9 Exam ple 2 Beaver Creek- Single Bridge roadway below t he ground. Addit ionally, t he last st at ion was ent ered as a value of 2000 feet . This st at ioning ensured t hat t he roadway and decking ext ended int o t he lim it s of t he cross sect ion geom et ry. As described previously, t he program will clip off t he area beyond t he lim it s of t he cross sect ion geom et ry. The US and D S Em ba nk m e nt SS ( upst ream and downst ream em bankm ent side slope) values were ent ered as 2 ( horizont al t o 1 vert ical) . These values are used for graphical represent at ion on t he profile plot and for t he WSPRO low flow m et hod. The user is referred t o Exam ple 13 - Bogue Chit t o Single Bridge ( WSPRO) for a discussion on t he use of t his param et er wit h t he WSPRO m et hod. The WSPRO m et hod is not em ployed for t his exam ple. At t he bot t om of t he D e ck / Roa dw a y D a t a Edit or , t here are t hree addit ional fields for dat a ent ry. The first is t he M a x Allow a ble Subm e r ge n ce . This input is a rat io of downst ream wat er dept h t o upst ream energy, as m easured above t he m inim um weir elevat ion. When t he rat io is exceeded, t he program will no longer consider t he bridge deck t o act as a weir and will swit ch t he com put at ion m ode t o t he energy ( st andard st ep) m et hod. For t his exam ple, t he default value of 0.95 ( 95 % ) was select ed, however t his value m ay be changed by t he user. The second field at t he bot t om of t he edit or is t he M in W e ir Flow Ele va t ion. This is t he elevat ion t hat det erm ines when weir flow will st art t o occur over t he bridge. I f t his field is left blank ( as for t his exam ple) , t he program will default t o use t he lowest high cord value on t he upst ream side of t he bridge. Finally, t he last field at t he bot t om of t he edit or is t he select ion of t he W e ir Cr e st Sha pe . This select ion will det erm ine t he reduct ion of t he weir flow coefficient due t o subm ergence. For t his exam ple, a broad crest ed weir shape was select ed. Upon ent ering all of t he above dat a, t he OK but t on was select ed t o exit t he D e ck / Roa dw a y D a t a Edit or . Br idge Pie r Ge om e t r y. From t he Br idge / Cu lve r t D a t a Edit or, select t he Pie r icon. This will result in t he display shown in Figure 2.8. The m odeler should not include t he piers as part of t he ground or bridge deck/ roadway because pier- loss equat ions use t he separat e bridge pier dat a during t he com put at ions. 2-10 Exam ple 2 Beaver Creek- Single Bridge Figure 2-8: Bridge Pier Data Editor The program will est ablish t he first pier as pier num ber 1. As shown in Figure 2.8, t he upst ream and downst ream st at ions were ent ered for t he cent erline of t he first pier. The upst ream and downst ream st at ions were based on t he geom et ry of t he cross sect ions locat ed im m ediat ely upst ream ( cross sect ion 5.41) and im m ediat ely downst ream ( cross sect ion 5.39) of t he bridge. The user needs t o be caut ious placing t he pier cent erline st at ions because t he Xcoordinat es for t he upst ream and downst ream cross sect ion st at ioning m ay be different . This is t o ensure t hat t he piers " line up" t o form t he correct geom et ry. For t his exam ple, t he pier cent erline st at ions are 470, 490, 510, 530, 550, 570, 590, 610, and 630 for t he nine piers. Each pier was set t o st art at an elevat ion of 200 feet ( t his elevat ion is below t he ground level and t he excess will be rem oved by t he program ) and end at an elevat ion of 216 feet ( t his elevat ion is inside t he bridge decking and t he excess was rem oved by t he program ) . Addit ionally, each pier had a cont inuous widt h of 1.25 feet . Aft er ent ering t he dat a, t he OK but t on was select ed and t he schem at ic of t he bridge wit h t he piers was displayed on t he Br idge / Cu lve r t D a t a Edit or as shown on Figure 2.9. ( Not e: The figure in t he t ext displays t he ineffect ive flow areas t hat will be added in t he next sect ion.) The cross sect ions shown in Figure 2.9 are developed by superim posing t he bridge dat a on t he cross sect ions im m ediat ely upst ream ( 5.41) and im m ediat ely downst ream ( 5.39) of t he bridge. The t op cross sect ion in Figure 2.9 reflect s t he geom et ry im m ediat ely inside t he bridge on t he upst ream side and t he bot t om cross sect ion reflect s t he geom et ry im m ediat ely inside t he bridge on t he downst ream side. 2-11 Exam ple 2 Beaver Creek- Single Bridge Figure 2-9: Bridge/Culvert Data Editor While viewing t he bridge, t he m odeler can select t o view j ust t he upst ream , j ust t he downst ream , or bot h of t he cross sect ion views. This is perform ed by select ing Vie w and t hen t he required opt ion. Addit ionally, from t he Vie w m enu, t he user should select H igh ligh t W e ir , Ope n in g Lid and Gr ound as well as H ighlight Pie r s. These opt ions enable t he m odeler t o view what t he program will consider as t he weir lengt h, bridge opening, and pier locat ions. Any errors in t he dat a m ay appear as inconsist ent im ages wit h t hese opt ions. Also, t he zoom - in opt ion will allow t he user t o exam ine dat a det ails. As a final not e for t he bridge geom et ry, a bit m ap im age of t he bridge was added t o t he geom et ry file ( denot ed by a red square on t he river syst em schem at ic, Figure 2.1) . The user can view t his im age by select ing t he Vie w Pict u r e icon on t he Ge om e t r ic D a t a Edit or. Ineffective Flow Areas As a final st ep for t he bridge geom et ry, any ineffect ive flow areas t hat exist ed due t o t he bridge ( or any ot her obst ruct ion) were ent ered. I neffect ive flow is used t o define an area of t he cross sect ion in which t he wat er will accum ulat e 2-12 Exam ple 2 Beaver Creek- Single Bridge but is not being act ively conveyed. At a bridge, ineffect ive flow areas norm ally occur j ust upst ream and downst ream of t he road em bankm ent , away from t he bridge opening. For t his exam ple, ineffect ive flow areas were included on bot h t he upst ream cross sect ion ( 5.41) and t he downst ream cross sect ion ( 5.39) . To det erm ine an init ial est im at e for t he st at ioning of t he ineffect ive flow areas, a 1: 1 rat io of t he dist ance from t he bridge t o t he cross sect ion was used. For t his exam ple, sect ion 5.41 is locat ed 30 feet upst ream of t he bridge. Therefore, t he left and right ineffect ive flow areas were set t o st art at 30 feet t o t he left and right of t he bridge opening. Sim ilarly, cross sect ion 5.39 is locat ed 30 feet downst ream from t he bridge and t he ineffect ive flow areas at t his cross sect ion were set at 30 feet t o t he left and right of t he bridge opening. To det erm ine t he init ial elevat ion of t he ineffect ive flow areas for t he upst ream cross sect ion, a value slight ly lower t han t he lowest high cord elevat ion was used. This ineffect ive flow elevat ion was chosen so t hat when t he wat er surface becom es great er t han t his ineffect ive elevat ion, t he flow would m ost likely be weir flow and would be considered as effect ive flow. At t he downst ream cross sect ion, t he elevat ion of t he ineffect ive flow area was set t o be slight ly lower t han t he low cord elevat ion. This elevat ion was chosen so t hat when weir flow occurs over t he bridge, t he wat er level downst ream m ay be lower t han t he high cord, but yet it will cont ribut e t o t he act ive flow area. ( Addit ional discussion of t he select ion of t hese elevat ions is described in t he calibrat ion sect ion of t his exam ple.) To ent er t he ineffect ive flow areas, from t he Ge om e t r ic D a t a Edit or select t he Cr oss Se ct ion icon. Toggle t o cross sect ion 5.41 and select Opt ion s and t hen I n e ffe ct ive Flow Ar e a s. This will result in t he display shown in Figure 2.10. The default opt ion ( norm al) is t o ent er t he areas as a left st at ion and elevat ion and/ or a right st at ion and elevat ion. For t his exam ple, bot h t he left and right ineffect ive flow areas were used. Figure 2-10: Normal Ineffective Flow Areas For Cross Section 5.41 The left and right ineffect ive flow st at ions were ent ered as 420 and 677 feet , respect ively. These values are 30 feet t o t he left and right of t he bridge opening, as discussed previously. The elevat ion was t hen ent ered as 216.7 feet , a value slight ly lower t han t he high cord elevat ion. These ent ries im ply t hat all t he wat er t o t he left of t he left st at ion and t o t he right of t he right 2-13 Exam ple 2 Beaver Creek- Single Bridge st at ion will be considered as ineffect ive flow unt il t he wat er level exceeds t he elevat ion of 216.7 feet . Sim ilarly, ineffect ive flow areas were set at river st at ion 5.39 wit h a left st at ion at 420 and a right st at ion at 677, bot h at an elevat ion of 215.0 feet . The OK but t on was select ed and t he ineffect ive flow areas appeared as green t riangles, as shown previously on Figure 2.9. Addit ionally, t he ineffect ive flow areas will appear on t he plot s of t he cross sect ions. Finally, a not e will appear in t he box at t he bot t om of t he Cr oss Se ct ion D a t a Edit or t hat st at es an ineffect ive flow exist s for each cross sect ion for which t his opt ion was select ed. Bridge Modeling Approach The bridge rout ines allow t he m odeler t o analyze t he bridge flows by using different m et hods wit h t he sam e geom et ry. The different m et hods are: low flow, high flow, and com binat ion flow. Low flow occurs when t he wat er only flows t hrough t he bridge opening and is considered as open channel flow ( i.e., t he wat er surface does not exceed t he highest point of t he low cord on t he upst ream side of t he bridge) . High flow occurs when t he wat er surface encount ers t he highest point of t he low cord on t he upst ream side of t he bridge. Finally, com binat ion flow occurs when bot h low flow or pressure flow occur sim ult aneously wit h flow over t he bridge. The m odeler needs t o select appropriat e m et hods for bot h t he low flow and for t he high flow m et hods. For t he com binat ion flow, t he program will use t he m et hods select ed for bot h of t he flows. From t he Ge om e t r ic D a t a Edit or , select t he Br idge / Cu lve r t icon and t hen t he Br idge M ode lin g Appr oa ch but t on. This will act ivat e t he Br idge M ode lin g Appr oa ch Edit or as shown in Figure 2.11. For t his exam ple, t here is only 1 bridge opening locat ed at t his river st at ion and t herefore t he bridge num ber was 1. The following sect ions describe t he addit ional param et ers of t he bridge m odeling edit or. The m odeler is referred t o Chapt er 6 of t he Use r ’s M a nu a l and Chapt er 5 of t he H ydr a u lic Re fe r e n ce M a n ua l for addit ional discussion on t he bridge m odeling approach edit or. Low Flow M e t hods. Low flow exist s when t he flow t hrough t he bridge is open channel flow. As can be seen in Figure 2.11, t he program has t he capabilit y of analyzing low flow wit h four m et hods: - Energy Equat ion ( St andard St ep) - Mom ent um Balance - Yarnell Equat ion ( Class A only) - WSPRO Met hod ( Class A only) 2-14 Exam ple 2 Beaver Creek- Single Bridge Figure 2-11: Bridge Modeling Approach Editor The Energy Equat ion ( St andard St ep) m et hod considers t he bridge as j ust being part of t he nat ural channel and requires Manning’s n values for t he frict ion losses t hrough t he bridge and coefficient s of cont ract ion and expansion. The Mom ent um Balance m et hod perform s a m om ent um balance t hrough t he bridge area and requires t he select ion of a drag coefficient , Cd. This coefficient is used t o est im at e t he force due t o t he wat er m oving around t he piers, t he separat ion of flow, and t he result ing downst ream wake. The Yarnell Equat ion is an em pirical equat ion based on lab experim ent s. Finally, t he WSPRO m et hod is an energy based m et hod developed by t he USGS for t he Federal Highway Adm inist rat ion. At t his t im e, t he m odeler needs t o select which m et hods t he program should com put e and which m et hod t he program should use. The m odeler can select t o have t he program com put e part icular m et hods or all of t he m et hods. Then, t he m odeler needs t o select which m et hod t he program will use as a final solut ion. Alt ernat ively, t he m odeler can select t he com put at ion of several or all of t he m et hods, and t hen have t he program use t he m et hod wit h t he great est energy loss for t he final solut ion. This will allow t he m odeler t o view t he result s of all t he m et hods and com pare t he result s of t he different t echniques. For t his exam ple, t he Energy, Mom ent um , and Yarnell m et hods were select ed t o be com put ed. For t he m om ent um m et hod, a drag coefficient Cd = 2.00 was ent ered for t he square nose piers and for t he Yarnell m et hod, a value of K = 1.25 was ent ered. Finally, t he m et hod t hat result ed in t he great est energy loss was select ed t o be used for t he solut ion. ( The user is referred t o Exam ple 13 for an applicat ion of t he WSPRO m et hod.) H igh Flow M e t hods. High flows occur when t he wat er surface elevat ion upst ream of t he bridge is great er t han t he highest point on t he low cord of 2-15 Exam ple 2 Beaver Creek- Single Bridge t he upst ream side of t he bridge. Referring t o Figure 2.11, t he t wo alt ernat ives for t he program t o com put e t he wat er surface elevat ions during t he high flows are: Energy Only ( St andard St ep) or Pressure and/ or Weir Flow. The Energy Only ( St andard St ep) m et hod regards t he flow as open channel flow and considers t he bridge as an obst ruct ion t o t he flow. Typically, m ost bridges during high flows m ay act prim arily as j ust an obst ruct ion t o t he flow and t he energy m et hod m ay be m ost applicable. As a second m et hod for t he analysis of high flows, t he program can consider t he flow t o be causing Pressure Flow and/ or Weir Flow. For pressure flow, t here are t wo possible scenarios. The first is when only t he upst ream side of t he bridge deck is in cont act wit h t he wat er. For t his scenario, t he subm erged inlet coefficient , Cd, was set t o be 0.34. ( This value was arrived at during t he calibrat ion, which is described lat er in t his exam ple.) The second scenario for pressure flow is when t he bridge const rict ion is flowing com plet ely full. For t his sit uat ion, t he subm erged inlet and out let coefficient was set t o 0.80. The program will begin t o calculat e eit her t ype of pressure flow when t he com put ed low flow energy grade line is great er t han t he highest point of t he upst ream low cord. Alt ernat ively, t he user can set t he elevat ion at which pressure flow will begin t o be checked, inst ead of t he highest low cord value. This value can be ent ered as t he last input t o t he Br idge M ode lin g Appr oa ch Edit or ( Figure 2.11) . For t his exam ple, t his field was left blank which im plies t hat t he program used t he highest value of t he low cord ( t he default ) . As an addit ional opt ion, t he user can select t o have t he program begin t o calculat e t he pressure flow by using t he value of t he wat er surface inst ead of t he value of t he energy grade line. This is accom plished from wit hin t he Br idge / Cu lve r t D a t a Edit or by select ing Opt ion s and t hen Pr e ssu r e flow cr it e r ia . This will result in t he display shown in Figure 2.12. For t his exam ple, t he opt ion t o use t he upst ream energy grade line was chosen. Finally, for t he high flow analysis, Weir Flow occurs when t he upst ream energy grade line elevat ion ( as a default set t ing) exceeds t he lowest point of t he upst ream high cord. The weir flow dat a was ent ered previously in t he D e ck / Roa dw a y D a t a Edit or . At t his point , all of t he bridge dat a have been ent ered. The user should exit t he geom et ry dat a edit ors and save t he geom et ry dat a. For t his exam ple, t he geom et ry dat a was saved as t he file " Beaver Cr. + Bridge - P/ W." Figure 2-12: Pressure Flow Check Criteria 2-16 Exam ple 2 Beaver Creek- Single Bridge Steady Flow Data To ent er t he st eady flow dat a, from t he m ain program window Edit and t hen St e a dy Flow D a t a were select ed. This act ivat ed t he St e a dy Flow D a t a Edit or as shown in Figure 2.13. For t his analysis on t he reach of Kent wood, t hree profiles were select ed t o be com put ed. The flow dat a were ent ered for river st at ion 5.99 ( t he upst ream st at ion) and t he flow values were 5000, 10000, and 14000 cfs. These flows will be considered cont inuous t hroughout t he reach so no flow change locat ions were used. Addit ionally, t he t hree profile nam es were changed from t he default values of " PF# 1," et c., t o " 25 yr," " 100 yr," and May ‘74 flood," respect ively. These nam es will be used t o represent t he flow profiles when viewing t he out put . Figure 2-13: Steady Flow Data Editor To ent er t he boundary condit ions, t he Re a ch Bou nda r y Condit ion s but t on was select ed and t his result ed in t he display shown in Figure 2.14. For t his exam ple, a subcrit ical analysis was perform ed. Therefore, a downst ream boundary condit ion was required for each flow value. The m ouse arrow was placed over t he downst ream field and t hen t he box was select ed ( highlight ed) . Then, 1 of t he 4 boundary condit ions was select ed and t his caused t he t ype of boundary condit ion t hat was chosen t o appear in t he downst ream end of t he reach. 2-17 Exam ple 2 Beaver Creek- Single Bridge Figure 2-14: Steady Flow Boundary Conditions For t his exam ple, Kn ow n W . S. was select ed. This caused t he input edit or as shown in Figure 2.15 t o appear. For each of t he flows, t he known downst ream wat er surface elevat ions of 209.5, 210.5, and 211.8 feet were ent ered for t he flows 1, 2, and 3, respect ively. These values were obt ained from observed dat a on t he USGS At las. For t he purposes of t he analysis, if t he downst ream boundary condit ions are not known, t hen t he m odeler should use an est im at ed boundary condit ion. However, t his m ay int roduce errors in t he region of t his est im at ed value. Therefore, t he m odeler needs t o have an adequat e num ber of cross sect ions downst ream from t he m ain area of int erest so t hat t he boundary condit ions do not effect t he area of int erest . Mult iple runs should be perform ed t o observe t he effect of changing t he boundary condit ions on t he out put of t he m ain area of int erest . For a det ailed explanat ion of t he t ypes of boundary condit ions, refer t o Chapt er 7 of t he Use r ’s M a n ua l and Chapt er 3 of t he H ydr a u lic Re fe r e n ce M a n ua l. Aft er ent ering t he boundary condit ion dat a, t he OK but t on was select ed t o exit t he edit or. This com plet ed t he necessary input for t he flow dat a and t he st eady flow dat a was t hen saved as " Beaver Cr. - 3 Flows." 2-18 Exam ple 2 Beaver Creek- Single Bridge Figure 2-15: Known Water Surface Boundary Conditions Pressure/Weir Flow Simulation To perform t he st eady flow analysis, from t he m ain program window Ru n and t hen St e a dy Flow Ana lysis were select ed. This act ivat ed t he St e a dy Flow Ana lysis W in dow as shown in Figure 2.16. First , it was ensured t hat t he geom et ry file and st eady flow file t hat were previously developed appeared in t he select ion boxes on t he right side of t he window. Then, for t his sim ulat ion, a subcrit ical flow analysis was select ed. Addit ionally, from t he St e a dy Flow Ana lysis window, Opt ion s and t hen Cr it ica l D e pt h Ou t pu t Opt ion were select ed. An " x" was placed beside t he opt ion for Cr it ica l Alw a ys Ca lcu la t e d. This m ay require addit ional com put at ion t im e during program execut ion, but t hen t he user can view t he crit ical dept h elevat ion at all river st at ions during t he review of t he out put . Figure 2-16: Steady Flow Analysis Select Opt ion s and t hen ensure t hat t here is a check m ark " " in front of Ch e ck da t a be for e e x e cu t ion . This will cause t he program t o check all of t he input dat a t o ensure t hat all pert inent inform at ion was ent ered. Next , t he opt ions were saved as a plan ent it led " Press/ Weir Met hod," wit h a Short I D 2-19 Exam ple 2 Beaver Creek- Single Bridge ent ered as " Press/ Weir." Finally, COM PUTE was select ed at t he bot t om of t he window. Review of Pressure/Weir Flow Output Aft er t he program has com plet ed t he analysis, t he last line should read " PROGRAM TERMI NATED NORMALLY." This window is closed by double clicking t he bar in t he upper left corner of t he display. From t he m ain program window, Vie w and t hen W a t e r Sur fa ce Pr ofile s were select ed. This displayed t he profile plot as shown in Figure 2.17, showing t he wat er surface elevat ions and crit ical dept h lines for all t hree profiles. ( Not e: t he variables t hat are displayed can be changed by select ing Opt ion s and t hen Va r ia ble s.) From Figure 2.17, it can be seen t hat all t hree of t he flow profiles are occurring in t he subcrit ical flow regim e. This ensures t hat for t he low flow analysis, Class A low flow ( subcrit ical flow) was occurring t hrough t he bridge. Low flow occurred for t he first ( 5000 cfs) and for t he second ( 10000 cfs) flow profiles. For t he high flow, t he m et hod of analysis was chosen t o be pressure/ weir flow. Pressure and weir flow occurred during t he t hird flow profile ( 14000 cfs) . One way t o det erm ine t he t ype of flow t hat occurred is by viewing t he bridge only out put t able. This t able is present ed in Figure 2.18 and was act ivat ed from t he m ain program window by select ing Vie w , Pr ofile Ta ble , St d. Ta ble s, and t hen Br idge On ly. Single Bridge - Example 2 Press/Weir Method Geom: Beaver Cr. + Bridge - P/W Kentwood 220 Flow: Beaver Cr. - 3 Flows Legend WS May '74 flood 215 WS 100 yr Elevation (ft) Crit May '74 flood WS 25 yr 210 Crit 100 yr Crit 25 yr 205 Ground 200 195 0 1000 2000 3000 4000 5000 6000 Main Channel Distance (ft) Figure 2-17: Profile Plot for Pressure/Weir Analysis For t his exam ple t here is only one bridge locat ed at river st at ion 5.40, as list ed in t he t able. Pressure flow calculat ions were set t o begin when t he energy grade line elevat ion of t he upst ream sect ion ( 5.41) was great er t han t he highest elevat ion of t he upst ream low cord ( 215.7 ft ) . The first colum n in Figure 2.18 shows t he energy grade line elevat ion of t he upst ream sect ion ( EG US) and t he second colum n shows t he elevat ion when pressure flow was set t o begin. A com parison of t hese t wo colum ns shows t hat pressure flow 2-20 Exam ple 2 Beaver Creek- Single Bridge occurred for t he t hird profile. Addit ionally, it can be seen t hat weir flow occurred for t he t hird profile, since t here is a weir flow value for t he t hird profile. The following sect ions det ail t he out put for t he first t wo profiles and t hen for t he t hird flow profile. Figure 2-18: Bridge Only Summary Table for Pressure/Weir Flow Fir st a n d Se cond Flow Pr ofile s. The first ( 5000 cfs) and second ( 10000 cfs) flow profiles were bot h com put ed using t he low flow m et hods of: Energy, Mom ent um , and Yarnell. From t he m ain program window, select View, Pr ofile Ta ble , St a n da r d Ta ble s, and t hen Br idge Com pa r ison. This will provide a com parison t able for t he different energy loss m et hods and is shown in Figure 2.19. I n Figure 2.19, t he t hree rows display t he result s for each of t he t hree flow profiles, in ascending order. The river st at ion is set at 5.4 ( t he only bridge locat ion for t his reach) . The fourt h colum n shows t he wat er surface elevat ion im m ediat ely upst ream of t he bridge. The sixt h, sevent h and eight h colum ns show t he result s of t he low flow m et hods t hat were chosen t o be com put ed: Energy, Mom ent um , and Yarnell Met hods, respect ively. The program com pared t he result s and used t he value wit h t he great est energy loss. For t he first and second profiles, t he energy m et hod calculat ed t he great est energy losses and t he program used t he result s of 213.31 and 215.67 feet , respect ively. 2-21 Exam ple 2 Beaver Creek- Single Bridge Figure 2-19: Bridge Comparison Table for Pressure/Weir Flow Analysis Th ir d Flow Pr ofile . The t hird flow profile was com put ed for a flow of 14000 cfs. As can be seen in Figure 2.18, approxim at ely 3050 cfs of t he t ot al flow was weir flow. The rem aining flow, approxim at ely 10950 cfs, was pressure flow t hrough t he bridge opening. As can be seen in Figure 2.19, t he energy grade line necessary for pressure- only flow was 221.66 feet . Since t his value is great er t han t he upst ream high cord, weir flow also developed. Therefore, t he program used t he pressure/ weir energy value as t he solut ion t o t he high flow m et hod, nam ely 217.68 feet . Energy Method Analysis As a second approach t o analyze t he t hree flows, t he energy m et hod will be used inst ead of t he pressure/ weir flow m et hod for t he high flows. From t he St e a dy Flow An a lysis W in dow , select File , Ope n Pla n , and t hen select " Energy Met hod." This will act ivat e t he plan t hat em ployed t he energy m et hod for t he analysis. The following discussion out lines t he procedure used t o develop t his plan. Energy Method Data and Simulation To ent er t he dat a for t he energy m et hod, from t he m ain program window Edit , Ge om e t r ic D a t a , t he Br idge / Cu lve r t icon, and t hen t he Br idge M ode lin g Appr oa ch icon were select ed. This act ivat ed t he Br idge M ode lin g Appr oa ch Edit or as was shown in Figure 2.11. The En e r gy On ly ( St a nda r d St e p) opt ion was t hen select ed as t he high flow m et hod ( inst ead of t he Pressure/ Weir m et hod) . Then, t he edit or was closed and t he geom et ry was saved as " Beaver Cr. + Bridge - Energy." Next , Run and t hen St e a dy Flow Ana lysis were select ed from t he m ain program window. This act ivat ed t he St e a dy Flow Ana lysis W indow . The geom et ry file was select ed as " Beaver Cr. + Bridge - Energy" and t he st eady flow file was " Beaver Cr. - 3 Flows" ( t he sam e st eady flow file as used previously) . Then, a Short I D was ent ered as " Energy" and t he opt ions were saved as t he plan " Energy Met hod." Finally, COM PUTE was select ed t o perform t he st eady flow analysis. 2-22 Exam ple 2 Beaver Creek- Single Bridge Review of Energy Method Output From t he m ain program window, select Vie w , Pr ofile Ta ble , St a n da r d Ta ble s, and t hen Br idge Com pa r ison. This bridge com parison t able is shown in Figure 2.20. For t he first and second profiles, t he t able shows t he sam e result s as for t he pressure flow analysis. This is as would be expect ed since t he first and second profiles were calculat ed using t he sam e low flow procedures. For t he t hird profile, t he energy m et hod was used t o calculat e t he energy losses t hrough t he bridge for t his high flow and result ed in an energy gradeline elevat ion of 217.38 feet . Figure 2-20: Bridge Comparison Table for Energy Method Analysis Evaluation of Cross Section Locations As st at ed previously, t he locat ions of t he cross sect ions and t he values select ed for t he expansion and cont ract ion coefficient s in t he vicinit y of t he bridge are crucial for accurat e predict ion of t he energy losses t hrough t he bridge st ruct ure. For t his exam ple, t he locat ions of t he cross sect ions and t he energy loss coefficient s were evaluat ed for t he high flow event . The following analysis is based on dat a t hat were developed for low flow event s occurring t hrough bridges and t he m odeler should use caut ion when applying t he procedure for ot her t han low flow sit uat ions. Each of t he reach lengt h and coefficient evaluat ion procedures are discussed in t he following sect ions. Expansion Reach Length The expansion reach lengt h, Le, is defined as t he dist ance from t he cross sect ion placed im m ediat ely downst ream of t he bridge t o t he cross sect ion where t he flow is assum ed t o have fully expanded. For t his exam ple, t his dist ance is from cross sect ion 5.39 t o cross- sect ion 5.29. I nit ially, t he expansion reach lengt h is est im at ed according t o observed field dat a or ot her appropriat e m et hod. For t his exam ple, observed dat a were available so t he init ial est im at e of t he expansion reach lengt h was obt ained from t he field observat ions. Aft er t he analysis, t he m odeler can evaluat e t he init ial est im at e of t he expansion reach lengt h. For t he analysis, it is recom m ended t o use t he regression result s from t he US Arm y Corps of Engineers ( USACE) st udy [ HEC1995] . The result s of t he st udy suggest t he use of Equat ion 2- 1 t o evaluat e 2-23 Exam ple 2 Beaver Creek- Single Bridge t he expansion reach lengt h. This equat ion is valid when t he m odeling sit uat ion is sim ilar t o t he dat a used in t he regression analysis. ( I n t he docum ent , alt ernat ive expressions are present ed for ot her sit uat ions.) The equat ion is: ⎛F ⎞ Le = ER(Lobs ) = −298 + 257⎜⎜ 5.39 ⎟⎟ + 0.918 Lobs + 0.00479Q ⎝ F5.29 ⎠ where: Le = ( 2- 1) expansion reach lengt h, ft ER = expansion rat io F5.39 = m ain channel Froude num ber at t he cross sect ion im m ediat ely downst ream of t he bridge ( cross sect ion 5.39 for t his exam ple) F5.29 = m ain channel Froude num ber at t he cross sect ion of fully expanded flow ( init ially cross sect ion 5.29 for t his exam ple) Lobs = average lengt h of obst ruct ion caused by t he t wo bridge approaches, ft Q = t ot al discharge, ft 3/ s ( Not e: The subscript s used in Equat ion 2- 1 and all subsequent equat ions reflect t he river st at ion num bering for t his exam ple.) From t he field dat a, t he average lengt h of t he obst ruct ion is approxim at ely 740 feet and t he t ot al discharge, Q, is 14000 cfs for t he high flow event . From t he init ial analysis, t he values of t he Froude num ber at cross- sect ion 5.39 was 0.37 and at cross sect ion 5.29 was 0.30. ( Bot h of t hese values were t he sam e for pressure/ weir and energy m et hods and are displayed on St a n da r d Ta ble 1 .) Subst it ut ing t he values int o Equat ion 2- 1 yielded t hat t he expansion reach lengt h, Le, was approxim at ely 778 feet . This equat ion has a st andard error of 96 feet , which yields an expansion reach lengt h range from 682 t o 874 feet t o define t he 68% confidence band. The dist ance used for t he expansion reach lengt h ( t he dist ance from cross sect ion 5.39 t o crosssect ion 5.29) was set t o be 500 feet in t he m ain channel, which is less t han t he recom m ended range from t he equat ion. The m odeler now has t he opt ion t o adj ust t his lengt h so t hat it is wit hin t he calculat ed range. Then, aft er a new analysis, t he new Froude num bers should be used t o calculat e a new expansion reach lengt h. I f t he geom et ry is not changing rapidly in t his region, t hen only 1 or 2 it erat ions should be necessary t o obt ain a const ant expansion reach lengt h value. For t his exam ple, t he locat ion of t he fully expanded cross sect ion was changed t o reflect t he new expansion reach lengt h ( 778 feet ) by int erpolat ing a new cross sect ion t o be locat ed 778 feet downst ream from cross sect ion 5.39. To accom plish t his, t he following st eps were t aken. First , t he pressure/ weir flow plan ( " Pressure/ Weir Met hod" ) was act ivat ed. Then, in t he 2-24 Exam ple 2 Beaver Creek- Single Bridge Ge om e t r ic D a t a Edit or , a cross sect ion was int erpolat ed bet ween cross sect ions 5.29 and 5.21* . This int erpolat ed cross sect ion ( 5.24* ) was set t o be at a dist ance of 278 feet downst ream from cross sect ion 5.29. Since cross sect ion 5.29 was already locat ed 500 feet downst ream from cross sect ion 5.39, t he locat ion of cross sect ion 5.24* was t hen 500 + 278 = 778 feet downst ream from cross sect ion 5.39. The cross sect ions 5.29, 5.27* , and 5.21* were t hen delet ed. Finally, t his new geom et ric dat a was saved as a file called " Bvr.Cr.+ Bridge P/ W: New Le, Lc." On t he St e a dy Flow Ana lysis W indow , a Short I D was ent ered as " P/ w+ NewLeLc" and t hen t he new geom et ry file and t he original st eady flow dat a file were saved as a plan ent it led " Press/ Weir Met hod: New Le, Lc." The Ge om e t r ic D a t a Edit or was t hen react ivat ed and t he Br idge M ode lin g Appr oa ch D a t a Edit or was select ed. The high flow m et hod was chosen t o be t he energy m et hod and t hen t he geom et ry dat a was saved as " Bvr.Cr.+ Bridge - Energy: New Le, Lc." The St e a dy Flow Ana lysis W indow was act ivat ed, a Short I D was ent ered as " En.+ New LeLc," and t he new energy geom et ry file and t he st eady flow dat a file were t hen saved as a new plan ent it led " Energy Met hod : New Le, Lc." This procedure creat ed t wo new plans, wit h each plan cont aining t he necessary int erpolat ed geom et ry and appropriat e high flow calculat ion m et hods. Each of t he t wo new plans were t hen execut ed and t he result ing flow param et er values were reent ered int o Equat ion 2- 1. ( Not e: The Froude num ber for river st at ion 5.29 was replaced by t he Froude num ber at river st at ion 5.24* in Equat ion 2- 1.) The final m ean value of t he expansion reach lengt h was t hen det erm ined t o be 750 feet , wit h a range of ± 96 feet t o define t he 68% confidence band. The adj ust ed reach lengt h value of 778 feet is wit hin t he confidence band and no addit ional it erat ions were com put ed. Finally, t he expansion rat io ( ER) as described in Equat ion 2- 1 should not exceed 4: 1 and should not be less t han 0.5: 1. For t his exam ple, t he final expansion rat io was ER = ( 778) / ( 740) = 1.05, which is wit hin t he accept able range. I n t he above procedure, t he m odeler is direct ed t o Chapt er 4 of t he H ydr a u lic Re fe r e n ce M a n u a l for addit ional inform at ion on cross sect ion int erpolat ion and t o Chapt er 5 of t he Use r ’s M a nua l for furt her discussion on working wit h proj ect s. Upon reviewing t he above procedures, t he m odeler can open eit her of t hese new plans and t he corresponding geom et ry and flow dat a files will be act ivat ed. For t his exam ple, t he result s of t he wat er surface profiles for t he new plans are approxim at ely equal t o t he result s obt ained from t he original geom et ry for bot h of t he pressure/ weir flow and energy m et hods, respect ively. However, t he m odeler should apply t he above procedures t o evaluat e t he locat ion of t he expansion reach lengt h for each specific applicat ion. Finally, during t he procedures as out lined above, if t he locat ion of t he expansion reach lengt h produces a dist ance sufficient ly far downst ream from t he bridge, t hen t he m odeler m ay be required t o include addit ional cross sect ions wit hin t his reach lengt h t o accurat ely predict t he energy losses. This m ay be accom plished by insert ing cross sect ions and providing t he appropriat e ineffect ive flow areas at each cross sect ion according t o t heir locat ion wit h respect t o t he bridge opening. 2-25 Exam ple 2 Beaver Creek- Single Bridge Contraction Reach Length The cont ract ion reach lengt h, Lc, is defined as t he dist ance from t he cross sect ion locat ed im m ediat ely upst ream of t he bridge ( 5.41) t o t he cross sect ion t hat is locat ed where t he flow lines are parallel and t he cross sect ion exhibit s fully effect ive flow ( 5.44) . To evaluat e t his reach lengt h, t he regression result s ( shown as Equat ion 2- 2 below) from t he US Arm y Corps of Engineers ( USACE) st udy [ HEC- 1995] was used. The equat ion is: ⎛F ⎞ ⎛Q Lc = CR (Lobs ) = 263 + 38.8⎜⎜ 5.39 ⎟⎟ + 257 ⎜⎜ ob ⎝ Q ⎝ F5.29 ⎠ where: Lc 2 ⎛n ⎞ ⎟⎟ − 58.7⎜⎜ ob ⎠ ⎝ nc ⎞ ⎟⎟ ⎠ 0 .5 + 0.161Lobs = cont ract ion reach lengt h, ft CR = cont ract ion rat io F5.39 = m ain channel Froude num ber at t he cross sect ion ( 2- 2) im m ediat ely downst ream of t he bridge ( cross sect ion 5.39 for t his exam ple) F5.29 = m ain channel Froude num ber at t he cross sect ion of fully expanded flow ( init ially cross sect ion 5.29 for t his exam ple) Q ob = discharge conveyed in t he t wo overbanks at cross sect ion 5.44, cfs Q = t ot al discharge, ft 3/ s nob = Manning n value for t he overbanks at sect ion 5.44 nc = Manning n value for t he m ain channel at sect ion 5.44 From t he field dat a and t he result s of t he init ial analysis, t he Froude num bers at sect ions 5.39 and 5.29 were 0.37 and 0.30, respect ively, t he t ot al over bank flow at cross sect ion 5.44 was approxim at ely 9780 cfs ( an average of 9880 for t he pressure/ weir flow and 9685 for t he energy m et hod) , t he t ot al flow was 14000 cfs, t he weight ed n value for bot h of t he overbanks was 0.069, t he n value for t he m ain channel was 0.04, and t he average lengt h of t he obst ruct ion was 740 feet . Subst it ut ion of t hese values int o Equat ion 2- 2 yielded t he cont ract ed reach lengt h of 478 feet . This equat ion has a st andard error of 31 feet which result s in a cont ract ion reach lengt h range from 447 t o 509 feet t o define t he 68% confidence band. For t his exam ple, t he dist ance from cross sect ion 5.44 t o cross sect ion 5.41 was set at 170 feet along t he m ain channel. Since t his value was out side of t he confidence range, t he reach lengt h was adj ust ed t o reflect t he new cont ract ion reach lengt h. The adj ust m ent of t he geom et ry for t he new cont ract ion reach lengt h was perform ed sim ilarly t o t he adj ust m ent procedure for t he expansion reach lengt h. A cross sect ion ( 5.49* ) was int erpolat ed bet ween river st at ions 2-26 Exam ple 2 Beaver Creek- Single Bridge 5.525* and 5.44 t hat was set t o be 308 feet upst ream of river st at ion 5.44. Then, t he reach lengt h from river st at ion 5.49* t o river st at ion 5.41 was 308 + 170 = 478 feet , t he required cont ract ion reach lengt h. This new river st at ion can be viewed by opening t he plan " Press/ Weir Met hod: New Le, Lc" for t he pressure/ weir m et hod or t he plan " Energy Met hod: New Le, Lc" for t he energy m et hod analysis. Finally, aft er t he subsequent analysis wit h t he new cont ract ion reach lengt h, t he new flow param et ers were ent ered int o Equat ion 2- 2 and yielded a cont ract ion reach lengt h of 499 feet , wit h a range from 468 t o 530 feet t o define t he 68% confidence band. The adj ust ed cont ract ion reach lengt h of 478 feet is wit hin t his range and no addit ional it erat ions were necessary. ( Not e: The Froude num ber for river st at ion 5.29 was replaced by t he Froude num ber at river st at ion 5.24* in equat ion 2- 2.) As a final crit eria, t he cont ract ion rat io ( CR) should not exceed 2.5: 1 nor should it be less t han 0.3: 1. For t his exam ple, t he final cont ract ion rat io was CR = ( 499) / ( 740) = 0.67, which is wit hin t he accept able range. Table 2- 1 shows a relat ionship of t he values com put ed for t he expansion reach lengt hs and t he cont ract ion reach lengt hs during t he it erat ions as described above. Addit ionally, t he t able shows t he values as det erm ined by t he USGS and t he t radit ional USACE m et hods. Table 2-1: Expansion and Contraction Reach Length Determinations Expansion or Contraction Reach Length Determination Method USGS Le Lc 200 200 Traditional USACE 2964 740 Initial Placement from field data 500 170 HEC-1995 1st iteration 770 478 HEC-1995 2nd iteration 747 499 As can be seen from t he dat a in Table 2.1, t he USGS m et hod will t ypically provide a m inim um crit eria and t he t radit ional USACE m et hod will provide a m axim um lengt h. The recent st udy [ HEC- 1995] was perform ed t o provide bet t er guidance for t he evaluat ion of t he reach lengt hs and t hese values fall wit hin t he range as det erm ined by t he previous t wo m et hods. Expansion Coefficient The expansion coefficient is used t o det erm ine t he am ount of energy loss due t o t he flow expanding bet ween t wo part icular cross sect ions. The research docum ent [ HEC- 1995] suggest s t he following relat ionship for t he value of t he expansion coefficient : ⎛D C e = −0.09 + 0.570⎜⎜ ob ⎝ Dc where: C e = ⎞ ⎛F ⎟⎟ + 0.075⎜⎜ 5.39 ⎠ ⎝ F5.29 ⎞ ⎟⎟ ⎠ ( 2- 3) expansion coefficient 2-27 Exam ple 2 Beaver Creek- Single Bridge Dob = hydraulic dept h ( flow area / t op widt h) for t he overbank at cross sect ion 5.29 Dc = hydraulic dept h in t he m ain channel at cross sect ion 5.29 From t he dat a for t he analysis, t he hydraulic dept h for t he overbank at cross sect ion 5.29 was 4.26 feet ( an average of 5.31 and 3.20 feet for t he LOB and ROB, respect ively, wit h t he values being consist ent for bot h t he pressure/ weir flow and energy m et hod) and t he hydraulic dept h of t he m ain channel was 7.20 feet . Subst it ut ion of t he values for t he variables yielded an expansion coefficient of 0.34. This is t he m edian value and t he range of ± 0.2 defines t he 95% confidence band for Equat ion 2- 3. Therefore, t he m odeler should use t he value of 0.34 as an init ial value and vary t he coefficient by ± 0.2. For t his exam ple, a value of 0.5 was init ially used for t he expansion coefficient in t he vicinit y of t he bridge. During t he it erat ions for t he cont ract ion and expansion reach lengt hs, t his coefficient was reevaluat ed for each it erat ion. For t he final value, t he hydraulic dept h in t he overbank at cross sect ion 5.24* was 4.11 feet ( an average of 5.06 and 3.16 feet for t he LOB and ROB, respect ively, wit h t he values being consist ent for bot h t he pressure/ weir flow and energy m et hod) and t he hydraulic dept h of t he m ain channel was 8.40 feet . This yielded an expansion coefficient of 0.27, ± 0.2. For t he exam ple, a final value of 0.5 was calibrat ed in order t o m at ch t he observed dat a. Contraction Coefficient The cont ract ion coefficient is used t o det erm ine t he am ount of energy loss due t o t he flow cont ract ing bet ween t wo part icular cross sect ions. The dat a of t he st udy [ HEC- 1995] did not lend it self t o regression of t he cont ract ion coefficient values and an approxim at e range is recom m ended by t he research. For t his exam ple, a range of 0.3 t o 0.5 is recom m ended by t he research. A value of 0.3 was used for t he cont ract ion coefficient in t he vicinit y of t he bridge. I n sum m ary, t he above recom m endat ions for t he expansion reach lengt h, t he cont ract ion reach lengt h, and t he expansion and cont ract ion coefficient s represent an im provem ent in t he general m et hodology behind t he predict ion of t hese values. The m odeler is recom m ended t o apply t hese new crit eria as a m ore subst ant ial m et hod for est im at ing t he t ransit ion reach lengt hs. As a final not e, aft er t he init ial analysis, t he expansion and t he cont ract ion reach lengt hs as well as t he expansion and cont ract ion coefficient s should be evaluat ed sim ult aneously. Then, adj ust m ent s should be m ade t o t he reach lengt h and coefficient values before a subsequent analysis is perform ed. Finally, t he new dat a should be used t o reevaluat e all of t he reach lengt hs and coefficient s. This procedure will ensure t hat t he m odeler is always using t he current flow dat a for t he analysis. 2-28 Exam ple 2 Beaver Creek- Single Bridge Model Calibration For t he high flow event , observed dat a were available as obt ained from t he USGS At las. Therefore t he wat er surface profiles calculat ed by t he m odel were calibrat ed t o reflect t he observed wat er surface profiles and weir flow. This calibrat ion occurred aft er t he reach lengt hs and coefficient s had been evaluat ed. From t he observed dat a, it was recorded t hat a flow of approxim at ely 3300 cfs occurred over t he highway em bankm ent . Therefore, a t arget value of weir flow was available for t he calibrat ion of t he m odel. From t he m ain m enu, select Vie w and t hen Cr oss Se ct ion Ta ble , Type , and t hen Cr oss Se ct ion . Select river st at ion 5.41 and profile 3 and t his will display t he t able shown in Figure 2.21. I n t he right colum n, t he flows in t he LOB, m ain channel, and ROB are shown as 1228.00, 9653.93, and 3118.07 cfs respect ively. Since t his cross sect ion is placed im m ediat ely upst ream of t he bridge, t he m aj orit y of t he flow in t he LOB and ROB will cont ribut e t o t he weir flow over t he bridge. From t he t op of t he t able, select Type and t hen select Br idge . I n t he left colum n, t he weir flow is list ed as being 3043.90 cfs. This is t he t ot al weir flow occurring over t he bridge. This value should be approxim at ely equal t o t he t ot al flow in t he LOB and ROB of river st at ion 5.41 of 1228.00 + 3118.07 = 4356.07. The calculat ed weir flow is less t han t his t ot al but all of t he flow at cross sect ion 5.41 in t he LOB and ROB will not cont ribut e t o t he weir flow, only a m aj or port ion of it . Furt herm ore, a t arget value of approxim at ely 3300 cfs of weir flow was observed. The t ot al weir flow was com put ed as being 3044 cfs, a close approxim at ion t o t he est im at ed weir flow. To obt ain t his close approxim at ion, t he weir flow coefficient was set t o a value of 2.6 t o account for t he inefficiency of t he bridge surface st ruct ure t o act as a t rue weir and since t he dept h of wat er over t he bridge was sm all com pared t o t he height of t he weir. Addit ionally, t he Manning’s n values were adj ust ed. Originally, t he Manning’s n values were t he average values obt ained from t he USGS At las. Then, t he Manning’s n values were raised slight ly in t he overbank and m ain channel areas t o decrease t he am ount of conveyance in t hese areas. This caused t he wat er surface profile and t he am ount of weir flow t o closer approxim at e t he observed dat a t hroughout t he river reach. I t should be not ed t hat t he n values were raised on a global scale. I ndividual specific n values should not be adj ust ed wit hout t aking int o account t he spat ial average of t he fact or. For t he pressure flow coefficient s, t he downst ream wat er surface inside t he bridge was calculat ed at a value slight ly lower t han t he low cord. This im plies t hat t he program was using t he sluice gat e ( subm erged inlet only) pressure flow relat ionship. Therefore, t he subm erged inlet coefficient was reduced t o decrease t he am ount of flow t hrough t he bridge. This increased t he upst ream energy and allowed m ore wat er t o flow over t he bridge t o concur wit h what happened during t he observed event . 2-29 Exam ple 2 Beaver Creek- Single Bridge Figure 2-21: Cross Section Table For Plan: P/W New LeLc Finally, for t he calibrat ion, t he ineffect ive flow areas at cross sect ion 5.41 and 5.39 were set t o balance t he flow going over t he weir. I nit ially, t he flow in t he LOB and ROB at cross sect ion 5.41 was drast ically larger t han t he flows in t he LOB and ROB at t he downst ream sect ion 5.39. This was due t o t he fact t hat t he ineffect ive flow area elevat ions at cross sect ion 5.39 were previously set t o a value in bet ween t he low cord and t he high cord. When t he flow cam e over t he weir, t he dept h downst ream was less t han t he ineffect ive flow elevat ion, so t he program init ially considered t he overbank area as ineffect ive flow. This is not a realist ic answer. When t he flow goes over t he weir it cont ribut es t o t he overbank flow at t he downst ream cross sect ion and t hen t his downst ream area should be considered as effect ive flow. Therefore, t he ineffect ive flow elevat ions were lowered t o allow t he weir flow t hat ent ered cross sect ion 5.39 t o becom e effect ive. These calibrat ions were perform ed because t he act ual flow dept hs for t he event were known. I f t hese act ual dat a were not known, t hen t he adj ust m ent of t he Manning’s n values, pressure flow coefficient s, and weir flow rat e could not be conduct ed t o t he refinem ent in t he previous discussion. However, t he balancing of t he weir flow t o t he flow in t he LOB and ROB at river st at ions 5.39 and 5.41 could be perform ed. The calibrat ion t o t he m odel account ed 2-30 Exam ple 2 Beaver Creek- Single Bridge for a m ore accurat e det erm inat ion of t he wat er surface profile t o t he observed dat a. Comparison of Energy and Pressure/Weir Flow Methods to Observed Data To com pare t he result s of t he analyses t o t he observed dat a, t he observed dat a was first ent ered in t he St e a dy Flow D a t a Edit or by select ing Opt ion s and t hen Obse r ve d W S. This act ivat ed t he edit or as shown in Figure 2.22 on which t he observed dat a were ent ered for t he flood event . This edit or was closed and t hen t he profile plot was act ivat ed and is shown in Figure 2.23. Figure 2.23 displays t he t hree wat er surfaces for each of t he t wo plans, as well as t he observed values. The display opt ions for t his figure were select ed under t he Opt ions m enu as: 1) Va r ia ble s - select t o display t he wat er surface and observed wat er surface; 2) Pr ofile s - select 1,2, and 3; and 3) Pla n s - select bot h t he " Energy Met hod: New Le Lc " plan and t he " Pressure/ Weir Flow: New Le Lc" plan. As shown in t he figure, bot h m et hods produced t he sam e wat er surface profiles for t he first t wo flows ( bot h of t he low flows) . This is as would be expect ed because bot h m et hods analyzed t he t wo low flows using t he sam e crit eria. For t he high flow, t he wat er surface profile for t he energy m et hod and t he pressure/ weir flow m et hod varied slight ly upst ream of t he bridge. The Zoom feat ure under t he Opt ions m enu can be used t o obt ain a closer view of t he profiles. Figure 2-22: Observed Water Surface Editor 2-31 Exam ple 2 Beaver Creek- Single Bridge Single Bridge - Example 2 1) P/W+NewLeLc 2/6/1998 Geom: Bvr.Cr.+Bridge - P/W: New Le, Lc Kentwood 220 2) En.+New LeLc 2/6/1998 Flow: Beaver Cr. - 3 Flows Legend WS May '74 flood - P/W+NewLeLc WS May '74 flood - En.+New LeLc WS 100 yr - En.+New LeLc WS 100 yr - P/W+NewLeLc 215 WS 25 yr - P/W+NewLeLc WS 25 yr - En.+New LeLc Ground Elevation (ft) Obs WS May '74 flood - P/W+NewLeLc Obs WS May '74 flood - En.+New LeLc 210 205 200 195 0 1000 2000 3000 4000 5000 6000 Main Channel Distance (ft) Figure 2-23: All 3 Flow Profiles for Press/Weir and Energy Methods Table 2.2 shows a t abular com parison of t he calculat ed wat er surface elevat ions for bot h t he pressure/ weir flow m et hod and t he energy m et hod t o t he observed dat a. The observed values wit h a * * denot e t hat t he value m ay be in quest ion due t o t here being only a few observed values in t he vicinit y of t he locat ion on t he at las or because t hose t hat were provided were not in t he act ive flow area. I n com parison of t he calculat ed values t o t he observed values, bot h of t he m odeling approaches were able t o predict t he act ual wat er surface elevat ions wit hin a reasonable t olerance. The largest errors occurred where t he observed wat er surface values are in quest ion. Addit ionally, t he observed values in t he t able are an average wat er surface elevat ion over t he area of effect ive flow where t he cross sect ions are locat ed. The one dim ensional m odel can only predict one result ing wat er surface; t herefore, t he fluct uat ions across t he cross sect ion will not occur in t he m odel as t hey did during t he act ual event . I n com parison of t he pressure/ weir m et hod t o t he energy m et hod, t he great est difference occurs at t he bridge st ruct ure. The wat er surface elevat ions for t he pressure/ weir flow m et hod inside t he bridge are est im at ed using t he upst ream and downst ream flow dept hs. 2-32 Exam ple 2 Beaver Creek- Single Bridge Table 2-2: Comparison of Water Surface Elevations for Q = 14000 cfs Pressure/Weir Energy Cross Section Calculated Absolute Error Calculated Absolute Error Observed 5.99 5.875* 5.76 5.685* 5.61 5.49* 5.41 5.40 - Br Up 5.40 - Br Dn 5.39 5.24* 5.13 5.065 5.00 220.00 218.99 218.46 218.23 218.09 217.91 217.44 217.44 217.44 215.62 214.64 213.33 212.54 211.80 0.00 -0.21 0.06 -0.07 -0.01 0.01 -0.36 219.95 218.87 218.29 218.04 217.88 217.66 217.12 215.86 215.26 215.62 214.64 213.33 212.54 211.80 -0.05 -0.33 -0.11 -0.26 -0.22 -0.24 -0.68 220.0 219.2** 218.4 218.3 218.1 217.9 217.8** NA NA 215.2** 214.6 213.6 212.5 211.8 0.42 0.04 -0.27 0.04 0.00 0.42 0.04 -0.27 0.04 0.00 Summary This exam ple dem onst rat ed t he use of HEC- RAS t o analyze a river reach t hat cont ains a single bridge crossing. The geom et ric dat a consist ing of t he cross sect ions and bridge geom et ry were ent ered for t he reach along Beaver Creek, as obt ained from t he USGS At las No. HA- 601. Three flow values were used for t he analysis, wit h t he largest flow coinciding wit h t he flood event in May 1974. The first plan consist ed of t he geom et ry dat a ( wit h t he high flow m et hod select ed as press/ weir) and t he flow dat a. A second plan was creat ed wit h t he select ion of t he energy m et hod for t he high flow analysis. Review of result s for t hese plans reflect ed t he necessit y for adj ust m ent s t o t he expansion and cont ract ion reach lengt hs. Aft er t he adj ust m ent s were m ade, t wo new plans were creat ed, one for t he pressure/ weir and one for t he energy m et hod for t he high flow analysis. The result s of t hese t wo new plans were t hen com pared t o t he observed wat er surface elevat ions. From t he com parison, t he pressure/ weir m et hod result ed wit h t he closest values t o t he observed wat er surface elevat ions. 2-33 Exam ple 3 Single Culvert - Single Bridge CH APT ER 3 Single Culvert (Multiple Identical Barrels) Purpose This exam ple is designed t o dem onst rat e t he use of HEC- RAS t o analyze t he flow of wat er t hrough a culvert . The program has t he capabilit y of analyzing flow t hrough a single culvert , m ult iple ident ical culvert s, and m ult iple nonident ical culvert s. A culvert t ype is defined by t he charact erist ics of: shape, size, chart , scale num ber, lengt h, Manning's n value, loss coefficient s, and slope ( upst ream and downst ream invert s) . I f a series of culvert s are of t he sam e t ype ( have ident ical charact erist ics) , t hen t he user can com bine t hese culvert s t o be cat egorized as one culvert I D wit h m ult iple ident ical barrels. For a given culvert I D, t he program can analyze up t o 25 ident ical barrels. This exam ple will analyze a single culvert t ype wit h t wo ident ical circular barrels. The ent ering of dat a and t he analysis of a culvert are very sim ilar t o t he procedures used for bridges. The user is referred t o Exam ple 2 for t he procedures of bridge analyses and t o Chapt er 6 of t he H ydr a u lic Re fe r e n ce M a n u a l for a det ailed discussion on m odeling culvert s. To review t he analysis of t his exam ple, from t he m ain window select File and t hen Ope n Pr oj e ct . Select t he proj ect labeled " Twin Circular Pipe - Exam ple 3." This will open t he proj ect and act ivat e t he following files: Plan: " Spring Creek Culvert s" Geom et ry: " Mult iple Pipe Geom et ry" Flow: " Mult iple Pipe Flow Dat a" Geometric Data To perform t he analysis, t he geom et ric dat a were ent ered first . The geom et ric dat a consist s of t he river syst em schem at ic, t he cross sect ion geom et ry, placem ent of t he cross sect ions, and t he culvert inform at ion. Each of t hese geom et ric dat a com ponent s is described in t he following sect ions. 3-1 Exam ple 4 Mult iple Culvert s River System Schematic From t he m ain program window, select Edit and t hen Ge om e t r ic D a t a and t he river syst em schem at ic of Spring Creek will appear, as shown in Figure 3.1. A river reach was drawn and t he river was labeled as " Spring Creek" and t he reach was t it led " Culvrt Reach." This river reach was init ially defined from t he surveyed inform at ion t o cont ain 9 cross sect ions, wit h river m ile 20.535 as t he upst ream cross sect ion and river m ile 20.000 as t he downst ream cross sect ion. The river st at ion 20.208* was int erpolat ed for t his exam ple, and will be discussed in a subsequent sect ion. Addit ionally, a culvert is displayed which was insert ed at river st at ion 20.237 during t he procedure of t his exam ple. Figure 3-1: River System Schematic For Spring Creek Cross Section Geometry To ent er t he cross sect ion dat a, from t he Ge om e t r ic D a t a Edit or, t he Cr oss Se ct ion icon was select ed. This act ivat ed t he Cr oss Se ct ion D a t a Edit or , 3-2 Exam ple 3 Single Culvert - Single Bridge as shown in Figure 3.2 for river st at ion 20.238. A descript ion of t he sect ion was ent ered as " Upst ream end of Culvert " and t he X- Y coordinat es were ent ered in t he t able on t he edit or. On t he right side of t he edit or, t he reach lengt hs t o t he next downst ream sect ion ( cross sect ion 20.227 for t his exam ple) were ent ered as 57 feet for t he LOB, m ain channel, and ROB. For t his cross sect ion, t he H or izon t a l va r ia t ion in n va lue s was select ed from t he Opt ions m enu. This creat ed an addit ional colum n in t he X- Y coordinat es sect ion in which t he Manning's n values were ent ered at t he locat ions along t he widt h of t he cross sect ion where t he n values change. For t his specific cross sect ion, t he n values only changed at t he left and right over bank locat ions. Therefore, t his horizont al variat ion opt ion was not necessary. The n values could have been ent ered direct ly on t he right side of t he dat a edit or in t he LOB, Channel, and ROB fields. This opt ion was m erely select ed t o display t his possibilit y. Figure 3-2: Cross Section Data Editor Addit ionally, on t he right side of t he dat a edit or, t he left and right st at ions of t he m ain channel were ent ered. For t his cross sect ion, t he left side of t he m ain channel is defined t o st art at st at ion 972 and end at t he right st at ion of 1027 feet . Finally, t he cont ract ion and expansion coefficient s were ent ered as 0.3 and 0.5, respect ively. These coefficient s are used by t he program t o det erm ine t he energy losses due t o t he flow cont ract ing or expanding as it t ravels from one cross sect ion t o t he next . Typical values of t hese coefficient s for gradual t ransit ions are 0.1 and 0.3 for cont ract ions and expansions, respect ively. However, at locat ions where t here are sudden changes in t he cross sect ion geom et ry ( i.e., flow int o or out of a culvert or bridge opening) , t he coefficient s m ay t ake larger values. The select ion of t hese coefficient s is 3-3 Exam ple 4 Mult iple Culvert s discussed in det ail in Chapt er 3 of t he H ydr a ulic Re fe r e nce M a nua l. For t his cross sect ion ( being t he sect ion im m ediat ely upst ream of t he culvert opening) , t he coefficient s were init ially select ed as 0.3 and 0.5 for t he cont ract ion and expansion, respect ively. Aft er t he flow analysis, ranges for t hese values were det erm ined by using t he m et hods out lined in t he HEC- 1995 research docum ent . These ranges were com pared t o t he select ed values and will be discussed near t he end of t his exam ple. The cross- sect ion inform at ion for t he ot her river st at ions were ent ered in a sim ilar fashion as for river st at ion 20.238. Finally, t he ineffect ive flow areas of t he cross sect ions were ent ered. This opt ion allows t he user t o define areas of t he cross sect ion t hat will cont ain wat er but t he wat er is not flowing in t he downst ream direct ion. This opt ion is t ypically used at cross sect ions in t he vicinit y of a culvert or bridge. For t his exam ple, t he ineffect ive flow opt ion was used at river st at ion 20.238 ( locat ed im m ediat ely upst ream of t he culvert ) and at river st at ion 20.227 ( locat ed im m ediat ely downst ream of t he culvert ) . From t he Cr oss Se ct ion D a t a Edit or , select Rive r St a t ion 20.238, Opt ion s, and t hen I n e ffe ct ive Flow Ar e a s. This will display t he I n e ffe ct ive Flow Edit or shown in Figure 3.3. River st at ion 20.238 was surveyed at a locat ion 5 feet upst ream from t he culvert . Typically, t he st at ioning of t he ineffect ive flow areas are set on a 1: 1 rat io t o t he dist ance from t he opening. When t he culvert dat a are ent ered, t he cent erline st at ions of t he t wo culvert s will be 996 and 1004 feet and each culvert will be 6 feet in diam et er. Therefore, t he left edge of t he opening is at st at ion 993 and t he right edge is at st at ion 1007. Using t he 1: 1 rat io, t he left ineffect ive flow st at ion was set t o be equal t o 5 feet left of t he left opening. Sim ilarly, t he right ineffect ive flow st at ion was set t o be equal t o 5 feet right of t he right side of t he openings. These values were ent ered as 988 and 1012 feet for t he left and right st at ions, respect ively. Finally, t he elevat ion of t he ineffect ive flow area was set t o be equal t o 33.7 feet , a value slight ly lower t han t he high cord on t he upst ream side of t he roadway. Sim ilarly, ineffect ive flow areas were set at cross sect ion 20.227 at st at ions of 991 and 1009 ( since t his cross sect ion was only 2 feet downst ream of t he culvert out let ) and at an elevat ion of 33.3 feet . The locat ion of t hese ineffect ive flow areas will be discussed furt her during t he analysis of t he out put . Typically, t he culvert inform at ion m ay be ent ered first and t hen t he m odeler can ent er t he locat ion of t he ineffect ive flow areas m ore readily wit h t he locat ion of t he culvert s known. Cross Section Placement From t he Geom et ric Dat a Edit or, select Tables and t hen Reach Lengt hs. This will display t he t able shown in Figure 3.4. Figure 3.4 displays t he init ial placem ent of t he cross sect ions as obt ained from t he field dat a available for t he analysis. ( The figure does not show t he inclusion of river st at ion 20.208* which will be added subsequent ly.) 3-4 Exam ple 3 Single Culvert - Single Bridge Figure 3-3: Ineffective Flow Editor at River Station 20.238 Figure 3-4: Reach Lengths Table For Spring Creek The placem ent of t he cross sect ions relat ive t o t he locat ion of t he culvert is crucial for accurat e predict ion of expansion and cont ract ion losses. The culvert rout ine ( as does t he bridge rout ine) ut ilizes four cross sect ions specifically locat ed on bot h sides of t he st ruct ure t o det erm ine t he energy losses t hrough t he culvert . ( Addit ionally t he program will int erpret t wo cross sect ions inside of t he culvert by superim posing t he culvert and roadway dat a ont o bot h t he im m ediat e downst ream and im m ediat e upst ream cross sect ions from t he culvert .) The following is a brief sum m ary for det erm ining t he locat ions of t he four cross sect ions. This procedure is ident ical t o t he procedure used for det erm ining t he cross sect ion locat ions for a bridge analysis. The m odeler should review t he discussion in Chapt er 6 of t he Use r 's M a n u a l and Chapt er 6 of t he H ydr a ulic Re fe r e nce M a nu a l for furt her discussion. 3-5 Exam ple 4 Mult iple Culvert s Fir st Cr oss Se ct ion . I deally, t he first cross sect ion should be locat ed sufficient ly downst ream from t he culvert so t hat t he flow is not affect ed by t he st ruct ure ( i.e., t he flow has fully expanded) . This dist ance, referred t o as t he expansion lengt h ( Le) , should be det erm ined by: field invest igat ion during high flows; t he procedure out lined in a recent st udy by t he USACE [ HEC1995] ; or ot her accept able procedure. For t his exam ple, t he crit eria developed by USACE [ HEC- 1995] research docum ent was ut ilized t o det erm ine t he expansion reach lengt h. To ut ilize t his m et hod, an init ial lengt h was est im at ed from values obt ained in t ables t hat are present ed in t he docum ent and provided in Appendix B of t he H ydr a u lic Re fe r e n ce M a n ua l. Then, aft er t he flow analysis was com plet ed, t he locat ion was evaluat ed based on equat ions developed from t he research. ( This evaluat ion will be discussed near t he end of t his exam ple.) First , t he following crit eria were required t o det erm ine t he locat ion of t he first cross sect ion: n ob / n c = 0.1 / 0.04 = 2.5 b/B = 14/145 = 0.10 S = (0.20/200 ) ⋅ 5280 = 5.28 ft / mile L obs = [(993 − 925) + (1070 − 1007 )] / 2 = 70 ft. where: n ob = Manning's n value for t he overbank at cross sect ion 20.251 nc = Manning's n value for t he m ain channel at cross sect ion 20.251 b = culvert opening widt h, ft ( m ) B = t ot al floodplain widt h, ft ( m ) S = slope, ft / m ile L obs = average lengt h of t he side obst ruct ion, ft Subst it ut ion of t he field dat a yields t he result s as shown above. Wit h t hese values, t he expansion rat io ( ER) was det erm ined t o range from 0.8 t o 2.0 from Table B- 1 in Appendix B of t he H ydr a u lic Re fe r e n ce M a n u a l. The expansion rat io ( ER) , is t he lengt h of expansion ( Le) divided by t he average lengt h of obst ruct ion ( Lobs) . For t his exam ple, an average value of 1.4 was init ially used for t he expansion rat io. Therefore, t he expansion reach lengt h will be t he expansion rat io t im es t he average lengt h of obst ruct ion: L e = (ER )(Lobs ) = (1.4)(70) = 100 ft 3-6 Exam ple 3 Single Culvert - Single Bridge From t he init ial values of t he cross sect ion locat ions, t he expansion reach lengt h is t he dist ance from cross sect ion 20.227 t o 20.189. This dist ance is init ially set at 200 feet . From t he above analysis, it was det erm ined t hat t he dist ance should be approxim at ely 100 feet . Therefore, an addit ional cross sect ion was placed 100 feet downst ream from cross sect ion 20.227. To produce t his cross sect ion, field dat a should be ut ilized. I f t his dat a is not available, t hen t he program has t he abilit y t o int erpolat e a cross sect ion. From t he Ge om e t r ic D a t a Edit or , Tools, XS I n t e r pola t ion , and t hen Be t w e e n 2 XS's were select ed. " Culvrt Reach" was select ed as t he river reach ( t he only reach in t his exam ple) and river st at ion 20.227 was ent ered as t he upper river st at ion ( t his will default t o river st at ion 20.189 as being t he lower river st at ion) . The m axim um dist ance bet ween t he int erpolat ed cross sect ions was set t o be 100 feet and t hen t he int erpolat ion was perform ed. This result ed in t he display shown in Figure 3.5. For addit ional inform at ion on cross sect ion int erpolat ion, refer t o Chapt er 4 of t he H ydr a u lic Re fe r e n ce M a n u a l and Chapt er 6 of t he Use r 's M a n ua l. The int erpolat ion window was closed and t he river schem at ic displayed t he new int erpolat ed cross sect ion at river st at ion 20.208* ( as shown in Figure 3.1) . The num ber 20.208 was t he default set t ing since t he dist ance chosen ( 100 ft ) was equal t o one half t he previous reach lengt h ( 200 ft ) . Figure 3-5: Cross Section Interpolation Aft er int erpolat ing t he new river st at ion, from t he Ge om e t r ic D a t a Edit or Ta ble s and t hen Re a ch Le n gt h s were select ed. This result ed in t he t able shown in Figure 3.4 except t hat t he int erpolat ed cross- sect ion 20.208* appeared and t he dist ances from cross sect ion 20.227 t o 20.208* were 100 3-7 Exam ple 4 Mult iple Culvert s feet and from 20.208* t o 20.189 were also 100 feet for t he LOB, channel, and ROB. The program now considered cross sect ion 20.208* as being t he locat ion of t he fully expanded cross sect ion. Se con d Cr oss Se ct ion . The second cross sect ion used by t he program t o analyze t he energy losses t hrough t he culvert is locat ed wit hin a few feet downst ream of t he st ruct ure. This sect ion should be close t o t he culvert ( wit hin a few feet ) and reflect t he effect ive flow area on t he downst ream side of t he culvert . Therefore, any ineffect ive flow areas out side of t he flow expanding out of t he culvert , should not be used for conveyance calculat ions. For t his exam ple, cross sect ion 20.227 was locat ed t wo feet downst ream from t he culvert . The ineffect ive flow areas were developed previously using t his dist ance. Finally, aft er t he culvert and roadway geom et ry were ent ered, t he program superim posed t he geom et ry ont o t his cross sect ion t o develop a cross sect ion inside t he culvert at t he downst ream end. Th ir d Cr oss Se ct ion. The t hird cross sect ion is locat ed wit hin a few feet upst ream from t he culvert and should reflect t he lengt h required for t he abrupt accelerat ion and cont ract ion of t he flow t hat occurs in t he im m ediat e area of t he opening. Sim ilar t o t he second cross sect ion, t his cross sect ion should also block t he ineffect ive flow areas on t he upst ream side of t he culvert . For t his exam ple, cross sect ion 20.238 was locat ed five feet upst ream of t he culvert . Sim ilar t o t he second cross sect ion, t he program will superim pose t he culvert geom et ry ont o t he t hird cross sect ion t o develop a cross sect ion inside t he culvert at t he upst ream end. Four t h Cr oss Se ct ion . The fourt h cross sect ion is locat ed upst ream from t he culvert where t he flow lines are parallel and t he cross sect ion exhibit s fully effect ive flow. The dist ance bet ween t he t hird and fourt h cross sect ion, referred t o as t he cont ract ion reach lengt h, can be det erm ined by: 1) field invest igat ion during high flows, 2) t he procedure out lined in a recent st udy by t he USACE [ HEC- 1995] ; or 3) ot her accept able procedure. For t his exam ple, t he crit eria developed by USACE [ HEC- 1995] research docum ent was ut ilized t o det erm ine t he cont ract ion reach lengt h. To ut ilize t his m et hod, an init ial lengt h was est im at ed from values obt ained in Table B.2 in Appendix B of t he H ydr a u lic Re fe r e n ce M a n ua l. To use t his m et hod, t he following crit eria were necessary: nob / nc = 0.1 / 0.04 = 2.5 S = 0.20 / 200 ⋅ 5280 = 5.28 ft / mile where t he variables are as described previously. Subst it ut ion of t he values yields t he result s as shown above. Wit h t hese values, t he cont ract ion rat io ( CR) was det erm ined t o range from 0.8 t o 1.5 from Table B- 2. The cont ract ion rat io is t he lengt h of cont ract ion ( Lc) divided by t he average lengt h of obst ruct ion. For t his exam ple, an average value of 1.15 was used for t he cont ract ion rat io. Therefore, t he cont ract ion reach lengt h will be t he cont ract ion rat io t im es t he average lengt h of obst ruct ion: Lc = (CR )(Lobs ) = (1.15)(70) = 80 ft. From t he init ial values of t he cross sect ion locat ions, t he cont ract ion reach lengt h is t he dist ance from cross sect ion 20.251 t o 20.238. This dist ance was 3-8 Exam ple 3 Single Culvert - Single Bridge init ially set at 70 feet . From t he above analysis, it was det erm ined t hat t he dist ance should be approxim at ely 80 feet . Because t hese values are so close t oget her, t he init ial value of 70 feet will be m aint ained. Finally, aft er t he flow analysis was perform ed, t he locat ion of t his cross sect ion was evaluat ed and will be discussed near t he end of t his exam ple. Culvert Data From t he Ge om e t r ic D a t a Edit or , t he Br idge / Cu lve r t icon was select ed. This act ivat ed t he Br idge Cu lve r t D a t a Edit or . To ent er t he culvert dat a, Opt ion s and t hen Add a Br idge a n d/ or Cu lve r t were first select ed. The locat ion for t he culvert was ent ered as 20.237. Then, t he bounding river st at ions ( 20.227 and 20.238) appeared on t he Br idge Cu lve r t D a t a Edit or . Next , t he deck/ roadway dat a and t hen t he culvert geom et ric dat a were ent ered. Each of t hese are discussed in t he following sect ions. D e ck / Roa dw a y D a t a . To ent er t he dat a for t he deck/ roadway, t he D e ck / Roa dw a y icon on t he left side of t he Br idge Cu lve r t D a t a Edit or was select ed. This act ivat ed t he D e ck / Roa dw a y D a t a Edit or as shown in Figure 3.6. Along t he t op row of t he deck/ roadway dat a edit or, t he user m ust first ent er t he dist ance from t he upst ream side of t he deck/ roadway t o t he cross sect ion t hat is placed im m ediat ely upst ream of t he culvert ( cross sect ion 20.238 for t his exam ple) . This dist ance was set at 10 feet . The next field is t he widt h of t he roadway. For t his exam ple, t his dist ance was 40 feet . The program will t hen add t he 10 feet and t he 40 feet t o obt ain 50 feet as t he dist ance from cross sect ion 20.238 t o t he downst ream end of t he deck/ roadway. From t he cross sect ion geom et ric dat a, t he dist ance from cross sect ion 20.238 t o 20.227 was 57 feet . This allowed for 7 feet of dist ance from t he downst ream side of deck/ roadway t o cross sect ion 20.227. The final field along t he t op row is t he weir coefficient . This coefficient is used when t he flow overt ops t he roadway and weir flow occurs. For t his exam ple, a value of 2.6 was select ed as t he weir coefficient for t he roadway. This value m ay be changed t o account for t he shape of t he roadway and t he degree of obst ruct ions along t he edge of t he roadway. Addit ional inform at ion on weir flow is present ed in Chapt er 6 of t he H ydr a ulics Re fe r e nce M a nua l. 3-9 Exam ple 4 Mult iple Culvert s Figure 3-6: Deck/Roadway Data Editor The cent ral port ion of t he edit or consist s of fields t o ent er t he st at ions and elevat ions of t he deck/ roadway. The values for t his exam ple are as shown in t he figure. I f t he upst ream and downst ream decking is ident ical, t hen t he user needs t o only ent er t he upst ream inform at ion and t hen select Copy Up t o D ow n. ( Not e: For culvert s, only t he high cord inform at ion is required. The program will aut om at ically block out t he area bet ween t he high cord and t he ground. For a bridge analysis, t he low cord inform at ion is required t o define t he bridge opening. For a culvert analysis, t he culvert dat a will define t he openings below t he high cord for t he locat ions of t he culvert s.) The next t wo fields are t he US a nd D S Em ba nk m e nt Side Slope s. These values were ent ered as 2 ( horizont al t o 1 vert ical) . For a culvert analysis, t hese values are only used for t he profile plot . The bot t om of t he edit or consist s of t hree addit ional fields. The first field is t he M a x im u m Allow a ble subm e r ge n ce rat io. This is t he rat io of downst ream flow dept h t o upst ream energy, as m easured from t he m inim um high cord of t he deck. When t his rat io is exceeded for a bridge analysis, t he program will swit ch from t he weir flow equat ion t o t he energy m et hod t o det erm ine t he upst ream flow dept h. For a culvert analysis, t his rat io is not used because t he program cannot perform a backwat er analysis t hrough a culvert flowing full. Therefore, t he weir analysis m et hod will always be used when overflow occurs. The second field is t he M in im um W e ir Flow Ele va t ion. This is t he elevat ion t hat t he program uses t o det erm ine when weir flow will begin. I f t his field is left blank, t he program will use t he lowest value of t he high cord on t he 3-10 Exam ple 3 Single Culvert - Single Bridge upst ream side of t he deck. Alt ernat ively, t he user can ent er a value for t he program t o st art checking for t he possibilit y of weir flow. For t his exam ple, an elevat ion of 33.7 feet was used. This is t he elevat ion of t he roadway above t he culvert openings on t he upst ream side of t he culvert . ( Not e: This is also t he m inim um elevat ion of t he high cord and t herefore, t his field could have been left blank.) Finally, t he last field requires t he select ion of t he weir crest shape: broad crest ed or ogee shaped. This select ion is used for t he t ype for subm ergence correct ion. For t his exam ple, a broad crest ed weir shape subm ergence correct ion was used. Wit h all of t he dat a ent ered, t he OK but t on was select ed t o exit t he D e ck / Roa dw a y D a t a Edit or . Culve r t Ge om e t r ic D a t a . To ent er t he culvert geom et ric dat a, from t he Br idge Cu lve r t D a t a Edit or , t he Cu lve r t icon was select ed. This act ivat ed t he Cu lve r t D a t a Edit or as shown in Figure 3.7. Each of t he fields for t he edit or are described in t he following sect ions. Culvert I D - By default , t he ident ifier for t he first culvert will be set t o " Culvert # 1." A culvert t ype is defined by t he shape, diam et er ( or rise and span) , chart num ber, scale, lengt h, n value, loss coefficient s, upst ream invert , and downst ream invert . I f all of t hese param et ers are t he sam e for each culvert , t hen t he m odeler will only have one culvert t ype. Then t he m odeler can ent er up t o 25 ident ical barrels for t his culvert t ype, wit h each barrel occurring at a different locat ion ( defined by t he upst ream cent erline and downst ream cent erline) . I f any of t he culvert param et ers change, t hen t he m odeler m ust define each culvert t hat is different as a separat e t ype ( t o a m axim um of 10 culvert t ypes at t he sam e river st at ion) , wit h each t ype cont aining up t o 25 ident ical barrels. For t his exam ple, t he culvert consist ed of only 1 culvert t ype ( since all of t he param et ers were t he sam e for each barrel) but it cont ained t wo ident ical barrels ( wit h each placed at separat e upst ream and downst ream cent erline locat ions) . Solut ion Crit eria - The user has t he opt ion t o select t o use t he result for inlet cont rol or out let cont rol as t he final answer for t he upst ream energy grade line value. The default m et hod is t o use t he highest of t he t wo values, as was select ed for t his exam ple. Shape - The culvert shape is chosen from t he eight available shapes: circular, box, ellipt ical, arch, pipe arch, sem i- circle, low arch, or high arch. For t his exam ple, t he culvert barrels were circular shape. To select t he shape, press t he down arrow on t he side of t he shape field and highlight t he desired shape. 3-11 Exam ple 4 Mult iple Culvert s Figure 3-7: Culvert Data Editor Diam et er, Rise, or Rise and Span - Depending on t he shape of t he culvert , t he m odeler m ust ent er t he inside dim ensions of t he culvert . For a circular pipe, only t he diam et er is required. For ot her shapes, t he rise is defined as t he inside vert ical m easurem ent and t he span is t he inside horizont al m easurem ent . ( Not e: For box culvert s wit h cham fered corners, refer t o t he discussion in Chapt er 6 of t he H ydr a u lic Re fe r e n ce M a nu a l.) For t his exam ple, t he circular culvert was set t o have a diam et er of 6 feet . Chart # - Each culvert t ype and shape is defined by a Federal Highway Adm inist rat ion Chart Num ber. Depress t he down arrow next t o t his field t o select t he appropriat e chart num ber. Once a culvert shape has been select ed, only t he corresponding chart num bers available for t hat culvert shape will appear in t he select ions. Descript ions for t he chart num bers appear in Chapt er 6 in t he H ydr a u lic Re fe r e n ce M a n ua l. For t his exam ple, t he culvert chart was select ed as " 1 - Concret e Pipe Culvert ." Scale - This field is used t o select t he Federal Highway Adm inist rat ion scale t hat corresponds t o t he select ed chart num ber and culvert inlet shape. Only t he scale num bers which are available for t he select ed chart num ber will appear for select ion. Descript ions for t he scale num bers appear in Chapt er 6 in t he H ydr a u lic Re fe r e n ce M a n ua l. The scale for t his exam ple was " 1 Square edge ent rance wit h head wall." Dist ance t o Upst ream XS - This is t he dist ance from t he inlet of t he culvert t o t he upst ream cross sect ion ( 20.238) . For t his exam ple, t his was a dist ance of 5 feet . On t he D e ck / Roa dw a y D a t a Edit or , a m easure of 10 feet was ent ered for t he dist ance from t he upst ream side of t he deck/ roadway t o t he 3-12 Exam ple 3 Single Culvert - Single Bridge upst ream cross sect ion. Therefore, t he culvert ent rance is locat ed m idway bet ween t he upst ream side of t he roadway and cross sect ion 20.238. Lengt h - This field is t he m easure of t he culvert ( in feet or m et ers) along t he cent erline of t he barrel. The lengt h of t he culvert for t his exam ple was 50 feet . The program will add t his 50 feet t o t he 5 foot dist ance from cross sect ion 20.238 ( t o t he culvert ent rance) and obt ain 55 feet . The reach lengt h from cross sect ion 20.238 t o 20.227 is 57 feet , which leaves 2 feet from t he exit of t he culvert t o t he downst ream cross sect ion. Ent rance Loss Coefficient - The value of t he ent rance loss coefficient will be m ult iplied by t he velocit y head at t he inside upst ream end of t he culvert t o obt ain t he energy loss as t he flow ent ers t he culvert . Typical values for t he ent rance loss coefficient can be obt ained from Tables 6.3 and 6.4 in t he H ydr a u lic Re fe r e n ce M a n ua l. The ent rance loss coefficient for t he concret e pipe in t his exam ple was set at 0.5. Exit Loss Coefficient - To det erm ine t he am ount of energy lost by t he wat er as it exit s t he culvert , t he exit loss coefficient will be m ult iplied by t he difference of t he velocit y heads from j ust inside t he culvert at t he downst ream end t o t he cross sect ion locat ed im m ediat ely downst ream of t he culvert exit . I n general, for a sudden expansion, t he exit loss coefficient should be set equal t o 1. However, t his value m ay range from 0.3 t o 1.0. For t his exam ple, t he exit loss coefficient was set t o be equal t o 1.0. Manning’s n for Top - This field is used t o ent er t he Manning's n value of t he t op and sides of t he culvert lining and is used t o det erm ine t he frict ion losses t hrough t he culvert barrel. Suggest ed n values for culvert linings are available in m any t ext books and also m ay be obt ained from Table 6.1 in t he H ydr a u lic Re fe r e n ce M a n ua l. Roughness coefficient s should be adj ust ed according t o individual j udgm ent of t he culvert condit ion. For t his exam ple, a Manning's n value of 0.013 was used for t he concret e culvert . Manning’s n Value for Bot t om – This field is used t o ent er t he Manning’s n value of t he bot t om of t he culvert . For m ost culvert s, t his field will be t he sam e as t he Manning’s n value for t he t op. However, if t he culvert has a nat ural bot t om , or som et hing has been placed in t he bot t om for fish passage, t he n value m ay vary. Dept h t o use Bot t om n – This field is used t o ent er a dept h inside of t he culvert t hat t he bot t om n value is applied t o. I f t he bot t om and t op n value are t he sam e, a value of zero should be ent ered. Dept h Blocked – This field is used t o fill in a port ion of t he culvert . The user ent ers a dept h, and everyt hing below t hat dept h is blocked out . Upst ream and Downst ream I nvert Elevat ion - These t wo fields are used t o ent er t he elevat ions of t he invert s. For a part icular culvert t ype, all of t he ident ical barrels will have t he sam e upst ream invert elevat ion and downst ream invert elevat ion. For t his exam ple, t he upst ream invert was set at an elevat ion of 25.1 feet and t he downst ream invert was 25.0 feet . Cent erline St at ions - This t able is used t o ent er t he st at ioning ( X- coordinat es) of t he cent erline of t he culvert barrels. The upst ream cent erline is based 3-13 Exam ple 4 Mult iple Culvert s upon t he X- coordinat es of t he upst ream cross sect ion ( 20.238) and t he downst ream cent erline is based upon t he X- coordinat es of t he downst ream cross sect ion ( 20.227) . This exam ple em ploys t wo culvert barrels, wit h t he cent erline of t he barrels occurring at st at ions 996 and 1004 feet , as m easured on bot h cross sect ions. For t his exam ple, t he X- coordinat e geom et ry of bot h cross sect ion 20.238 and cross sect ion 20.227 are referenced from t he sam e left st at ion st art ing point . Therefore, t he upst ream and downst ream cent erline st at ions are t he sam e value and t his will align t he culvert in t he correct configurat ion as being parallel t o t he channel. The m odeler m ust be caut ious t o ensure t hat t he cent erline st at ioning of t he culvert ends align t he culvert in t he correct posit ion. # I dent ical barrels - This field will aut om at ically display t he num ber of barrels ent ered by t he user ( det erm ined by t he num ber of cent erline st at ions ent ered) . Up t o 25 ident ical barrels can be ent ered for each culvert t ype, and t his exam ple consist ed of 2 ident ical barrels. This com plet ed t he necessary geom et ric dat a for t he analysis. The OK but t on at t he bot t om of t he Culve r t D a t a Edit or was select ed and t his displayed t he culvert as shown in Figure 3.8. The geom et ry dat a edit ors were t hen closed and t he geom et ry was saved as " Mult iple Pipe Geom et ry." Figure 3-8: Bridge/Culvert Data Editor For Spring Creek 3-14 Exam ple 3 Single Culvert - Single Bridge Steady Flow Data To perform t he st eady flow analysis t hrough t he culvert , t he user m ust ent er t he flow dat a and boundary condit ions for each flow profile. Each of t hese com ponent s is discussed below. Flow Data To ent er t he flow dat a, from t he m ain program window Edit and t hen St e a dy Flow D a t a were select ed. This act ivat ed t he St e a dy Flow D a t a Edit or as shown in Figure 3.9. For t his exam ple, 3 flow profiles were com put ed. A value of " 3" was ent ered as t he num ber of profiles and t he cent ral t able of t he edit or est ablished t hree colum ns for t he flow profiles. The flow values were t hen ent ered at t he upst ream river st at ion ( 20.535) as t he values of 250, 400, and 600 cfs. Addit ionally, t he profile nam es were changed t o be " 5 yr," " 10 yr," and " 25 yr." Figure 3-9: Steady Flow Data Editor Boundary Conditions To ent er t he boundary condit ions t he Bou n da r y Con dit ion s icon at t he t op of t he St e a dy Flow D a t a Edit or was select ed. This act ivat ed t he Bou nda r y Condit ion s Edit or as shown in Figure 3.10. This flow analysis was perform ed in t he subcrit ical flow regim e. Therefore, a boundary condit ion was est ablished at t he downst ream end of t he reach for each flow profile. For a det ailed discussion on t he boundary condit ions, t he m odeler is referred t o Chapt er 7 of t he Use r 's M a nua l and Chapt er 3 of t he H ydr a u lic Re fe r e n ce M a n u a l. From t he Boundary Condit ions Dat a Edit or, t he boundary condit ions were ent ered by first select ing t he Down St ream field and t hen 3-15 Exam ple 4 Mult iple Culvert s Kn ow n W . S. This act ivat ed t he known wat er surface boundary condit ion window as shown in Figure 3.11. Figure 3-10: Boundary Conditions Data Editor Figure 3-11: Known Water Surface Boundary Conditions As shown in Figure 3.11, a known wat er surface elevat ion was t hen ent ered for each of t he flow profiles t hat were com put ed. For t his exam ple, t he known wat er surface elevat ions of 29.8, 31.2, and 31.9 were ent ered for t he flows of 250, 400, and 600 cfs, respect ively. Once t he dat a were ent ered, t he OK but t on was select ed t o exit t his window. This com plet ed t he necessary st eady flow dat a for t he analysis and t he dat a were saved as " Mult iple Pipe Flow Dat a." Steady Flow Analysis To perform t he st eady flow analysis, from t he m ain program window Run and t hen St e a dy Flow Ana lysis were select ed. This act ivat ed t he St e a dy Flow 3-16 Exam ple 3 Single Culvert - Single Bridge Ana lysis W in dow as shown in Figure 3.12. A sh or t I D was ent ered as " Base Plan" and a subcrit ical flow analysis was select ed in t he lower left corner of t he edit or. From t he Opt ion s m enu, t he Se t Out pu t Opt ion s was select ed and t hen an " x" was placed next t o Cr it ica l Alw a ys Ca lcu la t e d. This will cause t he program t o always calculat e crit ical dept h at every cross sect ion. This will add com put at ional t im e t o larger analyses; however, t his will enable t he user t o view t he crit ical flow dept h along t he river reach. Addit ionally, from t he Opt ion s m enu, ensure t hat t here is a " " adj acent t o t he opt ion Ch e ck da t a be for e e x e cu t ion . Wit h t his opt ion, t he program will check t o ensure t hat all pert inent inform at ion is present before t he analysis is perform ed. I t cannot det erm ine t he accuracy of t he dat a. ( Not e: I f t here is a check m ark next t o t his opt ion, a select ion of t his opt ion will rem ove t he check m ark.) Finally, t he geom et ry file " Mult iple Pipe Geom et ry" and t he st eady flow file " Mult iple Pipe Flow Dat a" were saved as t he plan " Spring Creek Culvert s" , wit h a shirt I D of " Base Plan." Then, t he COM PUTE but t on was select ed t o perform t he st eady flow analysis. Figure 3-12: Steady Flow Analysis Window Output Analysis For t he analysis of t he out put , t he m odeler has various opt ions t o review t he dat a. For t his analysis, evaluat ions were perform ed for t he expansion and cont ract ion reach lengt hs and t he channel cont ract ion and expansion coefficient s. Then, t he wat er surface profiles were reviewed. Expansion and Contraction Reach Length Evaluation I nit ially t he reach lengt hs were det erm ined using t able values obt ained from t he U.S. Arm y Corps of Engineers' research docum ent [ HEC- 1995] and t he cross sect ions 20.208* and 20.251 were locat ed based on t hese init ial values. The t able values provided a range and t he average values were init ially used. Wit h t he program out put , t he equat ions developed in t he docum ent were ut ilized t o evaluat e t he locat ions ( and reach lengt hs) t hat were select ed. The 3-17 Exam ple 4 Mult iple Culvert s m odeler should be aware t hat t he regression equat ions were developed based on low flow condit ions for bridges and t he equat ions m ay not be pract ical for analyses of flow t hrough culvert s. Ex pa n sion Re a ch Le ngt h . Cross sect ion 20.208* was t he int erpolat ed sect ion t hat was assum ed t o be at t he locat ion where t he flow becam e fully expanded. To evaluat e t he locat ion of t his cross sect ion, t he relat ionship shown as Equat ion 3- 1 was used. Equat ion 3- 1 is applicable when t he widt h of t he floodplain and t he discharge is less t han t hose of t he regression dat a. The equat ion is: ER = where: ⎞ ⎛F Le = 0.421 + 0.485⎜⎜ 20.227 ⎟⎟ + 0.000018Q Lobs ⎝ F20.208* ⎠ ER = expansion ratio Le = expansion reach lengt h, ft Lobs = average lengt h of side obst ruct ion, ft F20.227 = ( 3- 1) m ain channel Froude num ber at t he cross sect ion im m ediat ely downst ream of t he culvert ( cross sect ion 20.227 for t his exam ple) F20.208* = m ain channel Froude num ber at t he cross sect ion of fully expanded flow ( cross sect ion 20.208* for t his exam ple) Q = t ot al discharge, ft 3/ s ( Not e: The subscript s used in Equat ion 3- 1 and all subsequent equat ions reflect t he river st at ion num bering for t his exam ple.) From t he analysis, t he Froude num bers at cross sect ions 20.227 and 20.208* , for t he flow of 600 cfs, are 0.32 and 0.14, respect ively. Subst it ut ing t hese values int o Equat ion 3- 1 yields an expansion rat io of 1.51. This value falls wit hin t he range of 0.8 – 2.0 as det erm ined previously from t he t able values. Wit h t his new expansion rat io, t he expansion reach lengt h is: Le = (ER )(Lobs ) = (1.51)(70 ) = 106 ft Addit ionally, t he expansion rat io has a st andard error of 0.26. Using t he range of t he ER from 1.25 ( = 1.51 - 0.26) t o 1.77 ( = 1.51 + 0.26) yields an Le range from 88 t o 124 feet t o define t he 68% confidence band for Equat ion 3- 1. The act ual dist ance from cross sect ion 20.227 t o cross- sect ion 20.208* was set at 100 feet . Therefore, t he exist ing expansion reach lengt h seem s appropriat e. I f t he exist ing lengt h had been significant ly out side of t he range of t he calculat ed expansion reach lengt h, t hen a second it erat ion for t he placem ent of t he fully expanded cross sect ion and an addit ional analysis m ay be warrant ed. As a final check, t he expansion rat io should not exceed 4: 1 and should not be less t han 0.5: 1. 3-18 Exam ple 3 Single Culvert - Single Bridge Con t r a ct ion Re a ch Le n gt h . Cross sect ion 20.251 is locat ed where t he flow lines are parallel t o t he m ain channel. To evaluat e t his locat ion, Equat ion 3- 2 from t he research docum ent [ HEC- 1995] was ut ilized. This equat ion is used when t he floodplain scale and dischargers are significant ly different t han t hose used in t he regression analysis and is: ⎞ ⎛F ⎛Q CR = 1.4 − 0.333⎜⎜ 20.227 ⎟⎟ + 1.86⎜⎜ ob ⎝ Q ⎝ F20.208* ⎠ where : CR = Lc = 2 ⎛n ⎞ ⎟⎟ − 0.19⎜⎜ ob ⎠ ⎝ nc ⎞ ⎟⎟ ⎠ 0.5 ( 3- 2) contraction ratio contraction reach length Qob = discharge conveyed by the two overbanks at cross section 20.251, cfs Q total discharge, cfs = nob = Manning's n value of the overbanks at cross section 20.251 nc Manning's n value for the main channel at cross section 20.251 = From t he analysis of t he 600 cfs profile, t he flow in t he t wo overbanks at cross sect ion 20.251 is 69.33 cfs and t he Manning's n values for t he overbanks and m ain channel at cross sect ion 20.251 are 0.10 and 0.04, respect ively. Subst it ut ing t hese values int o Equat ion 3- 2 yields a cont ract ion rat io of 0.39. The st andard error for t his equat ion is 0.19 which yields a range of t he CR from 0.20 t o 0.58. From t he result s cit ed in t he research docum ent , a m inim um cont ract ion rat io is 0.3: 1 and a m axim um rat io is 2.5: 1. The calculat ed average value of 0.39 is very close t o t he m inim um value. I f t his value is used, t he cont ract ion reach lengt h would be: Le = (CR )(Lobs ) = (0.39 )(70) = 27 feet This is t he m edian value for t he range of 14 t o 41 feet ( using CR = 0.20 and 0.58, respect ively) . The act ual dist ance used for t he cont ract ion reach lengt h ( t he lengt h from river st at ion 20.251 t o river st at ion 20.238) was 70 feet . For t his exam ple, t he cont ract ion reach lengt h was m aint ained at t he 70 feet value. However, an addit ional analysis was perform ed wit h t he 27 feet cont ract ion reach lengt h and no appreciable difference in t he wat er surface was observed t o reflect t he necessit y for t he change of t he cont ract ion reach lengt h t o 27 feet . Channel Contraction and Expansion Coefficients The coefficient s of cont ract ion ( Cc) and expansion ( Ce) are used t o det erm ine t he energy losses associat ed wit h t he changes in channel geom et ry. I nit ially, 3-19 Exam ple 4 Mult iple Culvert s in t he vicinit y of t he culvert , t he coefficient s were set at 0.3 and 0.5 for t he cont ract ion and expansion, respect ively. Each of t hese values will be evaluat ed. Ex pa n sion Coe fficie n t . The expansion coefficient can be obt ained from Equat ion 3- 3: ⎛D C e = −0.09 + 0.570⎜⎜ ob ⎝ Dc where : Ce = Dob = Dc = ⎞ ⎛F ⎞ ⎟⎟ + 0.075⎜⎜ 20.227 ⎟⎟ ⎠ ⎝ F20.208* ⎠ ( 3- 3) coefficient of expansion hydraulic dept h ( flow area divided by t he t op widt h) for t he overbank at cross sect ion 20.208* hydraulic dept h for t he m ain channel at cross sect ion 20.208* From t he analysis of t he 600 cfs profile, t he hydraulic dept hs for t he overbanks and t he m ain channel are 0.58 and 5.66 feet , respect ively. Subst it ut ion of t he values int o Equat ion 3- 3 yielded an expansion coefficient of 0.14. This is t he m edian value and t he range of ± 0.2 defines t he 95% confidence band for Equat ion 3- 3. For t his exam ple, a value of 0.5 was used. The value of t he expansion coefficient is generally larger t han t he value used for t he cont ract ion coefficient so t he value of 0.5 will rem ain as t he select ed value. The regression equat ion ( 3- 3) was developed for bridges wit h overbank areas larger t han t he current exam ple. Therefore, t he dat a for t his current exam ple m ay not be wit hin t he range of dat a used t o develop t he regression equat ion. The m odeler can perform a sensit ivit y of t his coefficient by changing t his coefficient and perform ing subsequent analyses. For t his exam ple, a value of 0.3 was used during a subsequent analysis and no appreciable difference was observed in t he result ing wat er surface. Con t r a ct ion Coe fficie n t . From t he research docum ent [ HEC- 1995] , t he cont ract ion coefficient is obt ained by first det erm ining t he relat ionship: b / B = 14 / 145 = 0.10 where : b = culvert opening widt h, ft ( m ) B = t ot al floodplain widt h, ft ( m ) From Table B- 3 of Appendix B in t he H ydr a u lic Re fe r e n ce M a n u a l, t he recom m ended cont ract ion coefficient range is 0.3 - 0.5. The value select ed for t his exam ple was t he m inim um value of 0.3, which reflect s a value in bet ween a t ypical cont ract ion and an abrupt cont ract ion. 3-20 Exam ple 3 Single Culvert - Single Bridge Water Surface Profiles From t he m ain program window, select Vie w and t hen W a t e r Sur fa ce Pr ofile s. This will result in t he display shown in Figure 3.13. I n t he figure, t he wat er surface elevat ions and t he energy gradelines are shown for all t hree flow profiles ( t he variables can be select ed from t he Opt ion s m enu) . As can be seen in t he figure, t he first flow of 250 cfs was able t o t ravel t hrough t he culvert wit hout subm erging t he ent rance. The second flow ( 400 cfs) caused t he headwat er and t ailwat er t o subm erge t he ent rance and exit of t he culvert , respect ively. Finally, t he t hird flow ( 600 cfs) caused an overt opping of t he roadway, which yielded weir flow. Figure 3-13: Water Surface Profiles For Spring Creek Culverts To invest igat e t he first flow profile, from t he m ain window select Vie w , Cr oss Se ct ion Ta ble , Type , and t hen Cu lve r t . Select t he river reach of " Culvrt Reach," river st at ion 20.237, profile 1, and culvert # 1. This will display t he t able shown in Figure 3.14. The left colum n of t he t able shows a t ot al flow rat e of 250 cfs t hrough t he culvert . Since t he culvert has t wo ident ical barrels, t his yields a flow of 125 cfs t hrough each barrel. The t able also shows t hat t he norm al dept h ( 3.56 ft ) was great er t han t he crit ical dept h ( 3.02 ft ) , which corresponds t o subcrit ical flow occurring t hrough t he culvert . At t he bot t om of t he left colum n, t he dat a shows t hat t he culvert did not flow full for any lengt h of t he culvert . Addit ional values such as t he velocit y in t he culvert at t he upst ream and downst ream ends are displayed. 3-21 Exam ple 4 Mult iple Culvert s Figure 3-14: Culvert Table For Flow=250 cfs To det erm ine t he cont rol of flow t hrough t he culvert ( i.e., inlet or out let ) , t he values of t he upst ream energy grade line necessary for inlet cont rol ( E.G. I C) and out let cont rol ( E.G. OC) are shown in t he left colum n of Figure 3.14. For t he specified flow of 250 cfs, t he upst ream energy grade line for inlet cont rol was 29.50 feet and t he upst ream energy grade line for out let cont rol was 30.57 feet . The program will select t he higher of t hese t wo values t o det erm ine which t ype of cont rol will occur ( since " Highest Upst ream EG" was select ed on t he Cu lve r t D a t a Edit or ) . For t his exam ple, out let cont rol occurred and t he energy gradeline used by t he program is list ed as t he energy grade line upst ream of 30.57 feet . Finally, by using t he values in Figure 3.14 and following t he decision flow chart shown as Figure 6.9 in t he H ydr a u lic Re fe r e n ce M a n ua l, t he m odeler can det erm ine t he procedure used by t he program t o det erm ine t he wat er surface profile. For t his flow of 250 cfs, t he program used t he Direct St ep Met hod t o calculat e t he wat er surface profile. For an analysis of t he second flow ( 400 cfs) , a sim ilar procedure can be followed. For t his exam ple, t he second flow result ed in full flow along t he 3-22 Exam ple 3 Single Culvert - Single Bridge ent ire lengt h of t he barrels of t he culvert . The upst ream wat er surface profile was det erm ined by using t he FHWA full flow equat ions. For t he t hird flow ( 600 cfs) , t he inlet and out let were subm erged and weir flow occurred over t he roadway. Select t he Cu lve r t t ype Cr oss Se ct ion Ta ble ( as perform ed for Figure 3.14) and select t he t hird flow profile. This will display t he t able shown in Figure 3.15. For t his profile, t he flow t hrough t he culvert was 526.53 cfs, 263.27 cfs t hrough each ident ical barrel. The energy grade line upst ream was calculat ed t o be 34.34 feet , which corresponds t o t he out let cont rol energy grade line as shown. The weir flow at river st at ion 20.237 result ed wit h a value of 600 - 526.53 = 73.47 cfs. This occurred from an X- coordinat e of 945.30 t o 1048.66, a dist ance of 103.36 feet . The m ain channel bank st at ions for cross sect ions 20.227 and 20.238 are at 972 and 1027. Therefore, t he weir flow from 945.3 t o 972 should balance wit h t he flow in t he LOB at river st at ions 20.227 and 20.238. Addit ionally, t he weir flow from 1027 t o 1048.66 should balance wit h t he flow in t he ROB at river st at ions 20.227 and 20.238. At river st at ion 20.237, t he am ount of weir flow from 945.3 t o 972 can be approxim at ed as: t he specific lengt h of weir divided by t he t ot al weir lengt h t im es t he weir flow. This was calculat ed as: (972.00 − 945.3) / (103.36) ⋅ (73.47 ) = 18.98cfs Sim ilarly, t he am ount of weir flow from 1027 t o 1048.66 is approxim at ely 15.4 cfs. Therefore, at river st at ions 20.227 and 20.238, t he flow in t he LOB should be approxim at ely 18.98 cfs and t he flow in t he ROB should be approxim at ely 15.4 cfs. To det erm ine t he am ount of flow in t he overbanks at cross sect ion 20.227, from t he Cr oss Se ct ion Ta ble window, select Type and t hen Cr oss Se ct ion . Toggle t o river st at ion 20.227 for t he t hird flow profile. The values for t he flow in t he LOB and ROB are zero at t his cross sect ion. By t oggling t o river st at ion 20.238, it was observed t hat t he flows in t he LOB and ROB were 36.2 and 34.31 cfs, respect ively. Therefore, t hese flow values in t he LOB and ROB for bot h river st at ions need t o be adj ust ed t o balance wit h t he am ount of weir flow. 3-23 Exam ple 4 Mult iple Culvert s Figure 3-15: Culvert Table For Flow=600 cfs The following discussion is provided as an exam ple procedure t hat can be ut ilized t o balance t he weir flow wit h t he overbank flow. The m odeler should com pare t he m agnit ude of t he weir flow t o t he t ot al flow rat e t o det erm ine if t he procedure is pract ical for t he specific sit uat ion. To adj ust t he LOB and ROB flow values, first t he sit uat ion at river st at ion 20.227 was analyzed. Since t here was not any flow in t he overbanks, t he ineffect ive flow elevat ion was lowered from 33.3 t o 32.0. This will allow for t he flow com ing over t he weir t o becom e act ive at t his downst ream cross sect ion. The elevat ion of 32.0 feet was chosen because it is slight ly lower t han t he calculat ed wat er surface ( 32.01 feet ) at river st at ion 20.227. ( The user m ust be caut ious not t o lower t his elevat ion t o a point where t he ineffect ive flow will im pact t he second flow profile. Each flow profile m ust be analyzed separat ely.) As a second st ep t o balance t he weir and overbank flows, at river st at ion 20.238 t he Manning's n values in t he overbanks were raised from 0.1 t o 0.4. Addit ionally, at river st at ion 20.227, t he Manning's n values for t he overbanks were decreased from 0.10 t o 0.06. Since t he n value is inversely proport ional 3-24 Exam ple 3 Single Culvert - Single Bridge t o t he flow rat e, t he increase in n value at river st at ion 20.238 will cause a decrease in t he flow rat e in t he overbank areas. Sim ilarly, t he decrease in t he n value at river st at ion 20.227 will cause an increase in t he flow rat e in t he overbank areas. Aft er t hese adj ust m ent s were m ade, t he geom et ry file was saved as " Adj ust ed I neffect ive + n Values." Then t his geom et ry file and t he st eady flow dat a file were saved as a plan ent it led " Sp. Cr. Culvert s - Adj . Weir Flow." The user can act ivat e t his plan t o review t he rem aining discussion of t he out put . Aft er t he adj ust ed plan was execut ed, t he weir flow at river st at ion 20.237 was det erm ined t o be 74.14 cfs, as shown in t he Culvert Table of Figure 3.16. This weir flow occurred from X- coordinat es of 945.23 t o 1048.66, a dist ance of 103.43 feet . As calculat ed previously, t he approxim at e port ion of t his weir flow t hat occurred from 945.23 t o 972 is: (972.00 − 945.23) / (103.43) ⋅ (74.14) = 19.19cfs Sim ilarly, t he port ion of t he weir flow from 1027 t o 1048.66 was approxim at ely 15.4 cfs. These flow values were t hen com pared t o t he flow values in t he LOB and ROB at river st at ions 20.227 and 20.238. At river st at ion 20.227, t he flow in t he LOB was 6.83 and t he flow in t he ROB was 5.57 cfs. These values are approxim at ely equal t o t he port ions of t he weir flow values as det erm ined above. Therefore, t hese flow rat es were considered as being balanced wit h t he weir flow. I f t he flows in t he overbanks had been higher t han t he port ions of t he weir flow, t hen t he Manning's n values in t he overbanks at river st at ion 20.227 would have been increased unt il a balance was achieved. At river st at ion 20.238, t he flow in t he left and right overbanks were 9.89 and 9.37 cfs, respect ively. These flow rat es were considered t o be reasonably in balance wit h t he port ions of t he weir flow. I f t he flow rat es were not in balance, t hen t he n values would have been adj ust ed furt her unt il a balance was achieved. For bot h river st at ions 20.227 and 20.238, it should be not ed t hat t he flow rat es do not exact ly m at ch t he port ions of t he weir flow as calculat ed above. An exact m at ch is not warrant ed because t he weir flow port ions were approxim at e and t he weir flow t hat cont ribut es t o t he left and right overbank is only a m inor port ion of t he t ot al flow rat e. I f observed high wat er m arks were available, t he m odeler could m ake adj ust m ent s t o t he dat a t o m ore accurat ely predict t he act ual wat er surface elevat ions. 3-25 Exam ple 4 Mult iple Culvert s Figure 3-16: Culvert Table for Adjusted n Values and Ineffective Flow Areas With Flow = 600 cfs For addit ional det ailed analysis of t he flow, t he m odeler should review t he energy losses associat ed wit h t he cont ract ion and expansion of t he flow in t he channel and t he ent rance and exit losses for t he culvert t o evaluat e t he select ed energy loss coefficient s. Finally, a t hree dim ensional view of t he wat er surface profiles is displayed in Figure 3.17. This was act ivat ed from t he m ain program window by select ing View and t hen X- Y- Z Perspect ive Plot s. The figure is available t o aid t he user t o view t he calculat ed wat er surface profiles. The wat er surface im age represent s t he hydraulic grade line at t he respect ive cross sect ion locat ions. 3-26 Exam ple 3 Single Culvert - Single Bridge Figure 3-17: 3-D Perspective Plot of Spring Creek Flow Profiles Summary For t his exam ple, a culvert was analyzed wit h t hree flows. The culvert was com posed of t wo ident ical circular barrels. During t he review of t he out put , it was det erm ined t hat init ially t he flow in t he left and right overbanks at t he upst ream and downst ream cross sect ions from t he culvert did not m at ch t he weir flow t hat was occurring. I n order t o balance t he weir flow wit h t he overbank flows, t he Manning's n values and t he ineffect ive flow areas were adj ust ed at t he cross sect ions t hat bound t he culvert . The next exam ple ( Exam ple 4) ut ilizes t his dat a set and adds anot her culvert t ype t o t he geom et ric dat a. This creat es a m ult iple culvert analysis, each wit h m ult iple ident ical barrels. 3-27 Exam ple 4 Mult iple Culvert s CH APT ER 4 Multiple Culverts Purpose This exam ple is designed t o dem onst rat e t he use of HEC- RAS t o analyze t he flow of wat er t hrough m ult iple ( non- ident ical) culvert s. The program has t he capabilit y of analyzing flow t hrough a single t ype of culvert , m ult iple ident ical t ypes of culvert s, and m ult iple non- ident ical t ypes of culvert s. A culvert t ype defines t he charact erist ics of t he culvert , which includes t he shape, slope, roughness, chart , and scale num ber. For a given culvert t ype, t he program can analyze up t o 25 ident ical barrels. This exam ple analyzed t wo culvert t ypes, each wit h t wo ident ical barrels. The ent ering of dat a and t he analysis of t hese culvert s was ident ical t o t he procedures used for t he single culvert t ype as perform ed for Exam ple 3. Addit ionally, t he dat a used for Exam ple 3 was m odified for t his exam ple t o include a second culvert t ype. Therefore, Exam ple 4 is present ed as a cont inuat ion of Exam ple 3 and t he m odeler should review t he dat a and t he procedures as perform ed in Exam ple 3 before reviewing Exam ple 4. The user is referred t o Exam ple 3 for t he basic procedures of culvert analyses and t o Chapt er 6 of t he Hydraulic Reference Manual for a det ailed discussion on m odeling culvert s. To review t he procedures perform ed for t his exam ple, from t he m ain program window select File and t hen Open Proj ect . Select t he proj ect labeled " Mult iple Culvert s - Exam ple 4." This will open t he proj ect and act ivat e t he following files: Plan: " Spring Creek Mult iple Culvert s" Geom et ry: " Mult iple Culvert Geom et ry" Flow: " Mult iple Culvert Flow Dat a" Geometric Data To perform t he analysis, t he geom et ric dat a was ent ered first . The geom et ric dat a consist s of t he river syst em schem at ic, t he cross sect ion geom et ry, placem ent of t he cross sect ions, and t he culvert inform at ion. Each of t hese geom et ric dat a com ponent s are described in t he following sect ions. 4-1 Exam ple 4 Mult iple Culvert s River System Schematic From t he m ain program window, select Edit and t hen Ge om e t r ic D a t a and t he river syst em schem at ic of Spring Creek will appear as shown in Figure 4.1. This river reach is defined by t en river st at ions, wit h river st at ion 20.535 as t he upst ream cross sect ion and river st at ion 20.000 as t he downst ream cross sect ion. The schem at ic is ident ical t o t he river reach as developed during Exam ple 3. Figure 4-1: River System Schematic For Spring Creek Cross Section Geometry The geom et ry of t he cross sect ions for t his exam ple are ident ical t o t he geom et ry of t he cross sect ions for Exam ple 3. The m odeler should review Exam ple 3 for t he st at ioning, elevat ions, reach lengt hs, Manning's n values, m ain channel bank st at ions, and cont ract ion and expansion coefficient s det erm ined for each cross sect ion. ( Not e: The Manning's n values for t he LOB and ROB at river st at ions 20.238 and 20.227 were reset t o t he original value 4-2 Exam ple 4 Mult iple Culvert s of 0.1.) Finally, t he ineffect ive flow areas for t he cross sect ions in t he vicinit y of t he culvert were adj ust ed aft er t he addit ional culvert inform at ion was added. Expansion and Contraction Reach Lengths The placem ent of cross sect ions in reference t o t he culvert , define t he expansion and cont ract ion reach lengt hs. These reach lengt hs are crucial for t he accurat e predict ion of t he energy losses t hrough t he culvert . The det erm inat ion of t he reach lengt hs was discussed in det ail during Exam ple 3. During t he analysis, it was observed t hat an addit ional cross sect ion was required t o be added t o account for t he expansion of t he flow. This addit ional cross sect ion was added as cross sect ion num ber 20.208* , wit h t he * indicat ing t hat t he cross sect ion was int erpolat ed using t he m et hods available by t he program . Aft er t he analysis for t his exam ple, t he expansion and cont ract ion reach lengt hs were again evaluat ed and will be discussed near t he end of t his exam ple. Culvert Data The culvert dat a consist s of ent ering t he deck/ roadway dat a and t he culvert geom et ric dat a. Each of t hese areas will be discussed as follows. D e ck / Roa dw a y D a t a . The deck and roadway dat a edit or is act ivat ed from t he m ain program window by select ing Edit , Ge om e t r ic D a t a , t he Br idge / Cu lve r t icon, and t hen t he D e ck / Roa dw a y icon. This will display t he D e ck / Roa dw a y D a t a Edit or as shown in Figure 3.6 of Exam ple 3. The values for t his current exam ple were exact ly t he sam e as t hose ent ered for Exam ple 3. Culve r t Ge om e t r ic D a t a . To ent er t he culvert geom et ric dat a, from t he Br idge / Culve r t D a t a Edit or select t he Cu lve r t icon. This will act ivat e t he Cu lve r t D a t a Edit or and display t he dat a for culvert # 1 as shown in Figure 4.2. Culvert # 1 is defined exact ly as described for Exam ple 3: a circular culvert of diam et er 6 feet wit h t wo ident ical barrels and t he ot her param et ers as shown in Figure 4.2. I n t he upper right corner of t he edit or, t he Re na m e but t on was select ed and t he new nam e " Circular" was ent ered. This will help t he m odeler during t he review of t he out put for t his exam ple. The out put analysis of Exam ple 3 showed t hat during t he flow of 600 cfs, t he flow overt opped t he roadway and creat ed weir flow. For t his current exam ple, we will consider t he possibilit y t hat t he flow m ust not overt op t he roadway and t hat t he m odeler desires t o inst all addit ional culvert s t o alleviat e t his problem . Alt ernat ively, t o reduce t he upst ream wat er surface dept h, t he m odeler has ext ensive opt ions available such as increasing t he diam et er of t he exist ing culvert s or adding ot her ident ical barrels t o t he culvert . For t his exam ple, however, t he opt ion of inst alling addit ional culvert s was pursued. 4-3 Exam ple 4 Mult iple Culvert s Figure 4-2: Circular Culvert Data Editor From t he Culvert Dat a Edit or ( as shown in Figure 4.2) , t he Add but t on in t he upper left corner was select ed. This cleared t he ent ry fields and creat ed a new input window as shown in Figure 4.3. The ident ificat ion nam e " Culvert # 2" appeared in t he Culvert I D field in t he upper right corner of t he edit or. The Renam e but t on, locat ed im m ediat ely below t he Culvert I D, was select ed and a new nam e " Box" was ent ered. The addit ional fields of t he Culvert Dat a Edit or will be described as follows. Solut ion Crit eria - The user has t he opt ion t o select t o use t he result for inlet cont rol or out let cont rol as t he final answer for t he upst ream energy grade line value. The default m et hod is t o use t he highest of t he t wo values, as was select ed for t his exam ple. Shape - The culvert shape is chosen from t he eight available shapes: circular, box, ellipt ical, arch, pipe arch, sem i- circle, low or high arch. For t his second culvert , t he culvert shape was select ed as box. To select t he shape, press t he down arrow on t he side of t he shape field and highlight t he desired shape. Diam et er, Rise, or Rise and Span - Depending on t he shape of t he culvert , t he m odeler m ust ent er t he inside dim ensions of t he culvert shape. For a box shape, t he rise ( vert ical dist ance) and span ( horizont al dist ance) m ust be ent ered. A value of 5 feet for t he span and 3 feet for t he rise were ent ered. ( Not e: For box culvert s wit h cham fered corners, refer t o t he discussion in Chapt er 6 of t he H ydr a u lic Re fe r e n ce M a n ua l.) 4-4 Exam ple 4 Mult iple Culvert s Figure 4-3: Box Culvert Data Editor Chart # - Each culvert t ype and shape is defined by a Federal Highway Adm inist rat ion Chart Num ber. Depress t he down arrow next t o t his field t o select t he appropriat e chart num ber. Once a culvert shape has been select ed, only t he corresponding chart num bers available for t hat culvert shape will appear in t he select ions. Descript ions for t he chart num bers appear in Chapt er 6 on Table 6.5 of t he H ydr a u lic Re fe r e n ce M a n ua l. For t his exam ple, t he culvert chart was select ed as " 10 - 90 degree headwall; Cham fered or beveled inlet edges." Scale - This field is used t o select t he Federal Highway Adm inist rat ion scale t hat corresponds t o t he select ed chart num ber and culvert shape. Only t he scale num bers which are available for t he select ed chart num ber will appear for select ion. Descript ions for t he scale num bers appear in Chapt er 6 on Table 6.5 of t he H ydr a u lic Re fe r e n ce M a n ua l. The scale for t his exam ple was " 2 - I nlet edges beveled ½ in / ft at 45 degrees ( 1: 1) ." Dist ance t o Upst ream XS - This is t he dist ance from t he inlet of t he culvert t o t he upst ream cross sect ion ( 20.238) . For t his exam ple, t his was a dist ance of 5 feet . On t he D e ck / Roa dw a y D a t a Edit or , a m easure of 10 feet was ent ered for t he dist ance from t he upst ream side of t he deck/ roadway t o t he upst ream cross sect ion. Therefore, t he culvert ent rance is locat ed m idway bet ween t he upst ream side of t he roadway and cross sect ion 20.238. Lengt h - This field is t he m easure of t he culvert ( in feet or m et ers) along t he cent erline of t he barrel. The lengt h of t he culvert for t his exam ple is 50 feet . 4-5 Exam ple 4 Mult iple Culvert s The program will add t his 50 feet t o t he 5 foot dist ance from cross sect ion 20.238 ( t o t he culvert ent rance) and obt ain 55 feet . The reach lengt h from cross sect ion 20.238 t o 20.227 is 57 feet , which leaves 2 feet from t he exit of t he culvert t o t he downst ream cross sect ion. Ent rance Loss Coefficient - The value of t he ent rance loss coefficient will be m ult iplied by t he velocit y head at t he inside upst ream end of t he culvert t o obt ain t he energy loss as t he flow ent ers t he culvert . Typical values for t he ent rance loss coefficient can be obt ained from Tables 6.3 and 6.4 in t he H ydr a u lic Re fe r e n ce M a n ua l. The ent rance loss coefficient for t he concret e box culvert was set at 0.2. Exit Loss Coefficient - To det erm ine t he am ount of energy lost by t he wat er as it exit s t he culvert , t he exit loss coefficient will be m ult iplied by t he difference of t he velocit y heads from j ust inside t he culvert at t he downst ream end t o t he cross sect ion locat ed im m ediat ely downst ream from t he culvert exit . I n general, for a sudden expansion, t he exit loss coefficient should be set equal t o 1. However, t his value m ay range from 0.3 t o 1.0. For t his exam ple, t he exit loss coefficient was set t o be equal t o 1.0. Manning’s n for Top - This field is used t o ent er t he Manning's n value of t he t op and sides of t he culvert lining and is used t o det erm ine t he frict ion losses t hrough t he culvert barrel. Suggest ed n values for culvert linings are available in m any t ext books and also m ay be obt ained from Table 6.1 in t he H ydr a u lic Re fe r e n ce M a n ua l. Roughness coefficient s should be adj ust ed according t o individual j udgm ent of t he culvert condit ion. For t his exam ple, a Manning's n value of 0.013 was used for t he concret e culvert s. Manning’s n Value for Bot t om – This field is used t o ent er t he Manning’s n value of t he bot t om of t he culvert . For m ost culvert s, t his field will be t he sam e as t he Manning’s n value for t he t op. However, if t he culvert has a nat ural bot t om , or som et hing has been placed in t he bot t om for fish passage, t he n value m ay vary. Dept h t o use Bot t om n – This field is used t o ent er a dept h inside of t he culvert t hat t he bot t om n value is applied t o. I f t he bot t om and t op n value are t he sam e, a value of zero should be ent ered. Dept h Blocked – This field is used t o fill in a port ion of t he culvert . The user ent ers a dept h, and everyt hing below t hat dept h is blocked out Upst ream and Downst ream I nvert Elevat ion - These t wo fields are used t o ent er t he elevat ions of t he invert s. For a part icular culvert t ype, all of t he ident ical barrels will have t he sam e upst ream invert elevat ion and downst ream invert elevat ion. For t his exam ple, t he upst ream invert was set at an elevat ion of 28.1 feet and t he downst ream invert was 28.0 feet . Cent erline St at ions - This t able is used t o ent er t he st at ioning ( X- coordinat es) of t he cent erlines of t he culvert barrels. The upst ream cent erlines are based upon t he X- coordinat es of t he upst ream cross sect ion ( 20.238) and t he downst ream cent erlines are based upon t he X- coordinat es of t he downst ream cross sect ion ( 20.227) . This exam ple em ploys t wo culvert barrels, wit h t he cent erlines of t he barrels occurring at st at ions 988.5 and 1011.5 feet , as m easured on bot h cross sect ions. For t his exam ple, t he X- coordinat e 4-6 Exam ple 4 Mult iple Culvert s geom et ry of bot h cross sect ion 20.238 and cross sect ion 20.227 are referenced from t he sam e left st at ion st art ing point . Therefore, t he upst ream and downst ream cent erline st at ions are t he sam e value and t his will align t he culvert in t he correct configurat ion as being parallel t o t he channel. The m odeler m ust be caut ious t o ensure t hat t he cent erline st at ioning of t he culvert ends align t he culvert in t he correct posit ion. # ident ical barrels - This field will aut om at ically display t he num ber of barrels ent ered by t he user ( det erm ined by t he num ber of cent erline st at ions ent ered) . Up t o 25 ident ical barrels can be ent ered for each culvert t ype, and t his box culvert consist ed of 2 ident ical barrels. This com plet ed t he necessary geom et ric dat a for t he culvert s. The OK but t on was select ed and t he final configurat ion of t he culvert s is as shown in Figure 4.4. ( Not e: The ineffect ive flow areas will be adj ust ed subsequent ly.) The m odeler should now close t he edit or and save t he dat a. Figure 4-4: Box and Circular Culverts at River Station 20.237 4-7 Exam ple 4 Mult iple Culvert s Ineffective Flow Areas Since addit ional culvert s were added at cross sect ion 20.237, t he ineffect ive flow areas at river st at ions 20.238 and 20.227 were adj ust ed for t he new geom et ry. From t he Ge om e t r ic D a t a Edit or , t he Cr oss Se ct ion icon and river st at ion 20.238 were select ed. Select Opt ion s and t hen I n e ffe ct ive Flow Ar e a s. This act ivat ed t he I n e ffe ct ive Flow Ar e a D a t a Edit or as shown in Figure 4.5. Figure 4-5: Ineffective Flow Area at River Station 20.238 The st at ioning of t he ineffect ive flow areas at cross sect ion 20.238 can be det erm ined by using a 1: 1 relat ionship t o t he dist ance of cross sect ion 20.238 from t he culvert ent rance. For t his exam ple, cross sect ion 20.238 is locat ed 5 feet upst ream from t he culvert ent rance. Therefore, t he left ineffect ive flow st at ion was set at 5 feet t o t he left of t he left edge of t he culvert openings. The left edge of t he culvert opening is at st at ion 986. This places t he left ineffect ive flow st at ion at st at ion 986 - 5 = 981 feet . Sim ilarly, t he right ineffect ive flow st at ion was set t o be 5 feet t o t he right of t he right edge of t he culvert opening. This equat es t o st at ion 1014 + 5 = 1019. The elevat ion of t he ineffect ive flow areas will rem ain as originally set for Exam ple 3, at an elevat ion of 33.7 feet . The ineffect ive flow areas at cross sect ion 20.227 are det erm ined in a sim ilar m anner as used for cross sect ion 20.238; however, cross sect ion 20.227 is placed at a dist ance of 2 feet downst ream of t he culvert exit . Therefore, t he ineffect ive flow st at ioning at cross sect ion 20.227 is 984 and 1016 for t he left and right st at ions, respect ively. The elevat ions for t he ineffect ive flow areas at cross sect ion 20.227 were set at 33.6, a value slight ly lower t han t he lowest downst ream high cord elevat ion. This com plet ed t he required geom et ric dat a and t he inform at ion was saved as t he geom et ry file " Mult iple Culvert Geom et ry." Steady Flow Data To perform a st eady flow analysis, t he user m ust ent er bot h t he flow profile values and t he boundary condit ions. For t his exam ple, t he profiles were com put ed for flows of 250, 400, and 600 cfs ( as was used for Exam ple 3) . 4-8 Exam ple 4 Mult iple Culvert s Addit ionally, t he boundary condit ions rem ained t he sam e as used for Exam ple 3. This included downst ream boundary condit ions of known wat er surface elevat ions of 29.8, 31.2, and 31.9 feet for t he t hree flows, respect ively. I f t he st age is uncert ain, t he m odeler should include a river reach long enough so t hat t he downst ream boundary condit ions do not im pact on t he calculat ed wat er surface profiles wit hin t he reach of int erest . This st eady flow dat a file was saved as " Mult iple Culvert Flow Dat a." Steady Flow Analysis To perform t he st eady flow analysis, from t he m ain program window Run and t hen St eady Flow Analysis were select ed. This act ivat ed t he window as shown in Figure 4.6. The geom et ry file " Mult iple Culvert Geom et ry," t he st eady flow file " Mult iple Culvert Flow Dat a," and a subcrit ical flow regim e were select ed. A Plan t it le of " Sping Creek Mult iple Culvert s" was ent ered, as well as a Short I D of " Mult Culvert " and t hen t he COM PUTE but t on was select ed t o perform t he st eady flow analysis. Figure 4-6: Steady Flow Analysis Output Analysis To review t he out put , t he m odeler has various opt ions and procedures. For t his analysis, evaluat ions will be perform ed for: t he expansion and cont ract ion reach lengt hs, t he channel cont ract ion and expansion coefficient s, and t he wat er surface profiles. Expansion and Contraction Reach Lengths I nit ially, during Exam ple 3, t he expansion and cont ract ion reach lengt hs were det erm ined using t able values obt ained from t he USACE research docum ent [ HEC- 1995] . These reach lengt h values were t hen com pared t o t he act ual dist ances of t he expansion reach lengt h ( from cross sect ion 20.227 t o cross 4-9 Exam ple 4 Mult iple Culvert s sect ion 20.189) and t he cont ract ion reach lengt h ( from cross sect ion 20.251 t o cross sect ion 20.238) . I t was t hen det erm ined t hat t he cont ract ion reach lengt h was adequat e for t he analysis; however, t he est im at ed expansion reach lengt h was less t han t he dist ance from cross sect ion 20.227 t o cross sect ion 20.189. Therefore, an addit ional cross sect ion, 20.208* , was int erpolat ed and included as t he locat ion where t he flow would fully expand. Aft er t he analysis for Exam ple 3, t he expansion and cont ract ion reach lengt hs were com put ed using regression equat ions and com pared t o t he predet erm ined values. For t his current exam ple, t he regression equat ions will again be used t o evaluat e t he expansion and cont ract ion reach lengt hs. Ex pa n sion Re a ch Le ngt h . Cross sect ion 20.208* was t he int erpolat ed sect ion t hat was assum ed t o be at t he locat ion where t he flow becam e fully expanded. To evaluat e t he locat ion of t his cross sect ion, t he relat ionship shown as Equat ion 4- 1 was used. Equat ion 4- 1 is applicable when t he widt h of t he floodplain and t he discharge is less t han t hose of t he regression dat a. The equat ion is: ER = ⎛F ⎞ Le = 0.421 + 0.485⎜⎜ 20.227 ⎟⎟ + 0.000018Q Lobs ⎝ F20.208* ⎠ where : ER = Le = ( 4- 1) expansion rat io expansion reach lengt h, ft Lobs = average lengt h of side obst ruct ion, ft F20.227 = m ain channel Froude num ber at t he cross sect ion im m ediat ely downst ream of t he culvert ( cross sect ion 20.227 for t his exam ple) F20.208* = m ain channel Froude num ber at t he cross sect ion of fully expanded flow ( cross sect ion 20.208* for t his exam ple) Q = t ot al discharge, ft 3/ s ( Not e: The subscript s used in Equat ion 4- 1 and all subsequent equat ions reflect t he river st at ion num bering for t his exam ple.) From t he analysis, t he Froude num bers at cross sect ions 20.227 and 20.208* for t he flow of 600 cfs are 0.18 and 0.14, respect ively. Subst it ut ing t hese values int o Equat ion 4- 1 yields an expansion rat io of 1.06. The st andard error for Equat ion 4- 1 is 0.26, which yields a range of t he ER from 0.80 t o 1.32 t o define t he 68% confidence band. For t his current exam ple, t he average lengt h of obst ruct ion is det erm ined t o be approxim at ely equal t o 60 feet . Wit h t his lengt h of obst ruct ion, t he expansion reach lengt h is: Le = (ER )(Lobs ) = (1.06)(60) ≈ 64 ft 4-10 Exam ple 4 Mult iple Culvert s This is t he m edian value of t he range from 50 t o 80 feet ( using ER = 0.80 and 1.32, respect ively) . The act ual dist ance from cross sect ion 20.227 t o cross sect ion 20.208* was set at 100 feet , which is only slight ly great er t han t he m axim um value of t he range as det erm ined from Equat ion 4- 1. Therefore, t he exist ing reach lengt h was not adj ust ed. Also, since t he regression equat ion was based on st udies conduct ed for low flow t hrough bridges and since t he flow for t his exam ple is less t han t he flow rat es used t o develop t he equat ion, t he expansion reach lengt h was not adj ust ed from t he exist ing value. Finally, t he result ing expansion rat io should not exceed 4: 1 nor should it be less t han 0.5: 1. Cont ract ion Reach Lengt h. Cross sect ion 20.251 is locat ed where t he flow lines are parallel t o t he m ain channel. To evaluat e t his locat ion, Equat ion 4- 2 will be ut ilized. This equat ion is used when t he floodplain scale and dischargers are significant ly different t han t hose used in t he regression analysis and is: ⎞ ⎛F ⎛Q CR = 1.4 − 0.333⎜⎜ 20.227 ⎟⎟ + 1.86⎜⎜ ob ⎝ Q ⎝ F20.208* ⎠ 2 ⎛n ⎞ ⎟⎟ − 0.19⎜⎜ ob ⎠ ⎝ nc where: CR = cont ract ion rat io Lc = cont ract ion reach lengt h Qob = ⎞ ⎟⎟ ⎠ 0.5 ( 4- 2) discharge conveyed by t he t wo overbanks at cross sect ion 20.251, cfs Q = n ob = nc = t ot al discharge, cfs Manning's n value of t he overbanks at sect ion 20.251 Manning's n value for t he m ain channel at cross sect ion 20.251 From t he analysis of t he 600 cfs profile, t he flow in t he t wo overbanks at cross sect ion 20.251 was 34.32 cfs and t he Manning's n values for t he overbanks and m ain channel at cross sect ion 20.251 are 0.10 and 0.04, respect ively. Subst it ut ing t hese values int o Equat ion 4- 2 yielded a cont ract ion rat io of 0.68. The st andard error for Equat ion 4- 2 is 0.19, which yields a CR range from 0.49 t o 0.87 t o define t he 68% confidence band. This range is less t han t he range obt ained from Table B- 2 of 0.8 - 1.5. Using t he cont ract ion rat io of 0.8 and an average obst ruct ion lengt h of 60 feet , t he cont ract ion reach lengt h is: Lc = (CR )(Lobs ) = (0.8)(60 ) = 48 feet The exist ing cont ract ion reach lengt h ( t he dist ance from cross sect ion 20.251 t o cross sect ion 20.238) is set at 70 feet, which is only slight ly great er t han t he calculat ed value of 48 feet . Due t o t he uncert aint y of t he regression equat ion and since t he dat a for t his exam ple were out side t he range of t he dat a used t o develop t he equat ion, t he cont ract ion reach lengt h was not 4-11 Exam ple 4 Mult iple Culvert s adj ust ed. Finally, t he result ing cont ract ion rat io should not exceed 2.5: 1 nor should it be less t han 0.3: 1. Channel Expansion and Contraction Coefficients The coefficient s of expansion ( Ce) and cont ract ion ( Cc) for flow in t he cross sect ions are used t o det erm ine t he energy losses associat ed wit h t he changes in channel geom et ry. I nit ially, in t he vicinit y of t he culvert , t he coefficient s were set at 0.5 and 0.3 for t he expansion and cont ract ion, respect ively. Each of t hese values will be reviewed. Ex pa n sion Coe fficie n t . The expansion coefficient can be obt ained from Equat ion 4- 3: ⎛D C e = −0.09 + 0.570⎜⎜ ob ⎝ Dc where: Ce = Dob = ⎞ ⎛F ⎞ ⎟⎟ + 0.075⎜⎜ 20.227 ⎟⎟ ⎠ ⎝ F20.208* ⎠ ( 4- 3) coefficient of expansion hydraulic dept h ( flow area divided by t he t op widt h) for t he overbank at cross sect ion 20.208* Dc = hydraulic dept h for t he m ain channel at cross sect ion 20.208* From t he analysis of t he 600 cfs profile, t he hydraulic dept hs for t he overbanks and t he m ain channel at river st at ion 20.208* are 0.58 and 5.66 feet , respect ively. Subst it ut ion of t he values int o Equat ion 4- 3 yields an expansion coefficient of 0.07. This is t he m edian value and t he range of ± 0.2 defines t he 95% confidence band for Equat ion 4- 3. For t his exam ple, a value of 0.5 was used. The value of t he expansion coefficient is generally larger t han t he value used for t he cont ract ion coefficient so t he value of 0.5 will rem ain as t he select ed value. The m odeler can perform a sensit ivit y of t his coefficient by changing t his coefficient and perform ing subsequent analyses. For t his exam ple, t he change in velocit y head from cross sect ion 20.227 t o 20.208* was only 0.06 feet . Since t his value is sm all, a change in t he expansion coefficient will only reflect a m inor change in t he result ing wat er surface elevat ion. Con t r a ct ion Coe fficie n t . From t he research docum ent [ HEC- 1995] , t he cont ract ion coefficient is obt ained by first det erm ining t he relat ionship: b / B = 28 / 145 ≈ 0.20 where: b = culvert opening widt h, ft ( m ) B = t ot al floodplain widt h, ft ( m ) From Table B- 3 in Appendix B of t he Hydraulic Reference Manual, t he recom m ended cont ract ion coefficient range is 0.3 - 0.5. The value select ed for t his exam ple was t he m inim um value of 0.3. 4-12 Exam ple 4 Mult iple Culvert s Water Surface Profiles From t he m ain program window, select Vie w and t hen W a t e r Sur fa ce Pr ofile s. This will result in t he display as shown in Figure 4.7. I n t he figure, t he wat er surface profiles are shown for all t hree flows. As can be seen in t he figure, t he wat er surface for t he first flow ( 250 cfs) was able t o t ravel t hrough t he culvert s wit hout subm erging t he inlet or out let . For t he second and t hird flow profiles, it can be seen t hat t he culvert ent rance was subm erged but t hat weir flow did not occur for eit her flow. Figure 4-7: Water Surface Profiles For Spring Creek To analyze t his furt her, t he m odeler can view t he profile out put t able t o det erm ine t he dept hs of flow at t he upst ream side of t he culvert s. From t he m ain program window, select Vie w , Pr ofile Ta ble , St d. Ta ble s, and t hen Culvert Only. This will display t he t able as shown in Figure 4.8. 4-13 Exam ple 4 Mult iple Culvert s Figure 4-8: Culvert Only Profile Table I n Figure 4.8, t he first t wo rows are for t he flow t hrough t he box and circular culvert s for t he flow of 250 cfs. Then t he second set of rows are for t he flow of 400 cfs, and finally t he last t wo rows are for t he flow of 600 cfs. For bot h t he box and t he circular culvert s, t he upst ream inside t op elevat ion was set at 31.1 feet . By com paring t his value t o t he upst ream wat er surface elevat ion ( W. S. US.) , it is det erm ined t hat bot h of t he culvert s were subm erged at t he ent rance for t he second and t hird flow profiles because t he upst ream wat er surface elevat ions were 31.83 and 33.22 feet , respect ively. Addit ional analysis of t he t able reveals t hat out let cont rol was t he t ype of flow occurring t hrough t he culvert for all 3 flow profiles, because t he out let energy grade line was great er t han t he inlet cont rol energy grade line. The flow t hrough each culvert , for each flow profile, is shown in t he colum n wit h t he heading " Culv Q." For exam ple, for t he first flow profile ( 250 cfs) , t here was 74.73 cfs flowing t hrough t he box culvert s ( 37.36 cfs t hrough each barrel) and 175.27 cfs flowing t hrough t he circular culvert s ( 87.64 cfs t hrough each barrel) . This t ot als 74.73 + 175.27 = 250 cfs and account s for t he t ot al flow rat e for t he first flow profile. Finally, t here are no values in t he weir flow colum n of t he t able, which signifies t hat weir flow did not occur for t hese flow rat es. This was an init ial goal t o develop a culvert syst em t hat produced no weir flow. The m odeler can now det erm ine t he available freeboard on t he upst ream side of t he roadway em bankm ent and adj ust t he sizes and shapes of t he culvert as deem ed necessary. For a m ore det ailed analysis of each culvert , select Vie w , Cr oss Se ct ion Ta ble , Type , and t hen Cu lve r t . Toggle t o profile 3 ( 600 cfs) and select t he " Box" as t he Cu lve r t I D . This will display t he t able as shown in Figure 4.9. This t able displays addit ional inform at ion for t he select ed culvert and flow profile such as t he lengt h of t he culvert flowing full and t he energy losses. The m odeler can com pare t hese losses wit h values obt ained for ot her ent rance and exit loss coefficient s. Finally, as displayed on t he previous t able, it can be seen t hat t here is no weir flow occurring at t his river st at ion. The m odeler can t hen t oggle t o t he circular culvert at t his river st at ion by select ing t he Cu lve r t I D fie ld. I f addit ional culvert s were locat ed at ot her river st at ions, t he dat a for t hese culvert s can be viewed by select ing t he appropriat e river st at ion. 4-14 Exam ple 4 Mult iple Culvert s Figure 4-9: Culvert Type Cross Section Table Finally, t he locat ion of t he ineffect ive flow areas will be reviewed. From t he m ain program window, select Vie w and t hen Cr oss Se ct ion s. Toggle t o river st at ion 20.238 and t his will display t he cross sect ion as shown in Figure 4.10. I n t he figure, it can be seen t hat t he wat er surface elevat ions did not exceed t he elevat ions set for t he ineffect ive flow areas. Addit ionally, t oggle t o river st at ion 20.227 and it can be seen t hat t he wat er surface elevat ion is lower t han t he elevat ions set for t he ineffect ive flow areas at t his cross sect ion. Since weir flow did not occur, t he ineffect ive flow areas set for cross sect ions 20.238 and 20.227 should reasonably reflect t he act ual flow condit ions. 4-15 Exam ple 4 Mult iple Culvert s Figure 4-10: Cross Section 20.238 of Spring Creek Summary This exam ple dem onst rat ed t he use of HEC- RAS t o analyze a river reach t hat cont ained a m ult iple culvert opening. The m ult iple culvert s consist ed of t wo culvert t ypes ( circular and box) , each wit h t wo ident ical barrels. Aft er t he flow analysis was com plet ed, t he expansion and cont ract ion reach lengt hs were evaluat ed and t he ineffect ive flow areas were reviewed. Finally, t he various out put feat ures ( flow profiles, cross sect ion t ype t ables, and profile t ables) were displayed t o show t he feat ures available for a review of t he out put . 4-16 Exam ple 5 Mult iple Openings CH APT ER 5 Multiple Openings Purpose This exam ple dem onst rat es t he analysis of a m ult iple opening. An opening is com prised of a bridge, a group of culvert s, or a conveyance area ( open channel flow ot her t han a bridge or culvert ) . The program can analyze up t o seven openings occurring at t he sam e river st at ion, and any num ber of bridge and culvert openings can be used. However, t he program is lim it ed t o a m axim um of t wo conveyance- t ype openings. Dat a ent ry for a conveyance- t ype opening and a bridge opening are sim ilar t o t he procedures used for Exam ple 1 and Exam ple 2, respect ively. Ent ering dat a for a culvert group is sim ilar t o t he procedures used for Exam ples 3 and 4. Therefore, it is recom m ended t hat t he m odeler be fam iliar wit h Exam ples 1 t hrough 4 before cont inuing wit h t his exam ple. To act ivat e t he dat a files for t his proj ect , from t he m ain program window select File and t hen Ope n Pr oj e ct . Select t he proj ect labeled " Mult iple Openings - Exam ple 5." To begin t his exam ple, t he final result s from t he pressure/ weir flow bridge analysis of Exam ple 2 were used as t he base st art ing condit ions. These dat a files are included wit h t his exam ple as: Plan: " Base Condit ions" Geom et ry: " Beaver Cr. + Single Bridge" Flow: " Beaver Cr. - 3 Flows" During t he m axim um flow event of 14000 cfs for Exam ple 2, t he flow overt opped t he roadway. For t his current exam ple, addit ional openings of a culvert group and a relief bridge were provided so t hat t he flow did not overt op t he roadway. These addit ional openings were included wit h t he exist ing bridge opening at t he sam e river st at ion. To perform t his current exam ple, t he geom et ry file " Beaver Cr. + Single Bridge" was act ivat ed. Then, t he procedures as out lined in t his exam ple were perform ed. Finally, t he geom et ry was t hen saved as " Culvert Group + Relief Bridge." This geom et ry file and t he st eady flow dat a file " Beaver Cr. - 3 Flows" were t hen saved as a new plan ent it led " Modified Condit ions." This final plan, wit h t he m ult iple opening geom et ry, is included wit h t he proj ect . 5-1 Exam ple 5 Mult iple Openings River System Geometric Data To perform t he analysis, t he geom et ric dat a were ent ered first . This dat a consist s of t he river syst em schem at ic, t he cross sect ion geom et ry, and t he placem ent of t he cross sect ions in relat ion t o t he bridge and culvert s. Each of t hese geom et ric dat a com ponent s are described in t he following sect ions. River System Schematic From t he m ain program window, select Edit and t hen Ge om e t r ic D a t a . This will display t he river syst em schem at ic as shown in Figure 5.1. The river reach is defined by 12 river st at ions wit h river m ile 5.0 as t he downst ream cross sect ion, as developed during Exam ple 2. Addit ionally, t here is a bridge at river st at ion 5.40, which is exact ly as described during Exam ple 2. Figure 5-1: River System Schematic 5-2 Exam ple 5 Mult iple Openings Cross Section Geometry The cross sect ion geom et ry consist s of t he cross sect ion X- Y coordinat es, reach lengt hs, Manning's n values, m ain channel bank st at ions, cont ract ion and expansion coefficient s, levees, et c. Each of t hese it em s are exact ly as described for t he cross sect ions in Exam ple 2. ( Not e: The ineffect ive flow areas will be adj ust ed subsequent ly.) Placement of the Cross Sections The placem ent of t he cross sect ions in reference t o a bridge or culvert opening is crucial for t he accurat e calculat ion of t he energy losses t hrough t he st ruct ure. As described during Exam ple 2, t he expansion and cont ract ion reach lengt hs were adj ust ed t o properly locat e t he cross sect ions in t he vicinit y of t he bridge. For t his current exam ple, t he expansion and cont ract ion reach lengt hs will be adj ust ed t o account for t he inclusion of a culvert group and a flow relief bridge. This adj ust m ent of t he reach lengt hs was perform ed aft er t he bridge and culvert dat a were ent ered and will be discussed in a subsequent sect ion of t his current exam ple. Bridge Geometry The bridge geom et ry is com posed of t he deck/ roadway dat a, t he pier and abut m ent s, and t he bridge m odeling approach. Each of t hese it em s will be discussed in t he following sect ions. Deck/Roadway Data From t he Ge om e t r ic D a t a Edit or , select t he Br dg/ Cu lv icon. This will act ivat e t he Br idge / Culve r t D a t a Edit or as shown in Figure 5.2. During Exam ple 2, t he reach of " Kent wood" was select ed and a bridge was placed at river st at ion of 5.40. Then t he deck/ roadway dat a were ent ered by select ing t he D e ck / Roa dw a y icon on t he left side of t he edit or. The deck and roadway dat a for t he m ain bridge are ident ical t o t he dat a ent ered for Exam ple 2. For t he current exam ple, a flow relief bridge was added at river st at ion 5.40. To add t his bridge, first t he bridge deck and roadway dat a were ent ered by select ing t he D e ck / Roa dw a y icon. This act ivat ed t he D e ck / Roa dw a y D a t a Edit or as shown in Figure 5.3. The addit ional high and low cord inform at ion for t he second bridge was t hen added t o provide for an opening for t he second bridge. This was accom plished by scrolling down t o t he end of t he exist ing dat a and t hen ent ering t he st at ions and elevat ions for t he high and low cords of t he second bridge. The dat a appears in Figure 5.3, showing t he bridge opening from X- coordinat es of 960 t o 1240, wit h t he low and high cords of 215.7 and 216.93 feet , respect ively. ( These values are t he sam e as used for t he first m ain bridge.) Aft er t he dat a were ent ered, t he edit or was closed. I t should be not ed t hat t he dist ance, widt h, weir coefficient , and 5-3 Exam ple 5 Mult iple Openings ot her param et ers of t he D e ck / Roa dw a y D a t a Edit or will be t he sam e for t he second bridge as for t he first bridge. Figure 5-2: Bridge/Culvert Data Editor Figure 5-3: Deck/Roadway Data Editor 5-4 Exam ple 5 Mult iple Openings Piers and Abutments The next st ep was t o ent er t he pier dat a. This was accom plished by select ing t he Pie r icon on t he left edge of t he Br idge / Cu lve r t D a t a Edit or ( t he edit or shown in Figure 5.2) . During Exam ple 2 for t he first bridge, each of t he nine piers was ent ered wit h a st art ing elevat ion of 200 feet and an ending elevat ion of 216 feet , and a widt h of 1.25 feet . The piers were locat ed st art ing at a cent erline st at ion of 470 and were placed at a dist ance of 20 feet on cent er, yielding an ending cent erline st at ion of 630. To add t he piers for t he second bridge, for t his current exam ple, t he Pie r icon was select ed and t he Add but t on was chosen. This creat ed a new pier ( # 10) and t he cent erline st at ion was set at 980. The st art ing ( 200 feet ) and ending ( 216 feet ) elevat ions for t his pier were t he sam e as for t he ot her piers. As before, t he elevat ions were chosen t o be below t he ground level and inside t he bridge decking. The program will aut om at ically rem ove t he pier area below t he ground and inside t he decking. Finally, t he Copy but t on was select ed t o ent er a t ot al of 13 addit ional piers, 20 feet on cent ers, ending at a cent erline st at ion of 1220. ( The bridge opening ended at an X- coordinat e of 1240 feet .) This com plet ed t he addit ion of t he new piers for t he flow relief bridge. Finally, any sloping abut m ent s should now be ent ered for t he analysis by select ing t he Sloping Abu t m e n t icon t he left side of t he Br idge Cu lve r t D a t a Edit or . For t his exam ple, t he bridge geom et ry did not include sloping abut m ent s. Bridge Modeling Approach From t he Br idge / Cu lve r t D a t a Edit or , select t he Br idge M ode ling Appr oa ch icon. This will act ivat e t he Br idge M ode lin g Appr oa ch Edit or . For a m ult iple opening analysis, if only one bridge m odeling approach is developed, t hen t he program will default t o use t hat approach for all of t he bridges. Alt ernat ively, t he user can develop an approach ( coefficient set ) for each of t he bridges in t he river st at ion. For t his current exam ple, t he Add but t on was select ed at t he t op of t he edit or for t he m ain bridge ( as developed during Exam ple 2) and t his creat ed a second bridge m odeling approach, which is shown in Figure 5.4. The dat a ent ered for t his second bridge m odeling approach are shown in Figure 5.4. This com plet ed t he input required for t he bridge geom et ry and t he OK but t on was select ed at t he bot t om of t he edit or. Next , t he culvert geom et ry was ent ered. 5-5 Exam ple 5 Mult iple Openings Figure 5-4: Relief Bridge Modeling Approach Editor Culvert Geometry To ent er t he culvert geom et ry, t he Cu lve r t icon was select ed from t he Br idge / Cu lve r t D a t a Edit or . This act ivat ed t he Cu lve r t D a t a Edit or as shown in Figure 5.5. The procedure for ent ering t he culvert dat a is sim ilar t o t he procedures as used during Exam ples 3 and 4. The following is a brief sum m ary of t he st eps used t o ent er t he culvert dat a for t his current exam ple. The first culvert I D will aut om at ically be set t o " Culvert # 1." This was changed t o " Box # 1" by select ing t he Re na m e but t on. Then t he Solut ion Crit eria was select ed as " Highest Upst ream Energy" and t he Shape " Box " was select ed. A rise of 4 feet and a span of 6 feet were t hen ent ered. Chart num ber 8 and Scale num ber 1 were select ed t o describe t he FHWA st andard culvert param et ers. Addit ionally, t he Dist ance t o Upst ream XS was ent ered as 20 feet , Lengt h was m easured t o be 60 feet , t he Manning's n - Value was set at 0.013, and t he Ent rance and Exit Loss Coefficient s were set at 0.5 and 1.0, respect ively. The upst ream and downst ream I nvert Elevat ions and t he upst ream and downst ream Cent erline St at ions were ent ered for each of t he 5 ident ical barrels, as shown in Figure 5.5, and t he # ident ical barrels displayed a value of 5. I t should be not ed t hat if t he m ult iple opening analysis had been configured as a bridge in bet ween t wo culvert groups, t hen t he t wo culvert groups should be ent ered as separat e culvert t ypes. This will enable t he program t o dist inguish bet ween t he different opening locat ions. Upon ent ering t he culvert inform at ion, t he OK but t on was select ed t o exit t he culvert edit or. 5-6 Exam ple 5 Mult iple Openings Figure 5-5: Box Culvert Data Editor Finally, t he user should highlight t he piers and bridge openings from t he Vie w m enu of t he Br idge / Culve r t D a t a Edit or . Then, zoom in t o view each of t he bridge openings and t he culvert barrels. This will enable t he user t o view any inconsist encies t hat m ay have developed during t he dat a ent ry. This com plet ed t he dat a ent ry for t he culvert s. Next , t he openings were defined for t he m ult iple flow analysis. Multiple Openings For t he m ult iple opening analysis, t he user m ust define t he st agnat ion lim it s for t he flow separat ion int o each of t he openings. Aft er t hese lim it s were defined, t he ineffect ive flow areas and t he Manning's n values were adj ust ed t o account for t he m ult iple openings. Each of t hese is discussed in t he following sect ions. Stagnation Limits As t he flow approaches t he river st at ion t hat cont ains a m ult iple opening, t he t ot al flow will divide upst ream from t he m ult iple openings so t hat a port ion will ent er int o each opening. Therefore, t o perform t he m ult iple opening analysis, t he user m ust ent er a left and right st at ion for each opening which defines t he X- coordinat e range of t he flow separat ion. The specific Xcoordinat e where t he flow separat es is called t he st agnat ion point and t his st agnat ion point is eit her det erm ined by t he program or set by t he user. To 5-7 Exam ple 5 Mult iple Openings perform t he m ult iple opening analysis, from t he Br idge / Cu lve r t D a t a Edit or , select t he M u lt iple Ope n ing Ana lysis icon. This will act ivat e t he M u lt iple Ope n ing Ana lysis D a t a Edit or as shown in Figure 5.6. Figure 5-6: Multiple Opening Analysis Data Editor First , t he order of t he openings are est ablished from left t o right as looking in t he downst ream direct ion. For t his exam ple, t here were t hree openings: a culvert group, t he m ain bridge opening, and t hen t he relief bridge opening. To ent er t he dat a, t he field under " Opening Type" and adj acent t o num ber 1 was select ed. Then, t he Cu lve r t Gr ou p icon was select ed, because t he first opening t ype was a culvert . This placed t he descript ion " Culvert Group" in t he first row, under t he heading " Opening Type." Next , t he upst ream left and right st agnat ion lim it s were ent ered for t he culvert group. These left and right st at ions will be used t o det erm ine where t he flow separat ed bet ween t he culvert group and t he bridge. For t his exam ple, t he left and right st agnat ion lim it s were est ablished as 0 and 390. Addit ionally, t he downst ream left and right st agnat ion lim it s were also ent ered as 0 and 390. The downst ream st at ions define t he X- coordinat e lim it s where t he flow from consecut ive openings will rej oin. Next , t he field under " Opening Type" and adj acent t o row num ber 2 was select ed. Then, t he Br idge icon was select ed and t he descript ion " Bridge" appeared as t he second opening t ype. The left and right st agnat ion lim it s were ent ered for t he bridge as 310 and 880 for bot h t he upst ream and downst ream side. Finally, t he t hird opening was select ed as " Bridge" and t he dat a ent ered as shown in Figure 5.6. As can be seen in Figure 5.6, t he right st agnat ion lim it for t he culvert group was set at 390 and t he left st agnat ion lim it for t he m ain bridge was set at 310. This creat ed an overlap area from 310 t o 390. Since t his overlap exist s, t he program will det erm ine t he act ual locat ion of t he st agnat ion point ( t he flow separat ion point ) bet ween t he culvert and t he m ain bridge. By ent ering t he dat a in t his fashion, t he st agnat ion point was t hen allowed t o vary for each flow profile, wit hin t he lim it s from 310 t o 390. Conversely, if t he right st agnat ion lim it of an opening coincides exact ly wit h t he left st agnat ion lim it 5-8 Exam ple 5 Mult iple Openings of t he next opening, t hen t he user has defined a specific st agnat ion point and t his point will be fixed for all flow profiles. For a conveyance t ype opening, in t he current version of t he program , a fixed st agnat ion point m ust be used on bot h sides of t he opening. For a furt her discussion on m ult iple opening analyses, refer t o Chapt er 6 of t he Use r 's M a n u a l and Chapt er 7 of t he H ydr a u lic Re fe r e n ce M a n ua l. Once all of t he dat a were ent ered int o t he M u lt iple Ope n ing Ana lysis D a t a Edit or , t he OK but t on was select ed. Then t he locat ions of t he st agnat ion lim it s can be viewed in t he display of t he Br idge / Cu lve r t D a t a Edit or as shown in Figure 5.2. The lim it s select ed for t he st agnat ion point s for each opening are shown above t he t wo cross sect ion plot s. For guidance on select ing t he st agnat ion lim it s, t here are t wo m ain obj ect ives. First , t here is a physical lim it . This im plies t hat t here m ight exist a physical at t ribut e of t he openings on t he cross sect ion t hat can be used t o det erm ine t he st agnat ion lim it s. For exam ple, t he left st agnat ion lim it for t he culvert was set at t he left edge of t he cross sect ion. Addit ionally, t he right st agnat ion lim it for t he culvert cannot be placed in t he m ain bridge opening. This would im ply t hat t he flow in front of t he bridge would go over t o t he culvert and t his is not a pract ical. Therefore, a physical right st agnat ion lim it for t he culvert would be t he left side of t he m ain bridge opening. Secondly, for guidance on select ing t he st agnat ion lim it s, t here exist s pract ical lim it s. For exam ple, t he flow in t he cross sect ion in bet ween t he culvert and t he m ain bridge m ust separat e at som e point t o t ravel int o eit her opening. Since t he bridge opening is larger t han t he culvert opening, m ore of t he flow will probably go t owards t he bridge opening. Therefore, t he right st agnat ion lim it for t he culvert should not be set all t he way over t o t he left edge of t he m ain bridge opening. The right lim it for t he culvert should be locat ed at a pract ical lim it before t he bridge opening. This pract ical lim it can be det erm ined by analyzing t he am ount of conveyance in t he area bet ween t he culvert and t he bridge, and t hen developing a reasonable est im at e of where t he st agnat ion lim it should be placed. Finally, it is recom m ended t hat t he user allow t he st agnat ion point s t o m igrat e ( where possible) rat her t han ent er specific fixed st agnat ion point s. This is im port ant when evaluat ing several flows during t he sam e run. Conversely, if t he st agnat ion lim it s are allowed t o m igrat e over a large dist ance, t he program m ay experience difficult y in converging t o a solut ion. When t his occurs, t he overlaps of t he st agnat ion lim it s should be reduced. Ineffective Flow Areas Before a st eady flow analysis was perform ed, t he ineffect ive flow areas were locat ed. From t he Ge om e t r ic D a t a Edit or, select t he Cr oss Se ct ion icon and t hen t oggle t o river st at ion 5.41. This is t he river st at ion im m ediat ely upst ream of t he m ult iple opening. For t his exam ple, blocked ineffect ive flow areas were set as shown in Figure 5.7. 5-9 Exam ple 5 Mult iple Openings Figure 5-7: Blocked Ineffective Flow Areas for River Station 5.41 Four ineffect ive flow area blocks were est ablished at t his river st at ion. These were locat ed: t o t he left of t he culvert group, in bet ween t he culvert group and t he m ain bridge, in bet ween t he m ain bridge and t he relief bridge, and finally t o t he right of t he relief bridge. I t should be not ed t hat during a m ult iple opening analysis, t he ineffect ive flow areas need t o be described using t he block m et hod, not t he norm al m et hod. The block m et hod allows t he user t o ent er ineffect ive flow areas in bet ween t he openings. Finally, ineffect ive flow blocks were defined at river st at ion 5.39 ( locat ed downst ream of t he m ult iple opening) . These ineffect ive blocked areas are shown as connect ed green lines on t he Br idge / Cu lve r t D a t a Edit or ( Figure 5.2) . The ineffect ive flow areas could have been ent ered along wit h t he cross sect ion geom et ry ( X and Y - coordinat es, et c.) ; however, for t his exam ple, t he locat ions for t he culvert group and relief bridge were est ablished first . Then, t he locat ions of t he ineffect ive flow areas were m ore readily ascert ained from t he locat ions of t he culvert s and bridges. Manning's n Values Due t o t he inclusion of t he culvert s and relief bridge, t he Manning's n values in t he overbank areas in t he vicinit y of t he bridge were adj ust ed. I t was assum ed t hat during inst allat ion of t hese relief openings, port ions of t he densely forest ed overbank areas would be cleared for const ruct ion access and t o allow t he flow t o ent er t he culvert s and relief bridge. Therefore, t he n values in t he overbank areas at river st at ions 5.41, 5.39, and 5.33* were adj ust ed t o an appropriat e value t o represent t he expect ed condit ions. Cross Section Locations As discussed previously, t he placem ent of t he cross sect ions in reference t o a bridge or culvert opening is im port ant for t he accurat e calculat ion of t he energy losses t hrough t he st ruct ure. For t his exam ple, it will be considered t hat t he m aj orit y of t he flow will t ravel t hrough t he m ain bridge opening at t he m ult iple opening river st at ion. Therefore, t he expansion and cont ract ion reach lengt hs for t he high flow event will be det erm ined based on t he m ain bridge opening. The following sect ions describe t he procedures used t o 5-10 Exam ple 5 Mult iple Openings det erm ine t he expansion and cont ract ion reach lengt hs as well as t he expansion and cont ract ion coefficient s. Expansion Reach Length To det erm ine an init ial est im at e for t he expansion reach lengt h, t he procedures as out lined in t he USACE research docum ent [ HEC- 1995] will be im plem ent ed. These procedures are discussed in Appendix B of t he H ydr a u lic Re fe r e n ce M a n ua l. First , t he expansion rat io ( ER) was est im at ed using t he expansion rat io t able ( Table B.1) . To det erm ine t he ER, t he following param et ers were necessary: b = 200 ft B = 850 − 310 = 540 ft b / B = 200 / 540 = 0.36 S = 8 ft / mi nob / nc = 1.75 Lobs = [(450 − 310) + (850 − 647 )] = 170 ft where: b = B = floodplain widt h cont ribut ing t o flow t hrough t he m ain bridge, ft S = slope, ft / m i m ain bridge opening widt h, ft nob = Manning's n value of t he overbanks nc Manning's n value of t he overbanks = Lobs = average obst ruct ion reach lengt h for t he floodplain widt h cont ribut ing flow t hrough t he bridge, ft The m ain bridge opening widt h, b, is obt ained from t he bridge geom et ric dat a and was det erm ined t o be 200 feet . The floodplain widt h for t his scenario, B, will be t he widt h of flow t hat cont ribut es t o t he m ain bridge opening and is t he dist ance from t he left st agnat ion point t o t he right st agnat ion point of t he m ain bridge opening. Since t hese st agnat ion point s were ent ered as float ing values, an approxim at e locat ion was assum ed for t his init ial det erm inat ion of t he expansion reach lengt h and t he value was est im at ed as 540 feet . Addit ionally, t he average lengt h of t he side obst ruct ions, Lobs , was est im at ed at 170 feet . This value was det erm ined by only considering t he floodplain widt h bet ween t he left and right st agnat ion point s for t he m ain bridge. Finally, t he b/ B rat io and t he slope of t he river reach are used t o det erm ine 5-11 Exam ple 5 Mult iple Openings an init ial est im at e of t he expansion rat io from t he " Ranges of Expansion Rat ios," Table B.1 in Appendix B of t he H ydr a ulic Re fe r e nce M a nu a l. From t he t able, t he ER was found t o range from 1.3 - 2.0. An average value of 1.7 was used and t his result ed wit h an expansion reach lengt h, Le , of: Lc = (CR )(Lobs ) = (1.7 )(170) = 290 ft For t his exam ple, t he expansion reach lengt h is t he m ain channel dist ance from cross sect ion 5.39 t o cross sect ion 5.24* which equals 778 ft . Therefore, an addit ional cross sect ion was added at a dist ance of 290 feet downst ream from cross sect ion 5.39 based on t he est im at ed expansion reach lengt h as det erm ined above. To insert t he addit ional cross sect ion, field dat a should be used. I f t his is not available, t hen t he user can ut ilize t he int erpolat ion rout ines. Then, t he int erpolat ed cross sect ion should be com pared wit h t he exist ing geom et ry and t opographic m aps. For t his exam ple, t he int erpolat ion m et hod was ut ilized t o obt ain a cross sect ion at a dist ance of 290 feet downst ream from river st at ion 5.39. To perform t his int erpolat ion, it would be necessary t o int erpolat e bet ween river st at ions 5.39 and 5.24* . However, t he program will not allow for int erpolat ion bet ween an exist ing river st at ion and a previously int erpolat ed sect ion. Therefore, t he int erpolat ion would be required from river st at ion 5.39 t o river st at ion 5.13. Since t his was a very long river reach, an alt ernat ive approach was em ployed by obt aining dat a from t he USGS At las No. HA- 601 ( This at las provided t he dat a for Exam ple 2.) . From t he at las, t he dat a for river st at ion num ber 5.29 was ent ered int o t he exist ing geom et ry dat a file. Then, an int erpolat ion was perform ed bet ween river st at ions 5.39 and 5.29. The int erpolat ion procedure was perform ed by opening t he Ge om e t r ic D a t a Edit or , t hen select ing t he Cr oss Se ct ion icon, Opt ion s, t hen Add a n e w Cr oss Se ct ion . River st at ion 5.29 was ent ered as t he new locat ion for t he cross sect ion and t he dat a for river st at ion 5.29 were ent ered, wit h t he downst ream reach lengt hs being from river st at ion 5.29 t o 5.13* . Since river st at ion 5.29 was added, t he exist ing reach lengt hs for river st at ions 5.39 were adj ust ed t o 320, 500, and 580 feet for t he LOB, m ain channel, and ROB, respect ively. Then, from t he Ge om e t r ic D a t a Edit or, t he following was select ed: Tools, XS I nt e r pola t ion , Be t w e e n 2 XS's. The upper river st at ion was set t o be 5.39 and t his caused t he lower river st at ion t o be 5.29. A m axim um dist ance of 100 feet was ent ered and t he int erpolat ion was perform ed. This yielded 4 new river st at ions bet ween 5.39 and 5.29, each 100 feet apart . The int erpolat ed river st at ions of 5.37* , 5.35* , and 5.31* were delet ed and t he program adj ust ed t he reach lengt hs accordingly. This produced t he river st at ion 5.33* , locat ed 300 feet downst ream from river st at ion 5.39. For furt her discussion on t he int erpolat ion procedures, refer t o Chapt er 6 of t he Use r 's M a nua l and Chapt er 4 of t he H ydr a ulic Re fe r e n ce M a n u a l. The goal was t o obt ain a river st at ion 290 feet downst ream from 5.39, and t his dist ance of 300 feet was det erm ined t o be appropriat e for an init ial locat ion. 5-12 Exam ple 5 Mult iple Openings Contraction Reach Length To det erm ine an init ial est im at e for t he cont ract ion reach lengt h, a sim ilar procedure as for t he expansion reach lengt h was used. From Table B.2 " Ranges of Cont ract ion Rat ios," it was det erm ined t hat t he cont ract ion rat io ( CR) ranged from 0.8 t o 1.4. An average value of 1.1 was select ed and t his yielded a cont ract ion reach lengt h, Lc , of: Lc = (CR )(Lobs ) = (1.1)(170) = 190 ft For t he current exam ple, t he cont ract ion reach lengt h is t he dist ance from river st at ion 5.49* t o river st at ion 5.41, a m ain channel dist ance of 478 feet . Therefore, a new cross sect ion, locat ed a dist ance of 190 feet upst ream from river st at ion 5.41 was insert ed. The dat a for t his new cross sect ion was obt ained from t he USGS at las, nam ely river m ile 5.44. This river st at ion is locat ed 170 feet upst ream from river st at ion 5.41 and was considered appropriat e for an init ial est im at e of t he cont ract ion reach lengt h. Finally, t he reach lengt h values for river st at ion 5.61 were adj ust ed t o account for t he inclusion of t he new cross sect ion. Coefficients of Expansion and Contraction The coefficient s of expansion and cont ract ion are used by t he program t o det erm ine energy losses due t o t he change in cross sect ional area of t he flow. I n t he vicinit y of t he bridge and culvert openings, t he expansion and cont ract ion coefficient s were chosen as 0.5 and 0.3, respect ively. These values represent coefficient s in a range bet ween a t ypical bridge sect ion and an abrupt t ransit ion. I n t he areas t hroughout t he rem aining port ion of t he river reach, t he expansion and cont ract ion coefficient s were set at 0.3 and 0.1, respect ively. All of t hese values are init ial est im at es and should be reviewed by t he user t o det erm ine t heir im pact on t he result ing wat er surface elevat ions. Aft er t he expansion and cont ract ion reach lengt hs were m odified and t he expansion and cont ract ion coefficient s were det erm ined, t he adj ust ed geom et ry was saved as a file ent it led " Culvert Group + Relief Bridge." Then, t his geom et ry file and t he st eady flow dat a file were saved as a new plan ent it led " Modified Condit ions." By saving new files, t he original dat a set obt ained from Exam ple 2 rem ained unchanged and t his will allow for a com parison bet ween t he m ult iple opening dat a and t he dat a t hat cont ained j ust t he single bridge geom et ry. Finally, by act ivat ing t he new adj ust ed geom et ry plan, t he user can view t he reach lengt hs by act ivat ing t he Ge om e t r ic D a t a Edit or , and t hen select ing Ta ble s, and Re a ch Le n gt h s. This t able is shown in Figure 5.8. Sim ilarly, t he coefficient s can be viewed by select ing Ta ble s and t hen Coe fficie n t s. 5-13 Exam ple 5 Mult iple Openings Figure 5-8: Reach Lengths Table for Modified Conditions Plan Steady Flow Analysis Aft er all of t he geom et ric dat a were ent ered, t he st eady flow dat a file was creat ed. From t he m ain program window, select Edit and t hen St e a dy Flow D a t a . Three profiles were select ed t o be calculat ed wit h flows of 5000, 10000, and 14000 cfs. Then, t he downst ream boundary condit ions were est ablished as 209.5, 210.5, and 211.8. This st eady flow dat a file is ident ical t o t he file produced during Exam ple 2, and was used for t his exam ple. The user is referred t o Exam ple 2 for a furt her discussion on developing t his st eady flow dat a file. Finally, t he st eady flow analysis was perform ed. From t he m ain program window, Run and t hen St e a dy Flow Ana lysis was select ed. A short ident ificat ion for t he plan was ent ered as " Mult Open." A subcrit ical flow regim e was select ed and t he analysis was perform ed by select ing COM PUTE. Multiple Opening Output Analysis This exam ple dem onst rat es t he use of t he HEC- RAS program t o analyze m ult iple openings t hat occur at t he sam e river st at ion. Therefore, t his analysis will concent rat e on t he review of t he m ult iple opening out put . For a det ailed discussion on t he review of t he individual culvert and bridge openings, refer t o Exam ple 2 for t he bridge analysis and t o Exam ples 3 and 4 for t he culvert analysis. This analysis will review: t he evaluat ion of t he expansion and cont ract ion reach lengt hs; t he wat er surface profiles; and finally t he m ult iple opening profile t able. 5-14 Exam ple 5 Mult iple Openings Cross Section Placement Evaluation Aft er t he analysis was perform ed, t he expansion and cont ract ion reach lengt hs were evaluat ed using t he regression equat ions out lined in t he recent USACE docum ent [ HEC- 1995] and which also appear in Appendix B of t he H ydr a u lic Re fe r e n ce M a n ua l. These reach lengt hs were evaluat ed for t he m ain bridge opening during t he largest flow event . However, t he result s from t he regression equat ions did not provide reasonable result s for t he current exam ple. One of t he problem s t hat arose was t hat t he com put ed cont ract ion reach lengt hs were longer t han t he expansion reach lengt hs. This is not reasonable because t ypically, t he cont ract ion reach lengt h is short er t han t he expansion reach lengt h. This com put ed result m ay have arisen because t he dat a for t he exam ple are not wit hin t he range of dat a used t o develop t he regression equat ions. The alt ernat e equat ions, provided by t he docum ent , also produced inconsist ent result s. The regression equat ions were developed based on single bridge opening dat a set s. Therefore, t hey m ay not apply for a m ult iple opening bridge. The m odeler should always use engineering j udgm ent t o t he result s obt ained from t hese equat ions. For t his exam ple, t he reach lengt hs est im at ed at t he beginning of t he exam ple will be used for t he final analysis. These reach lengt hs were based on average expansion and cont ract ion rat ios for t he m ain bridge opening. I t was considered t hat t hese rat ios provided a reasonable basis for est im at ing t he expansion and cont ract ion reach lengt hs. I t should be not ed t hat t hese reach lengt hs were significant ly less t han t he reach lengt hs used in Exam ple 2, wit h j ust t he m ain bridge opening. Wit h t he m ult iple openings, t he flow does not have t o cont ract and expand as m uch as it would for a single opening. Water Surface Profiles From t he m ain program window, select Vie w and t hen W a t e r Sur fa ce Pr ofile s. This will result in t he display shown in Figure 5.9. The figure shows t he t hree wat er surface profiles for t he t hree flows of 5000, 10000, and 14000 cfs. By zoom ing in on t he m ult iple opening locat ion, it can be seen t hat t he wat er surface for t he high flow did not over t op t he bridge decking and t his was t he original goal for inst alling t he relief bridge and culvert group. 5-15 Exam ple 5 Mult iple Openings Figure 5-9: Water Surface Profiles for Modified Conditions Plan Multiple Opening Profile Table To review t he m ult iple opening profile t able, from t he m ain program window select Vie w , Pr ofile Ta ble , St d. Ta ble s, and t hen M u lt iple Ope n ing. This will display t he t able shown in Figure 5.10. ( Not e: The t able colum ns widt hs in Figure 5.10 were reduced t o display t he full t able cont ent s in t he figure. Therefore, t he colum n headings m ay not reflect t he full descript ions.) 5-16 Exam ple 5 Mult iple Openings Figure 5-10: Multiple Opening Profile Table As shown in Figure 5.10, t he rows in t he t able are divided int o t hree groups, one for each profile. The first t hree rows are for t he first flow of 5000 cfs, t he second group is for t he flow of 10000 cfs, and t he t hird group is for t he flow of 14000 cfs. The second colum n in t he t able displays t he river st at ions and t he t ype of t he m ult iple opening, in t he order as t hey were ent ered in t he M u lt iple Ope n ing Ana lysis D a t a Edit or . The t hird colum n displays t he t ot al flow rat e t hrough each of t he opening t ypes. For exam ple, during t he first flow profile ( 5000 cfs) , t here was 106.28 cfs flowing t hrough t he culvert group, 4448.10 cfs t hrough t he m ain bridge, and finally 445.62 cfs t hrough t he relief bridge. The sum of t hese values equals 5000 cfs. The fift h colum n displays t he calculat ed upst ream energy gradeline elevat ion for each opening. During t he m ult iple opening analysis, t he program perform s an it erat ive procedure t o balance t he upst ream energy for all t he openings. To do t his, t he program st art s wit h an init ial flow dist ribut ion t hrough each opening and t hen calculat es t he upst ream energy for each opening. I f t he energy values are wit hin a specified t olerance ( 0.05 ft ) , t hen t he solut ion is final. I f t he energy values for each opening are not wit hin t he specified t olerance, t hen a new flow dist ribut ion is est im at ed and t he procedure is repeat ed, up t o a m axim um of 30 it erat ions. To det erm ine t he ranges for t he flow dist ribut ion, t he st agnat ion lim it s are used. For a furt her discussion on t he m ult iple opening solut ion schem e, t he user is referred t o Chapt er 6 of t he Use r 's M a nua l and Chapt er 7 of t he H ydr a u lic Re fe r e n ce M a n u a l. I n reviewing t he calculat ed energy gradeline values, it can be seen t hat for t he t hree flow profiles, t he energy gradeline elevat ions were balanced wit hin t he specified default t olerance of 0.05 feet . Wit h t hese energy gradeline values, t he program t hen calculat es an upst ream wat er surface elevat ion for each opening by subt ract ing t he velocit y head from t he energy gradeline. These wat er surface elevat ions are displayed in t he sixt h colum n. 5-17 Exam ple 5 Mult iple Openings Finally, t he last t wo colum ns of t he m ult iple opening profile t able display t he calculat ed left and right st agnat ion point s. These st agnat ion point s are t he flow dist ribut ion lim it s t hat were det erm ined by t he program in order t o balance t he upst ream energy gradelines. For t he first flow profile, it can be seen t hat t he flow dist ribut ion was est ablished from upst ream X- coordinat es of 73.61 t o 310 for t he culvert , from 310 t o 700 for t he m ain bridge, and from 700 t o 1287 for t he relief bridge. For t he culvert , t he program used a left st agnat ion point of 73.61 feet . This value is t he X- coordinat e where t he culvert wat er surface elevat ion of 213.22 int ersect ed t he left side of t he cross sect ion. The right st agnat ion point for t he culvert was det erm ined t o be 310 feet . Therefore, in order t o balance t he upst ream energy gradelines, t he program det erm ined t hat t he flow rat e t hrough t he culvert required an upst ream conveyance t hat encom passed cross sect ion st at ion 73.61 t o 310. Sim ilarly, for t he first flow profile, t he program det erm ined t hat t he flow t hrough t he m ain bridge opening would be from an upst ream X- coordinat e of 310 t o 700 and t he flow rat e t hrough t he relief bridge would be from upst ream X- coordinat es of 700 t o 1287. The value of 1287 is t he Xcoordinat e where t he relief bridge wat er surface elevat ion of 213.23 coincided wit h t he right edge of t he cross sect ion. Upon reviewing t he left and right st agnat ion point s for t he t hird flow profile, it can be seen t hat t he st agnat ion point bet ween t he culvert and t he m ain bridge is a value of 310 feet as opposed t o t he previous value of 390. Therefore, in order t o balance t he upst ream energy grade line elevat ions for t he t hree openings, a great er port ion of t he t ot al flow was required t o t ravel t hrough t he m ain bridge opening during t his higher flow event . Sim ilarly, t he left culvert st agnat ion point and t he right relief bridge st agnat ion point have changed t o reflect t hat t he higher wat er surface elevat ions are approaching t he lim it s of t he cross sect ion widt h. Finally, t he M u lt iple Ope n ing Pr ofile Ta ble provides addit ional inform at ion such as t he t ot al cross sect ional flow area and t he t op widt h of t he effect ive flow. The descript ions for t he colum n headings will appear in t he dialog box at t he bot t om of t he t able when an ent ry in t he specific colum n is select ed. As discussed previously, t he energy gradeline elevat ions shown in t he M u lt iple Ope n ing Pr ofile Ta ble are t he energy values for each of t he openings, upst ream of t he openings. However, since t he program is a one dim ensional m odel, t he program m ust det erm ine only one energy grade line value t o use at t he upst ream cross sect ion. To det erm ine t his energy value, t he program uses a flow weight ing m et hod t o det erm ine t he average energy at t he upst ream cross sect ion. Then, t his average energy is used t o calculat e one wat er surface elevat ion for t he ent ire upst ream cross sect ion. To review t he energy gradeline and wat er surface elevat ions t hat were used as t he final answer for t he upst ream cross sect ion, from t he m ain program window select Vie w , Cr oss Se ct ion Ta ble , Type , and t hen Cr oss Se ct ion . Toggle t o river st at ion 5.41 ( t he upst ream cross sect ion for t his exam ple) and select profile 3. This will display t he t able as shown in Figure 5.11. 5-18 Exam ple 5 Mult iple Openings For t he t hird flow profile, t he program calculat ed t hat t he upst ream energy gradeline elevat ions for t he culvert , m ain bridge, and relief bridge were 216.55, 216.58, and 216.57 feet , respect ively, as shown in t he M u lt iple Ope n in g Pr ofile Ta ble . However, as described above, t he program can only use one energy grade line elevat ion at t he upst ream cross sect ion. The flow weight ed upst ream energy gradeline elevat ion used for cross sect ion 5.41 is shown in Figure 5.11 t o be 216.58. Addit ionally, t he program had calculat ed t he upst ream wat er surface elevat ions for each of t he t hree openings as 216.54, 216.14, and 216.54, respect ively, as shown in t he M u lt iple Ope n in g Pr ofile Ta ble . However, t he program can only use one wat er surface elevat ion at t he upst ream cross sect ion. To obt ain t his one wat er surface elevat ion, t he program used t he average energy value, subt ract ed t he average velocit y head for t he ent ire cross sect ion of 0.38, and det erm ined t hat t he upst ream wat er surface elevat ion was 216.20, as shown in Figure 5.11. This wat er surface elevat ion is calculat ed from t he average energy of t he upst ream sect ion. The act ual wat er surface elevat ions at t he bridge are m ore likely reflect ed by t he values as shown in t he M u lt iple Ope n ing Pr ofile Ta ble . As a final com ponent of t he analysis, t he flow dist ribut ion for t he t hree openings was com pared t o t he flow in t he LOB, m ain channel, and ROB at t he river st at ions upst ream and downst ream of t he openings. From t he M u lt iple Ope n in g Pr ofile Ta ble ( Figure 5.10) , t he flow for t he t hird profile t hrough t he culvert , m ain bridge, and relief bridge were 567.05, 9953.13, and 3479.82 cfs, respect ively. Since t he culvert group is locat ed in t he LOB, t he m ain bridge is locat ed over t he m ain channel, and t he relief bridge is locat ed in t he ROB, t hese flow values should approxim at e t he flows in t he LOB, m ain channel, and ROB at river st at ions 5.41 and 5.39. As shown in Figure 5.11, t he flows for t he t hird profile in t he LOB, m ain channel, and ROB were 676.03, 10182.89, and 3141.08 cfs, respect ively. Sim ilarly, t he flows at river st at ion 5.39 were 705.59, 9931.64, and 3362.77 cfs. These flow dist ribut ions are sim ilar and reflect t he t ransit ion of t he flow rat es across t he cross sect ions. 5-19 Exam ple 5 Mult iple Openings Figure 5-11: Cross Section Table for Profile 3, River Station 5.41 Summary The geom et ry of Exam ple 2 was m odified t o prevent weir flow from occurring over t he m ain bridge decking. This was accom plished by defining a culvert group and a relief bridge on t he left and right side of t he m ain bridge, respect ively. These addit ional openings lowered t he wat er surface upst ream of t he bridge so t hat weir flow did not occur. Figure 5.12 shows a com parison of t he t hird wat er surface profile for t he m ult iple opening and for t he original river reach wit h j ust t he m ain bridge. To develop t he figure, select Vie w and t hen W a t e r Su r fa ce Pr ofile s from t he m ain program window. Then select Opt ion s and Pla ns and choose bot h of t he plans. Finally, Opt ion s and Pr ofile s were chosen and only t he t hird profile was select ed t o be plot t ed. This result ed in t he display shown in Figure 5.12, which clearly shows t hat t he m odified condit ions decreased t he upst ream wat er surface profile so t hat no weir flow occurred. 5-20 Exam ple 5 Mult iple Openings Figure 5-12: Third Flow Profile for Base Conditions vs. Multiple Openings Plans Aft er t he analysis was perform ed, t he user can review t he flow param et ers for t he culvert and t he relief bridge and adj ust t he size of t hese openings t o develop t he m ost pract ical alt ernat ive t o prevent t he weir flow from occurring. To com pare t he result s in t abular form at , from t he m ain program window select Vie w and t hen Pr ofile Ta ble . St a nda r d Ta ble 1 was t hen select ed from t he St d. Ta ble s m enu. Finally, bot h of t he plans and only t he t hird profile were select ed from t he Opt ion s m enu and t his result ed in t he t able as shown in Figure 5.13. By com paring t he values in t he t able, t he user can obt ain required inform at ion t o assist in t he det erm inat ion of any changes t hat m ay be necessary. For exam ple, as can be seen in Figure 5.13, t he change in t he wat er surface elevat ion at river st at ion 5.41 was 1.24 feet ( from 217.44 t o 216.20 feet ) . The m odeler can use t his inform at ion t o det erm ine if any addit ional decrease is necessary. 5-21 Exam ple 5 Mult iple Openings Figure 5-13: Standard Table 1 for Base and Modified Plans, Third Profile 5-22 Exam ple 6 Floodway Det erm inat ion CH APT ER 6 Floodway Determination Purpose This exam ple dem onst rat es t he use of HEC- RAS t o perform a floodplain encroachm ent analysis. Floodplain and floodway evaluat ions are of subst ant ial int erest t o planners, land developers, and engineers, and are t he basis for floodplain m anagem ent program s. Most of t he st udies are conduct ed under t he Nat ional Flood I nsurance Program and follow t he procedures in t he " Flood I nsurance St udy Guidelines and Specificat ions for St udy Cont ract ors," FEMA 37 ( Federal Em ergency Managem ent Agency, 1985) . FEMA 37 defines a floodway " ...as t he channel of a river or ot her wat ercourse and t he adj acent land areas t hat m ust be reserved in order t o discharge t he base flood wit hout cum ulat ively increasing t he wat er- surface elevat ion by m ore t han a designat ed height ." Norm ally, t he base flood is t he one- percent chance event ( 100- year recurrence int erval) , and t he designat ed height is one foot , unless t he st at e has est ablished a m ore st ringent regulat ion for m axim um rise. The floodway is usually det erm ined by an encroachm ent analysis, using an equal loss of conveyance on opposit e sides of t he st ream . For purposes of floodway analysis, t he floodplain fringe rem oved by t he encroachm ent s is assum ed t o be com plet ely blocked. For t his exam ple, t he floodplain encroachm ent analysis was perform ed t o det erm ine t he m axim um encroachm ent possible, const rained by a 1 foot m axim um increase in wat er surface elevat ion from t he nat ural profile. The geom et ric dat a used in t his exam ple are ident ical t o t he cross- sect ion and bridge geom et ric dat a used in Exam ple 2. To review t he dat a files for t he current exam ple, from t he m ain program window select File and t hen Ope n Pr oj e ct . Select t he proj ect labeled " Floodway Det erm inat ion - Exam ple 6." This will open t he proj ect and act ivat e t he following files: Plan: " Met hod 5 Encroachm ent " Geom et ry: " Exist ing Condit ions" Flow: " Base + 1 ft Target Dept h" 6-1 Exam ple 6 Floodway Det erm inat ion Floodplain Encroachment Analysis Procedure Current ly, t he HEC- RAS program has 5 m et hods t o det erm ine floodplain encroachm ent s. These m et hods are: Met hod 1 - User ent ers right and left encroachm ent st at ions Met hod 2 - User ent ers fixed t op widt h Met hod 3 - User specifies t he percent reduct ion in conveyance Met hod 4 - User specifies a t arget wat er surface increase Met hod 5 - User specifies a t arget wat er surface increase and m axim um change in energy For a det ailed discussion on each of t hese m et hods, t he user is referred t o Chapt er 9 of t he Hydraulic Reference Manual. The goal of perform ing a floodplain encroachm ent analysis is t o det erm ine t he lim it s of encroachm ent t hat will cause a specified change in wat er surface elevat ion. To det erm ine t he change in wat er surface elevat ion, t he program m ust first det erm ine a nat ural profile wit h no encroachm ent s. This base profile is t ypically com put ed using t he one percent chance discharge. The com put ed profile will define t he floodplain, as shown in Figure 6.1. Then, by using one of t he 5 encroachm ent m et hods, t he floodplain will be divided int o Δ Water Surface Natural Water Surface Encroached Water Surface Cross Section View Plan View Main Channel Floodway Fringe Floodway 100 - Year Floodplain Figure 6-1: Floodway Definition Sketch 6-2 Floodway Fringe Exam ple 6 Floodway Det erm inat ion t wo zones: t he floodway fringe and t he floodway. The floodway fringe is t he area blocked by t he encroachm ent . The floodway is t he rem aining port ion of t he floodplain in which t he one- percent chance event m ust flow wit hout raising t he wat er surface m ore t han t he t arget am ount . For t his exam ple, t he following procedure was em ployed t o perform t he encroachm ent analysis: • Det erm ine t he 100- year flood profile • Met hod 5 opt im izat ion procedure • Met hod 4 - wit h 3 t arget dept hs • Met hod 4 - wit h 1 t arget dept h • Met hod 1 - final delineat ion of floodway • Review of floodway delineat ion sket ch To perform t he floodplain encroachm ent analysis for t his exam ple, t he first st ep was t o develop a m odel of t he river reach t hat would com put e t he 100year flood profile. This m odel m ust be developed and calibrat ed t o t he fullest ext ent possible because it defines t he base flood elevat ions and all subsequent calculat ions will be based upon t his profile. This was accom plished in Exam ple 2. Aft er t he base profile was com put ed, t he Met hod 5 procedure was chosen as an init ial at t em pt t o calculat e t he encroachm ent s. Met hod 5 will t ypically calculat e reasonable encroachm ent st at ions for " well behaved" st ream s. That is, for st ream s t hat exhibit m inor changes in cross sect ion geom et ry and have sm all losses due t o bridges and culvert s. I f t he river reach has abrupt changes in geom et ry or orient at ion, cont ains a flow cont rolling st ruct ure, or t he encroachm ent s encount er t he m ain channel bank st at ions, t hen Met hod 5 m ay produce errat ic result s at t hese locat ions. I f Met hod 5 produces inconsist ent result s, t hen Met hod 4 m ay be ut ilized. Met hod 4 is frequent ly used for a floodplain encroachm ent analysis. The init ial approach is t o use t his m et hod wit h several t arget wat er surface increases. Finally, aft er t he result s are obt ained from t he Met hod 4 analysis, Met hod 1 was used t o furt her refine t he encroachm ent st at ions. The m odeler should sket ch t he floodway on a t opographic m ap t o visually inspect t he floodway and allow for sm oot h t ransit ions. The com put ed floodway is considered prelim inary, in t hat t he regulat ing com m unit y m ust approve and adopt . Each of t hese st eps, as perform ed for t his exam ple, are discussed in det ail in t he following sect ions. Base Flood Profile To perform t he floodway analysis, t he user m ust first det erm ine t he nat ural ( exist ing condit ions) 100- year flood wat er surface profile for t he river reach. 6-3 Exam ple 6 Floodway Det erm inat ion Therefore, a m odel of t he exist ing river syst em m ust first be developed and calibrat ed t o t he fullest ext ent possible. For t his current exam ple, t he river reach and bridge geom et ric dat a of Exam ple 2 were used. During Exam ple 2, t he HEC- RAS program was used t o develop a calibrat ed m odel of t he " Kent wood" Reach of Beaver Creek for a flow of 14000 cfs. During t he analysis of t hat flood event , it was det erm ined t hat t he pressure/ weir m et hod produced wat er surface values t hat were com parable t o t he observed dat a. Verificat ion t hat t he m odel is adequat ely m odeling t he river syst em is an im port ant st ep before st art ing t he floodway analysis. For t his exam ple, t he pressure/ weir geom et ry file from Exam ple 2 was used. This file was renam ed t o be " Exist ing Condit ions" and was used for all of t he plans developed here. Method 5 Optimization Procedure I n general, when perform ing a floodway analysis, encroachm ent Met hods 4 and 5 are norm ally used t o get a first cut at t he floodway. For t his exam ple, Met hod 5 was used as an init ial at t em pt t o det erm ine t he encroachm ent st at ions. Encroachm ent Met hod 5 is an opt im izat ion schem e t hat will use a t arget increase in t he wat er surface elevat ion and/ or a m axim um lim it for t he increase in energy t o obt ain t he encroachm ent st at ions. The program will at t em pt t o m eet t he t arget wat er surface while m aint aining an increase in energy t hat is less t han t he m axim um . Method 5 Steady Flow Data To perform t he Met hod 5 encroachm ent analysis, t he flow dat a were first ent ered. From t he m ain program window, select Edit and t hen St e a dy Flow D a t a . This act ivat ed t he St e a dy Flow D a t a Edit or . For t he Met hod 5 analysis, 2 wat er surface profiles were chosen t o be calculat ed. The first profile was used t o det erm ine t he base profile and t he second profile was used t o det erm ine t he encroached profile. The flow values for bot h of t he profiles were ent ered as 14000 cfs, t he flow value t hat t he m odel was calibrat ed. Then, t he Bou nda r y Con dit ion s icon was select ed and t he D ow n st r e a m Know n W a t e r Su r fa ce elevat ions were ent ered as 211.8 and 212.8. The first downst ream boundary condit ion ( 211.8) was det erm ined during Exam ple 2. The second downst ream boundary condit ion ( 212.8) was set at 1 foot higher t o coincide wit h t he m axim um possible change in downst ream wat er surface elevat ion. This account ed for t he possibilit y of fut ure encroachm ent s downst ream of t he m odeled reach. Finally, t he st eady flow dat a was saved as " Base + 1 ft Target Dept h." Method 5 Encroachment Data To ent er t he dat a for encroachm ent Met hod 5, from t he m ain program window select Ru n , St e a dy Flow Ana lysis, Opt ions, and t hen En cr oa ch m e n t s. This will act ivat e t he En cr oa chm e n t s D a t a Edit or as shown in Figure 6.2. The edit or and t he ent ering of dat a is divided int o t he 6-4 Exam ple 6 Floodway Det erm inat ion following sect ions: global inform at ion; reach and river st at ion inform at ion; and m et hod and t arget values. The following sect ions describe each of t he dat a ent ry it em s. For a furt her discussion of t he dat a ent ry procedure, t he user is referred t o Chapt er 9 of t he Use r 's M a n u a l. Figure 6-2: Encroachment Data Editor – Method 5 Analysis Global I nform at ion. The global inform at ion is applied t o all of t he reaches and cross sect ions t hat will be select ed for t he analysis. The first input for t he global inform at ion is t he Equa l Conve ya nce Re duct ion box. I f t his box is select ed, t hen t he program will encroach by sim ult aneously rem oving an equal am ount of conveyance on bot h sides of t he m ain channel. As t he am ount of conveyance is rem oved, if one of t he encroachm ent s reaches t he m ain channel bank st at ion ( or t he offset ) , t hen t he program will cont inue t o encroach on t he ot her side unt il t he t arget values are obt ained or unt il t he encroachm ent on t he ot her side reaches t he m ain channel bank st at ion ( or t he offset ) . I f t he equal conveyance box is not select ed, t hen t he program will encroach by m aint aining a loss of conveyance in proport ion t o t he dist ribut ion of t he nat ural overbank conveyance. The equal conveyance reduct ion applies t o Met hods 3, 4, and 5; and, for t his exam ple, t he opt ion was select ed. The next global inform at ion it em s are t he Le ft ba nk offse t and t he Righ t ba nk offse t . These offset s lim it t he dist ance of t he encroachm ent s. Wit hout an offset , encroachm ent s can go up t o t he bank st at ions, elim inat ing t he ent ire overbank. For t his exam ple, t he offset s were set t o be 10 feet for bot h t he left and right bank. Therefore, t he lim it of encroachm ent was 10 feet t o 6-5 Exam ple 6 Floodway Det erm inat ion t he left of t he left channel bank st at ion and 10 feet t o t he right of t he right channel bank st at ion. Re a ch a n d Rive r St a t ion I nfor m a t ion . The next it em s t o select in t he encroachm ent s edit or are t he Rive r and Re a ch t hat will be analyzed. For t his exam ple, t here is only one river and reach: t he " Kent wood" reach on t he river " Beaver Creek." Next , t he St a r t ing Rive r St a t ion and Ending Rive r St a t ion were ent ered. The analysis was set t o begin at river st at ion 5.99 and end at river st at ion 5.00, t he ent ire river reach. Finally, t he Pr ofile was select ed. For a Met hod 5 analysis, only 2 profiles are necessary. The first profile will be used t o det erm ine t he base wat er surface profile and cannot be select ed in t he encroachm ent s dat a edit or. The second profile is select ed t o be used for t he Met hod 5 analysis. M e t h od a nd Ta r ge t Va lu e s. Met hod 5 was select ed for t his analysis. When a m et hod is select ed, t he dat a ent ry fields required for t hat m et hod will appear im m ediat ely under t he m et hod field. For Met hod 5, t he fields Target W S cha nge ( ft ) and Ta r ge t EG ch a nge ( ft ) appeared. A t arget wat er surface change of 1.0 foot and a t arget energy change of 1.2 feet were ent ered. Typically, t he energy t arget will be chosen t o be slight ly great er t han t he wat er surface t arget . The energy t arget will act as an upper lim it during t he it erat ions t o prevent t he encroachm ent from get t ing very large. The next st ep is t o select t he range of t he river reach t hat will be analyzed, for t he t arget values t hat were ent ered. For t his exam ple, t he Se t Se le ct e d Ra n ge but t on was select ed and t his applied Met hod 5 and t he chosen t arget s t o t he select ed range of river st at ions 5.99 t o 5.00 for t he Beaver Creek reach. By select ing t his but t on, t he fields in t he t able were filled wit h t he corresponding m et hod and values. I n t he t able, since Met hod 5 was select ed, t he heading Va lu e 1 corresponds t o t he t arget wat er surface change and Va lu e 2 corresponds t o t he t arget energy change. When ot her m et hods are select ed, t he value 1 and value 2 colum ns will represent t he specific dat a input it em s for t he m et hod. ( Not e: Som e m et hods only require 1 value.) As a final not e, t he user can now edit t he dat a t able and change any of t he m et hods and value it em s for any specific river st at ion. For t his exam ple, t he t able was not edit ed at t his t im e. The OK but t on was t hen select ed at t he bot t om of t he encroachm ent edit or. This prom pt ed t he St e a dy Flow Ana lysis W indow t o appear. Then t he geom et ry file " Exist ing Condit ions" and t he st eady flow file " Base + 1 ft Target Dept h" were saved as t he plan " Met hod 5 Encroachm ent ." Finally, t he Short I D was ent ered as " M5" and t he COM PUTE but t on was select ed for t he subcrit ical flow analysis. Method 5 Output Review The out put of t he encroachm ent analysis can be viewed bot h graphically and in t abular form at . For t his analysis, t he encroachm ent dat a t ables were reviewed. From t he m ain program window, select Vie w , Pr ofile Sum m a r y Ta ble , and t hen St d. Ta ble s. The program generat es 3 encroachm ent t ables, wit h each t able providing som e of t he sam e inform at ion and addit ional dat a. For t his analysis, select En cr oa ch m e n t 1 . A port ion of t his t able is shown in Figure 6.3. The figure displays t he bot t om port ion of t he t able. 6-6 Exam ple 6 Floodway Det erm inat ion The t able is divided int o set s of rows, wit h each set cont aining t wo rows. The first row in each set is for t he un- encroached profile and t he second row is for t he encroached profile. Colum ns one and t wo show t he reach and river st at ions and t he t hird colum n shows t he calculat ed wat er surface elevat ion. The fourt h colum n shows t he difference bet ween t he first profile and each of t he encroached profiles. St art ing at river st at ion 5.00 ( at t he bot t om of t he t able) , t he difference in t he wat er surface elevat ions for t he encroached profile is 1 foot because t he downst ream boundary condit ion set t he elevat ion change of 1 foot . Review of t he m et hod 5 result s shows t hat t he m et hod provided reasonable result s up t o t he bridge t o river st at ion 5.39. However, at t he bridge t he m et hod produced a negat ive surcharge. Furt her upst ream , t he encroachm ent m et hod produced result s up t o t he 1.0 foot allowable rise. This m et hod had difficult y det erm ining t he encroachm ent s around t he bridge because t he bridge hydraulics perform ed like a local cont rol. This will be discussed furt her in t he Met hod 4 analysis. From t he analysis of t he Met hod 5 out put , it was det erm ined t hat t he result s were not accept able upst ream of t he bridge and an alt ernat e procedure should be t hen undert aken. The result s from Met hod 5 up t o t he bridge could be used as a st art ing point for fut ure analysis wit h a different m et hod. Figure 6-3: Encroachment Table 1 for Method 5 Analysis 6-7 Exam ple 6 Floodway Det erm inat ion Method 4 Encroachment Analysis - Trial 1 An alt ernat ive approach t o perform t he encroachm ent analysis is t o use Met hod 4. The Met hod 4 analysis is sim ilar t o Met hod 5, wit hout t he it erat ive solut ion t echnique. To perform t he Met hod 4 analysis, t he program uses t he following procedure: 1) First , t he program com put es t he base wat er surface profile by using t he dat a from t he first profile in t he st eady flow dat a edit or. Wit h t his profile, t he program calculat es ( am ong ot her param et ers) t he wat er surface profile and t he conveyance for each river st at ion. 2) For t he second profile, st art ing at t he first river st at ion, t he program t akes t he user supplied t arget wat er surface increase and adds t his value t o t he base wat er surface elevat ion. Wit h t he increased wat er surface elevat ion, t he program calculat es t he new conveyance at t his river st at ion. ( Not e: The first river st at ion is locat ed at t he downst ream end of t he river syst em for a subcrit ical flow analysis.) 3) The program t hen det erm ines t he increase in conveyance bet ween t he base profile and t he increased wat er surface profile. One half of t his increase in conveyance will be rem oved from each side of t he cross sect ion fringe, if t he equal conveyance opt ion was select ed. I f t he equal conveyance opt ion was not select ed, t hen t he program will rem ove t he conveyance from bot h sides in proport ion t o t he nat ural conveyance. I n eit her case, t he difference of conveyance will be rem oved from t he cross sect ion, if possible. 4) To rem ove t he conveyance, t he program st art s at t he lim it s of t he increased wat er surface profile and encroaches on bot h sides t owards t he m ain channel. As t he conveyance is rem oved from bot h sides, t he program checks t o det erm ine if t he encroachm ent has reached t he m ain channel bank st at ion ( or t he offset ) on t hat side. I f t he m ain channel bank st at ion ( or offset ) is encount ered, t hen t he program will st op encroaching on t hat side and will m ake up t he difference on t he ot her side. I f t he encroachm ent on t he ot her side encount ers t he m ain channel bank st at ion ( or offset ) , t hen t he program can no longer cont inue t o encroach. 5) Once t he increase in conveyance has been rem oved from t he cross sect ion, wit h t he higher wat er surface elevat ion, t he encroachm ent st at ions are set . Also, t he conveyance at t he cross sect ion wit h t he higher wat er surface is now t he sam e as t he original conveyance at t he cross sect ion ( if possible) . Then t he program uses t he new geom et ry of t he encroached cross sect ion t o det erm ine t he dept h of flow at t hat cross sect ion. Since t he geom et ry of t his river st at ion has changed, t he value of t he frict ion slope and velocit y head will change. Also, t he m agnit ude of t he expansion or cont ract ion losses will change. Therefore, when t he program calculat es t he wat er surface elevat ion wit h t he new geom et ry, t he dept h of flow will t ypically be different t han t he t arget value ent ered by t he user. I n ot her words, even t hough t he t ot al conveyance is t he sam e at t his river stat ion, t he geom et ry, frict ion slope, and energy losses are different and t his will produce a different flow dept h at t his river st at ion. Oft en, t he result ing dept h of flow will be great er t han t he t arget increase in wat er surface elevat ion. Therefore, t he first run wit h Met hod 4 is 6-8 Exam ple 6 Floodway Det erm inat ion t ypically applied wit h several t arget values, usually sm aller t han t he m axim um increase. 6) The program t hen m oves t o t he next river st at ion and st eps 2 t hrough 5 are repeat ed. This process cont inues unt il t he last river st at ion is evaluat ed. Method 4 Steady Flow Data - Trial 1 To perform t he Met hod 4 encroachm ent analysis, t he flow dat a was first ent ered. The St e a dy Flow D a t a Edit or was act ivat ed and 4 wat er surface profiles were chosen t o be calculat ed. The first profile is st ill t he base profile. The second, t hird and fourt h profiles were used t o det erm ine t he encroached profiles wit h different t arget dept hs. The flow values for all of t he profiles were ent ered as 14000 cfs, t he 1 percent chance flood event . Then, t he Bou nda r y Condit ion s icon was select ed and t he D ow nst r e a m Know n W a t e r Sur fa ce elevat ions were ent ered as 211.8, 212.8, 212.8, and 212.8. The first downst ream boundary condit ion ( 211.8) was det erm ined during Exam ple 2. The ot her downst ream boundary condit ions ( 212.8) were set 1 foot higher t o coincide wit h t he m axim um possible change in downst ream wat er surface elevat ion. This account ed for t he possibilit y of fut ure encroachm ent s downst ream of t he m odeled reach. Finally, t he st eady flow dat a was saved as " Base + 3 Target Dept hs." Method 4 Encroachment Data - Trial 1 The Met hod 4 encroachm ent dat a were t hen ent ered, sim ilar t o t hat for Met hod 5. First , t he En cr oa ch m e n t D a t a Edit or was select ed from t he Opt ion s m enu of t he St e a dy Flow Ana lysis window. The encroachm ent edit or is shown in Figure 6.4. Then, t he global inform at ion of equal conveyance reduct ion and a 10 foot left and right offset were select ed. The reach was select ed as " Kent wood" and t he st art ing and ending river st at ions were set as 5.99 and 5.00, respect ively. Next , profile 2 and Met hod 4 were select ed. Since Met hod 4 was chosen, t his caused t he dat a ent ry box Ta r ge t W S cha nge ( ft ) t o appear. A t arget value of 0.8 feet was t hen ent ered and t he Se t Se le ct e d Ra nge but t on was chosen. This filled in t he t able wit h t he Met hod 4 and 0.8 foot change in wat er surface for t he ent ire reach. Finally, t he t arget value for river st at ion 5.00 was changed t o 1.0 foot . This will assum e t hat t he encroachm ent m at ched t he t arget wat er surface of t he downst ream boundary condit ion. I f t he m odeler is aware of t he act ual wat er surface increase at t his river st at ion ( from ot her encroachm ent analyses) , t hen t his value should be used. Typically, t his inform at ion is not known and t herefore t he m odeler should include river st at ions below t he area of int erest so t hat t he boundary condit ions do not effect t he region of t he st udy. Next , Pr ofile 3 was select ed by depressing t he down arrow adj acent t o t he profile field. Then M e t h od 4 was chosen and a Ta r ge t W S cha n ge ( ft ) of 0.9 feet was ent ered. The Se t Se le ct e d Ra nge but t on was select ed and t his filled in t he t able wit h Met hod 4 and t arget values of 0.9 feet for t he select ed range. Then, t he t arget value at river st at ion 5.00 was changed t o 1.0 foot , as perform ed previously. This procedure was repeat ed once m ore wit h t he fourt h profile for Met hod 4 and a t arget wat er surface change of 1.0 6-9 Exam ple 6 Floodway Det erm inat ion foot . The user should not e t hat t his m et hod only requires one dat a input it em and, t herefore, t he dat a will appear under " Value 1" of t he t able. The OK but t on was t hen select ed t o close t he encroachm ent edit or. Finally, t he geom et ry file " Exist ing Condit ions" and t he st eady flow dat a file " Base + 3 Target Dept hs" were saved as a plan ent it led " Met hod 4 Encroachm ent - Trial 1." The Shor t I D in t he St e a dy Flow Ana lysis W indow was ent ered as " M4 - Trial 1." This ident ificat ion will assist t he user when analyzing t he out put . Then, t he COM PUTE but t on was select ed t o perform t he calculat ions. Figure 6-4: Encroachment Data Editor for Method 4 – Trial 1 Method 4 Output - Trial 1 To review t he out put , t he En cr oa ch m e n t 1 t able was select ed and a port ion of t his t able is shown as Figure 6.5. For each river st at ion, t here are four rows of dat a in t he t able. The first row is for t he nat ural, un- encroached profile. The second, t hird, and fourt h rows are for t he second, t hird, and fourt h profiles. These profiles were set wit h t arget values of 0.8, 0.9, and 1.0 foot , respect ively ( except for t he first river st at ion which had a const ant t arget of 1.0 foot ) . The first non- fixed colum n of t he t able shows t he wat er surface elevat ion for each profile. The second colum n displays t he change in wat er surface from t he nat ural profile for t he encroached river st at ion. Addit ional colum n headings show t he calculat ed value of t he energy gradeline, flow, calculat ed encroachm ent st at ions ( by t oggling t o t he right in t he t able) , et c. Depending upon t he required inform at ion, t he user can select 6-10 Exam ple 6 Floodway Det erm inat ion one of t hree encroachm ent t ables. Furt her discussion of t he encroachm ent t ables is present ed in Chapt er 9 of t he Use r 's M a nua l. Figure 6-5: Encroachment Table 1 for Method 4 – Trial 1 For t his review of t he first run of Met hod 4, t he m ain concern is wit h t he change in wat er surface elevat ion. The encroachm ent process and result ing wat er surface elevat ions were det erm ined using t he 6 st eps as described previously at t he beginning of t his sect ion. For river st at ion 5.00, t he change in wat er surface was 1.0 foot for all of t he t arget values because t he downst ream boundary condit ions were set t o be 1 foot higher t han t he base profile. At river st at ion 5.13, t he changes in wat er surface were 0.94, 0.97, and 1.01 feet for t he t arget values of 0.8, 0.9, and 1.0 feet . This shows t hat t he act ual result ing wat er surface is generally great er t han t he t arget values. Furt her review of t he t able shows t he various result ing wat er surface elevat ions for t he t arget dept hs. To cont inue t he encroachm ent analysis process, a Met hod 4 analysis was again calculat ed, however t his was perform ed wit h only 1 t arget dept h for each river st at ion. The t arget dept hs t hat were used in t he subsequent analysis were t he t arget dept hs t hat result ed in a wat er surface change as close t o 1 foot wit hout exceeding 1 foot . For exam ple, at river st at ion 5.13, t he result ing change in wat er surface t hat is as close t o 1 foot as possible wit hout exceeding 1 foot is 0.97 feet . This value was obt ained from a t arget increase of 0.9 feet from t he t hird profile. Therefore, for t he next t rial, a t arget value of 0.9 was used at river st at ion 5.13. Likewise, a t arget of 0.80 was used at river st at ion 5.24* because t his t arget yielded a change in wat er surface of 0.94 feet . Table 6.1 shows t he values t hat were used for t he subsequent analysis. 6-11 Exam ple 6 Floodway Det erm inat ion Table 6-1: Selected Target Values Station Target Δ WS from Trial 1 5.99 5.875* 5.76 5.685* 5.61 5.49* 5.41 5.40 (Bridge) 5.39 5.24* 5.13 5.065* 5.00 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 0.9 0.8 0.9 1.0 1.0 0.86 0.67 0.58 0.52 0.49 0.43 0.17 0.17 0.95 0.94 0.97 1.00 1.00 I t should be not ed t hat for t he bridge river st at ion ( 5.40) , t he user can only ent er one t arget value int o t he encroachm ent dat a edit or. Therefore, only one t arget value appears in Table 6.1. Addit ionally, since t he pressure/ weir opt ion is being used as t he high flow analysis m et hod, t he program will use t he encroachm ent s calculat ed at river st at ion 5.39 as t he encroachm ent s for river st at ions 5.40 and 5.41. This will be discussed furt her in t he proceeding sect ion and addit ional discussion is provided in Chapt er 9 of t he H ydr a u lic Re fe r e n ce M a n ua l. Method 4 Encroachment Analysis - Trial 2 The next st ep t o define t he encroachm ent s was t o again use a Met hod 4 analysis, but wit h only 1 t arget dept h for each river st at ion. To perform t he analysis, a st eady flow dat a file was first developed and t hen t he encroachm ent dat a were ent ered. Finally, t his sect ion will review t he out put from t he second run using t he Met hod 4 analysis. Method 4 Steady Flow Data - Trial 2 Since t his analysis only requires t wo profiles, t he st eady flow dat a file as developed for t he Met hod 5 analysis was used. This file, " Base + 1 ft Target Dept h," included only 2 profiles ( 14000 cfs each) and had t he downst ream known wat er surface boundary condit ions set at 211.8 and 212.8 feet . Method 4 Encroachment Data - Trial 2 To ent er t he dat a for t he second Met hod 4 analysis, t he Encr oa chm e nt D a t a Edit or was act ivat ed from t he St e a dy Flow Ana lysis W indow . This encroachm ent edit or is shown in Figure 6.6. As ent ered previously, t he equal conveyance opt ion was select ed and a left and right offset of 10 feet were ent ered. The reach of " Kent wood" was select ed ( t he only reach in t his exam ple) and t he st art ing and ending river st at ions were 5.99 and 5.00, 6-12 Exam ple 6 Floodway Det erm inat ion respect ively, which included t he ent ire river reach. Then t he profile was select ed as 2 ( since t he first profile is used t o calculat e t he base profile) . For t his analysis, Met hod 4 was select ed for each river st at ion and t he t arget wat er surface values for each river st at ion were obt ained from Table 6.1, as discussed previously. At t his point , t he user can ent er t he dat a direct ly int o t he t able. A 4 was placed adj acent t o each river st at ion under t he " Met hod" colum n and t he t arget values for each river st at ion were ent ered direct ly int o t he t able under " Value 1," a port ion of which is shown in Figure 6.6. ( The rem aining values can be observed by using t he t oggle arrows on t he right side of t he edit or.) Finally, t he OK but t on was select ed t o exit t he dat a edit or. Figure 6-6: Encroachment Data Editor for Method 4 – Trial 2 A new plan was creat ed wit h t he geom et ry dat a file " Exist ing Condit ions" and t he st eady flow dat a file " Base + 1 ft Target Dept h." These files were saved as t he plan " Met hod 4 Encroachm ent - Trial 2." The Shor t I D was ent ered as " M4 - Trial 2" and t he COM PUTE but t on was t hen select ed. Method 4 Output - Trial 2 The out put from t he encroachm ent analysis can be viewed in eit her t abular or graphical form . For a t abular review, t he user can select from 1 of 3 t ables defined by t he program ( or t he user can creat e a t able) . For t his review, a port ion of t he En cr oa ch m e n t 1 Ta ble is shown in Figure 6.7. ( Not e: The flow colum ns have been rem oved from t he t able in t he t ext .) 6-13 Exam ple 6 Floodway Det erm inat ion As described previously, t he first non- fixed colum n is t he result ing wat er surface elevat ion and t he second colum n is t he difference in t he wat er surface profile from t he first profile. The goal of t his analysis is t o det erm ine t he encroachm ent s so t hat t he result ing wat er surface does not change by m ore t han 1 foot . As can be seen by t he result s in t he t able, t he change of wat er surface for river st at ions 5.00 and 5.065* are bot h 1.00 feet . For river st at ion 5.13, t he change in wat er surface is 1.01 feet . This value was obt ained wit h a t arget value of 0.9 feet . Therefore, t o decrease t he result ing wat er surface elevat ions at t his river st at ion, t he t arget value for t his river st at ion m ust be decreased and a subsequent Met hod 4 analysis perform ed. This it erat ive process of changing t he t arget values and reviewing t he out put can det erm ine t he floodway t hat will result in a change of wat er surface less t han 1 foot . When perform ing a subcrit ical flow analysis, t he user should begin t his it erat ive process at t he downst ream cross sect ion and work upst ream . Addit ionally, t he user should not at t em pt t o adj ust a large quant it y of t arget values at t he sam e t im e. For t his exam ple, t he t arget values for t he river st at ions below t he bridge ( 5.00 t hrough 5.29) were adj ust ed first . Then t he bridge sect ion was analyzed and finally t he upst ream river st at ions were adj ust ed. This procedure will allow t he user t o focus on specific river sect ions and adj ust t hese t arget values before m oving ont o t he furt her upst ream river st at ions. Figure 6-7: Encroachment Table 1 for Method 4 – Trial 2 As an addit ional review of t he encroachm ent 1 t able, it can be seen t hat t he left and right encroachm ent st at ions t hat were calculat ed for river st at ion 5.39 were 440.00 and 1144.54. These encroachm ent s were t hen used for 6-14 Exam ple 6 Floodway Det erm inat ion river st at ions 5.40 and 5.41. This is a default m et hod for t he program since t he pressure/ weir m et hod was used for t he bridge high flow analysis. I f t he energy m et hod had been used, t hen t he program would allow for separat e encroachm ent st at ions t hroughout t he bridge. Finally, t he left encroachm ent st at ion of 440 at river st at ion 5.39 is 10 feet t o t he left of t he m ain channel bank st at ion. Therefore, t he program encroached up t o t he left offset on t his side of t he m ain channel. ( This also occurred at river st at ions 5.00, 5.065* , and 5.13.) I f t he offset s had not been used, t hen t he left encroachm ent would have cont inued up t o t he m ain channel bank st at ion. When t his occurs, addit ional wet t ed perim et er will be added t o t he m ain channel. This will cause t he conveyance of t he m ain channel t o decrease and t he t ot al loss of conveyance at t he cross sect ion m ay be great er t han if t he encroachm ent did not encount er t he m ain channel. Therefore, t his m ay reduce t he am ount of encroachm ent on t he right side of t he channel since an addit ional loss of conveyance had already occurred. To det erm ine t he percent reduct ion of conveyance rem oved from each side, t he En cr oa ch m e nt Ta ble 2 can be viewed. A port ion of t his t able is shown as Figure 6.8. From t he t able, it can be seen t hat for river st at ion 5.00, an approxim at ely equal am ount of conveyance was rem oved from each side of t he m ain channel ( 15.43 and 15.53 percent for t he left and right sides, respect ively) . This occurred even t hough t he encroachm ent encount ered t he left offset . However, for river st at ion 5.065* , t he encroachm ent also encount ered t he left offset but t he percent reduct ion of left and right conveyance is not equal. The percent of conveyance rem oved at river st at ion 5.065* is 10.79 and 18.89 for t he left and right sides, respect ively. This im plies t hat aft er t he left encroachm ent reached t he left offset , t he program needed t o rem ove an addit ional am ount of conveyance from t he left . Therefore, t he program rem oved t hat am ount from t he right side in addit ion t o t he am ount required t o be rem oved from t he right side. This caused t he percent of conveyance rem oved t o be unequal on bot h sides of t he m ain channel. 6-15 Exam ple 6 Floodway Det erm inat ion Figure 6-8: Encroachment Table 2 for Method 4 – Trial 2 Method 4 Encroachment Analysis - Trial 3 To furt her define t he encroachm ent s, an it erat ive process was perform ed by changing t he t arget values at t he river st at ions and t hen execut ing t he Met hod 4 analysis. Before t he it erat ive process was st art ed, t he dat a was saved as a plan ent it led " Met hod 4 Encroachm ent - Trial 3." Then, as m ent ioned previously, t he it erat ions were perform ed first for t he river st at ions below t he bridge ( 5.00 t hrough 5.29) , t hen t he bridge vicinit y was analyzed ( 5.39, 5.40, and 5.41) , and finally t he upst ream river sect ions were evaluat ed ( 5.49* t hrough 5.99) . The t arget values and result ing rise in wat er surface which yielded t he m ost pract ical result s are shown in Table 6.2. 6-16 Exam ple 6 Floodway Det erm inat ion Table 6-2: Final Target Values Station Target Δ WS for M4 -Trial 3 5.99 5.875* 5.76 5.685* 5.61 5.49* 5.41 5.40 (Bridge) 5.39 5.24* 5.13 5.065* 5.00 0.60 0.95 1.40 1.80 2.00 2.00 1.10 1.10 1.10 1.05 0.80 0.95 1.00 1.00 0.99 0.87 0.72 0.63 0.44 0.12 0.12 1.00 1.00 1.00 1.00 1.00 The final t arget wat er surface values used and t he result ing change in wat er surface are list ed in Table 6.2. These values were obt ained from t he Encr oa chm e nt Ta ble 1 as discussed previously. I n t he vicinit y of t he bridge, a t arget value of 1.1 foot at river st at ion 5.39 ( j ust downst ream of t he bridge) was found t o result in t he m ost pract ical encroachm ent s t hrough t he bridge. I f a higher t arget value was used, t he program would encroach furt her t owards t he m ain channel and a slight ly higher wat er surface value would be obt ained at river st at ions 5.39, 5.40, and 5.41. I f t he encroachm ent s at t he bridge were m oved closer t o t he m ain channel, t hen t his would furt her increase t he upst ream wat er surface. The increase in upst ream wat er surface is in effect before t he upst ream encroachm ent s are calculat ed. Therefore, t he upst ream encroachm ent s are lim it ed from t he st art because t he upst ream wat er surface elevat ion is already great er t han t he nat ural profile. As t he t arget value at river st at ion 5.39 was increased beyond 1.1, t he program could only provide m inor encroachm ent dist ances at river st at ion 5.49* . This creat ed an errat ic t ransit ion in t he floodway at river st at ion 5.49* . As a com pensat ion bet ween t he bridge encroachm ent const rict ion and init ial upst ream rise, t he t arget value of 1.1 foot at river st at ion 5.39 was det erm ined t o be m ost pract ical. Addit ionally, at river st at ion 5.40 ( t he bridge) and 5.41, t he change in wat er surface was only 0.12 feet . This wat er surface elevat ion only increased slight ly due t o t wo fact ors. First , t he rise in wat er surface upst ream of t he bridge ( river st at ion 5.41) is cont rolled by t he bridge st ruct ure it self, due t o t he occurrence of pressure and weir flow. The increase in wat er surface at sect ion 5.39 did not cause enough subm ergence on t he weir t o increase t he upst ream headwat er. Secondly, t he conveyance reduct ion at 5.40 and 5.41 rem oved only t he weir flow t hat was occurring. This reduct ion of weir flow was not sufficient enough t o cause t he wat er surface t o rise dram at ically. This im plies t hat t he pressure flow was dom inat e t hrough t he bridge opening. The m odeler should check t he bridge solut ion t o det erm ine t he value of t he pressure flow. For t his exam ple, t he pressure flow t hrough t he bridge was 12177.60 cfs, a m aj or port ion of t he t ot al flow of 14000 cfs. 6-17 Exam ple 6 Floodway Det erm inat ion I t should be em phasized t hat t he Met hod 4 it erat ions were cont inued unt il a pract ical floodway was developed. Aft er t he Met hod 4 procedure was com plet ed, t he result s were used in a Met hod 1 analysis which is discussed in t he following sect ion. Method 1 Encroachment Analysis Typically, t he floodplain encroachm ent m et hod result s are convert ed t o Met hod 1 t o perform m inor adj ust m ent s for sm oot hing t he floodplain. To perform a Met hod 1 analysis, t he user m ust ent er t he left and right encroachm ent st at ions for each cross sect ion. For t his exam ple, t he encroachm ent st at ions as det erm ined by t he Met hod 4 it erat ive procedure were used for t he Met hod 1 analysis. To perform t he analysis, first t he st eady flow dat a was ent ered and t hen t he encroachm ent dat a was ent ered. Finally, t his sect ion will discuss t he out put from t he Met hod 1 analysis. Method 1 Steady Flow Data For t he Met hod 1 analysis, only 2 flow profiles were used. Therefore, t he st eady flow dat a file " Base + 1 ft Target Dept h" was used for t his analysis. This was t he sam e file as used for t he Met hod 5, t he Met hod 4 - Trial 2, and t he Met hod 4 - Trial 3 plans. Method 1 Encroachment Data To ent er t he encroachm ent dat a, t he En cr oa ch m e nt D a t a Edit or was act ivat ed from t he St e a dy Flow Ana lysis window. The encroachm ent edit or was opened from t he plan t hat cont ained t he final Met hod 4 it erat ive result s. Then, t he I m por t t o M e t h od 1 icon was select ed. This opt ion prom pt s t he program t o read t he final encroachm ent result s from t he current ly opened plan, and t o aut om at ically convert t hose out put result s t o encroachm ent Met hod 1 input . Once t he dat a appeared in t he t able, t he OK but t on was select ed. Then t he geom et ric file " Exist ing Condit ions" and t he st eady flow dat a file " Base + 1ft Target Dept h" were saved as t he plan " Met hod 1 Encroachm ent ." The Shor t I D was ent ered as " M1" and t he COM PUTE but t on was select ed. Method 1 Output The out put from t he Met hod 1 analysis should be ident ical t o t he out put from t he Met hod 4 it erat ive plan out put . This was verified by com paring t he result ing changes in wat er surface elevat ion at t he river st at ions. At t his point , t he user can fine t une and adj ust t he encroachm ent s as deem ed necessary by adj ust ing t he left and right encroachm ent st at ions in t he En cr oa chm e n t D a t a Edit or . For t his exam ple, no furt her adj ust m ent s were m ade. 6-18 Exam ple 6 Floodway Det erm inat ion To review t he out put in graphical form , from t he m ain program window select Vie w and t hen X- Y- Z Pe r spe ct ive Plot s. This will result in t he display as shown in Figure 6.9. As can be seen in Figure 6.9, t he encroachm ent st at ions appear t o follow a sm oot h t ransit ion t hroughout t he river reach. However, t he user m ust be aware of t he fact t hat t his plot is based upon t he Xcoordinat es as ent ered by t he user. I f t he X- coordinat es for t he cross sect ions are not all est ablished from t he sam e left baseline, t hen t he plot m ay not be accurat ely port raying t he correct configurat ion of t he floodway. The m odeler should sket ch t he result ing encroachm ent s and floodway on a t opographic m ap t o view t he correct alignm ent of t he floodway. At t his point , furt her refinem ent for t he locat ions of t he encroachm ent s st at ions should be m ade. Figure 6-9: 3-D Perspective Plot of Method 1 Analysis I n addit ion t o t he 3- D plot , t he user can also view t he individual cross sect ion plot s t o see t he locat ion of t he encroachm ent st at ions. By using t he inform at ion from t he encroachm ent t ables, t he cross sect ion plot s, t he 3D plot , and t he user developed t opographic plot , t he encroachm ent st at ions should be evaluat ed for t he required const raint s and t he t ransit ions of t he floodway. 6-19 Exam ple 6 Floodway Det erm inat ion Summary To perform t he floodway analysis for t his exam ple, a Met hod 5 procedure was first at t em pt ed. This procedure can yield reasonable result s for a sm oot h t ransit ioning river reach. However, for t his exam ple, t he bridge st ruct ure in t he river reach caused difficult ies in t he Met hod 5 analysis and t he program did not yield reliable result s upst ream of t he bridge. To cont inue t he analysis, a Met hod 4 procedure was em ployed. First , 3 t arget dept hs were used t o obt ain a first cut at t he encroachm ent st at ions. Then, t he Met hod 4 procedure was em ployed it erat ively wit h one t arget value for each river st at ion t o furt her define t he encroachm ent s. Aft er t he encroachm ent s appeared t o be well est ablished, t he result s were im port ed t o Met hod 1 for a final check on t he encroachm ent s and t o perform any addit ional sm oot hing of t he floodway t ransit ions. When perform ing a floodway analysis, t he general approach is t o at t em pt t o encroach on bot h sides of t he wat er course wit hout increasing t he wat er surface elevat ion by som e predefined am ount . The user should also be aware of ot her const raint s such as velocit y lim it s and equal conveyance reduct ion requirem ent s, which m ay be const raining t he floodway delineat ion. Addit ionally, t he floodway m ust be consist ent wit h local developm ent plans and provide reasonable hydraulic t ransit ions t hroughout t he st udy reach. These t ransit ions m ust be det erm ined by plot t ing t he encroachm ent st at ions ont o a t opographic m ap. The user should not rely on t he 3- D plot provided wit h t he program due t o t he const raint s of t he plot as described previously. 6-20 Exam ple 7 Mult iple Plans CH APT ER 7 Multiple Plans Purpose This exam ple will dem onst rat e t he use of working wit h m ult iple plans. Each river hydraulics applicat ion const it ut es a proj ect , which is a collect ion of files t hat are associat ed wit h t he applicat ion. A proj ect is divided int o one or m ore plans. Each plan associat es specific files of t he proj ect t o be grouped t oget her. Therefore, each plan can represent a developm ent st age or analysis phase of t he proj ect . I nit ially, t his exam ple will briefly discuss t he elem ent s of a proj ect and t he elem ent s of a plan. The m odeler is referred t o Chapt er 5 of t he User’s Manual for a furt her discussion on working wit h proj ect s and a discussion of t he files t hat com prise a plan. Specifically, t his exam ple will illust rat e t he use of m ult iple plans by analyzing t he exist ing geom et ric condit ions of t he river reach and t hen analyzing a proposed change t o t he geom et ry. To review t he dat a files for t his exam ple, from t he m ain program window select File and t hen Open Proj ect . Select t he proj ect labeled “ Napa Cr. Bridge Proj ect Exam ple 7.” This will open t he proj ect and act ivat e t he following files: Plan: “ Exist ing Plan Dat a” Geom et ry: “ Exist ing Geom et ry” Flow: “ 100 year flow” Elements of a Project A proj ect is com prised of all of t he files t hat are used t o develop a m odel, as well as a list of default variables t hat are used for t he analysis. The files t hat const it ut e t he proj ect are list ed in Table 7.1. For each file, t he t able list s t he file t ype, t he file ext ension, and t he m et hod of creat ion of t he files ( by t he user or by t he program ) . 7-1 Exam ple 7 Mult iple Plans Table 7-1: Project Files File Type Extension Created By: Plan Geometry Steady Flow Unsteady Flow Sediment Data Hydraulic Design Run Output .P## .G## .F## .U## .S## .H## .R## .O## user user user user user user program program Not e: # # refers t o an ext ension num ber from 01 t o 99. As t he file t ypes are creat ed, t he program will num ber t he ext ensions in consecut ive order st art ing at 01. The run and out put file ext ension num bers will always coincide wit h t he ext ension num ber of t he plan t hat t he program used t o creat e t he files. Finally, t he proj ect also specifies t he default variables. These variables include t he syst em of unit s ( English or SI ) and t he cont ract ion and expansion coefficient s. These variables can be changed by t he user t hrough t he program int erface. Elements of a Plan A proj ect is com prised of one or m ore plans. Each plan cont ains: a short ident ifier; a list of files associat ed wit h t he plan; and a descript ion of t he sim ulat ion opt ions t hat were set for t he analysis. Each of t hese t hree it em s are discussed as follows. The short ident ifier is ent ered in t he St e a dy Flow Ana lysis W in dow . This ident ifier appears while viewing t he out put . I t is used t o ident ify t he out put from a specific plan while viewing t he out put from m ult iple plans. I f t his ident ifier is changed, t hen t he user m ust re- com put e t he plan in order for t he out put file t o reflect t he change. The m ain funct ion of t he plan is t o associat e a group of files. The plan can associat e one file ext ension from each t ype of file. For t his exam ple, t here were t wo geom et ry files and one st eady flow file t hat were creat ed. The first geom et ry file was creat ed t o describe t he exist ing condit ions of t he river reach and had an ext ension “ .G01” . The second geom et ry file described t he proposed geom et ry of a new bridge along t he sam e river reach and, since it was t he second geom et ry file t hat was creat ed, it had an ext ension “ .G02.” Finally, a st eady flow dat a file was creat ed t hat cont ained t he 100- year flow event . This st eady flow file had an ext ension “ .F01.” For t his proj ect , it was desired t o com pare t he result s of t he exist ing geom et ry t o t he proposed geom et ry for t he sam e flow event . Therefore, t wo plans were creat ed. The first plan associat ed t he exist ing geom et ry file 7-2 Exam ple 7 Mult iple Plans ( .G01) wit h t he 100- year st eady flow dat a ( .F01) . The second plan associat ed t he proposed geom et ry ( .G02) wit h t he sam e 100- year st eady flow dat a ( .F01) . I n t his m anner, a second st eady flow dat a file wit h t he sam e inform at ion was not required t o be developed. I nst ead, t he second plan m erely associat ed t he second geom et ry file wit h t he original st eady flow dat a file. Aft er bot h plans were com put ed, t he out put from t he first plan ( .O01) and t he out put from t he second plan ( .O02) were t hen easily com pared graphically and in t abular form . This will be discussed short ly. I t should be not ed t hat a plan cannot cont ain a com binat ion of a st eady flow and an unst eady flow file. A plan can only include one t ype of file t hat cont ains flow inform at ion. Last ly, t he plan cont ains a descript ion of t he sim ulat ion opt ions t hat were set for t he analysis. These sim ulat ion opt ions include: m axim um t olerances for calculat ions, m axim um num ber of it erat ions, log out put level, frict ion slope m et hod, et c. These sim ulat ion opt ions can be changed by t he user. Existing Conditions Analysis The m ain focus of t he rem aining discussion will concent rat e on t he m et hod of creat ing m ult iple plans and analyzing m ult iple plan out put . The geom et ry and st eady flow dat a files developed for t his exam ple are briefly discussed in t he following sect ions. Existing Conditions Geometry A geom et ry file was creat ed t hat m odeled t he exist ing condit ions for a reach of Napa Creek. This reach is a m anm ade channel wit h four bridge crossings. To view t he river schem at ic, from t he m ain program window select Edit and t hen Ge om e t r ic D a t a . This will act ivat e t he Ge om e t r ic D a t a Edit or and display t he river syst em schem at ic as shown in Figure 7.1. The river reach is defined by 84 river st at ions. The user can view t he geom et ric dat a for each river st at ion by select ing t he Cr oss Se ct ion icon from t he Ge om e t r ic D a t a Edit or . The dat a for each river st at ion is com prised of : a descript ion; X and Y coordinat es; downst ream reach lengt hs, Manning’s n values; m ain channel bank st at ions; and cont ract ion and expansion coefficient s. 7-3 Exam ple 7 Mult iple Plans Figure 7-1: Napa Creek River System Schematic Addit ionally, a levee was placed on t he left side river st at ions 200 and 300 and ineffect ive flow areas were est ablished at river st at ions: 956 and 1002; 1208 and 1229; 1318 and 1383; 2484 and 2540. Each of t hese four groupings are for t he four bridge locat ions in t he river reach. Finally, t he expansion and cont ract ion reach lengt hs for each bridge were est im at ed using t he expansion and cont ract ion rat ios obt ained from Table B.1 and B.2 in Appendix B of t he H ydr a u lic Re fe r e n ce M a n ua l. The focus of t his proj ect is t o replace t he exist ing bridge st ruct ure locat ed at river st at ion 2512. To view t he exist ing bridge, from t he Ge om e t r ic D a t a Edit or select t he Br idge / Cu lve r t icon and t oggle t o river st at ion 2512. This will display t he Sem inary St reet Bridge at river st at ion 2512 as shown in Figure 7.2. The bridge deck and roadway inform at ion were ent ered by select ing t he D e ck / Roa dw a y icon on t he left side of t he edit or. Addit ionally, t he Br idge M ode lin g Appr oa ch icon was select ed and t he appropriat e inform at ion 7-4 Exam ple 7 Mult iple Plans provided ( These procedures were also applied t o develop t he ot her 3 bridges in t he river reach) . Aft er all of t he geom et ric dat a were ent ered, t he geom et ry file was saved. This was perform ed from t he Ge om e t r ic D a t a Edit or by select ing File and t hen Save Geom et ry Dat a As. The t it le was ent ered as “ Exist ing Geom et ry” and t he OK but t on was select ed. Figure 7-2: Seminary Street Bridge at River Station 2512 Steady Flow Data The next st ep was t o develop t he st eady flow dat a file. To creat e t his file, from t he m ain program window Edit and t hen St e a dy Flow D a t a were select ed. This act ivat ed t he St e a dy Flow D a t a Edit or as shown in Figure 7.3. One profile was select ed t o be analyzed for t he reach “ Sout h Reach.” The flow value of 4070 cfs, represent ing t he one- percent chance flood, was ent ered at river st at ion 3800 ( t he upst ream river st at ion) and a downst ream known wat er surface elevat ion of 13 feet was ent ered by select ing t he Bou nda r y Condit ion s icon. Finally, t he st eady flow dat a were saved. To perform t his, from t he St e a dy Flow D a t a Edit or , File and t hen Sa ve Flow 7-5 Exam ple 7 Mult iple Plans D a t a As were select ed. The t it le “ 100 year flow” was ent ered and t he OK but t on was select ed. The edit or was t hen closed. Figure 7-3: Steady Flow Data Editor Existing Conditions Plan Once t he geom et ric dat a and st eady flow dat a were ent ered and saved, a plan t hat associat ed t hese t wo files was creat ed. To perform t his, from t he m ain program window, Ru n and t hen St e a dy Flow Ana lysis were select ed. This act ivat ed t he St e a dy Flow Ana lysis W in dow as shown in Figure 7.4. Next , a Shor t I D was ent ered as “ Exist ing.” The geom et ry file “ Exist ing Geom et ry” and t he st eady flow file “ 100 year flow” were select ed by using t he down arrows on t he right side of t he window ( Not e: At t his point , only one geom et ry and one flow file exist ed and it was not necessary t o use t he arrows.) . A subcrit ical analysis was chosen as t he Flow Re gim e and t hen, File and Sa ve Pla n As were select ed. The t it le ” Exist ing Plan Dat a” was ent ered and t he OK but t on select ed. This creat ed a plan t hat associat ed t he exist ing condit ions geom et ry file wit h t he st eady flow file. This plan had an ext ension “ .P01” because it was t he first plan creat ed. Aft er t he plan was saved, t he COM PUTE but t on was select ed t o execut e t he program . During t he execut ion, a run file wit h t he ext ension “ .R01” and an out put file wit h t he ext ension “ .O01” were creat ed. The ext ension num ber 01 for bot h t he run and out put files correspond wit h t he plan wit h t he sam e ext ension num ber. 7-6 Exam ple 7 Mult iple Plans Figure 7-4: Steady Flow Analysis Window – Existing Conditions Plan Existing Conditions Output The exist ing condit ions out put review will be lim it ed t o viewing t he profile for t he river reach. A m ore det ailed analysis will be perform ed when com paring t he exist ing and proposed m odel out put in a subsequent sect ion. To view t he profile plot of t he river reach, from t he m ain program window select Vie w and t hen W a t e r Su r fa ce Pr ofile s. This will display t he profile as shown in Figure 7.5. The first part of t he heading at t he t op of t he profile is t he nam e of t he proj ect : “ Napa Cr. Bridge Proj ect - Exam ple 7.” The second part of t he heading is t he nam e of t he plan: “ Exist ing Plan Dat a.” Finally, t he dat e t hat t he out put file was creat ed also appears in t he heading. Napa Cr. Bridge Project - Example 7 Existing Plan Data Geom: Existing Geometry South Reach Elevation (ft) 30 Flow: 100 year flow Legend 25 EG 100 yr 20 WS 100 yr Ground 15 10 5 0 -5 0 500 1000 1500 2000 2500 3000 3500 4000 Main Channel Distance (ft) Figure 7-5: Existing Conditions Profile The profile of t he exist ing condit ions analysis shows t hat t he upst ream bridge at river st at ion 2512 was overt opped during t he 100- year flow event . I t was 7-7 Exam ple 7 Mult iple Plans proposed t hat a new bridge be inst alled t o replace t he exist ing bridge. The new bridge would be designed so t hat t he 100- year flow event did not im pact t he bridge decking. To evaluat e t his proposed bridge replacem ent , t he exist ing condit ions geom et ry file was changed and a new plan was creat ed. This procedure is out lined in t he following sect ions. Proposed Conditions Analysis For t he proposed condit ions, t he bridge at river st at ion 2512 will be replaced by a new bridge. To perform t his, first t he geom et ry file was changed t o reflect t he proposed condit ions. Then, a new plan was creat ed wit h t he new proposed geom et ry file and t he original st eady flow file. This procedure is out lined below. Proposed Conditions Geometric Data To change t he geom et ry for t he bridge at river st at ion 2512, first t he geom et ry file “ Exist ing Geom et ry” was act ivat ed. Then, t his geom et ry file was saved as a new geom et ry file. This was perform ed by select ing File and t hen Sa ve Ge om e t r y D a t a As from t he Ge om e t r ic D a t a Edit or . The t it le “ Proposed Bridge” was ent ered and t he OK but t on was chosen. This saved t he geom et ry as a new geom et ry file. Then, all subsequent changes were m ade t o t he “ Proposed Bridge” geom et ry file. This enabled t he “ Exist ing Geom et ry” file t o rem ain unchanged. Wit h t he “ Proposed Bridge” geom et ry file, t he Ge om e t r ic D a t a Edit or was act ivat ed and t he Br idge / Cu lve r t icon was select ed. River st at ion 2512 was chosen at t he t op of t he edit or and t he D e ck / Roa dw a y icon was select ed. The exist ing bridge dat a was delet ed and t he new inform at ion was ent ered. The new bridge decking was proposed t o have a high cord elevat ion 1 foot higher t han t he exist ing bridge deck. This elevat ion was chosen as an init ial est im at e for t he proposed bridge and can be alt ered aft er t he out put is reviewed. Aft er t he decking was ent ered, t he pier dat a was ent ered by select ing t he Pier icon from t he Br idge / Cu lve r t D a t a Edit or. Two piers were ent ered at st at ions 67 and 82. The pier edit or was closed and t he result ing bridge appeared as shown in Figure 7.6. Finally, t he D e scr ipt ion was m odified t o “ Sem inary St . Bridge - Proposed.” The Br idge M ode ling Appr oa ch Edit or was not alt ered and t he Br idge / Cu lve r t D a t a Edit or was closed. 7-8 Exam ple 7 Mult iple Plans Figure 7-6: Seminar Street Bridge - Proposed Since t he bridge geom et ry changed at river st at ion 2512, t he expansion and cont ract ion reach lengt hs were adj ust ed in t he vicinit y of t he bridge. Then, t he ineffect ive flow areas were reest ablished at river st at ions 2484 and 2540. This concluded t he changes t o t he geom et ric dat a, and t he geom et ry file was saved by select ing Sa ve Ge om e t r y D a t a from t he File m enu of t he Ge om e t r ic D a t a Edit or . Steady Flow Data The st eady flow dat a for t he analysis of t he proposed bridge will be t he sam e flow dat a used wit h t he exist ing geom et ry. Therefore, t here were no adj ust m ent s m ade t o t he st eady flow dat a file “ 100 year flow.” 7-9 Exam ple 7 Mult iple Plans Proposed Conditions Plan A new plan was creat ed from t he geom et ry file wit h t he proposed bridge and t he st eady flow dat a file. To perform t his, from t he m ain program window Ru n and St e a dy Flow Ana lysis were select ed. A Shor t I D was ent ered as “ Proposed” in t he upper right corner of t he window. The geom et ry file “ Proposed Bridge” and t he st eady flow file “ 100 year flow” were chosen by select ing t he down arrows on t he right side of t he window. A subcrit ical analysis was chosen as t he Flow Re gim e . Then, File and Sa ve Pla n As were select ed. The t it le “ Proposed Plan” was ent ered and t he OK but t on was select ed. This creat ed a plan t hat associat ed t he proposed condit ions geom et ry file wit h t he st eady flow file. This plan had an ext ension “ .P02” because it was t he second plan creat ed. The COM PUTE but t on was select ed t o execut e t he program . During t he execut ion, a run file wit h t he ext ension “ .R02” and an out put file wit h t he ext ension “ .O02” were creat ed. The ext ension num ber 02 for bot h t he run and out put files correspond wit h t he plan num ber. Proposed Conditions Output At t his point , t he user can act ivat e t he wat er surface profile plot for t he proposed condit ions, as perform ed for t he exist ing condit ions out put . The next sect ion will com pare t he result s of t he t wo plans and t he t wo wat er surface profiles sim ult aneously. Comparison of Existing and Proposed Plans To com pare t he out put from t he t wo plans, t he user can view t he result s graphically and in t abular form at . This com parison will describe t he m et hods t o view t he out put for bot h plans sim ult aneously. Profile Plot To view t he profile plot of bot h plans, from t he m ain program window select View and t hen Wat er Surface Profiles. Then, select Opt ions and Plans. This will act ivat e t he pop- up window shown in Figure 7.7. The plan select ion window is divided int o t wo part s: an opt ion for com paring m ult iple geom et ries at t he t op, and a box cont aining all of t he available plans t o view out put for. To select plans for viewing t here out put , sim ple check t he box in front of each plan label. Addit ionally, t he Select All and Clear All but t ons can be used. For t his exam ple, bot h plans were select ed by choosing t he Select All but t on. Then, t he OK but t on was chosen t o exit t he window. This result ed in t he profile as shown in Figure 7.8. The opt ion for com paring geom et ries allows t he user t o plot t he out put and geom et ric dat a for t wo plans sim ult aneously. Since t he invert and channel geom et ry did not change bet ween t hese t wo plans, t here was no benefit t o select ing t his opt ion. 7-10 Exam ple 7 Mult iple Plans Figure 7-7: Plan Selection Box Napa Cr. Bridge Project - Example 7 Plan: Geom: Proposed Bridge 1) Existing 2) Proposed Flow: 100 year flow Napa Creek South Reach 30 Legend 25 WS 100 yr - Existing WS 100 yr - Proposed Elevation (ft) 20 Ground 15 10 5 0 -5 0 500 1000 1500 2000 2500 3000 3500 4000 Main Channel Distance (ft) Figure 7-8: Profiles of Both Existing and Proposed Plans Figure 7.8 shows t he profile for bot h plans. The heading displays t he inform at ion as discussed previously. The legend shows t hat t here are t wo wat er surface profiles plot t ed in t he figure. The first profile is labeled ” WS 100 yr - Exist ing” and is a solid line. The label “ WS 100 yr” refers t o t he label of t he flow dat a for t he first wat er surface profile, while t he label “ Exist ing” refers t o t he Plan Shor t I D t hat was ent ered in t he St e a dy Flow Ana lysis W indow . Therefore, t his wat er surface is for t he Exist ing Condit ion plan. Sim ilarly, t he label “ WS 100 yr - Proposed” is t he 100 yr wat er surface profile for t he “ Proposed” plan dat a. 7-11 Exam ple 7 Mult iple Plans Since bot h plans only had one flow ent ered, only one wat er- surface profile can be plot t ed for each plan. I f ot her flow profiles had been com put ed, t hen t he user could also select t o plot t hose profiles. I t should be not ed t hat since t he profiles were plot t ed from t he proposed condit ions plan, t he geom et ry t hat is displayed in Figure 7.8 is from t he proposed condit ions plan. I n ot her words, t he bridge at river st at ion 2512 displays t he geom et ry ( elevat ion) of t he proposed bridge. I f t his procedure had been perform ed from wit hin t he exist ing condit ions plan, t hen t he geom et ry of t he profile would exhibit t he exist ing condit ions geom et ry. I n eit her case, t he wat er surface profiles for each plan are plot t ed as calculat ed for t hat plan. Finally, Figure 7.8 clearly shows t he decrease in t he upst ream wat er surface due t o t he proposed bridge allowing t he flow t o pass com plet ely under t he bridge. Cross Section Plots I n a sim ilar m anner, t he wat er surface for bot h plans can be viewed on t he cross sect ion plot s. This is perform ed by select ing Vie w and t hen Cr ossSe ct ion s from t he m ain program window. River st at ion 2512 ( upst ream inside bridge) was t hen chosen and t his displayed t he cross sect ion plot as shown in Figure 7.9. I t should be not ed t hat once t he opt ion was select ed t o display t he profiles from bot h of t he plans, t his opt ion will rem ain in effect globally unt il ot herwise select ed. This allows t he user t o only act ivat e t his feat ure once, inst ead of having t o set t he opt ion for each t able and plot t hat is request ed. This opt ion can be ret urned t o t he default of only viewing t he current plan inform at ion when viewing any of t he plot s or t ables. Napa Cr. Bridge Project - Example 7 Plan: 1) Existing 2) Proposed Geom: Proposed Bridge Flow: 100 year flow RS = 2512 BR U Seminary St. bridge - Proposed .08 .035 .08 30 Legend WS 100 yr - Existing 25 Elevation (ft) WS 100 yr - Proposed 20 Ground Ineff 15 Bank Sta 10 5 0 20 40 60 80 100 120 140 160 Station (ft) Figure 7-9: Cross Section 2512 for Proposed Plan showing both Existing and Proposed Profiles Addit ionally, t he program will revert back t o only displaying t he current plan inform at ion whenever a new plan or proj ect is opened. 7-12 Exam ple 7 Mult iple Plans I n reference t o Figure 7.9, t he headings and legend are as described previously. The cross sect ion was select ed from wit hin t he proposed geom et ry plan and t herefore t he bridge shown is t he proposed bridge. The first wat er surface is for t he exist ing condit ions plan and t he second wat er surface is for t he proposed condit ions plan. Standard Table I n addit ion t o graphical displays, t he user can com pare t he out put in t abular form . From t he m ain program window, select Vie w and t hen Pr ofile Sum m a r y Ta ble . By select ing St a n da r d Ta ble 1 , t he t able as shown in Figure 7.10 will appear. The first t wo colum ns of t he t able in Figure 7.10 display t he river reach and river st at ion. The t hird colum n ident ifies which plan t he dat a are from . The ident ifiers in t his colum n are obt ained from t he Sh or t I D ent ered in t he St e a dy Flow D a t a Edit or . The rem aining port ion of t he t able displays inform at ion for each plan such as t ot al flow, energy gradeline elevat ion, wat er surface elevat ion, et c. By present ing t he dat a in t his form at , t he m odeler can easily com pare t he out put for each plan. Figure 7-10: Standard Table 1 for Both Existing and Proposed Plans As an addit ional not e, if a river st at ion only appears in one of t he plans, t hen t he t able will only display t he dat a for t hat plan. This occurs for river st at ion 2549* and 2471* , which are only used in t he proposed geom et ry plan. These river st at ions can be viewed by using t he down arrows on t he right side of t he t able. 7-13 Exam ple 7 Mult iple Plans Bridge Only Table I n a sim ilar fashion t o t he first st andard t able, t he Br idge On ly Ta ble was act ivat ed from t he St d. Ta ble s pull down m enu and is shown as Table 7.2. To insert t his t able int o t he t ext , File , and t hen Copy t o Clipboa r d were select ed. Then, t he t able was past ed int o t his docum ent and appeared as shown in Table 7.2. Figure 7-11: Bridge Only Table for both Existing and Proposed Plans As for t he st andard t able, t he river reach and river st at ions are shown in t he first t wo colum ns and t he Shor t I D s are used t o ident ify t he plans in t he t hird colum n. This t able shows t hat for t he bridge at river st at ion 2512, weir flow occurred for t he exit ing condit ions bridge but did not occur for t he proposed bridge geom et ry plan. The dat a for t he ot her t hree bridges in t he t able are t he sam e for bot h plans since t here was only a change in t he geom et ry at t he upst ream bridge. X-Y-Z Perspective Plot As a final view of t he out put , a 3D view of t he river reach is shown in Figure 7.11. This plot was act ivat ed from t he m ain program window by select ing Vie w and t hen X- Y- Z Pe r spe ct ive Plot s. Only a port ion of t he Napa Creek reach is shown in t he figure for clarit y. The figure displays t he 3D plot from river st at ion 3300 t o river st at ion 2200. This was perform ed by select ing t he St a r t and En d down arrows and select ing t he appropriat e river st at ions. The m odeler can select various azim ut h and rot at ion angles t o obt ain differing views of t he river reach. The river st at ions on t he plot are aligned according t o t he configurat ion as drawn on t he Rive r Syst e m Sche m a t ic. 7-14 Exam ple 7 Mult iple Plans Figure 7-12: X-Y-Z Perspective Plot of a Portion of Napa Creek for Both Existing and Proposed Plans Summary For Exam ple 7, t he concept of m ult iple plan analysis wit hin a single proj ect was discussed. There are several advant ages t o using a m ult iple plan analysis. One of t hese advant ages is t he use of a single flow dat a file for m ult iple geom et ry sim ulat ions. This reduces t he need for ident ical flow files. Anot her advant age pert ains t o t he analysis of t he out put . Wit h m ult iple plans, t he user can select t o have t he dat a from any num ber of plans displayed collect ively. This allow s for a proficient com parison of t he plans. For t his exam ple, t he m ult iple plans were developed by alt ering t he geom et ry of t he river reach. Conversely, a m ult iple plan analysis could be com posed of plans t hat relat e changes of user- select ed coefficient s such as energy loss coefficient s, Manning’s n values, and ent rance and exit loss coefficient s. By 7-15 Exam ple 7 Mult iple Plans underst anding t he concept of m ult iple plan analyses, t he user can em ploy a m ore efficient procedure for analyzing a proj ect . 7-16 Exam ple 8 Looped Net work CH APT ER 8 Looped Network Purpose This exam ple was perform ed t o dem onst rat e t he analysis of a river reach t hat cont ains a loop. The loop is caused by a split in t he m ain channel t hat form s t wo st ream s which j oin back t oget her. The focus of t his exam ple is on t he developm ent of t he looped net work and t he balancing of t he flows t hrough each branch of t he loop. The st ream j unct ions will be discussed briefly; however, a m ore det ailed discussion of st ream j unct ions can be found in exam ple 10. N ot e : Sin ce t h is e x a m ple w a s de ve lope d, w e h a ve a dde d t h e a bilit y t o h a ve t h e pr ogr a m opt im ize t h e flow split for you . Ex a m ple a pplica t ion 1 5 show s h ow t o u se t h e split flow opt im iza t ion r ou t ine . To review t he dat a files for t his exam ple, from t he m ain program window select File and t hen Ope n Pr oj e ct . Select t he proj ect labeled “ Looped Net work - Exam ple 8.” This will open t he proj ect and act ivat e t he following files: Plan: “ Looped Plan” Geom et ry: “ Looped Geom et ry” Flow: “ 10, 50, and 100 year flow event s” Geometric Data The geom et ric dat a for t his exam ple consist s of t he river syst em schem at ic, t he cross sect ion dat a, and t he st ream j unct ion dat a. Each of t hese com ponent s are discussed below. River System Schematic To view t he river syst em schem at ic, from t he m ain program window select Edit and t hen Ge om e t r ic D a t a . This will act ivat e t he Ge om e t r ic D a t a Edit or and display t he river syst em schem at ic as shown in Figure 8.1. The schem at ic shows t he layout of t he t wo rivers. Spruce Creek is broken int o t hree river reaches: Upper Spruce Creek, Middle Spruce Creek, Lower Spruce Creek. Bear Run is left as a single river reach. The flow in Upper Spruce 8-1 Exam ple 8 Looped Net work Creek split s at Tusseyville t o form Bear Run and Middle Spruce Creek. Bear Run is approxim at ely 1500 feet in lengt h and Middle Spruce Creek is approxim at ely 1000 feet long. These t wo st ream s t hen j oin at Coburn t o form Lower Spruce Creek. Figure 8-1: River System Schematic for Spruce Creek and Bear Run Cross Section Data Aft er t he river reaches were sket ched t o form t he river syst em schem at ic, t he cross sect ion dat a were ent ered. The dat a were ent ered by select ing t he Cr oss Se ct ion icon from t he Ge om e t r ic D a t a Edit or. For each cross sect ion, t he geom et ric dat a consist ed of t he: X- Y coordinat es, downst ream reach lengt hs, Manning’s n values, m ain channel bank st at ions, t he cont ract ion and expansion coefficient s, and, if applicable, left or right levees. Aft er all of t he geom et ric dat a were ent ered, File and t hen Sa ve Ge om e t r y D a t a As were select ed from t he Ge om e t r ic D a t a Edit or . The t it le “ Looped 8-2 Exam ple 8 Looped Net work Geom et ry” was ent ered and t he OK but t on select ed. This was t he only geom et ry file for t his exam ple. Stream Junction Data The final geom et ric com ponent was t he dat a for t he st ream j unct ion. These dat a were ent ered by select ing t he Ju n ct ion icon on t he Ge om e t r ic D a t a Edit or . This caused t he Ju n ct ion D a t a Edit or t o appear as shown in Figure 8.2. First , t he dat a for t he j unct ion at Tusseyville was ent ered by select ing t he appropriat e Junct ion Nam e at t he t op of t he edit or. Then a Descript ion was ent ered as “ Spruce Creek Split .” Figure 8-2: Junction Data Editor for Tusseyville Junction The next piece of inform at ion required was t he Lengt h Across Junct ion. These are t he dist ances from t he downst ream river st at ion of Upper Spruce t o t he upst ream river st at ions of Middle Spruce and Bear Run. I n general, t he cross sect ions t hat bound a j unct ion should be placed as close t o t he j unct ion as possible. This will allow for a m ore accurat e calculat ion of t he energy losses across t he j unct ion. These values were ent ered as 80 and 70 feet , for t he dist ances t o Middle Spruce and Bear Run, respect ively. The last it em in t he j unct ion edit or is t he com put at ion m ode. Eit her t he Energy or t he Mom ent um m et hod m ust be select ed. The energy m et hod ( t he default m et hod) uses a st andard st ep procedure t o det erm ine t he wat er surface across t he j unct ion. The m om ent um m et hod t akes int o account t he angle of t he t ribut aries t o evaluat e t he forces associat ed wit h t he t ribut ary flows. For t his exam ple, t he flow velocit ies were low and t he influence of t he t ribut ary angle was considered insignificant . Therefore, t he energy m et hod was select ed for t he analysis. For a furt her discussion on st ream j unct ions, t he user is referred t o exam ple 10 and t o chapt er 4 of t he H ydr a u lic Re fe r e n ce M a n ua l. Aft er t he dat a were ent ered for t he Tusseyville Junct ion, t he Apply D a t a but t on was select ed. The down arrow adj acent t o t he Junct ion Nam e was depressed t o act ivat e t he second j unct ion at Coburn. At t his j unct ion, t he descript ion “ Confluence of Bear Run and Middle Spruce” was ent ered. Next , a lengt h of 70 feet was ent ered from Bear Run t o Lower Spruce and 85 feet for 8-3 Exam ple 8 Looped Net work t he dist ance from Middle Spruce t o Lower Spruce. Again, t he energy m et hod was select ed and t he Apply D a t a but t on was chosen before closing t he j unct ion edit or. Steady Flow Data The st eady flow dat a were ent ered next . These dat a consist ed of t he profile dat a and t he boundary condit ions. Each of t hese it em s is discussed as follows. Profile Data To ent er t he st eady flow dat a, t he St e a dy Flow D a t a Edit or was act ivat ed from t he m ain program window by select ing Edit and t hen St e a dy Flow D a t a . This opened t he edit or as shown in Figure 8.3. On t he first line of t he edit or, t he num ber of profiles was chosen t o be 3. These profiles will represent t he 10, 50, and 100 - year flow event s. When t he num ber of profiles is ent ered, t he t able expands t o provide a colum n for each profile. Figure 8-3: Steady Flow Data Editor – Looped Plan – 1st Flow Distribution To ent er t he flow dat a, a flow value m ust be ent ered at t he upst ream end of each reach. The program will consider t he flow rat e t o be const ant t hroughout t he reach unless a change in flow locat ion is ent ered. For t his exam ple, t he flow will be const ant t hroughout each reach. The t hree profiles will be for flow values of 300, 800, and 1000 cfs. These values were ent ered as t he flow rat es for Upper Spruce and Lower Spruce. 8-4 Exam ple 8 Looped Net work For t he flow rat es t hrough Middle Spruce and Bear Run, t he user m ust est im at e t he am ount of flow for each reach. Then, aft er t he analysis, t he user m ust com pare t he energy values at t he upst ream ends of Middle Spruce and Bear Run. I f t he energy values differ by a significant am ount , t hen t he flow rat es t hrough t he t wo reaches m ust be redist ribut ed and a second analysis perform ed. This process will cont inue unt il t he upst ream energies are wit hin a reasonable t olerance. This procedure im plies t hat t he upst ream cross sect ions of Middle Spruce and Bear Run are locat ed close t o t he j unct ion. Therefore, t he energy value at t hese t wo locat ions should be approxim at ely equal. For t his first at t em pt at a flow dist ribut ion, t he values of 170 and 130 cfs were ent ered for t he first profile for Middle Spruce and Bear Run, respect ively. Sim ilarly, flow values of 450 and 350 were ent ered for t he second profile and 560 and 440 for t he t hird profile. Aft er t he analysis, t he upst ream energies for each profile were com pared t o det erm ine if t he flow dist ribut ion was appropriat e. This will be discussed in a subsequent sect ion. Boundary Conditions Aft er t he flow dat a were ent ered, t he boundary condit ions were est ablished. This was perform ed by select ing t he Bou nda r y Con dit ion s icon from t he t op of t he St e a dy Flow D a t a Edit or . This result ed in t he display as shown in Figure 8.4. As shown in Figure 8.4, t he boundary condit ions t able will aut om at ically cont ain any int ernal boundary condit ions such as st ream j unct ions. The user is required t o ent er t he ext ernal boundary condit ions. For t his exam ple, a subcrit ical flow analysis was perform ed; t herefore, t he ext ernal boundary condit ion at t he downst ream end of Lower Spruce was specified. N or m a l D e pt h was chosen wit h a slope of 0.0004 ft / ft . Aft er t he boundary condit ion was ent ered, t he edit or was closed and t he flow dat a was saved as “ 10, 50, and 100 year flow event s.” Figure 8-4: Steady Flow Boundary Conditions for Looped Network 8-5 Exam ple 8 Looped Net work Steady Flow Analysis Aft er t he geom et ric and flow dat a were ent ered, t he files were t hen saved as a plan. This was perform ed by select ing Run and t hen St e a dy Flow Ana lysis from t he m ain program window. This act ivat ed t he St e a dy Flow Ana lysis W indow as shown in Figure 8.5. I n t he st eady flow window, first t he Sh or t I D of “ Loop” was ent ered. Next , t he geom et ry file “ Looped Geom et ry” and t he st eady flow dat a file “ 10, 50, and 100 year flow event s” were select ed by depressing t he down arrows on t he right side of t he window. Figure 8-5: Steady Flow Analysis Window ( Not e: Since t here was only 1 geom et ry file and only 1 flow file, t his was not necessary.) Then, File and Sa ve Pla n As were select ed and t he t it le “ Looped Plan” was ent ered. The OK but t on was select ed and t he plan t it le appeared near t he t op of t he st eady flow window. Finally, t he Flow Re gim e was select ed as subcrit ical and t he COM PUTE but t on was select ed. Analysis of Results for Initial Flow Distribution The user can review t he result s of t he analysis bot h graphically and in t abular form at . For t his exam ple, t his discussion will init ially be concerned wit h t he flow dist ribut ion as select ed for Bear Run and Middle Spruce. To det erm ine t he adequacy of t he previously chosen flow dist ribut ion, t he energy gradeline elevat ions at t he upst ream end of Bear Run and Middle Spruce will be com pared. To det erm ine t he calculat ed energy values, t he Ju n ct ion Ta ble was reviewed and a port ion of t he t able is shown in Figure 8.6. This t able was act ivat ed from t he m ain program window by select ing Vie w , Pr ofile Sum m a r y Ta ble , St d. Ta ble s, and t hen Ju nct ion Ta ble 1 . The rows in t he t able in Figure 8.6 are divided int o groups of t hree, one row for each of t he t hree profiles. The first colum n of t he t able displays t he river reach, t he second colum n displays t he river st at ion, and t he t hird colum n list s t he wat er surface elevat ion for t he part icular river st at ion. As can be seen in Figure 8.6, for t he river reach of Middle Spruce at t he river st at ion 1960 ( t he 8-6 Exam ple 8 Looped Net work upst ream st at ion) , t he flow rat es were 170, 450, and 560 cfs, and t he energy gradeline elevat ions were 23.37, 25.19, and 25.67 feet for t he t hree flow profiles. The energy gradeline elevat ions for t he upst ream river st at ion of Bear Run ( river st at ion 1470) were 23.10, 24.96, and 25.52 feet . By com paring t hese values, it can be seen t hat t he energy gradelines differ by 0.27, 0.23, and 0.15 feet for t he t hree profiles, respect ively. Since t he upst ream river st at ions on Middle Spruce and Bear Run were locat ed close t o t he st ream j unct ion, t he energy gradeline elevat ions for t hese t wo river st at ions should be approxim at ely equal. Therefore, t he flow rat es for Middle Spruce and Bear Run were redist ribut ed and a subsequent analysis was perform ed. This is discussed in t he next sect ion. Figure 8-6: Junction Table for First Estimate of Flow Distribution Steady Flow Analysis with New Flow Distribution Aft er reviewing t he energy gradeline values at t he upst ream river st at ions for Middle Spruce and Bear Run, t he flow rat es for t hese river reaches were redist ribut ed. Since t he energy values for Bear Run were lower t han t hat of Middle Spruce for all t hree of t he profiles, a great er port ion of t he t ot al flow was apport ioned t o Bear Run for all of t he profiles. To perform t his, t he St e a dy Flow D a t a Edit or was act ivat ed and t he flow values were adj ust ed. Then a subsequent analysis was perform ed and t he energy values com pared. This procedure was cont inued unt il t he energy values were wit hin a reasonable t olerance. Table 8.1 shows t he final flow dist ribut ion and t he result ing energy gradeline values for t he upst ream river st at ions of Middle Spruce and Bear Run. 8-7 Exam ple 8 Looped Net work Addit ionally, t he t able show s t he energy gradeline values for t he downst ream river st at ion of Upper Spruce Creek. These values should be great er t han t he energy values for t he upst ream river st at ions of Middle Spruce and Bear Run. The final energy values for Middle Spruce and Bear Run are wit hin a reasonable t olerance for each profile. Therefore, t he flow dist ribut ion as shown in Table 8.1 was considered as a reasonable est im at e of t he flow rat es t hrough each river reach. Table 8-1: Final Flow Distribution for Looped Plan Reach River Station Profile Upper Spruce Middle Spruce Bear Run Upper Spruce Middle Spruce Bear Run Upper Spruce Middle Spruce Bear Run 2040 1960 1470 2040 1960 1470 2040 1960 1470 1 1 1 2 2 2 3 3 3 Flow Rate (cfs) 300 154 146 800 420 380 1000 535 465 Energy Gradeline Elevation (ft) 23.29 23.25 23.24 25.15 25.08 25.08 25.67 25.60 25.60 Analysis of Results for Final Flow Distribution For an addit ional review of t he flow dist ribut ion for t he looped plan, t he profile plot is shown in Figure 8.7. To act ivat e t he profile plot , from t he m ain program window select Vie w and t hen W a t e r Su r fa ce Pr ofile s. For t his plot , t he reaches of Upper Spruce, Middle Spruce, and Lower Spruce Creek were select ed. This represent s t he flow along t he right side of t he river schem at ic. Sim ilarly, t he flow along t he left edge of t he river schem at ic can be viewed by select ing t he river reach Bear Creek inst ead of Middle Spruce. This is perform ed by select ing Opt ion s, Re a ch e s, and t hen t he appropriat e river reach. Summary As a sum m ary for t his exam ple, a river syst em t hat cont ained a loop was analyzed. The flow rat es for t he branches of t he loop were init ially est im at ed and, aft er an init ial analysis, t he upst ream energy values for each branch were com pared. Since t he init ial energy values were not wit hin a reasonable t olerance, t he flow rat es t hrough each branch were redist ribut ed and a subsequent analysis perform ed. This procedure was cont inued unt il t he upst ream energy values for t he t wo branches were wit hin a reasonable t olerance. By perform ing t he flow dist ribut ion and energy com parison in t his 8-8 Exam ple 8 Looped Net work m anner, it was necessary t hat t he cross sect ions around t he j unct ion were spaced close t oget her. Figure 8-7: Profile Plot for Looped Network 8-9 Exam ple 9 Mixed Flow Analysis CH APT ER 9 Mixed Flow Analysis Purpose This exam ple dem onst rat es t he analysis of a river reach t hat cont ains bot h subcrit ical and supercrit ical flow. This m ixed flow problem is caused by a bridge st ruct ure t hat const rict s t he flow enough t o force it t o pass t hrough crit ical dept h, creat ing a backwat er effect and causing subcrit ical flow im m ediat ely upst ream from t he bridge. The discussion of t his exam ple will focus on t he analysis of t he m ixed flow regim e. Addit ionally, t he bridge st ruct ure was analyzed using bot h t he energy m et hod and t he pressure flow m et hod. The result s of t hese m et hods are t hen com pared. For a m ore det ailed discussion on bridge analyses, t he user is referred t o chapt er 6 of t he Use r ’s M a n u a l and t o chapt er 5 of t he H ydr a u lic Re fe r e n ce M a n ua l. To review t he dat a files for t his exam ple, from t he m ain program window select File and t hen Ope n Pr oj e ct . Select t he proj ect labeled “ Mixed Flow Exam ple 9.” This will open t he proj ect and act ivat e t he following files: Plan: “ Put ah Creek Bridge” Geom et ry: “ Base Geom et ry Dat a - Energy” Flow: “ 100 Year Discharge” Geometric Data The geom et ric dat a for t his exam ple consist s of t he river syst em schem at ic, t he cross sect ion dat a, t he locat ions of t he cross sect ions, and t he bridge dat a. Each of t hese com ponent s is discussed below. River System Schematic To view t he river syst em schem at ic, from t he m ain program window select Edit and t hen Geom et ric Dat a. This will act ivat e t he Geom et ric Dat a Edit or and display t he schem at ic, as shown in Figure 9.1. The schem at ic shows t he layout of a sect ion of Put ah Creek, which consist s of 20 cross sect ions. Cross sect ion 12 is t he upst ream river st at ion and cross sect ion 1 is t he downst ream 9-1 Exam ple 9 Mixed Flow Analysis river st at ion. Addit ionally, a bridge was locat ed at river st at ion 7 and will be discussed in a subsequent sect ion. Figure 9-1: Putah Creek River System Schematic Cross Section Data The dat a for each cross sect ion is com prised of : a descript ion, t he X- Y coordinat es, downst ream reach lengt hs, Manning’s n values, m ain channel bank st at ions, and t he expansion and cont ract ion coefficient s. The dat a used for t his exam ple can be viewed by select ing t he Cross Sect ion icon on t he Geom et ric Dat a Edit or ( Figure 9.1) . I t should be not ed t hat t he whole num ber cross sect ions were obt ained from field dat a and t he cross sect ions wit h an * were int erpolat ed. This will be discussed in t he following sect ion. 9-2 Exam ple 9 Mixed Flow Analysis Location of the Cross Sections The locat ion of t he cross sect ions in relat ion t o a bridge are crucial for t he accurat e calculat ion of t he expansion and cont ract ion losses. The bridge rout ine ut ilizes four cross sect ions, t wo upst ream and t wo downst ream from t he st ruct ure, t o det erm ine t he energy losses t hrough t he st ruct ure. The m odeler is referred t o chapt er 6 of t he Use r ’s M a n ua l and chapt er 5 of t he H ydr a u lic Re fe r e n ce M a n ua l for addit ional discussion on t he locat ion of cross sect ions and for m odeling bridges. For t his exam ple, t he flow used for t his analysis will rem ain in t he m ain channel during t he event . Addit ionally, t here is only one pier for t he bridge and t he cross sect ions in t he vicinit y of t he bridge do not reflect m aj or changes in geom et ry. Therefore, t here is no m aj or expansion or cont ract ion losses occurring in t he vicinit y of t he bridge. Since t he flow in t he m ain channel is supercrit ical, t he cross sect ions were placed close t oget her t o m ore accurat ely calculat e t he energy losses along t he channel. The cross- sect ion dat a from t he field survey were 100 feet apart . These dat a were ent ered and t hen addit ional cross sect ions were int erpolat ed at 50 feet int ervals. This was perform ed from wit hin t he Ge om e t r ic D a t a Edit or by select ing Tools, XS I n t e r pola t ion, and t hen W it h in a Re a ch. This act ivat ed t he XS I n t e r pola t ion by Re a ch W indow as shown in Figure 9.2. Figure 9-2: Cross Section Interpolation by Reach Window To perform t he int erpolat ion, t he reach of Put ah Creek and t he st art ing and ending river st at ions of 12 and 1 were select ed as shown in Figure 9.2. Then, a m axim um dist ance of 50 feet was ent ered and t he I nt erpolat e XS’s but t on was select ed. This creat ed t he int erpolat ed cross sect ions along t he ent ire river reach. Aft er t he int erpolat ion, each int erpolat ed cross sect ion was reviewed t o det erm ine t he adequacy of t he int erpolat ion. For addit ional discussion on cross sect ion int erpolat ion, t he user is referred t o chapt er 6 of t he User’s Manual and t o chapt er 4 of t he Hydraulic Reference Manual. 9-3 Exam ple 9 Mixed Flow Analysis As a final review of t he cross sect ion locat ions, from t he Ge om e t r ic D a t a Edit or select Ta ble s and t hen Re a ch Le ngt hs. This will act ivat e t he Re a ch Le ngt hs Ta ble as shown in Figure 9.3. As can be seen in t he t able, t he final channel reach lengt hs are 50 feet for each cross sect ion, except t hrough t he bridge. Figure 9-3 Reach Lengths Table for Putah Creek Bridge Data To ent er t he bridge dat a for t his exam ple, first t he deck/ roadway dat a, t hen t he pier dat a, and finally t he bridge m odeling approach dat a were ent ered. These com ponent s are described in t he following sect ions. D e ck / Roa dw a y D a t a . From t he Ge om e t r ic D a t a Edit or , select t he Br idge / Cu lve r t icon. This will act ivat e t he Br idge / Cu lve r t D a t a W in dow . Then select t he D e ck / Roa dw a y icon on t he left side of t he window. This will act ivat e t he D e ck / Roa dw a y D a t a Edit or as shown in Figure 9.4. As shown in t he Figure 9.4, t he first it em on t he t op row of t he edit or is t he dist ance from t he river st at ion im m ediat ely upst ream of t he bridge ( river st at ion 8) t o t he upst ream side of t he bridge. For t his exam ple, t his dist ance was set at 10 feet . The next it em is t he widt h of t he deck/ roadway and t his dist ance was 90 feet . The program will t hen add t he 10 feet and t he 90 feet t o obt ain 100 feet as t he dist ance from t he river st at ion 8 t o t he downst ream side of t he bridge. From t he Re a ch Le n gt h s Ta ble , it can be seen t hat t he dist ance from river st at ion 8 t o river st at ion 6 was 110 feet . Therefore, t he program will allow for 10 feet of dist ance from t he downst ream side of t he bridge t o river st at ion 6 ( t he river st at ion locat ed im m ediat ely downst ream of 9-4 Exam ple 9 Mixed Flow Analysis t he bridge) . The last it em on t he t op row of t he edit or is t he weir coefficient , which was set at 2.9. Figure 9-4: Deck/Roadway Data Editor The cent ral port ion of t he edit or consist s of t he st at ion and elevat ion dat a for t he low and high cords of t he deck/ roadway. These values were ent ered as shown. Finally, t he bot t om port ion of t he edit or consist s of t he dat a ent ry for t he weir flow calculat ions. For t his exam ple, weir flow did not occur and t his dat a will not be em phasized. For addit ional discussion on t he deck/ roadway dat a, t he user is referred t o exam ple 2 for bridges and t o exam ple 3 for culvert s. The OK but t on was t hen select ed t o exit t he edit or. Pie r D a t a . To ent er t he pier dat a, t he Pie r icon was select ed from t he Br idge / Cu lve r t D a t a Edit or . This act ivat ed t he Pie r D a t a Edit or. For t his exam ple, t he bridge geom et ry consist ed of only one pier locat ed at a cent erline st at ion of 150 and a widt h of 8 feet . This dat a was ent ered and t hen t he edit or was closed. This concluded t he input of t he bridge geom et ry and t he bridge appeared in t he Br idge / Cu lve r t D a t a Edit or as shown in Figure 9.5. As a final not e for t he bridge geom et ry, t here were no ineffect ive flow areas defined for t he analysis. This was due t o t he fact t hat t he flow for t he analysis rem ained in t he m ain channel and t he bridge geom et ry did not creat e any appreciable ineffect ive flow areas. This will becom e m ore apparent during t he review of t he out put . 9-5 Exam ple 9 Mixed Flow Analysis Figure 9-5: Bridge/Culvert Data Editor Br idge M ode ling Appr oa ch. The final com ponent of t he geom et ric dat a is t he ent ering of t he coefficient s for t he bridge analysis. This was perform ed by select ing t he Br idge M ode lin g Appr oa ch icon on t he Br idge / Cu lve r t D a t a Edit or . This act ivat ed t he Br idge M ode lin g Appr oa ch Edit or as shown in Figure 9.6. The first select ion is t he low flow com put at ion m et hods. For t his exam ple, t he energy and m om ent um m et hods were select ed. Then, t he Highest Energy Answer field was select ed. This will inform t he program t o use t he great er answer of t he energy and t he m om ent um m et hods for t he final solut ion of t he low flow analysis. The next select ion was t he m et hod for t he high flow analysis. For t his sim ulat ion, t he energy m et hod was select ed. ( A subsequent analysis was perform ed wit h t he pressure/ weir m et hod and will be discussed lat er.) 9-6 Exam ple 9 Mixed Flow Analysis Figure 9-6: Bridge Modeling Approach Editor for Energy Method Analysis This concluded t he geom et ric input for t he analysis and t he dat a was t hen saved as “ Base Geom et ry Dat a - Energy.” Next , t he st eady flow dat a were ent ered for t he sim ulat ion. Steady Flow Data To ent er t he st eady flow dat a, first t he profile dat a and t hen t he boundary condit ions were ent ered. These dat a com ponent s are discussed below. Profile Data To ent er t he st eady flow profile dat a, from t he m ain program window Edit and t hen St e a dy Flow D a t a were select ed. This act ivat ed t he St e a dy Flow D a t a Edit or as shown in Figure 9.7. On t he t op row of t he edit or, t he num ber of profiles was chosen t o be one. When t his num ber was ent ered, t he t able port ion of t he edit or adj ust ed for t his num ber of profiles. Then, t he 100- year flow rat e of 3200 cfs was ent ered at t he upst ream end of t he river reach; t here were no flow change locat ions. Finally, t he boundary condit ions were ent ered. 9-7 Exam ple 9 Mixed Flow Analysis Figure 9-7: Steady Flow Data for Puta Creek Boundary Conditions To ent er t he boundary condit ions, t he Bou nda r y Con dit ion s icon was select ed from t he St e a dy Flow D a t a Edit or ( Figure 9.7) . This act ivat ed t he Bou nda r y Condit ion s D a t a Edit or as shown in Figure 9.8. Since t he flow t hrough t he river reach is supercrit ical, t he analysis will be perform ed in t he m ixed flow regim e. This will allow for t he com put at ions of bot h subcrit ical and supercrit ical flow profiles, if t hey are found t o occur. Therefore, t he user m ust ent er bot h an upst ream and a downst ream boundary condit ion. As can be seen in Figure 9.8, a Norm al Dept h upst ream boundary condit ion was select ed wit h a slope of 0.01 ft / ft . Addit ionally, a downst ream boundary condit ion was select ed as Crit ical Dept h. The select ion of t hese boundary condit ions will be discussed in t he analysis of t he out put . For addit ional discussion on boundary condit ions, t he m odeler is referred t o chapt er 7 of t he Use r ’s M a n u a l. At t his point , t he flow dat a was saved as “ 100 Year Discharge.” 9-8 Exam ple 9 Mixed Flow Analysis Figure 9-8: Steady Flow Boundary Conditions Steady Flow Analysis Aft er all of t he geom et ric and st eady flow dat a were ent ered, t he st eady flow analysis was perform ed. This was accom plished by select ing from t he m ain m enu Ru n and t hen St e a dy Flow Ana lysis. This act ivat ed t he St e a dy Flow Ana lysis W indow as shown in Figure 9.9. As shown in Figure 9.9, first a Shor t I D was ent ered as “ Energy.” Then t he geom et ry file “ Base Geom et ry Dat a - Energy” and t he st eady flow file “ 100 Year Discharge” were select ed by using t he down arrows on t he right side of t he window. ( Not e: The select ion of t hese files was not necessary since t here exist ed only one geom et ry file and only one flow file at t his t im e.) Then t he Flow Re gim e was select ed as “ Mixed” and t he inform at ion was saved as a plan by select ing File and t hen Sa ve Pla n As. The t it le “ Put ah Creek Bridge - Energy” was ent ered and t he OK but t on was select ed. Then t his plan t it le appeared at t he t op of t he st eady flow window ( as well as on t he m ain program window) . Finally, t he COM PUTE but t on was select ed t o perform t he analysis. 9-9 Exam ple 9 Mixed Flow Analysis Figure 9-9: Steady Flow Analysis Window Review of Output for Energy Analysis The m odeler can review t he out put in bot h graphical and in t abular form . For t his analysis, first t he wat er surface profile was plot t ed and t hen t he profile t able and t he cross sect ion t able for t he bridge were reviewed. Water Surface Profile To view t he wat er surface profile, from t he m ain program window select Vie w and t hen W a t e r Su r fa ce Pr ofile s. This will display t he profile as shown in Figure 9.10. The profile shows t he energy gradeline, t he wat er surface, and t he crit ical dept h for t he flow of 3200 cfs ( t he only flow for t his exam ple) . To perform t he m ixed flow analysis, t he program will first com put e a subcrit ical flow profile for t he ent ire river reach st art ing at t he downst ream river st at ion. The program will flag any locat ion t hat default ed t o crit ical dept h. Next , t he program will perform a supercrit ical analysis for t he river reach st art ing at t he upst ream river stat ion. During t his phase, t he program will com pare t he specific force for t he supercrit ical flow t o t he specific force for t he subcrit ical flow at any river st at ion t hat has a valid answer in bot h flow regim es. The flow regim e wit h t he great er specific force will cont rol at t hat river st at ion. For a furt her discussion on m ixed flow analysis, t he user is referred t o t he sect ion “ Mixed Flow Regim e Calculat ions” in chapt er 4 of t he H ydr a u lic Re fe r e n ce M a n ua l. For t his exam ple, it can be seen in Figure 9.10 t hat t he flow is supercrit ical at t he upst ream end of t he river reach because t he wat er surface is below t he crit ical dept h line. This was det erm ined by com paring t he specific force of t he user defined upst ream norm al dept h boundary condit ion wit h t he subcrit ical flow answer. The program had det erm ined t hat t he specific force of t he supercrit ical flow boundary condit ion was great er t han t hat of t he subcrit ical flow answer and t herefore used t he upst ream boundary condit ion. The 9-10 Exam ple 9 Mixed Flow Analysis program t hen cont inued in t he downst ream direct ion wit h a supercrit ical flow profile. Figure 9-10: Water Surface Profile for Energy Analysis With Mixed Flow Regime When t he program calculat ed t he wat er surface profile for river st at ion 9, it det erm ined t hat t here was a valid answer for bot h t he subcrit ical and supercrit ical flow profiles. The program t hen com pared t he specific force of bot h of t hese flow regim es and det erm ined t hat t he subcrit ical flow had a great er specific force. This im plies t hat t he flow at river st at ion 9 was subcrit ical and t hat a hydraulic j um p developed upst ream of t his river st at ion. This can be seen in Figure 9.10 t o have occurred bet ween t he m ain channel st at ions of 710 and 760 ( river st at ions 9 and 9.5* ) . This hydraulic j um p occurred because t he cross sect ion geom et ry in t he vicinit y of t he bridge caused a const rict ion of t he flow and a backwat er was creat ed upst ream from t he bridge. This backwat er creat ed a subcrit ical profile im m ediat ely upst ream of t he bridge and a hydraulic j um p was necessary for t he flow t o t ransit ion from supercrit ical t o subcrit ical. 9-11 Exam ple 9 Mixed Flow Analysis Figure 9-11: Standard Table 2 Profile Table for Energy Method Analysis To view t he calculat ed values of t he wat er surface elevat ions, crit ical dept h, and energy gradeline, t he St andard Table 1 profile t able was act ivat ed from t he m ain program window by select ing View, Profile Sum m ary Tables, and t hen St d. Table 1. This t able is shown as Figure 9.11 and shows a wat er surface elevat ion of 1280.85 and a crit ical wat er surface elevat ion of 1281.57 at river st at ion 9.5* . This wat er surface elevat ion is less t han t he crit ical dept h and im plies a supercrit ical flow regim e. At river st at ion 9, t he wat er surface elevat ion of 1282.08 is great er t han t he crit ical wat er surface of 1281.02 and im plies a subcrit ical flow regim e. The m odeler can use t his t able t o det erm ine all of t he com put ed values t hat are displayed on t he profile plot as shown in Figure 9.10. Referring back t o Figure 9.10, as t he calculat ions cont inued t hrough t he bridge, Class B low flow was found t o occur since t he flow did not encount er t he low cord of t he bridge and t he flow passed t hrough crit ical dept h under t he bridge. For Class B low flow, t he program will set t he wat er surface at crit ical dept h at eit her t he upst ream inside or downst ream inside cross sect ion of t he bridge. The program will calculat e t he specific force for crit ical dept h at bot h of t hese sect ions and set t he flow at crit ical dept h at t he sect ion t hat is t he m ost const rict ed and has t he great er specific force. For t his exam ple, t he flow was set at crit ical dept h at t he bridge upst ream inside cross sect ion, as shown in Figure 9.10. Addit ionally, if t he specific force of bot h cross- sect ions are approxim at ely equal, t hen t he program will use t he locat ion ent ered by t he user. The locat ion can be select ed from wit hin t he Bridge/ Culvert Dat a Edit or by select ing Opt ions and t hen Mom ent um Class B default s. Finally, a supercrit ical profile cont inued downst ream of t he bridge t o t he last downst ream cross sect ion. The downst ream boundary condit ion had been set at crit ical dept h. However, t he program det erm ined t hat t he supercrit ical flow solut ion at t he downst ream end had a great er specific force t han t he boundary condit ion and used t he supercrit ical flow answer. 9-12 Exam ple 9 Mixed Flow Analysis Water Surface Profiles for Subcritical and Supercritical Flow Analyses To perform t he analysis, t he m ixed flow regim e had been select ed. I f t he user had select ed a subcrit ical or supercrit ical flow regim e for t he analysis, t he out put would have reflect ed various warnings and not es int ended t o alert t he user of possible inconsist encies wit h t he result s. For exam ple, if t he user had select ed a subcrit ical flow regim e, t he wat er surface profile would have appeared as shown in Figure 9.12. Figure 9-12: Water Surface profile for Energy Analysis with Subcritical Flow Regime As can be seen in Figure 9.12, t he wat er surface coincided wit h t he crit ical dept h line for t he m aj orit y of t he river st at ions. A review of t he Sum m a r y of Er r or s, W a r n in gs a nd N ot e s would reveal t he repet it ion of t he warning: “ During t he st andard st ep it erat ions, when t he assum ed wat er surface was set equal t o crit ical dept h, t he calculat ed wat er surface cam e back below crit ical dept h. This indicat es t hat t here is not a valid subcrit ical answer. The program default ed t o crit ical dept h.” This warning is issued when t he user has request ed a subcrit ical flow analysis but t he program could not det erm ine a subcrit ical flow dept h at t he specified cross sect ion. Since a subcrit ical solut ion was not possible, t he program used crit ical dept h at t his locat ion and cont inued on wit h t he calculat ions. This warning m ay be associat ed wit h t oo long of reach lengt hs bet ween cross sect ions or t he fact t hat t he flow analysis should be perform ed in t he supercrit ical or m ixed flow regim es. I f t he user had select ed t o perform a supercrit ical flow analysis, t he wat er surface profile would have appeared as shown in Figure 9.13. As can be seen in t he figure, t here is an inconsist ent drop in t he energy gradeline im m ediat ely upst ream of t he bridge. A review of t he warnings at t he upst ream inside bridge cross sect ion revealed t hat t he energy equat ion could 9-13 Exam ple 9 Mixed Flow Analysis not be balanced wit hin t he specified num ber of it erat ions and t he program default ed t o crit ical dept h at t his locat ion. The user should perform t he com put at ions in t he m ixed flow regim e t o det erm ine if a subcrit ical flow profile exist s in t he river reach. The program can only provide for bot h subcrit ical and supercrit ical flow answers when t he m ixed flow regim e is select ed. Figure 9-13: Water Surface profile for Energy Analysis with Supercritical Flow Regime The analysis of t he river reach in t he subcrit ical and supercrit ical flow regim es are not provided as plans for t his exam ple. They were com put ed and present ed t o show what would develop if t hese flow regim es had been select ed. However, t he m odeler can readily select t hese ot her flow regim es and execut e t he program t o observe t he out put . For an addit ional discussion for t he descript ions of t he warnings, errors, and not es, t he user is referred t o exam ple 1 and t o chapt er 10 of t he Use r ’s M a n ua l. Profile Table - Bridge Comparison Ret urning t o t he m ixed flow analysis of t he river reach, it was observed t hat during t he flow event , Class B low flow was found t o occur at t he bridge. For t he low flow analysis, t he energy and t he m om ent um m et hods had been select ed t o be com put ed for t he analysis in t he Br idge M ode ling Appr oa ch Edit or . To det erm ine which m et hod t he program used for t he final answer, from t he m ain program window select Vie w , Pr ofile Su m m a r y Ta ble , St d. Ta ble s, and t hen Br idge Com pa r ison. This will act ivat e t he Bridge Com parison Profile Table as shown in Figure 9.14. 9-14 Exam ple 9 Mixed Flow Analysis Figure 9-14: Bridge Comparison Profile Table for Energy Method Analysis The first t wo colum ns in t he t able show t he reach and river st at ion for t he bridge locat ion. For t his exam ple, t he bridge is locat ed at river st at ion 7. The t hird colum n shows t he energy gradeline elevat ion t hat was used as t he final answer for t he analysis, 1282.99 ft . The fourt h colum n displays t he wat er surface elevat ion ( 1282.10 ft ) t hat corresponds t o t he energy gradeline in colum n t hree. The fift h colum n displays t he bridge m et hod t hat was select ed as t he final answer. Finally, t he sixt h and sevent h colum ns show t he result s of t he energy and m om ent um m et hods since t hese t wo m et hods were select ed t o be com put ed. As can be seen in t he t able, t he energy low flow m et hod produced a result of 1282.22 ft for t he energy gradeline. The m om ent um m et hod produced a result of 1282.99 for t he upst ream energy gradeline. The program select ed t he m om ent um m et hod for t he final solut ion because t he bridge is exhibit ing class B flow, and t he m om ent um m et hod is t he default solut ion when class B flow occurs. Cross Section Table - Bridge As an addit ional review of t he out put for t he bridge, t he cross sect ion t able was act ivat ed from t he m ain program window by select ing Vie w , Cr oss Se ct ion Ta ble , Type , and t hen Br idge . This displayed t he Br idge Cr oss Se ct ion Ta ble as shown in Figure 9.15. For t his exam ple, t here was only one bridge locat ed on Put ah Creek at river st at ion 7. The left side of t he t able shows t he energy and wat er surface elevat ions for t he river st at ion im m ediat ely upst ream of t he bridge ( as shown in Figure 9.14) . The right side of t he t able displays inform at ion for t he t wo cross sect ions locat ed inside of t he bridge. The bot t om port ion of t he t able displays any errors, warnings, and not es for t he cross sect ion. As is shown in Figure 9.15, t wo of t he not es t hat appear at t his river st at ion not ify t he m odeler t hat Class B low flow was com put ed for t his bridge st ruct ure. Whenever Class B low flow is found t o occur, t he m odeler should perform t he analysis in t he m ixed flow regim e m ode. 9-15 Exam ple 9 Mixed Flow Analysis Figure 9-15: Bridge Type Cross-Section Table for Energy Method This com plet ed t he review for t he energy m et hod analysis. As a final review of t he wat er surface profile as shown in Figure 9.10, it can be seen t hat t he wat er surface upst ream of t he bridge did not encount er t he bridge decking for t he energy m et hod analysis and t herefore was calculat ed as a low flow profile. However, t he wat er surface elevat ion is very close t o t he bridge decking and, due t o t he t urbulent wave act ion of t he flow, m ay j um p t o pressure flow during t he event . Therefore, an addit ional analysis was perform ed wit h t he pressure/ weir flow opt ion select ed for t he high m et hod. This is discussed furt her in t he next sect ion. Pressure/Weir Analysis The wat er surface profile in t he vicinit y of t he bridge was calculat ed as low flow for t he energy m et hod analysis. However, for a pressure flow analysis, t he program will com pare t he energy gradeline value of t he flow wit h t he low cord of t he bridge decking t o det erm ine when pressure flow will begin t o 9-16 Exam ple 9 Mixed Flow Analysis occur. As can be seen in Figure 9.10, t he energy gradeline elevat ion is great er t han t he low cord at t he upst ream side of t he bridge. Therefore, t he river reach was re- analyzed using t he pressure/ weir m et hod for t he high flow com put at ions. To select t he pressure/ weir m et hod, t he geom et ry file “ Base Geom et ry Dat a Energy” was act ivat ed. Then t he Br idge / Cu lve r t icon and t he Br idge M ode lin g Appr oa ch icon were select ed. The “ Pressure/ Weir Met hod” was t hen chosen for t he high flow analysis. This Br idge M ode ling Appr oa ch Edit or is shown as Figure 9.16. Figure 9-16: Bridge Modeling Approach Editor for Pressure/Weir Flow Analysis For t he pressure/ weir analysis, t he edit or allows t hree input coefficient s. The first coefficient is for t he flow sit uat ion when only t he upst ream side of t he bridge decking is subm erged. For t his exam ple, t he field was left blank so t hat t he t able values would be used by t he program . The second coefficient is for t he flow sit uat ion when bot h t he upst ream and downst ream sides of t he bridge decking are subm erged. This coefficient was left at a value of 0.8, t he default value. The final field is for t he m odeler t o ent er an elevat ion value for t he program t o use t o det erm ine when t o begin t he pressure flow calculat ions. Pressure flow calculat ions will begin when t he low flow energy gradeline value is great er t han t he value ent ered in t his field. I f t he field is left blank ( as for t his exam ple) , t hen t he program will use t he highest low cord of t he bridge decking on t he upst ream side. Once all of t he dat a had been ent ered, t he edit or was closed by select ing t he OK but t on. Next , t he ineffect ive flow areas were locat ed im m ediat ely upst ream of t he set t o begin 10 feet t o t he left of t he flow area was set t o begin 10 feet t o added at river st at ion 8 ( t he river st at ion bridge) . A left ineffect ive flow area was bridge opening and a right ineffect ive t he right of t he right side of t he bridge 9-17 Exam ple 9 Mixed Flow Analysis opening. Bot h of t hese ineffect ive flow areas were set at an elevat ion of 1285 feet , t he high cord elevat ion of t he bridge. Then, t he geom et ry file was saved as “ Base Geom et ry Dat a - Press/ Weir.” Next , t his geom et ry file and t he st eady flow dat a file were saved as a plan. This was perform ed by first act ivat ing t he St e a dy Flow Ana lysis W indow from t he m ain program window. The st eady flow window is shown in Figure 9.17. Then, t he geom et ry and st eady flow file were select ed by depressing t he down arrows on t he right side of t he window. Figure 9-17: Steady Flow Analysis Window for Pressure/Weir Analysis Next , t he Shor t I D “ Press/ Weir” was ent ered in t he upper right corner of t he edit or and t he flow regim e “ Mixed” was select ed. Finally, File and Sa ve Pla n As were select ed and t he t it le “ Put ah Creek Bridge - Press/ Weir” was ent ered. This creat ed a new plan wit h t he pressure/ weir geom et ry file and t he st eady flow dat a file. The plan nam e t hen appeared at t he t op of t he st eady flow analysis window ( as well as on t he m ain program window) . Aft er t he new plan was creat ed, t he COM PUTE but t on was depressed t o act ivat e t he calculat ions of t he wat er surface profile. The user can act ivat e t his plan by select ing File , Ope n Pla n , and t hen t he plan “ Put ah Creek Bridge - Press/ Weir” t o review t he rem aining discussion of t his exam ple. Review of Output for Pressure/Weir Analysis For t he out put for t he pressure/ weir analysis, t his discussion will review t he wat er surface profile, t he expansion and cont ract ion reach lengt hs, t he bridge com parison t able, t he bridge cross sect ion t able, and finally t he 3- D plot . Water Surface Profile The wat er surface profile for t he pressure/ weir analysis is shown in Figure 9.18. As can be seen in t he figure, t he upst ream wat er surface profile begins in t he supercrit ical flow regim e. However, t he energy gradeline at t he cross 9-18 Exam ple 9 Mixed Flow Analysis sect ion im m ediat ely upst ream of t he bridge was great er t han t he highest value of upst ream low cord. Therefore, during t he com put at ions, pressure flow was found t o occur and t he wat er surface profile developed as pressure flow t hrough t he bridge. This pressure flow caused a backwat er effect and creat ed a subcrit ical flow profile upst ream of t he bridge. For t he flow t o t ransit ion from a supercrit ical t o a subcrit ical profile, a hydraulic j um p occurred in bet ween river st at ions 11 and 11.5* . The flow t hrough t he bridge st ruct ure is again Class B flow because t he flow passed t hrough crit ical dept h wit hin t he bridge. Finally, t he downst ream profile is supercrit ical t o t he downst ream cross sect ion. As before, it was necessary t o perform t he analysis in t he m ixed flow regim e in order t o obt ain a wat er surface profile in bot h t he subcrit ical and supercrit ical flow regim es. Figure 9-18: Water Surface profile for Pressure/Weir Flow Analysis Expansion and Contraction Reach Lengths As st at ed previously, t he locat ions of t he cross sect ions in t he vicinit y of a bridge are crucial for t he accurat e predict ion of t he energy losses t hrough t he st ruct ure. For t his exam ple, t he dist ance from river st at ion 6 t o 5.5 * defines t he expansion reach lengt h and t he dist ance from river st at ion 8.5* t o 8 defines t he cont ract ion reach lengt h. Each of t hese reach lengt hs are evaluat ed below based upon t he procedures as out lined in appendix B of t he H ydr a u lic Re fe r e n ce M a n ua l. However, t hese procedures were developed based on subcrit ical flow t hrough bridges. Therefore, only t he t able values will be used t o provide a general guidance for t he reach lengt hs. 9-19 Exam ple 9 Mixed Flow Analysis Ex pa n sion Re a ch Le ngt h . To est im at e t he expansion reach lengt h from Table B.1, t he following inform at ion was required: b = 90 B = 190 b / B = 0.50 S = 50 nob / nc = 0.035 / 0.025 = 1.4 Lobs = 45 where: b = B = floodplain widt h, ft S = bed slope, ft / m i nob = Manning’s n value of t he overbank nc = Manning’s n value of t he m ain channel Lobs = bridge opening widt h, ft average lengt h of obst ruct ion, ft From Table B.1, t he expansion rat io ( ER) was det erm ined t o be in t he range from 1.2 - 1.5. Using an average value of 1.3 yields an expansion reach lengt h ( Le) of: Le = (ER )(Lobs ) = (1.1)(45) = 50 feet From t he geom et ric dat a, t he dist ance from river st at ion 6 t o 5.5* was set at 50 feet . This value is approxim at ely equal t o t he expansion reach lengt h as det erm ined above and t he locat ion of t he river st at ions were not adj ust ed. Con t r a ct ion Re a ch Le n gt h . To est im at e t he cont ract ion reach lengt h, t he cont ract ion rat io from Table B.2 was det erm ined t o be in t he range from 0.8 1.4. Using an average value of 1.1 yielded a cont ract ion reach lengt h ( Lc) of: Lc = (CR )(Lobs ) = (1.1)(45) = 50 feet From t he geom et ric dat a, t he cont ract ion reach lengt h was set t o be 50 feet . For t his exam ple, t he flow in t he m ain channel did not exhibit a large degree of cont ract ion or expansion losses. This allow ed for short er expansion and cont ract ion reach lengt hs, as det erm ined above. As st at ed previously, t he t able values were used as a general guide, because t he dat a of t he exam ple were not wit hin t he range of t he dat a used t o develop t he regression equat ions. 9-20 Exam ple 9 Mixed Flow Analysis Bridge Comparison Table As was shown in Figure 9.18, t he wat er surface reflect ed pressure flow t hrough t he bridge st ruct ure. To det erm ine why t his energy value was select ed, t he user can review t he Bridge Com parison Table. This t able is act ivat ed from t he m ain program window by select ing View, Profile Sum m ary Table, St d. Tables, and t hen Bridge Com parison. This t able is shown in Figure 9.19. As described previously, t he first t wo colum ns in t he t able show t he reach and river st at ion of t he bridge locat ion. The t hird colum n shows t he bridge m et hod t hat was used as t he final answer. The fourt h colum n shows t he final energy gradeline value used for t he analysis. The fift h colum n shows t he wat er surface t hat corresponds t o t he energy value in colum n four. The next four colum ns ( Energy, Mom ent um , Yarnell, and WSPRO) show t he calculat ed energy gradeline values for t hese low flow m et hods. For t his exam ple, only t he energy and t he m om ent um m et hods were select ed t o be calculat ed for t he low flow analysis. The solut ion of t he energy gradeline for t he energy m et hod is 1282.22 feet . The m om ent um m et hod produced an answer of 1282.99 feet . Therefore, t he program used t he value of 1282.99 as t he answer for t he low flow analysis ( t his is not necessarily t he final answer as is discussed subsequent ly) . Figure 9-19: Bridge Comparison Table for Pressure/Weir Flow Analysis The t ent h colum n ( Prs O EG) displays t he energy gradeline necessary for only pressure flow t o be occurring t hrough t he bridge. For t his exam ple, t his value is 1284.79 feet . The program t hen com pared t his pressure only energy gradeline t o t he energy gradeline t hat was used for t he low flow analysis ( 1282.99) . The great er of t he t wo values was t hen used as t he final answer. For t his exam ple, t he pressure only energy gradeline was t he great er value and t he program t hen used t he pressure only m et hod as t he final solut ion. The nint h colum n ( Prs/ Wr EG) shows t he calculat ed energy gradeline value for t he sit uat ion when bot h pressure and weir flow would occur. This sit uat ion did not develop for t his exam ple. For a furt her discussion for bridge analyses, t he user is referred t o exam ple 2 and t o chapt er 6 of t he Use r ’s M a n u a l and chapt er 5 of t he H ydr a u lic Re fe r e n ce M a n ua l. Bridge Detailed Output Table As a final t able for t he review of t he pressure/ weir flow, t he user can select t he Bridge Det ailed Out put Table. This is act ivat ed from t he m ain program 9-21 Exam ple 9 Mixed Flow Analysis window by select ing Vie w , D e t a ile d Ou t pu t Ta ble , Type , and t hen Bridge. This will display t he t able as shown in Figure 9.20. As discussed previously, t he left side of t he t able shows t he energy gradeline and t he wat er surface for t he cross sect ion im m ediat ely upst ream of t he bridge. ( These values are t he sam e as was shown in Figure 9.19.) Addit ionally, t he left side of t he t able shows t hat t here was no weir flow occurring over t he bridge decking. The right side of t he t able displays inform at ion for t he t wo cross sect ions locat ed inside of t he bridge. Figure 9-20: Bridge Detailed Output Table for Pressure/Weir Flow Analysis The bot t om of t he t able displays t he errors, warnings, and not es for t he river st at ion. At t his bridge locat ion, t he not es shown in t he figure indicat ed t hat t he sluice gat e equat ion was used for pressure flow. This equat ion was used because t he wat er surface elevat ion at t he river st at ion im m ediat ely below t he bridge was less t han t he lowest value of t he low cord for t he bridge. 9-22 Exam ple 9 Mixed Flow Analysis X-Y-Z Perspective Plot As a final review of t he pressure/ weir flow analysis, t he X- Y- Z Pe r spe ct ive plot was viewed. This plot was act ivat ed from t he m ain program window by select ing Vie w and t hen X- Y- Z Pe r spe ct ive Plot s. This plot is shown as Figure 9.21. The user m ust be aware of t he fact t hat t his plot can be aligned according t o left or right edges of t he cross sect ions or by t he m ain channel left , cent erline, or right bank st at ions. Addit ionally, t he alignm ent is based upon t he X- coordinat es as ent ered by t he user. I f t he X- coordinat es for t he cross sect ions are not all est ablished from t he sam e left baseline, t hen t he plot m ay not be accurat ely port raying t he correct configurat ion of t he river syst em . Figure 9-21: X-Y-Z Perspective Plot for Pressure/Weir Analysis Summary As a sum m ary for t his exam ple, a profile plot for bot h t he energy and pressure flow analysis is shown as Figure 9.22. Once t he plot was act ivat ed, Opt ion s and Pla ns were chosen and bot h plans were select ed t o be displayed. The heading at t he t op of t he figure displays t he Short I D’s t hat 9-23 Exam ple 9 Mixed Flow Analysis were used for each plan : 1) Energy and 2) Press/ Weir. The legend displays t wo lines for t he crit ical dept h and t wo lines for t he wat er surface. Bot h of t he crit ical dept h lines will coincide since t he flow rat e was t he sam e for bot h plans. For t he wat er surface profiles, t he lines are labeled “ WS 100yr Energy” and “ WS 100yr - Pressure” for t he energy and pressure m et hods respect ively. ( Not e: For t his exam ple, each plan only had one profile.) Sim ilarly, t he legend descript ion for t he solid wat er surface profile signifies t hat t his line is for t he first profile of t he energy plan. Figure 9-22: Water Surface profiles for both Energy and Pressure Analysis A review of Figure 9.22 shows a significant difference in t he calculat ed wat er surface profiles for t he t wo plans. During t he energy analysis, t he wat er surface does not encount er t he bridge decking and t his lead t o a low flow profile. However, t he pressure analysis det erm ined t hat t he wat er surface cam e in cont act wit h t he upst ream side of t he bridge. Wit h bot h of t hese analyses, t he m odeler m ust use engineering j udgm ent t o det erm ine which profile is act ually occurring. Realist ically, for t his exam ple, as t he flow rat e begins t o increase t o t he value of 3200 cfs, t he flow will m ost likely be a low flow profile as calculat ed by t he energy m et hod. At t he flow rat e of 3200 cfs, t he flow m ay also init ially be occurring as t he low flow profile. However, t he wat er surface im m ediat ely upst ream of t he bridge has risen due t o t he const rict ion of t he cross sect ions in t he vicinit y of t he bridge. I f t he flow is sedim ent laden and as debris begins t o accum ulat e in t he vicinit y of t he bridge opening, t he wat er surface m ay begin t o fluct uat e due t o t he t urbulent nat ure of t he flow. These wat er surface fluct uat ions m ay becom e great enough t o cause t he wat er surface t o 9-24 Exam ple 9 Mixed Flow Analysis com e in cont act wit h t he upst ream low cord of t he bridge. When t his occurs, t he flow m ay “ j um p” t o becom e pressure flow t hrough t he bridge opening. 9-25 Exam ple 10 St ream Junct ion CH APT ER 1 0 Stream Junction Purpose This exam ple was perform ed t o dem onst rat e t he analysis of a st ream j unct ion. The program can analyze 12 different t ypes of j unct ions. These 12 t ypes of problem s are obt ained by com bining t he 3 flow regim es ( subcrit ical, supercrit ical, and m ixed) wit h t he 2 geom et ric configurat ions ( com bining or split t ing) and t he 2 analysis m et hods ( energy and m om ent um ) . For t his exam ple, a subcrit ical flow com bining j unct ion was analyzed using bot h t he energy and t he m om ent um m et hods. The discussion of t his exam ple will focus on t he analysis of t he st ream j unct ion. The m odeler is referred t o chapt er 4 of t he H ydr a u lic Re fe r e n ce M a n u a l for addit ional discussion on m odeling st ream j unct ions. For looped net works, t he m odeler is referred t o exam ple 8. To review t he dat a files for t his exam ple, from t he m ain program window select File and t hen Ope n Pr oj e ct . Select t he proj ect labeled “ St ream Junct ion - Exam ple 10.” This will open t he proj ect and act ivat e t he following files: Plan: “ Junct ion - Energy” Geom et ry: “ Base Geom et ry - Energy Junct ion” Flow: “ 10 Year Profile” Geometric Data The geom et ric dat a for t his exam ple consist s of t he river syst em schem at ic, t he cross sect ion placem ent , t he cross sect ion dat a, and t he st ream j unct ion dat a. Each of t hese com ponent s are discussed below. River System Schematic To view t he river syst em schem at ic, from t he m ain program window select Edit and t hen Ge om e t r ic D a t a . This will act ivat e t he Ge om e t r ic D a t a Edit or and display t he river syst em schem at ic as shown in Figure 10.1. The schem at ic shows t he layout of t he t wo rivers ( Spring Creek and Spruce Creek) broken int o t hree reaches: Upper Reach, Lower Reach, and Spruce 10-1 Exam ple 10 St ream Junct ion Creek. The Upper and Lower Reach of Spring Creek are divided at t he j unct ion wit h Spruce Creek. This j unct ion occurs at t he cit y of Pot t sville. Figure 10-1: River System Schematic To creat e t he river syst em schem at ic, t he Rive r Re a ch icon was select ed and a line was drawn in t he downst ream direct ion. Then, t he program request ed t he nam e of t he r ive r a n d r e a ch. The t it les “ Spring Creek” and “ Upper Reach” were ent ered respect ively. Then t he River Reach icon was select ed again and t he “ Lower Reach” was sket ched. The program request ed t it les for t his river reach and t hen prom pt ed for a t it le of t he st ream j unct ion. The nam e “ Pot t sville” was ent ered for t he st ream j unct ion t it le. Finally, t he River Re a ch icon was select ed a t hird t im e and t he Spruce Creek t ribut ary was drawn and labeled. This creat ed t he river syst em schem at ic as shown in Figure 10.1 ( wit hout t he river st at ions) . The cross sect ion dat a for t he river st at ions were ent ered next and are described subsequent ly. 10-2 Exam ple 10 St ream Junct ion Cross Section Placement The locat ion of t he cross sect ions in relat ion t o t he st ream j unct ion are crucial for t he accurat e calculat ion of t he energy losses and t he wat er surface across t he j unct ion. There are t hree crit eria t hat can be used as guidelines for t he placem ent of t he cross sect ions. First , t he cross sect ions should be placed close t o t he st ream j unct ion. This will allow for a m ore accurat e evaluat ion of t he energy losses when perform ing an energy analysis. For a m om ent um analysis, t he program assum es t hat t he wat er surface at t he t wo upst ream sect ions of t he j unct ion are equal. Therefore, t o m inim ize t he error associat ed wit h t his assum pt ion, t he cross sect ions should be closely spaced around t he j unct ion. The second crit erion is t hat t he dat a used for t he cross sect ions does not overlap. The cross sect ion dat a is acquired from a line perpendicular t o t he flow lines. I f t hese lines of cross- sect ion dat a int ersect upst ream of t he j unct ion, t hen t he flow area m ay be account ed for t wice and produce incorrect result s. As shown in t he schem at ic in Figure 10.2, t he cross sect ions 7 and 1 for t he Upper Reach and Spruce Creek would not be port raying accurat e flow cross sect ion dat a. Part of t he flow area would be account ed for t wice and, addit ionally, t he cross sect ions would not cont ain t he flow in t he overbank areas. The cross sect ions num bered 8 and 2 would m ore accurat ely port ray t he flow sit uat ion because t hey do not int ersect and t he ent ire flow area is cont ained wit hin t he cross sect ion dat a. Sp r uce C reek U pp er R each Main Chan nel Lim it o f W ater Surface 8 7 2 1 6 L o wer R each Figure 10-2: Cross Section Placement Schematic Finally, a t hird crit erion is concerned wit h t he fact t hat t he program is a onedim ensional m odel. Therefore, t he cross sect ions should be locat ed in regions where t he flow direct ion is perpendicular t o t he sect ion. For exam ple, as shown in Figure 10.2, t he cross sect ion num ber 6 should be placed 10-3 Exam ple 10 St ream Junct ion adequat ely downst ream from t he j unct ion so t hat t he flow is predom inat ely in t he downst ream direct ion. This cross sect ion should not be placed in t he j unct ion where t he t urbulent m ixing of t he flow is occurring. However, as discussed previously, t he cross sect ions should be placed close t o t he st ream j unct ion t o accurat ely evaluat e t he energy losses across t he j unct ion and t o provide a reasonable result for t he m om ent um m et hod, which equat es t he t wo upst ream wat er surface elevat ions. Observat ions of wat er surface elevat ions at high flows can assist t he m odeler in det erm ining t he appropriat e locat ions for t he cross sect ions. Cross Section Data To ent er t he cross sect ion dat a, from t he Ge om e t r ic D a t a Edit or select t he Cr oss Se ct ion icon on t he left side of t he window. This will act ivat e t he Cr oss Se ct ion D a t a Edit or as shown in Figure 10.3. Cross sect ion dat a were ent ered for each of t he t hree river reaches for t his exam ple. The t op port ion of t he edit or shows t he river, reach and t he river st at ion. The river st at ions correspond t o t he river m iles of t he specific river reach. Addit ionally, a descript ion was ent ered for each river st at ion. Figure 10-3:Cross Section Data Editor The left side of t he edit or is where t he st at ion and elevat ion dat a for t he cross sect ion coordinat es were ent ered. The right side of t he edit or displays t he ent ered values for t he downst ream reach lengt hs, Manning’s n values, m ain channel bank st at ions, and t he cont ract ion and expansion coefficient s. The downst ream reach lengt hs for t he last cross sect ion of each river reach should 10-4 Exam ple 10 St ream Junct ion be set at zero or left blank. Therefore, for t his exam ple, t he downst ream reach lengt hs at t he river st at ions of 10.106, 10.000, and 0.013 for Upper Reach, Lower Reach, and Spruce Creek, respect ively, were set at 0. Finally, any levees, ineffect ive flow areas, blocked obst ruct ions, et c. would be ent ered at t his t im e. For t his exam ple, t he flow and cross sect ional dat a did not provide for t he use of any of t hese opt ions. Stream Junction Data - Energy Method The final com ponent of t he geom et ric dat a for t his exam ple is t he st ream j unct ion dat a. To ent er t he j unct ion dat a, from t he Ge om e t r ic D a t a Edit or select t he Ju n ct ion icon on t he left side of t he window. This will act ivat e t he Ju n ct ion D a t a Edit or as shown in Figure 10.4. Figure 10-4: Junction Data Editor for Energy Method To ent er t he st ream j unct ion dat a, first one of t he st ream j unct ions was select ed by depressing t he down arrow adj acent t o t he Ju nct ion N a m e box. For t his exam ple, t here was only one j unct ion, which had been nam ed “ Pot t sville” and t his j unct ion nam e aut om at ically appeared. Next , a descript ion for t he j unct ion was ent ered. The ent ire descript ion can be viewed by select ing t he “ ...” but t on. The “ ...” but t on can t hen be re- select ed t o exit t he descript ion display. The next it em of inform at ion required is t he st ream lengt hs across t he j unct ion. The t able at t he bot t om left side of t he edit or will aut om at ically display t he nam es of t he river reaches at t he j unct ion for which t he user m ust ent er t he reach lengt hs. For t his exam ple, a reach lengt h of 80 feet was ent ered as t he dist ance across t he j unct ion from Upper Reach t o Lower Reach. The program will t hen use t his dist ance of 80 feet as t he lengt h from river st at ion 10.106 ( t he downst ream river st at ion of Upper Reach) t o river st at ion 10.091 ( t he upst ream river st at ion of Lower Reach) . Sim ilarly, a dist ance of 70 feet was ent ered as t he lengt h across t he j unct ion from t he upst ream river st at ion on Lower Reach ( 10.091) t o t he downst ream river st at ion on Spruce Creek ( 0.013) . 10-5 Exam ple 10 St ream Junct ion The last it em for t he Ju n ct ion D a t a Edit or is t he Com pu t a t ion M ode . The user m ust select eit her t he energy or t he m om ent um m et hod for t he com put at ional procedure. For t his exam ple, t he energy m et hod was select ed. Aft er t he discussion of t he out put for t he energy m et hod analysis, t he m om ent um m et hod will be select ed and t he result s from t he t wo m et hods will be com pared. A discussion on t he com put at ional procedures for each m et hod will be addressed during t he review of t he out put for each m et hod. The select ion of t he energy m et hod for t he j unct ion analysis com plet ed t he geom et ric input for t his exam ple. The j unct ion edit or was t hen closed by select ing t he OK but t on. Finally, t he geom et ric dat a was t hen saved by select ing File and t hen Sa ve Ge om e t r ic D a t a As from t he Ge om e t r ic D a t a Edit or . The t it le “ Base Geom et ry - Energy Junct ion” was ent ered for t he nam e of t he file. The next procedure was t o ent er t he st eady flow dat a. Steady Flow Data To ent er t he st eady flow dat a, from t he m ain program window select Edit and t hen St e a dy Flow D a t a . This will act ivat e t he St e a dy Flow D a t a Edit or as shown in Figure 10.5. For t his exam ple, t he num ber of profiles was select ed as one. When t his num ber was ent ered, t he t able for t he st eady flow dat a adj ust ed t o account for t he num ber of profiles t hat were select ed. Next , t he flow values were ent ered. The user m ust ent er a flow value at t he upst ream end of each river reach and t he t able for t he flow dat a will aut om at ically display t he upst ream river st at ions for each river reach. The values of 1100, 3000, and 4100 were t hen ent ered as t he flow values at t he upst ream river st at ions for Spruce Creek, Upper Reach, and Lower Reach, respect ively. Aft er t he st eady flow values were ent ered, t he boundary condit ions were t hen assigned. This was perform ed by select ing t he Boun da r y Condit ion s icon at t he t op of t he window. This act ivat ed t he Boun da r y Condit ions D a t a Edit or as shown in Figure 10.6. As shown in t he figure, a t able is displayed t hat list s all of t he river reaches. The t able will aut om at ically display any int ernal boundary condit ions such as st ream j unct ions. These int ernal boundary condit ions are based upon how t he river syst em was defined by t he geom et ric dat a. The user can t hen ent er any ext ernal boundary condit ion for each river reach. 10-6 Exam ple 10 St ream Junct ion Figure 10-5: Steady Flow Data Editor Figure 10-6: Boundary Conditions Data Editor For t his exam ple, a subcrit ical analysis was perform ed and t herefore a downst ream boundary condit ion was required t o be ent ered for t he Lower Reach of Spring Creek. To ent er t his boundary condit ion, t he downst ream field for Lower Reach was select ed and t hen t he boundary condit ion N or m a l D e pt h was chosen. A slope of 0.001 was t hen ent ered for t his boundary condit ion. For a furt her discussion on boundary condit ions, t he user is referred t o chapt er 7 of t he Use r ’s M a n u a l and t o chapt er 3 of t he H ydr a u lic Re fe r e n ce M a n u a l. Aft er all of t he st eady flow dat a had been ent ered, t he st eady flow dat a file was t hen saved by select ing File and t hen Sa ve St e a dy Flow D a t a As from 10-7 Exam ple 10 St ream Junct ion t he St e a dy Flow D a t a Edit or . The t it le “ 10 Year Profile” was t hen ent ered and t he OK but t on select ed. Steady Flow Analysis (Stream Junction Energy Method) Aft er t he flow dat a were ent ered, t he st eady flow dat a file and t he geom et ry file were saved as a plan. This was perform ed by first select ing Ru n and t hen St e a dy Flow Ana lysis from t he m ain program window. This act ivat ed t he St e a dy Flow An a lysis W in dow as shown in Figure 10.7. Figure 10-7: Steady Flow Analysis Window At t he t op of t he St e a dy Flow Ana lysis W indow , a Shor t I D was ent ered as “ Energy.” The next st ep was t o select t he appropriat e flow regim e for t he analysis. For t his exam ple, t he Subcrit ical regim e was select ed. Then, t he geom et ry file “ Base Geom et ry - Energy Junct ion” and t he st eady flow file “ 10 Year Profile” were select ed by depressing t he down arrows on t he right side of t he window. ( Not e: At t his point in t he exam ple, t here was only one geom et ry and one flow file. Therefore, t his st ep was not necessary.) To save t hese files as a plan, select File and t hen Sa ve Pla n As. The t it le “ Junct ion Energy” was t hen ent ered as t he plan t it le and t he OK but t on was select ed. This associat ed t he geom et ry and t he st eady flow file as a plan and t he nam e of t he plan t hen appeared on t he St e a dy Flow Ana lysis W indow ( as well as on t he m ain program window) . Finally, t he COM PUTE but t on was select ed t o perform t he analysis. Review of Output for Stream Junction Energy Analysis To review t he out put for t he analysis, t he user can evaluat e t he dat a in bot h graphical and t abular form at . For t his exam ple, t he wat er surface profile and t he st andard t able 2 profile t able will be reviewed. 10-8 Exam ple 10 St ream Junct ion Water Surface Profile To view t he wat er surface profiles for t he analysis, from t he m ain program window select Vie w and t hen W a t e r Sur fa ce Pr ofile s. This will act ivat e t he profile plot as shown in Figure 10.8. The profile in Figure 10.8 displays t he energy gradeline, t he wat er surface elevat ion, and t he crit ical dept h line for t he reaches of Upper Reach and Lower Reach. From t he figure, it can be seen t hat t he flow regim e is subcrit ical because t he wat er surface profile is above t he crit ical dept h line. Addit ionally, t he energy gradeline displays a const ant increase in energy in t he upst ream direct ion. Abrupt changes in t he wat er surface profile or t he energy gradeline should prom pt t he user t o closely exam ine t he flow sit uat ion at t hese locat ions. Stream Junction - Example 10 Junction - Energy 6/2/1998 Geom: Base Geometry - Energy Junction Flow: 10 Year Profile Lower Reach Upper Reach 78 Legend 76 EG 10 yr WS 10 yr 74 Elevation (ft) Crit 10 yr 72 Ground 70 68 66 64 62 0 200 400 600 800 1000 1200 Main Channel Distance (ft) Figure 10-8: Water Surface Profile for Energy Junction At t his t im e, t he user can select which reaches t o be displayed by select ing Opt ion s and t hen Re a ch e s. I n t his m anner, t he wat er surface profile for t he com binat ion of Spruce Creek and Lower Reach can be viewed. The user can also select t o have all t hree reaches displayed sim ult aneously. To det erm ine t he wat er surface profile across t he st ream j unct ion, t he program used t he energy based solut ion rout ine for t his plan. Since t his was a subcrit ical flow analysis, t he program st art ed t he calculat ions at t he downst ream end of t he Lower Reach and com put ed t he wat er surface profile up t o t he upst ream river st at ion of Lower Reach ( 10.091) . Then t he program perform ed st andard st ep calculat ions separat ely across t he st ream j unct ion t o each of t he downst ream river st at ions of Upper Reach and Spruce Creek. During each of t he separat e calculat ions, t he frict ion losses and t he cont ract ion and expansion losses were calculat ed t o balance t he energy from river st at ion 10.091 t o each of t he river st at ions 10.106 and 0.013 of Upper Reach and Spruce Creek, respect ively. By perform ing t he calculat ions in t his m anner, t he downst ream wat er surface elevat ions of Upper Reach and Spruce Creek do not necessarily have t o coincide. 10-9 Exam ple 10 St ream Junct ion Standard Table 2 As a furt her review of t he out put , from t he m ain program window select Vie w and t hen Pr ofile Sum m a r y Ta ble . Then select St d. Ta ble s and t hen St a n da r d Ta ble 2 . This will result in t he display as shown in Figure 10.9. The first t wo colum ns in t he t able are in fixed form at and display t he river reach and t he river st at ioning. The colum ns in t he non- fixed area of t he t able ( as shown in Figure 10.9) display t he energy gradeline, t he wat er surface elevat ion, t he velocit y head, t he frict ion losses, and t he cont ract ion/ expansion losses. The rem aining port ion of t he t able can be viewed by depressing t he left and right arrows at t he bot t om of t he window. The t able in Figure 10.9 can be reviewed t o follow t he st andard st ep com put at ions across t he st ream j unct ion. The energy gradeline elevat ion for t he upst ream river st at ion of Lower Reach ( 10.091) was 75.86 ft . When calculat ing t he energy losses across t he st ream j unct ion from river st at ion 10.091 t o 10.106 ( t he downst ream river st at ion of Upper Reach) , t he program det erm ined t hat t he frict ion loss was 0.09 feet and t he cont ract ion/ expansion loss was 0.06 feet . These values are displayed in t he row for t he Upper Reach st at ion of 10.106. By sum m ing t hese losses, a t ot al energy loss of 0.10 + 0.06 = 0.16 feet is obt ained. Then, t his 0.16 feet of energy was added t o t he energy of 75.86 feet t o obt ain an energy value of 0.16 + 75.86 = 76.02 feet at river st at ion 10.106. ( Not e: The t able only displayed t he values t o t wo decim al places and rounding of num erical values occurred.) The st andard st ep procedure was t hen cont inued upst ream t hrough t he reach of Upper Reach. Figure 10-9: Profile Standard Table 2 for Energy Junction Analysis Sim ilarly, t he user can t oggle t he t able t o display t he inform at ion for Spruce Creek and follow t he sam e procedure t o det erm ine t he energy losses across t he j unct ion from t he upst ream river st at ion of Lower Reach t o t he 10-10 Exam ple 10 St ream Junct ion downst ream river st at ion of Spruce Creek. ( Not e: I f t he t able does not display t he inform at ion for all of t he river reaches, t he user can select t he appropriat e reaches for display under t he Opt ion s m enu.) Steady Flow Analysis (Stream Junction Momentum Method) Aft er t he energy m et hod was used t o analyze t he st ream j unct ion, t he com put at ion procedure was changed t o t he m om ent um m et hod. This was perform ed by opening t he Ge om e t r ic D a t a Edit or and select ing t he Ju n ct ion icon on t he left side of t he window. This will act ivat e t he Junct ion D a t a Edit or as shown in Figure 10.10. The com ponent s of Jun ct ion N a m e , D e scr ipt ion, and Re a ch Le ngt h s were kept t he sam e as described for t he energy m et hod analysis. However, t he Com pu t a t ion M ode was select ed as Mom ent um for t he subsequent analysis. For t he m om ent um m et hod, t he user m ust ent er t he angles at which t he reaches are ent ering or leaving t he j unct ion. For a flow com bining sit uat ion ( such as t his exam ple) , t he user m ust ent er t he angles of t he inflow reaches as m easured from a line perpendicular t o t he upst ream cross sect ion of t he out flow reach. ( Not e: Figure 4.9 in t he H ydr a u lic Re fe r e n ce M a n ua l will assist t he user t o visualize t he flow angles.) Figure 10-10: Junction Data Editor for Momentum Method For t his exam ple, t he t ribut ary angle from Upper Reach t o Lower Reach was ent ered as 0 degrees. This im plies t hat t he flow will cont inue in a st raight line. The flow angle from Spruce Creek t o Lower Reach was t hen ent ered as 45 degrees, as m easured from t he survey dat a. Finally, t he user m ust select whet her t he program should include t he weight and/ or t he frict ion t erm s in t he m om ent um equat ion. For t his exam ple, t he t erm s were included by select ing t he appropriat e boxes in t he lower right corner of t he window. The user should refer t o chapt er 4 of t he H ydr a u lic Re fe r e n ce M a n ua l for a furt her discussion of t he m om ent um equat ions. 10-11 Exam ple 10 St ream Junct ion Aft er t hese changes were m ade, t he Apply D a t a but t on was select ed and t he j unct ion edit or was closed. Since t his geom et ry file was changed, it was t hen saved as a new file. This was perform ed by select ing File and t hen Sa ve Ge om e t r y As. The t it le “ Base Geom et ry - Mom ent um Junct ion” was ent ered and t he OK but t on select ed. Then t he Ge om e t r ic D a t a Edit or was closed. From t he m ain program window, Run and t hen St e a dy Flow Ana lysis were t hen select ed. This act ivat ed t he St e a dy Flow Ana lysis W indow as shown in Figure 10.11. Figure 10-11: Steady Flow Analysis Window for Momentum Method I n t he upper right corner of t he window, a Shor t I D was ent ered as “ Mom ent um .” Then, t he geom et ry file “ Base Geom et ry - Mom ent um Junct ion” and t he flow file “ 10 Year Profile” were select ed by depressing t he down arrows on t he right side of t he window. Next , t he Flow Re gim e was select ed as Subcrit ical. Then, File and Sa ve Pla n As were select ed and t he t it le “ Junct ion - Mom ent um ” was ent ered. This plan t it le t hen appeared at t he t op of t he window ( as well as on t he m ain program window) . Finally, t he COM PUTE but t on was select ed t o perform t he analysis. Review of Output for Stream Junction Momentum Analysis To review t he out put for t he analysis, t he user can evaluat e t he dat a in bot h graphical and t abular form at . For t his exam ple, t he wat er surface profile and t he st andard t able 2 profile t able will be reviewed. Water Surface Profile To view t he wat er surface profiles for t he analysis, from t he m ain program window select Vie w and t hen W a t e r Sur fa ce Pr ofile s. This will act ivat e t he profile plot as shown in Figure 10.12. The profile plot shown in Figure 10.12 is sim ilar t o t he plot as shown in Figure 10.8, except Figure 10.12 is for t he result s of t he m om ent um analysis of t he 10-12 Exam ple 10 St ream Junct ion st ream j unct ion. Figure 10.12 shows t he energy gradeline, t he wat er surface elevat ion, and t he crit ical dept h line. The profile is seen t o be occurring in t he subcrit ical flow regim e. As discussed previously, t he user can select ot her reaches t o display t he corresponding wat er surface profiles. Stream Junction - Example 10 Junction - Momentum 6/2/1998 Geom: Base Geometry - Momemtum Junction Flow: 10 Year Profile Lower Reach Upper Reach 78 Legend 76 EG 10 yr Elevation (ft) 74 WS 10 yr 72 Crit 10 yr 70 Ground 68 66 64 62 0 200 400 600 800 1000 1200 Main Channel Distance (ft) Figure 10-12: Water Surface Profiles for Momentum Junction Analysis To det erm ine t he wat er surface profiles, t he program st art ed at t he downst ream end of t he Lower Reach ( since t his was a subcrit ical flow analysis) and used t he st andard st ep procedure up t o t he upst ream end of Lower Reach. At t he st ream j unct ion, t he program t hen used t he m om ent um m et hod t o balance t he forces across t he j unct ion. The m om ent um m et hod ( for t his exam ple) will solve sim ult aneously t he forces in t he X- direct ion for t he flow at river st at ions 10.091 ( t he upst ream river st at ion of Lower River) , 10.106 ( t he downst ream river st at ion of Upper Reach) , and 0.013 ( t he downst ream river st at ion of Spruce Creek) . The X- direct ion is det erm ined as t he direct ion of t he flow out of t he j unct ion ( t he direct ion of flow at river st at ion 10.091) . Since t he wat er surface elevat ions at t he downst ream ends of Upper Reach and Spruce Creek are t wo unknown values and are solved sim ult aneously, t he program will assum e t hat t hese wat er surface elevat ions are equal t o each ot her. Therefore, it is necessary t hat t he cross sect ions be placed close t o t he st ream j unct ion in order t o m inim ize t he error associat ed wit h t his assum pt ion. For a m ore det ailed discussion on t he m om ent um m et hod analysis, t he user is referred t o chapt er 4 of t he H ydr a u lic Re fe r e n ce M a n u a l. Standard Table 2 As a furt her review of t he out put , from t he m ain program window select View and t hen Profile Table. Then select St d. Tables and t hen St andard Table 2. This will result in t he display as shown in Figure 10.13. As discussed previously, t he first t wo colum ns in t he t able are in fixed form at and display 10-13 Exam ple 10 St ream Junct ion t he river reach and t he river st at ioning. ( Not e: For t his t able, all 3 river reaches were select ed t o be displayed.) The colum ns in t he non- fixed area of t he t able display t he energy gradeline, t he wat er surface elevat ion, t he velocit y head, t he frict ion losses, and t he cont ract ion/ expansion losses. The rem aining port ion of t he t able can be viewed by depressing t he left and right arrows at t he bot t om of t he window. As shown in Figure 10.13, t he wat er surface elevat ions for Lower Reach are exact ly t he sam e values in t he previous run because not hing has changed in t he downst ream reach. However, for t his plan, t he wat er surface elevat ions across t he st ream j unct ion were det erm ined using t he m om ent um m et hod. As discussed previously, t o perform t he m om ent um calculat ions at t he st ream j unct ion, t he program will equat e t he t wo upst ream wat er surface elevat ions. This is seen t o have occurred as t he wat er surface elevat ions at river st at ion 10.106 ( t he downst ream st at ion of Upper Reach) and river st at ion 0.013 ( t he downst ream river st at ion of Spruce Creek) are bot h equal t o 75.50 feet . Then, t he program det erm ined separat ely t he rem aining wat er surface profiles for Upper Reach and Spruce Creek by using t he st andard st ep procedure in t he upst ream direct ion. Figure 10-13: Standard Profile Table 2 for Momentum Junction Analysis Comparison of Energy and Momentum Results To com pare t he wat er surface profiles for t he energy and t he m om ent um analyses of t he st ream j unct ion, t he wat er surface profile plot was select ed t o view bot h of t he plans. ThiSur fa ce Pr ofile s fros was perform ed by eslect ing 10-14 Exam ple 10 St ream Junct ion Vie w and t hen W a t e r m t he m ain program window. Then, under t he Opt ion s m enu, t he reaches were select ed as Upper Reach and Lower Reach. Finally, under t he Opt ion s m enu again, bot h Pla n s were select ed. This result ed in t he display as shown in Figure 10.14. Figure 10.14 shows t he wat er surface elevat ions for Upper Reach and Lower Reach for bot h m et hods of j unct ion analysis. At t he t op of t he figure, t he heading list s t he proj ect nam e “ St ream Junct ion - Exam ple 10” and t he short ident ifiers list ed for each plan. Stream Junction - Example 10 2) Energy Geom: Base Geometry - Momemtum Junction Flow: 10 Year Profile Lower Reach Upper Reach 78 Elevation (ft) 1) Momentum Legend 76 WS 10 yr - Momentum 74 WS 10 yr - Energy Crit 10 yr - Momentum 72 Crit 10 yr - Energy 70 Ground 68 66 64 62 0 200 400 600 800 1000 1200 Main Channel Distance (ft) Figure 10-14: Water Surface profiles for Upper Reach and Lower Reach for Both Energy and Momentum Junction Analyses By visually com paring t he t wo result s, it can be seen t hat t he calculat ed wat er surface profile for Lower Reach was t he sam e for bot h plans. However, t he wat er surface profile for Upper Reach was different . This is due t o t he fact t hat t he st art ing downst ream wat er surface elevat ion at river st at ion 10.106 of Upper Reach was different , for t he t wo m et hods of com put at ion across t he j unct ion. I f t he st andard st ep procedure was allowed t o cont inue for a longer dist ance upst ream on Upper Reach, bot h of t he wat er surface profiles would event ually converge. At t his t im e, t he user can select t o view t he com binat ion of Spruce Creek and Lower Reach and observe a sim ilar result . The profile would show t hat t he m om ent um m et hod produced a higher result ing wat er surface profile on Spruce Creek t han t he energy m et hod. However, t he difference of t he wat er surface profiles for Spruce Creek is not as significant as t hat for Upper Reach. 10-15 Exam ple 10 St ream Junct ion The energy m et hod uses frict ion and t he coefficient s of cont ract ion and expansion in det erm ining t he energy losses across t he j unct ion. The user can adj ust t hese coefficient s t o account for any abrupt t ransit ions t hat occur in t he cross sect ional area. Addit ionally, t he user could adj ust t he Manning’s n value at t he st ream j unct ion t o account for addit ional int ernal energy losses associat ed wit h t he j unct ion. By adj ust ing t hese param et ers, t he calculat ed wat er surface profile can be calibrat ed t o act ual m easured wat er surface elevat ions. For t he m om ent um m et hod, t he program det erm ines t he wat er surface elevat ions across t he st ream j unct ion by t aking int o account t he forces associat ed wit h t he flow. To balance t he forces across t he j unct ion, t he program only uses t he forces in t he X- direct ion. This direct ion is det erm ined as being perpendicular t o t he out flow direct ion ( for a flow com bining sit uat ion) . Therefore, t he t ribut ary angles, as ent ered by t he user, are crucial for t he accurat e calculat ion of t he forces. Addit ionally, as for t he energy m et hod, t he Manning’s n values can be adj ust ed t o account for addit ional frict ion losses associat ed wit h t he st ream j unct ion. Summary Bot h t he energy and t he m om ent um m et hods were used t o det erm ine t he wat er surface profiles across t he st ream j unct ion. For t his exam ple, t he result ing wat er surface profiles differed upst ream of t he j unct ion for t he t wo calculat ion procedures. The energy m et hod used t he st andard st ep procedure wit h t he coefficient s of expansion and cont ract ion and t he Manning’s n value t o account for energy losses across t he j unct ion. Wit h t he energy m et hod, t he program calculat ed separat ely t he result ing upst ream wat er surface elevat ions. The m om ent um m et hod equat ed t he forces in one dim ension and used t he t ribut ary angles t o balance t he forces at t he st ream j unct ion. Addit ionally, t he Manning’s n values are used t o account for frict ion losses. The m om ent um m et hod should be used when t he t ribut ary flow angles play an im port ant role in influencing t he wat er surface around t he j unct ion. However, in order t o solve t he m om ent um calculat ions, t he upst ream wat er surface elevat ions were equat ed. To reduce t he error associat ed wit h t his assum pt ion, t he cross sect ions should be locat ed close t o t he st ream j unct ion. The m om ent um m et hod is an at t em pt at a m ore t heoret ical analysis of t he st ream j unct ion. However, t he user should be aware of t he lim it at ions of t his one- dim ensional analysis. To det erm ine t he m ost applicable m et hod for t he analysis, t he user should com pare t he result s t o observed dat a and calibrat e t he m odel as deem ed appropriat e. 10-16 Exam ple 11 Bridge Scour CH APT ER 1 1 Bridge Scour Purpose This exam ple will dem onst rat e t he use of HEC- RAS t o perform a bridge scour analysis. To perform t he analysis, t he user m ust first develop a hydraulic m odel of t he river reach t hat cont ains t he bridge. This m odel should be calibrat ed t o t he fullest ext ent possible in order t o accurat ely det erm ine t he hydraulics of t he river reach. Once t his m odel is developed, t he bridge scour com put at ions can t hen be perform ed. The scour com put at ions in HEC- RAS are com prised of t hree com ponent s: cont ract ion scour, pier scour, and abut m ent scour. The scour equat ions for t hese com ponent s are based upon t he m et hods out lined in Hydraulic Engineering Circular No. 18 ( FHWA, 1995) . The program does not have t he capabilit y t o perform long- t erm aggradat ion or degradat ion. The user m ust det erm ine t he long- t erm effect s before applying t he bridge scour com put at ions in HEC- RAS. The procedures for perform ing long- t erm effect s are discussed in t he HEC No. 18 publicat ion. This exam ple will focus upon t he analysis of t he bridge scour. The m odeler is referred t o chapt er 6 of t he Use r ’s M a n ua l and t o chapt er 5 of t he H ydr a u lic Re fe r e n ce M a n u a l for addit ional discussion on m odeling bridges. Addit ionally, t he m odeler is referred t o chapt er 12 of t he Use r ’s M a n ua l, chapt er 10 of t he H ydr a u lic Re fe r e n ce M a n ua l, and t o HEC No. 18 for furt her discussion on t he scour com put at ions. This exam ple is adapt ed from t he exam ple problem cont ained wit hin t he HEC No. 18 publicat ion. To review t he dat a files for t his exam ple, from t he m ain program window select File and t hen Ope n Pr oj e ct . Select t he proj ect labeled “ Bridge Scour - Exam ple 11.” This will open t he proj ect and act ivat e t he following files: Plan: “ Scour Plan 1” Geom et ry: “ Base Geom et ry” Flow: “ 100- Year Discharge” Hydr Design: “ Hydraulic Design Dat a” 11-1 Exam ple 11 Bridge Scour Geometric Data To view t he geom et ric dat a for t he river syst em , from t he m ain program window select Edit and t hen Geom et ric Dat a. This will act ivat e t he Geom et ric Dat a Edit or and display t he river syst em schem at ic as shown in Figure 11.1. The schem at ic displays t he nine river st at ions along t he reach of Pine Creek, wit h river st at ion 10.90 as t he upst ream sect ion. The user can view t he cross sect ion dat a for each river st at ion by select ing t he Cross Sect ion icon on t he left side of t he Geom et ric Dat a Edit or. Figure 11-1: River System Schematic Along t his reach of Pine Creek, a bridge was ent ered at river st at ion 10.36. The bridge dat a were ent ered by select ing t he Br dg/ Cu lv icon on t he left side of t he Ge om e t r ic D a t a Edit or . This act ivat ed t he Br idge / Cu lve r t D a t a Edit or as shown in Figure 11.2. Then, t he bridge inform at ion for t he deck/ roadway, piers, sloping abut m ent s, and bridge m odeling approach were ent ered by select ing t he appropriat e icons on t he left side of t he Br idge / Cu lve r t D a t a Edit or . The bridge opening bet ween t he sloping 11-2 Exam ple 11 Bridge Scour abut m ent s is approxim at ely 600 feet wide and t he bridge is support ed by six piers, each wit h a widt h of 5 feet . The high and low cord values for t he bridge deck are 22 and 18 feet , respect ively. The user can select t he appropriat e icons t o review t he bridge dat a. Figure 11-2: Bridge/Culvert Data Editor Aft er all of t he geom et ric dat a had been ent ered, t he edit ors were closed and t he geom et ry was saved as “ Base Geom et ry.” Next , t he st eady flow dat a were ent ered. Steady Flow Data To ent er t he st eady flow dat a, from t he m ain program window Edit and t hen St e a dy Flow D a t a were select ed. This act ivat ed t he St e a dy Flow D a t a Edit or and one profile wit h a flow value of 30000 cfs was ent ered. This flow rat e represent s t he 1 percent chance event ( 100- year discharge) for t he river reach. Next , a downst ream boundary condit ion was ent ered as Norm al Dept h 11-3 Exam ple 11 Bridge Scour wit h a slope of 0.002 ft / ft . Then, t he flow dat a were saved wit h a t it le of “ 100- Year Discharge.” Steady Flow Analysis Aft er t he geom et ric and st eady flow dat a were ent ered, t he st eady flow analysis was perform ed. First , Run and t hen St e a dy Flow Ana lysis were select ed from t he m ain program window. Then, a Short I D was ent ered as “ Plan 01” and a subcrit ical analysis was select ed. Next , Opt ions and t hen Flow D ist r ibu t ion Loca t ion s were select ed from t he St e a dy Flow Ana lysis W indow . This act ivat ed t he Flow D ist r ibut ion Edit or as shown in Figure 11.3. Figure 11-3: Flow Distribution Editor for Pine Creek To perform t he bridge scour calculat ions, t he program requires det ailed values of t he dept h and velocit y wit hin t he cross sect ions locat ed j ust upst ream from t he bridge ( cross sect ion 10.37 for t his exam ple) and at t he approach sect ion ( cross sect ion 10.48) . Therefore, t he m odeler is required t o set t he flow dist ribut ion opt ion for t hese t wo cross sect ions. For t his exam ple, t he flow dist ribut ions were select ed for t he ent ire river reach. As shown in Figure 11.3, t he left and right overbanks were divided int o 5 subsect ions each, and t he m ain channel was divided int o 20 subsect ions. This will allow t he program t o produce det ailed result s of t he dist ribut ion of dept h and velocit y at t he cross sect ions. The num ber of subsect ions is dependent upon such fact ors as t he cross sect ion geom et ry, t he bridge opening widt h, and t he num ber of piers. The m odeler should perform t he hydraulic calculat ions wit h different num bers of subsect ions t o evaluat e t he im pact on t he bridge scour result s. I t is recom m ended t o use fewer subsect ions, however, an adequat e num ber of 11-4 Exam ple 11 Bridge Scour subsect ions is required t o det erm ine t he hydraulic propert ies. For t his exam ple, t he bridge scour calculat ions were also perform ed using 10 subsect ions for t he m ain channel, and no appreciable changes were observed in t he scour result s. For a furt her discussion on t he flow dist ribut ion opt ion, t he m odeler is referred t o chapt er 7 of t he Use r ’s M a n ua l and t o chapt er 4 of t he H ydr a u lic Re fe r e n ce M a n ua l. Finally, t he flow dist ribut ion edit or was closed and t he dat a were saved as a plan ent it led “ Scour Plan 1.” The COM PUTE but t on was t hen select ed t o execut e t he analysis. At t his point , t he m odeler should review t he out put from t he hydraulic analysis and calibrat e t he m odel. I t is im port ant t o obt ain a good working m odel of t he river syst em before at t em pt ing t o perform a bridge scour analysis. For t his exam ple, t he hydraulic analysis included t he evaluat ion of t he expansion and cont ract ion reach lengt hs according t o t he procedures as out lined in t he H ydr a ulic Re fe r e nce M a nua l. Finally, aft er a working m odel has been developed, t he user should evaluat e t he long- t erm aggradat ion or degradat ion for t he river reach and incorporat e t his analysis int o t he working m odel. Hydraulic Design - Bridge Scour Aft er a working m odel of t he river reach is developed and t he long- t erm effect s for t he river syst em are evaluat ed, t he m odeler can perform t he bridge scour com put at ions. The scour com put at ions are perform ed by select ing Ru n , H ydr a u lic D e sign Fu n ct ions, Fu n ct ion s, and t hen Scou r a t Br idge s. This will act ivat e t he Br idge Scou r Edit or as shown in Figure 11.4. The t op of t he edit or is used t o select t he River, Reach, River St at ion, and Profile num ber for t he scour analysis. For t his exam ple, t he river and reach is Pine Creek, t he bridge is locat ed at river st at ion 10.36, and t he scour analysis was for t he first profile. The rem aining port ion of t he edit or is divided int o t hree areas: input dat a t abs, a graphic, and a result s window. There are t hree t abs, one for each of t he t hree t ypes of scour com put at ions: cont ract ion, pier, and abut m ent . The graphic displays t he bridge cross sect ion ( inside upst ream ) . When t he Com pu t e but t on is select ed, t he scour result s will be displayed graphically on t he cross sect ion and in t abular form at in t he result s window. The following sect ions describe t he param et ers for each of t he t hree dat a t abs. 11-5 Exam ple 11 Bridge Scour Figure 11-4: Hydraulic Design: Bridge Scour Editor – Contraction Tab Contraction Scour Cont ract ion scour occurs when t he flow area of a st ream is reduced by a nat ural cont ract ion or bridge const rict ing t he flow. There are t wo form s of cont ract ion scour: live bed and clear wat er. The equat ions for t he cont ract ion scour are present ed in chapt er 10 of t he H ydr a u lics Re fe r e n ce M a n ua l and t he variables for t he equat ions are list ed on t he left side of t he cont ract ion t ab, as shown in Figure 11.4. Addit ionally, t he cont ract ion t ab is divided int o t hree colum ns: for t he LOB ( left overbank) , m ain channel, and ROB ( right overbank) . This allows t he program t o calculat e t he cont ract ion scour for each of t he t hree areas of t he cross sect ion. When t he Br idge Scour Edit or is act ivat ed, t he program will search t he out put file from t he hydraulic analysis and fill in t he values for t he variables on t he cont ract ion t ab wit h t he appropriat e result s, as shown in Figure 11.4. ( Not e: As shown in t he figure, t he values for Y0, Q2, and W2 are zero for t he ROB because t he right sloping abut m ent ext ended int o t he m ain channel.) The user can override any of t hese values by sim ply ent ering in a new value at t he appropriat e locat ion. For t he cont ract ion scour analysis, t he user is only required t o provide t he D50 m ean size fract ion of t he bed m at erial, t he 11-6 Exam ple 11 Bridge Scour wat er t em perat ure for t he K1 fact or, and select t he equat ion t o be used for t he analysis. For t his exam ple, t he D50 was ent ered as 2.01 m m , for each of t he LOB, m ain channel, and ROB. To ent er t he wat er t em perat ure, t he K1 icon was select ed and t his act ivat ed t he K1 D a t a Edit or as shown in Figure 11.5. As shown in Figure 11.5, t he wat er t em perat ure was ent ered as 60 F and t hen t he program aut om at ically det erm ined t hat t he K1 value was 0.59, 0.59, and 0.59 for t he LOB, m ain channel, and ROB, respect ively. This edit or was t hen closed. Figure 11-5: K1 Data Editor Finally, t he down arrows adj acent t o Equat ion were select ed and t he default opt ion was chosen. This inform ed t he program t o use eit her t he clear wat er or t he live bed scour equat ion as det erm ined from equat ion 10- 1 in t he H ydr a u lic Re fe r e n ce M a n ua l. To perform t he cont ract ion scour com put at ions, t he Com pu t e but t on at t he t op of t he edit or was select ed. When t he calculat ions were com plet ed, t he result s appeared in t abular form in t he lower right corner of t he edit or and in graphical form on t he bridge cross- sect ion plot , as shown in Figure 11.4. As a review of t he result s for t he cont ract ion scour, t he crit ical velocit y ( Vc) for t he LOB was det erm ined t o be 2.63 ft / s, from equat ion 10- 1. This value is great er t han t he velocit y at t he approach sect ion ( V1 = 2.00) in t he LOB; t herefore t he clear wat er scour equat ion was used for t he LOB, as list ed in t he sum m ary t able. Com parat ively, t he live- bed scour equat ion was used for t he m ain channel because t he crit ical velocit y ( Vc = 2.99) was less t han t he approach sect ion velocit y ( V1 = 4.43) , in t he m ain channel. Finally, t he cont ract ion scour dept h ( Ys) was det erm ined t o be 2.07 and 6.65 feet for t he LOB and m ain channel, respect ively. As a final not e, t here was no cont ract ion scour in t he ROB because t he right abut m ent ext ended int o t he m ain channel. These cont ract ion scour dept hs are also shown on t he graphic display of t he bridge cross sect ion in Figure 11.4. 11-7 Exam ple 11 Bridge Scour Pier Scour To ent er t he dat a for t he pier scour analysis, t he Pie r Ta b was select ed. This t ab is shown in Figure 11.6. For t he pier scour analysis, t he m odeler has t he opt ion of using eit her t he CSU or t he Froehlich equat ion. As for t he cont ract ion scour t ab, t he program will aut om at ically fill in t he values for t he variables from t he result s of t he hydraulic analysis. The user m ay replace any of t hese values by changing t he value in t he appropriat e field. Figure 11-6: Hydraulic Design: Bridge Scour Editor – Pier Tab For t his exam ple, t he Maxim um V1 Y1 opt ion was select ed t o inform t he program t o use t he m axim um value of t he dept h and velocit y values, as opposed t o t he values upst ream from each pier. Then, Met hod was select ed as t he “ CSU equat ion.” Next , t he Pier # opt ion was select ed as “ Apply t o All Piers” t o inform t he program t hat t he dat a will be used for all of t he piers. ( The user has t he opt ion of ent ering t he dat a for each individual pier.) Next , t he Shape of t he piers was select ed as “ Round nose” which set t he K1 value t o be 1.00. Then, t he D50 was ent ered as 2.01 m m . The angle was set t o be 0 degrees which set t he K2 value t o be 1.00. Next , t he bed condit ion was select ed as “ Clear- Wat er Scour” ( t his set K3 = 1.1) and t he D95 was ent ered as 2.44 m m . 11-8 Exam ple 11 Bridge Scour This com plet ed t he required user input and t hen t he Com pu t e but t on was select ed. The result s were t hen displayed graphically and in t he sum m ary t able and showed t hat t he pier scour dept h ( Ys) was 10.85 feet , as shown in Figure 11.6. ( Not e: When t he com put e but t on was select ed, t he program aut om at ically com put ed all 3 scour dept hs: cont ract ion, pier, and abut m ent .) Abutment Scour To ent er t he dat a for t he abut m ent scour, t he Abu t m e n t Ta b was select ed and is shown in Figure 11.7. For t he abut m ent scour com put at ions, t he program can use eit her t he Froehlich or t he HI RE equat ion. The variables for t he equat ions appear on t he left side of t he t ab and t heir values for t he left and right abut m ent were aut om at ically obt ained from t he hydraulic analysis result s. To perform t he abut m ent scour analysis, t he user m ust ent er t he abut m ent shape, t he skew angle, and select t he equat ion t o be used. For t his exam ple, t he shape ( K1) was select ed as “ Spill- t hrough abut m ent .” This set t he K1 value t o be 0.55. Then, t he Skew angle was ent ered as 90 degrees and t his set K2 t o be 1.00, for bot h t he left and right abut m ent . Finally, t he Equat ion was select ed as “ Default .” Wit h t his select ion, t he program will calculat e t he L / y1 rat io t o det erm ine which equat ion t o use. The m odeler is referred t o chapt er 10 of t he H ydr a u lic Re fe r e n ce M a n ua l for a furt her discussion on t he scour equat ions. This com plet ed t he dat a ent ry for t he abut m ent scour and t he Com put e but t on was select ed. The result s were t hen displayed on t he graphic and in t he sum m ary t able, as shown in Figure 11.7. The result s show t hat t he HI RE equat ion was used for bot h t he left and right abut m ent and t he m agnit ude of t he scour was 10.92 and 14.88, respect ively. Addit ionally, t he sum m ary t able displayed t he values of t he Froude num bers used for t he calculat ion. 11-9 Exam ple 11 Bridge Scour Figure 11-7: Hydraulic Design: Bridge Scour Editor – Abutment Scour Total Bridge Scour The t ot al bridge scour is t he com binat ion of t he cont ract ion scour and t he local scour ( pier or abut m ent ) . To review t he t ot al scour, t he user can t oggle t o t he bot t om of t he sum m ary t able. For t his discussion, a port ion of t he sum m ary t able is shown as Table 11.1. This t able was obt ained by select ing Copy Ta ble t o Clipboa r d under t he File m enu. 11-10 Exam ple 11 Bridge Scour Table 11-1 Summary of Results for Bridge Scour Contraction Scour Ys: Eqn: Left 2.07 Clear Channel Right 6.65 Live Default Pier Scour All Piers: Ys= Eqn= 10.85 CSU equation Abutment Scour Abutment Ys: Equation: Left 10.92 HIRE Right 14.88 HIRE Combined Scour Depths Pier Scour + Contraction Scour Left Bank: 12.92 Channel: 17.50 Left abut + contr: 12.98 Right abut + contr: 21.53 The first t hree port ions of t he t able display t he result s of t he cont ract ion, pier, and abut m ent sour, as discussed previously. The final port ion of t he t able displays t he com bined scour dept hs. For t his exam ple, t he pier and cont ract ion scour was 12.92 feet ( = 10.85 + 2.07) for t he left bank and 17.50 feet ( = 10.85 + 6.65) for t he m ain channel. Addit ionally, t he t ot al left abut m ent and cont ract ion scour was 12.98 feet ( = 10.92 + 2.07) and t he right abut m ent and cont ract ion scour was 21.53 feet ( = 14.90 + 6.65) . The cont ract ion scour for t he right abut m ent was t he cont ract ion scour for t he m ain channel because t he right abut m ent ext ended int o t he m ain channel. Finally, t he t ot al scour is displayed graphically, as shown in Figure 11.8. ( Not e: The graphic has been zoom ed in t o see m ore det ail.) As shown in t he legend, t he long dashed line represent s t he cont ract ion scour and t he short dashed line port rays t he t ot al scour. This graphic was obt ained by select ing Copy Plot t o Clipboa r d from t he File m enu. 11-11 Exam ple 11 Bridge Scour Bridge Scour RS = 10.36 Legend 20 WS PF#1 Ground Ineff 15 Bank Sta Contr Scour 10 Elevation (ft) Total Scour 5 0 -5 -10 1000 1200 1400 Station (ft) Figure 11-8: Total Bridge Scour Plot Summary To perform t he bridge scour com put at ions, t he user m ust first develop a m odel of t he river syst em t o det erm ine t he hydraulic param et ers. Then, t he program will aut om at ically incorporat e t he hydraulic result s int o t he bridge scour edit or. The user can adj ust any of t he values t hat t he program has select ed. For each part icular scour com put at ion, t he m odeler is required t o ent er only a m inim al am ount of addit ional dat a. The result s for t he scour analysis are t hen present ed in t abular form and graphically. Finally, t he user can select D e t a ile d Re por t from t he Br idge Scour Edit or t o obt ain a t able displaying a full list ing of all t he input dat a used and t he result s of t he analysis. 11-12 Exam ple 12 I nline St ruct ure CH APT ER 1 2 Inline Structure Purpose This exam ple will dem onst rat e t he use of HEC- RAS t o analyze a river reach t hat cont ains an inline weir and gat ed spillways. For each inline st ruct ure locat ion, t he program can analyze up t o 10 gat e groups, wit h a m axim um of 25 gat es per group. To perform t he analysis, t he user m ust ent er t he geom et ric dat a for t he weir and gat ed spillway, along wit h t he geom et ry of t he river reach. Then, t he user m ust set t he num ber of gat es t hat are open and t he opening height of each gat e group for each flow profile. The m odeler is referred t o Chapt er 6 of t he User’s Manual for discussion on ent ering t he geom et ric dat a for t he weir and gat ed spillways, Chapt er 7 of t he User’s Manual for ent ering t he gat e opening flow dat a, and Chapt er 8 of t he Hydraulic Reference Manual for t he hydraulic analysis procedures for analyzing t he flow t hrough t he gat e openings and over t he weir. To review t he dat a files for t his exam ple, from t he m ain program window select File and t hen Open Proj ect . Select t he proj ect labeled “ I nline st ruct ure - Exam ple 12.” This will open t he proj ect and act ivat e t he following files: Plan: “ Gat ed Spillway” Geom et ry: “ Gat e Geom et ry wit h 3 Gat e Groups” Flow: “ 8 Flow Profiles” Geometric Data To view t he geom et ric dat a for t he river syst em , from t he m ain program window select Edit and t hen Ge om e t r ic D a t a . This will act ivat e t he Ge om e t r ic D a t a Edit or and display t he river syst em schem at ic as shown in Figure 12.1. The schem at ic displays t he 35 river st at ions of t he reach “ Weir Reach” on “ Nit t any River” , wit h river st at ion 60.1 as t he upst ream cross sect ion and 36.85 as t he downst ream cross sect ion. 12-1 Exam ple 12 I nline St ruct ure Figure 12-1: River System Schematic for Nittany River Cross Section Data The cross sect ion dat a consist s of t he X- Y coordinat es, Manning’s n values, cont ract ion and expansion coefficient s, et c. The user can view t his dat a for each river st at ion by select ing t he Cr oss Se ct ion icon on t he left side of t he Ge om e t r ic D a t a Edit or . For t his exam ple, an inline st ruct ure was added at river st at ion 41.75 and will be discussed in t he next sect ion. Figure 12.2 displays t he reach lengt hs in t he vicinit y of t he weir and was act ivat ed by select ing Ta ble s and t hen Re a ch Le n gt hs from t he Ge om e t r ic D a t a Edit or . Inline Structure To add an in lin e st r u ct u r e , t he I nline St ruct ure icon was select ed from t he left side of t he Ge om e t r ic D a t a Edit or . This act ivat ed t he I n lin e St r u ct u r e 12-2 Exam ple 12 I nline St ruct ure D a t a Edit or as shown in Figure 12.3. First t he reach “ Weir Reach” was select ed. Then, Opt ion s and Add a n I n lin e St r u ct ur e were select ed and river st at ion 41.75 was ent ered as t he locat ion for t he weir. The schem at ic t hen displayed t he cross sect ion dat a for t he river st at ion im m ediat ely upst ream of t he weir locat ion: nam ely river st at ion 41.76 for t his exam ple. A descript ion for t he weir was t hen ent ered as “ I nline Weir and Spillway.” Figure 12-2: Reach Length Table for Nittany River Figure 12-3: Inline Structure Data Editor 12-3 Exam ple 12 I nline St ruct ure To ent er t he dat a for t he weir, t he W e ir / Em ba n k m e nt icon was select ed from t he left side of t he I n lin e St r u ct u r e D a t a Edit or . This act ivat ed t he I n lin e St r uct u r e St a t ion Ele va t ion D a t a Edit or as shown in Figure 12.4. This edit or is sim ilar t o t he deck/ roadway edit or used for bridges and culvert s. Figure 12-4: Inline Structure Station Elevation Data Editor The t op row of t he edit or consist s of t hree dat a ent ry fields. For t he first field, t he user m ust ent er t he Dist ance from t he upst ream cross sect ion ( 41.76) t o t he upst ream side of t he weir. For t his exam ple, t his dist ance was 20 feet . Next , t he Widt h of t he weir was ent ered as 50 feet . This is a t ot al dist ance of 70 feet . From Figure 12.2, it can be seen t hat t he dist ance from river st at ion 41.76 t o 41.74 is 90 feet . Therefore, t he dist ance from t he downst ream end of t he weir t o cross- sect ion 41.74 is 20 feet . The last field in t he t op row of t he edit or is t he Weir Coefficient . This will be discussed short ly. The cent ral port ion of t he edit or consist s of a t able in which t he user m ust ent er t he st at ion and elevat ion dat a for t he weir. For t his exam ple, t he em ergency spillway is locat ed on t he left at an elevat ion of 9.5 feet from St at ion 61 t o 190; however, t he ent ire t op- of- dam is defined. The first st at ion of t he weir was ent ered as 0 and t he last st at ion is at 1000 feet . Wit h t hese weir st at ions and elevat ion, t he program will block out t he ent ire area below t he weir crest . I n t his m anner, t he dat a ent ry is sim ilar as t hat for a culvert . Addit ionally, it should be not ed t hat t he weir st at ion values of 0 and 1000 occur beyond t he lim it s of t he cross sect ion dat a. As for t he bridge and culvert rout ines, t he program will aut om at ically “ clip off” t he excess area so t hat t he weir coincides wit h t he cross sect ion geom et ry. 12-4 Exam ple 12 I nline St ruct ure The next fields are for t he upst ream and downst ream em bankm ent side slopes. For t his exam ple, t he slope of t wo was ent ered for t he US and D S Em ba n k m e n t S.S. fields. At t he bot t om of t he edit or are several ot her required variables. The Min Weir Flow Elevat ion was left blank which im plies t hat t he lowest elevat ion of t he weir will be used t o det erm ine when weir flow begins t o occur. Finally, t he shape of t he weir was ent ered as “ Ogee” for t he Subm ergence crit eria. When ogee was select ed, t he edit or expanded t o allow for t wo m ore fields of ent ry. These fields are t he Spillway Approach Height and Design Energy Head. The approach height was ent ered as 24 feet and t he design head was 3 feet for t he ogee shape. To det erm ine t he weir coefficient wit h t hese design param et ers, t he Cd but t on was select ed and t he program calculat ed a coefficient of 3.95, as shown in Figure 12.5. The “ Yes” but t on was select ed and t hen t he coefficient appeared at t he t op of t he I n lin e St r u ct ur e St a t ion Ele va t ion D a t a Edit or in t he Weir Coefficient field. I f t he weir shape had been select ed as “ Broad Crest ed” , t he user is required t o ent er t he value of t he weir coefficient . This com plet ed t he dat a ent ry for t he weir. Next , t he dat a for t he gat es were ent ered. Figure 12-5: Ogee Weir Shape Coefficient Gated Spillways To ent er t he dat a for t he gat es, t he Ga t e icon was select ed from t he I n lin e St r u ct ur e D a t a Edit or ( Figure 12.3) . This act ivat ed t he Ga t e Edit or as shown in Figure 12.6. For t his exam ple, 15 radial gat es were ent ered. The gat es were divided int o 3 groups, wit h 5 gat es in each group. The gat es were divided int o t hree groups t o allow for flexibilit y when set t ing t he gat e opening height s. This will be discussed furt her when t he opening height s are set in t he st eady flow dat a edit or. 12-5 Exam ple 12 I nline St ruct ure Figure 12-6: Gate Editor When t he Ga t e Edit or was act ivat ed, t he first gat e was labeled as “ Gat e # 1.” For t his exam ple, t he Renam e but t on was select ed and t he label “ Left Group” was ent ered. Next , t he Height , Widt h, and I nvert for t he gat es of t he Left Group were ent ered as 10, 30, and 0 feet , respect ively. On t he right side of t he edit or, t he cent erline st at ions for t he five gat es in t he “ Left Group” were ent ered as shown in Figure 12.6. As t hese values were ent ered, t he count er field # Openings increased t o represent t he t ot al num ber of gat es for t he group ( 5 for t his exam ple) . The rem aining port ion of t he edit or is divided int o t wo sect ions, one for t he gat e dat a and one for weir dat a. The gat e dat a is used when t he wat er surface upst ream of t he gat e is great er t han 1.25 t im es t he gat e opening ( as m easured from t he gat e invert ) . At t his wat er surface elevat ion, t he gat e is cont rolling t he flow rat e. The weir dat a is t he shape of t he weir under t he gat e and is used when t he upst ream wat er surface is less t han or equal t o t he gat e opening. At t his wat er surface elevat ion, t he weir under t he gat e is cont rolling t he flow t hrough t he gat e opening ( i.e., t he wat er is not in cont act wit h t he gat e) . For t he gat e dat a, t he Discharge Coefficient was ent ered as 0.8. The next field is t he Gat e Type. By select ing t he down arrow, t he t ype “ Radial” was chosen. When t he gat e t ype was select ed, t he Trunnion Exponent , Opening Exponent , Head Exponent , and Trunnion Height values were aut om at ically set 12-6 Exam ple 12 I nline St ruct ure t o 0.16, 0.72, 0.62, and 10.0 respect ively. The orifice coefficient of 0.8 was ent ered for fully subm erged flow condit ions. For t he weir dat a, t he Shape was select ed as “ Ogee” . This caused t he edit or t o add t he dat a fields for Spillway Approach Height and Design Energy Head. The dist ances of 14 and 3 feet were t hen ent ered for each of t hese fields, respect ively. Finally, t he Cd but t on was select ed and a window appeared sim ilar t o Figure 12.5, wit h a coefficient of 3.91. The “ Yes” but t on was select ed and t he weir coefficient appeared in t he weir dat a area at t he bot t om of t he Ga t e Edit or . This com plet ed t he dat a ent ry for t he gat es in t he “ Left Group.” Next , t he Add but t on at t he t op of t he Ga t e Edit or was select ed and t his added anot her gat e group. The group was renam ed t o “ Cent er Group” and t he dat a for 5 new gat es were ent ered exact ly as for t he Left Group, except for t he cent erline st at ions. Finally, a t hird gat e group was added and renam ed “ Right Group,” wit h t he dat a ent ry as for t he t wo previous groups wit h new cent erline st at ions. The OK but t on was select ed at t he bot t om of t he Ga t e Edit or and t he gat es appeared on t he I n line St r u ct u r e D a t a Edit or as shown in Figure 12.3. ( Not e: The ineffect ive flow areas will be ent ered subsequent ly.) At t his point , t he user should zoom in on t he gat e openings t o ensure t hat t hey do not overlap and appear as int ended. The I n line St r u ct u r e D a t a Edit or was t hen closed. Ineffective Flow Areas As perform ed for bridges and culvert s, ineffect ive flow areas should be ent ered on t he cross sect ions t hat bound t he inline st ruct ure. For t his exam ple, t he cross sect ion t hat is upst ream of t he st ruct ure is 41.76 and t he cross sect ion downst ream of t he st ruct ure is 41.74. To ent er t he ineffect ive flow areas, t he Cr oss Se ct ion icon was select ed from t he Ge om e t r ic D a t a Edit or ( Figure 12.1) . Then, river st at ion 41.76 was select ed and I n e ffe ct ive Flow Ar e a s was select ed from t he Opt ion s m enu. This act ivat ed t he I n e ffe ct ive Flow Edit or as shown in Figure 12.7. The dist ance from t he inline st ruct ure ( river st at ion 41.75) t o river st at ion 41.76 is 20 feet . The left edge of t he gat es at river st at ion 41.75 is 205. Therefore, t he left ineffect ive flow area was set t o begin at 205 - 20 = 185. Sim ilarly, t he right ineffect ive flow area was set at 745 ( = 725 + 20) . The elevat ion on t he left is 9.5 feet , at t he t op of t he spillway, and t he right is 13.5, t he t op- of- dam . The OK but t on on t he edit or was select ed and sim ilar ineffect ive flow areas were ent ered at river st at ion 41.74. 12-7 Exam ple 12 I nline St ruct ure Figure 12-7: Ineffective Flow Editor Cross Section Placement The final com ponent of t he geom et ric dat a concerns t he placem ent of t he cross sect ions in reference t o t he inline st ruct ure. As for bridges and culvert s, t he flow will cont ract t o ent er t he gat e openings and expand aft er t he exit ing t he gat e openings. The program will use 4 cross sect ions locat ed on bot h sides of t he st ruct ure t o define t he cont ract ion and expansion of t he flow t hrough t he st ruct ure. To provide guidance for t he expansion reach lengt h and cont ract ion reach lengt h, t he t ables in Appendix B of t he H ydr a ulic Re fe r e n ce M a n ua l were ut ilized. These t ables were developed based on dat a for flow t hrough bridges, however, t hey were used t o provide general guidance. To det erm ine t he expansion reach lengt h, t he following dat a was used: b = 520 B = 660 b / B = 0.79 S = 0.4 nob / nc = 1 where: 12-8 b = gate openings area, ft B = floodplain width, ft S = channel slope, ft/mi nob = Manning’s n value of the overbank at river station 41.78 nc Manning’s n value of the main channel at river station 41.78 = Exam ple 12 I nline St ruct ure From Table B.1, t he expansion rat io (ER) is approxim at ely 2.0. Using an average lengt h of obst ruct ion (Lobs) of approxim at ely 100 feet yields an expansion reach lengt h (Le) of: Le = (ER )(Lobs ) = (2.0 )(100) = 200 feet The expansion reach lengt h is m easured downst ream from river st at ion 41.74. Therefore, a cross sect ion ( 41.70) was placed 200 feet downst ream from river st at ion 41.74. River st at ion 41.70 represent s t he cross sect ion where t he flow is fully expanded. For t he cont ract ion reach lengt h, t he cont ract ion rat io (CR) was obt ained as 1.0 from Table B.2. Wit h t his value, t he cont ract ion reach lengt h (Lc) is: Lc = ( CR) ( Lobs) = ( 1.0) ( 100) = 100 feet The cont ract ion reach lengt h is m easured upst ream from river st at ion 41.76. Therefore, a cross sect ion ( 41.78) was placed 100 feet upst ream from river st at ion 41.76. River st at ion 41.78 represent s t he cross sect ion where t he flow lines are parallel. As a final not e, t he values for b, B, and Lobs were approxim at ed for t he flow rat e of 75,000 cfs. As t he flow rat e changes, t he lengt h of expansion and cont ract ion would also change. For t his exam ple, t he values t hat were det erm ined for t his flow rat e were held const ant for all of t he flow rat es. This concluded t he ent ry for all of t he geom et ric dat a. At t his point , t he geom et ric dat a was saved as t he file “ Gat e Geom et ry wit h 3 Gat e Groups.” Next , t he flow dat a was ent ered. Steady Flow Data The flow dat a consist ed of t hree com ponent s: t he flow rat es for each profile; t he boundary condit ions; and t he gat e elevat ion set t ings. Each of t hese com ponent s are described in t he following sect ions. Flow Profiles To ent er t he flow dat a, t he St e a dy Flow D a t a Edit or ( as shown in Figure 12.8) was act ivat ed from t he m ain program window by select ing Edit and t hen St e a dy Flow D a t a . For t his exam ple, t he num ber of flow profiles was select ed as 7. When t his num ber was ent ered, t he t able in t he cent ral port ion of t he edit or expanded t o provide 7 colum ns of dat a ent ry. The river reach “ Weir Reach” ( t he only reach for t his exam ple) and t he upst ream river st at ion of 60.1 appeared ( by default ) as t he locat ion for t he flow dat a. The seven flow values of 5000, 10000, 20000, 30000, 40000, 50000, and 75000 cfs were ent ered as shown in Figure 12.8. No addit ional flow change locat ions were ent ered. 12-9 Exam ple 12 I nline St ruct ure Figure 12-8: Steady Flow Data Editor Boundary Conditions Aft er t he flow dat a was ent ered, t he boundary condit ions were ent ered by select ing t he Re a ch Bou nda r y Con dit ion s but t on at t he t op of t he St e a dy Flow D a t a Edit or . This act ivat ed t he Bou nda r y Con dit ion s Edit or as shown in Figure 12.9. For t his exam ple, a subcrit ical analysis was perform ed. Therefore, boundary condit ions were ent ered at t he downst ream end of t he river reach. The field under Downst ream was select ed and t hen Rat ing Curve was chosen. This act ivat ed t he Ra t in g Cur ve Edit or as shown in Figure 12.10. The flow values and corresponding wat er surface elevat ions were t hen ent ered in t he edit or, a port ion of which is shown in Figure 12.10. ( Not e: I f t he flow rat e for a profile is less t han t he first rat ing curve dat a point , t hen t he program will linearly int erpolat e a st art ing elevat ion bet ween t he first rat ing curve point and t he downst ream cross sect ion invert .) Aft er t he dat a were ent ered, t he OK but t on was select ed t o close t he edit or. This caused t he t it le “ Rat ing Curve” t o appear in t he “ Downst ream ” field, as shown in Figure 12.9. The OK but t on was t hen select ed on t he Bou nda r y Condit ion s Edit or . 12-10 Exam ple 12 I nline St ruct ure Figure 12-9: Boundary Conditions Editor Figure 12-10: Rating Curve Editor Gate Openings The final dat a ent ry for t he analysis was t he gat e opening height s. To ent er t his dat a, from t he St e a dy Flow D a t a Edit or , Opt ion s and t hen I nlin e Spillw a y Ga t e Ope n ings were select ed. This act ivat ed t he I n line Spillw a y Ga t e Ope nin gs Edit or as shown in Figure 12.11. 12-11 Exam ple 12 I nline St ruct ure Figure 12-11: Inline Spillway Gate Openings Editor At t he t op port ion of t he edit or, t he River “ Nit t any River,” Reach “ Weir Reach” and t he River St at ion “ 41.75” were select ed. The Descript ion is t he sam e as was ent ered in t he I n lin e St r u ct u r e D a t a Edit or ( Figure 12.3) . The # Gat e Groups field shows t hat t here are 3 gat e groups at t his river st at ion. The t able in t he cent ral port ion of t he edit or has 3 rows for t his exam ple, one row for each of t he gat e groups. The first colum n list s t he descript ions for t he gat e groups, as t hey were nam ed in t he Ga t e Edit or ( Figure 12.6) . The second colum n displays t he num ber of gat e openings for each gat e group ( 5 for each gat e group for t his exam ple) . The t hird colum n displays t he m axim um gat e height for each gat e group ( 10 feet for each gat e group for t his exam ple) . The rem aining port ion of t he edit or consist s of ent ry fields for t he num ber of gat es opened and t he opening height s of t he gat es for each flow profile. For t his exam ple, for profile 2, t he Left and Right Gat e Groups were set t o have 2 gat es open, each wit h an opening height of 3 feet . The Cent er Group was set t o have 5 gat es open, each at 5 feet . Since t he gat es were ent ered as t hree groups, t he flexibilit y exist ed t o have each gat e group opened at different height s. I f all 15 gat es had been ent ered as only one group, t hen all of t he gat es t hat were open would have t o have been set at t he sam e opening height . The user can t oggle across t he t able t o view t he num ber of gat es open and t he gat e opening height s for all of t he profiles. During t he analysis of t he out put , t he various gat e set t ings will be discussed. This concluded t he dat a ent ry for t his exam ple. At t his point , t he OK but t on at t he bot t om of t he edit or was select ed and t he flow dat a was saved as “ 7 Flow Profiles.” Steady Flow Analysis Aft er all of t he dat a had been ent ered, t he st eady flow analysis was perform ed by act ivat ing t he St e a dy Flow Ana lysis W indow . This window was act ivat ed from t he m ain program window by select ing Run and t hen St e a dy Flow An a lysis, and is shown in Figure 12.12. 12-12 Exam ple 12 I nline St ruct ure Figure 12-12: Steady Flow Analysis Window First , t he Short I D was ent ered as “ 3 groups.” The geom et ry file was t hen select ed as ” Gat e Geom et ry wit h 3 Gat e Groups” and t he flow file was “ 8 Flow Profiles.” Next , t he Flow Regim e was select ed as “ Subcrit ical.” Then, File and Save Plan As were chosen and t he inform at ion was saved as t he plan “ Gat ed Spillway.” This plan nam e t hen appeared on t he St e a dy Flow Ana lysis W indow , as well as on t he m ain program window. Finally, t he COM PUTE but t on was select ed t o perform t he analysis. Output Analysis For t he analysis of t he out put , t he wat er surface profiles, t he inline st ruct ure t ype cross sect ion t able, and t he inline st ruct ure t ype profile t able will be reviewed. Each of t hese are discussed in t he following sect ions. Water Surface Profiles The wat er surface profiles are shown in Figure 12.13. This figure was act ivat ed from t he m ain program window by select ing Vie w and t hen W a t e r Su r fa ce Pr ofile s. The figure shows all 7 of t he flow profiles. 12-13 Exam ple 12 I nline St ruct ure Inline Weir and Gated Spillay - Ex 12 Geom: Gate Geometry with 3 Gate Groups 40 Flow: 7 Flow Profiles Legend WS PF#7 Elevation (ft) 20 WS PF#6 WS PF#5 0 WS PF#4 WS PF#3 -20 WS PF#2 WS PF#1 -40 -60 Ground 0 20000 40000 60000 80000 100000 120000 140000 Main Channel Distance (ft) Figure 12-13: Water Surface Profiles for Nittany River Inline Structure Detailed Output Table To review t he flow param et ers t hrough t he gat e openings, t he I n line St r u ct ur e t ype D e t a ile d Ou t pu t Ta ble was act ivat ed and is show in Figure 12.14. This t able was act ivat ed from t he m ain program window by select ing Vie w , D e t a ile d Out put Ta ble , Type , and t hen I n lin e St r u ct u r e . At t he t op of t he t able, t he Reach was select ed as “ Weir Reach“ and t he river st at ion was 41.75 ( t he cross sect ion for t he inline st ruct ure) . The profile was select ed as “ 1” and t he Gat e I D was select ed as “ Cent er Group.” For t his profile, t he Left and Right Gat e Groups did not have any gat es opened; t herefore, only t he Cent er Group will be discussed. The Cent er Group had been set ( as shown in Figure 12.11) t o have 5 gat es open at a height of 5 feet . Figure 12.14 displays t his inform at ion in t he right colum n. Wit h a gat e invert of - 10 and a gat e opening height of 5, t he t op of t he gat e opening was at - 5 feet . The left side of Figure 12.14 shows t hat t he wat er surface at river st at ion 41.76 was at an elevat ion of 4.56 feet . Therefore, t he wat er surface did not com e int o cont act wit h t he t op of t he gat e opening and weir flow t hrough t he gat e openings occurred. The weir dat a t hat was use t o calculat e t he upst ream energy grade line was t he dat a t hat had been ent ered in t he Ga t e Edit or ( Figure 12.6) , not t he weir dat a as ent ered in t he I n line St r u ct u r e St a t ion Ele va t ion D a t a Edit or ( Figure 12.4) . Addit ionally, t he Gat e Area field shows a gat e flow area of 136.81 ft 2. Wit h a gat e opening height of 5 feet and a widt h of 30 feet , t he t ot al gat e opening area is 150 ft 2. This shows t hat t he gat e area was not flowing full. 12-14 Exam ple 12 I nline St ruct ure Figure 12-14: Inline Structure Output Table for Profile 1 To review t he dat a for t he second profile, t he down arrow for t he Profile field was depressed and “ PF# 2” was select ed. The I n lin e St r uct u r e Type D e t a ile d Ou t pu t Ta ble for profile 2 is shown in Figure 12.15. For t his profile for t he Cent er Group, 5 gat es were set t o an opening height of 5 feet , as before ( as shown in t he right colum n of t he t able) . Wit h an invert at 0 and an opening height of 5, t he t op of t he gat e openings were at an elevat ion of 5.00 feet . The upst ream wat er surface elevat ion is shown t o be at 4.04 feet , which is above t he t op of t he gat e openings. Addit ionally, t he Gat e Area field shows a flow area of 121.34 ft 2 ( for each gat e opening) . This equals t he gat e opening area ( 4.04 ft high x 30 feet wide) in which wat er was flowing. The dept h of flow ( as m easured from t he invert of t he gat e) was 4.04 feet , which is less t han t he gat e opening height . Therefore, t he flow was st ill being com put ed as weir flow. 12-15 Exam ple 12 I nline St ruct ure Figure 12-15: Inline Structure Output Table for Profile 2 Addit ionally, for t he second profile, t he Left and Right Gat e Groups were each set t o have 2 gat es open, at a height of 3 feet . By depressing t he arrow for t he Gat e I D field, t he Left ( or Right ) group can be select ed. For t his group, gat e- cont rolled flow occurred t hrough t he gat e openings because t he t op of t he gat e openings were at an elevat ion of 3 feet . The field Gat e Q Tot al shows t hat 2926.11 cfs was t he t ot al flow t hrough t he gat e openings. Since t he Left and Right groups had t he sam e gat e set t ings, t he t ot al flow in t he cross sect ion was 2 t im es t he flow in t he Left Group plus t he flow in t he Cent er Group = 2( 2926.11) + 4147.78 = 10000 cfs, t he t ot al flow rat e for t he second profile. Sim ilarly, for t he rem aining profiles, t he flows t hrough t he gat e openings can be reviewed by pressing t he down arrow next t o t he Profile: box. The W e ir Type D e t a ile d Out pu t Ta ble for profile 7 is shown in Figure 12.16. For t his profile, t he weir flow dat a is shown on t he left side of t he t able, based on t he dat a as ent ered in t he I n lin e St r uct u r e St a t ion Ele va t ion D a t a Edit or ( Figure 12.4) . The t ot al weir flow is shown t o be 34955.94 cfs. Because t he Left , Cent er, and Right Gat e Groups were ent ered wit h t he sam e gat e set t ings, t he t ot al flow in t he cross sect ion is 3( 13348.02) + 34955.94 = 75,000 cfs, t he t ot al flow for t he profile. The t able also displays ot her weir dat a such as t he left and right st at ion, average dept h, and subm ergence. 12-16 Exam ple 12 I nline St ruct ure Figure 12-16: Inline Structure Output Table for Profile 7 Inline Structure Profile Summary Table Finally, t he I n lin e St r uct u r e Pr ofile Sum m a r y Ta ble is shown in Figure 12.17. This figure was act ivat ed from t he m ain program window by select ing Vie w , Pr ofile Ta ble , St d. Ta ble s, and t hen I n lin e St r u ct u r e . The figure displays t he wat er surface elevat ions, energy grade line, and t ot al weir and gat e flows for each of t he profiles. This t able shows t hat weir flow only occurred for t he last t wo profiles, and can be used t o assist in t he det erm inat ion of t he gat e set t ings t o adj ust t he am ount of weir flow and gat e flow. 12-17 Exam ple 12 I nline St ruct ure Figure 12-17: Inline Structure Profile Table Summary This exam ple com put ed 7 flow profiles for t he reach of Nit t any River, which included an inline weir and spillway. The gat es for t he inline st ruct ure were divided int o 3 groups, wit h 5 gat es in each group. This provided for flexibilit y when set t ing t he num ber of gat es opened and t he gat e opening height s for each profile because t he opening height s m ust be t he sam e for all of t he gat es opened in each gat e group. By reviewing t he wat er surface profiles and t he inline st ruct ure t ables, t he user can det erm ine t he t ype of flow t hrough t he gat e openings and det erm ine if adj ust m ent s t o t he gat e set t ings are required t o provide for a select ed wat er surface elevat ion. The I n line St r u ct u r e Ou t pu t t able provides det ailed out put for each gat e group, for any profile. The Pr ofile Su m m a r y Ou t pu t Ta ble - I n line St r u ct u r e provides upst ream energy and wat er surface elevat ions along wit h t he t ot al weir and gat e flow. For t he m axim um discharge profile, t he ent ire weir profile is overflowing, a condit ion t hat m ay not be st ruct urally sound. 12-18 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) CH APT ER 1 3 Bogue Chitto - Single Bridge (WSPRO) Purpose This exam ple dem onst rat es t he use of HEC- RAS t o analyze a river reach t hat cont ains a single bridge crossing. The river for t his exam ple is a sect ion of Bogue Chit t o locat ed near Johnst on St at ion, Mississippi. The bridge crossing is locat ed along a count y road, near t he m iddle of t he river reach. The field dat a for t his exam ple were obt ained from t he Unit ed St at es Geological Survey ( USGS) Hydrologic At las No. HA- 591. This at las is one part of a series developed t o provide dat a t o support hydraulic m odeling of flow at highway crossings in com plex hydrologic and geographic set t ings. The bridge, cross sect ion geom et ry, and high wat er flow dat a were used t o evaluat e t wo flood flows. The first flood had a peak discharge of 25000 cfs and occurred on Decem ber 7, 1971, const it ut ing a recurrence int erval of 50 years. The second event had a peak discharge of 31500 cfs and occurred on March 25, 1973, wit h a recurrence int erval great er t han 100 years. I t should be not ed t hat m odelers t ypically do not have access t o high wat er m arks and act ual field flow m easurem ent s at bridges during t he peak event s. However, for t his exam ple, since t he observed peak wat er surface elevat ions were available, t hey were com pared t o t he out put from HEC- RAS. For t his analysis, t he wat er surface profiles were det erm ined by using t he WSPRO [ FHWA, 1990] rout ine, which is an available low flow bridge hydraulics m et hod in t he HEC- RAS program . This exam ple will focus upon t he ent ering of dat a and review of t he out put for a bridge analysis using t he WSPRO m et hod. The user should be fam iliar wit h ent ering bridge dat a, as perform ed for Exam ple 2. The user is referred t o Chapt er 5 of t he H ydr a u lic Re fe r e n ce M a n ua l and t o Chapt er 6 of t he Use r ’s M a nua l for addit ional discussion concerning bridge analyses. To review t he dat a files for t his exam ple, from t he m ain program window select File and t hen Ope n Pr oj e ct . Select t he proj ect labeled “ Bogue Chit t o, MS - Exam ple 13.” This will open t he proj ect and act ivat e t he following files: Plan: “ WSPRO Bridge Analysis” Geom et ry: “ Bridge Crossing near Johnst on St at ion” Flow: “ 50 and 100 year flows” 13-1 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Geometric Data The geom et ric dat a for t his exam ple consist s of t he river syst em schem at ic, cross sect ion dat a, cross sect ion placem ent , bridge geom et ric dat a, ineffect ive flow areas, and t he bridge m odeling approach. Each of t hese it em s are discussed below. River System Schematic To view t he river syst em schem at ic, from t he m ain program window select Edit and t hen Ge om e t r ic D a t a . This will act ivat e t he Ge om e t r ic D a t a Edit or and t he screen will display t he schem at ic, as shown in Figure 13.1. For t his exam ple, t he river syst em is com posed of one river and only one reach. The river is labeled “ Bogue Chit t o” and t he river reach is “ Johnst on St a.” The river syst em was defined init ially wit h 11 cross sect ions beginning at river m ile 50.00 as t he downst ream cross sect ion and river m ile 56.97 as t he upst ream cross sect ion. The init ial cross sect ion dat a were obt ained from t he USGS At las, and cross sect ions were int erpolat ed along t he river reach t o provide addit ional cross sect ion dat a. Figure 13-1: River System Schematic 13-2 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) The edit ing com m ands of Add Poin t s t o a Re a ch and M ove Obj e ct were used t o curve t he river syst em schem at ic. This was perform ed for aest het ic purposes only, and does not effect t he hydraulic com put at ions. Cross Section Geometric Data To ent er t he cross sect ion dat a, t he Cr oss Se ct ion icon on t he left side of t he Ge om e t r ic D a t a Edit or was select ed. This act ivat ed t he Cr oss Se ct ion D a t a Edit or , as shown in Figure 13.2. Then, Add a n e w cr oss se ct ion was select ed under t he Opt ion s m enu t o creat e each new cross sect ion. For each cross sect ion, t he geom et ric dat a consist ed of t he: descript ion, X- Y coordinat es, reach lengt hs, Manning’s n values, m ain channel bank st at ions, and cont ract ion and expansion coefficient s. ( Not e: The ineffect ive flow areas will be discussed in a subsequent sect ion.) Manning’s n values, and m ain channel bank st at ions were obt ained from t he field dat a displayed on t he USGS at las. A sum m ary t able of t he reach lengt hs, Manning’s n values, or cont ract ion and expansion coefficient s for t he cross sect ions can be seen by select ing t he relevant list ing under t he Tables m enu on t he Ge om e t r ic D a t a Edit or. The sum m ary t able of t he reach lengt hs for t he cross sect ions is shown in Figure 13.3. Figure 13-2: Cross Section Data Editor for River Station 52.29 13-3 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-3: Reach Lengths for Bogue Chitto Cross Section Placement The reach lengt hs, as shown in Figure 13.3, det erm ine t he placem ent of t he cross sect ions. The placem ent of t he cross sect ions relat ive t o t he locat ion of t he bridge is crucial for accurat e predict ion of expansion and cont ract ion losses. The bridge rout ine ut ilizes four cross sect ions t o det erm ine t he energy losses t hrough t he bridge. ( Addit ionally t he program will int erpret t wo cross sect ions inside of t he bridge by superim posing t he bridge dat a ont o bot h t he im m ediat e downst ream and upst ream cross sect ions from t he bridge.) The following is a brief sum m ary for t he init ial est im at ion of t he placem ent of t he four cross sect ions. The m odeler should review t he discussion in Chapt er 6 of t he Use r ’s M a n ua l and Chapt er 5 of t he H ydr a u lic Re fe r e n ce M a nu a l for furt her det ail. First Cross Sect ion. I deally, t he first cross sect ion should be locat ed sufficient ly downst ream from t he bridge so t hat t he flow is not affect ed by t he st ruct ure ( i.e., t he flow has fully expanded) . This dist ance ( t he expansion reach lengt h) should generally be det erm ined by field invest igat ion during high flows and will vary depending on t he degree of const rict ion, t he shape of t he const rict ion, t he m agnit ude of t he flow, and t he velocit y of t he flow. I n order t o provide bet t er guidance t o det erm ine t he locat ion of t he fully expanded cross sect ion, a st udy was perform ed by t he Hydrologic Engineering Cent er [ HEC- 1995] . This st udy focused on det erm ining t he expansion reach lengt h, t he cont ract ion reach lengt h, and t he expansion and cont ract ion energy loss coefficient s. The result s of t he st udy are sum m arized in Appe ndix B of t he H ydr a u lic Re fe r e n ce M a n u a l. 13-4 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) To det erm ine an init ial est im at e of t he expansion reach lengt h, t he following inform at ion was required: b = 450 ft B = 5000 ft b / B = 0 .1 S = (25.7 ft ) / (36790 ft ) ⋅ (5280 ft / mi ) = 3.7 ft / mi nob / nch = (0.13) / (0.05) = 2.6 Lobs = 1770 ft where: b = bridge opening widt h B = t ot al floodplain widt h S = slope nob = Manning’s n value for t he overbank nch = Manning’s n value for t he m ain channel Lobs = average lengt h of t he side obst ruct ions Wit h t he above inform at ion, an init ial est im at e of t he expansion reach lengt h ( Le) was obt ained by using t he t able values in Appe ndix B of t he H ydr a u lic Re fe r e n ce M a n ua l. From Table B.1, an average value of t he expansion rat io ( ER) was 1.2. Using t his value, t he expansion reach lengt h is: Le = (ER )(Lobs ) = (1.2)(1770 ft ) = 2120 ft From t he reach lengt hs t able ( Figure 13.3) , t he dist ance from cross sect ion 52.36 t o 52.00 is 1956 feet ( = 426 + 1530) . Therefore, cross sect ion 52.00 was init ially considered as t he cross sect ion of fully expanded flow. Since cross sect ion 52.29 is in t he zone of flow expansion, ineffect ive flow areas were placed in t he overbank areas. This will be discussed furt her during t he det erm inat ion of t he ineffect ive flow areas. Aft er t he st eady flow analysis was perform ed, t he expansion reach lengt h was evaluat ed using regression equat ions t hat are present ed in t he HEC st udy [ HEC- 1995] . The equat ions require flow param et ers at t he init ially chosen locat ion and cannot be evaluat ed unt il aft er t he st eady flow analysis is perform ed. These procedures will be described near t he end of t his exam ple. Second Cross Sect ion. The second cross sect ion used by t he program t o analyze t he energy losses t hrough t he bridge is locat ed a short dist ance downst ream of t he st ruct ure. This sect ion should be very close t o t he bridge and reflect t he effect ive flow area on t he downst ream side of t he bridge. For 13-5 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) t his exam ple, a roadway em bankm ent sloped gradually from t he roadway decking on bot h sides of t he roadway. Cross sect ion 52.36 was locat ed at t he t oe of t he roadway em bankm ent and was used t o represent t he effect ive flow area on t he downst ream side of t he bridge opening. The program will superim pose t he bridge geom et ry ont o t his cross sect ion t o develop a cross sect ion inside t he bridge at t he downst ream end. Third Cross Sect ion. The t hird cross sect ion is locat ed a short dist ance upst ream from t he bridge and should reflect t he lengt h required for t he abrupt accelerat ion and cont ract ion of t he flow t hat occurs in t he im m ediat e area of t he opening. As for t he previous cross sect ion, t his cross sect ion should also exhibit t he effect ive flow areas on t he upst ream side of t he bridge. For t his exam ple, cross sect ion 52.38 was locat ed at t he t oe of t he roadway em bankm ent on t he upst ream side of t he bridge. Sim ilar t o t he previous cross sect ion, t he program will superim pose t he bridge geom et ry ont o t his cross sect ion t o develop a cross sect ion inside t he bridge at t he upst ream end. Fourt h Cross Sect ion. The fourt h cross sect ion is locat ed upst ream from t he bridge where t he flow lines are parallel and t he cross sect ion exhibit s fully effect ive flow. To det erm ine an init ial est im at e of t he cont ract ion reach lengt h ( Lc) , a value of t he cont ract ion rat io ( CR) was obt ained as 0.8 from Table B.2, Appe ndix B of t he H ydr a u lic Re fe r e n ce M a n u a l. This yields a cont ract ion reach lengt h of: Lc = (CR )(Lobs ) = (0.8)(1770 ft ) = 1400 ft From t he reach lengt hs t able ( Figure 13.3) , t he dist ance from cross sect ion 52.46 t o 52.38 is 380 feet . For t his exam ple, cross sect ion 52.46 was init ially used as t he sect ion where t he flow lines were parallel. Aft er t he st eady flow analysis, t he locat ion of t his cross sect ion was evaluat ed using t he procedures as out lined in t he recent HEC st udy [ HEC- 1995] . This evaluat ion will be present ed in t he discussion near t he end of t his exam ple. Addit ionally, t he HEC st udy [ HEC- 1995] provided guidance t o det erm ine t he expansion and cont ract ion coefficient s. The cont ract ion and expansion coefficient s are used by t he program t o det erm ine t he t ransit ion energy losses bet ween t wo adj acent cross sect ions. From t he dat a provided by t he recent HEC st udy [ HEC- 1995] , gradual t ransit ion cont ract ion and expansion coefficient s are 0.1 and 0.3, and t ypical bridge cont ract ion and expansion coefficient s are 0.3 and 0.5, respect ively. For sit uat ions near bridges where abrupt changes are occurring, t he coefficient s m ay t ake larger values of 0.5 and 0.8 for cont ract ions and expansions, respect ively. A list ing of t he select ed values for t he river reach can be viewed by select ing Ta ble s and t hen Coe fficie n t s from t he Ge om e t r ic D a t a Edit or. This t able is shown in Figure 13.4 and displays t he values select ed for t he river cross sect ions. Typical gradual t ransit ion values were select ed for st at ions away from t he bridge. However, near t he bridge sect ion, t he coefficient s were increased t o 0.3 and 0.5 t o represent great er energy losses. For addit ional discussion concerning cont ract ion and expansion coefficient s at bridges, refer t o Chapt er 5 of t he H ydr a u lic Re fe r e n ce M a n u a l. Aft er t he st eady flow analysis, t he select ion of t he coefficient s were evaluat ed and will be discussed near t he end of t his exam ple. 13-6 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-4: Contraction and Expansion Coefficients This com plet ed t he input for t he cross sect ion geom et ric dat a. Next , t he bridge geom et ry dat a was ent ered as out lined in t he proceeding sect ion. Bridge Geometry Data To perform t he hydraulic analysis, t he bridge geom et ry was ent ered next . This sect ion provides a brief sum m ary of t he input for t he bridge geom et ry including t he bridge deck/ roadway, sloping abut m ent s, and bridge piers. Br idge D e ck a nd Roa dw a y Ge om e t r y. From t he Ge om e t r ic D a t a Edit or, select t he Br idge / Cu lve r t icon. To creat e t he bridge cross sect ions, t he river was select ed as “ Bogue Chit t o,” t he reach was “ Johnst on St a,” and t hen Opt ion s and Add a Br idge a nd/ or Cu lve r t were select ed. The bridge river st at ion was t hen ent ered as 52.37. Next , t he dat a for t he bridge deck were ent ered. The D e ck / Roa dw a y icon was select ed and t he D e ck / Roa dw a y D a t a Edit or appeared as shown in Figure 13.5. 13-7 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-5: Deck/Roadway Data Editor The first input at t he t op of t he edit or is t he dist ance from t he upst ream side of t he bridge deck t o t he cross sect ion im m ediat ely upst ream from t he bridge ( cross sect ion 52.38) . This dist ance was det erm ined t o be 26 feet from t he USGS at las. I n t he next field, t he bridge deck widt h of 31 feet was ent ered. This is a t ot al dist ance of 31 + 26 = 57 feet . From t he reach lengt hs t able ( Figure 13.3) , t he dist ance from cross sect ion 52.38 t o 52.36 is 84 feet . This leaves 84 - 57 = 27 feet from t he downst ream side of t he bridge deck t o cross- sect ion 52.36. Finally, at t he t op of t he D e ck / Roa dw a y D a t a Edit or , a weir flow coefficient of 2.6 was select ed for t he analysis. The cent ral sect ion of t he D e ck / Roa dw a y Edit or is com prised of colum ns for input of t he st at ion, high cord elevat ion, and low cord elevat ion for bot h t he upst ream and downst ream sides of t he bridge deck. The dat a were ent ered from left t o right in cross sect ion st at ioning and t he area bet ween t he high and low cord com prised t he bridge st ruct ure. The st at ioning of t he upst ream side of t he deck was based on t he st at ioning of t he cross sect ion locat ed im m ediat ely upst ream . Likewise, t he st at ioning of t he downst ream side of t he deck was based on t he st at ioning of t he cross sect ion placed im m ediat ely downst ream . I f bot h t he upst ream and downst ream dat a are ident ical, t he user needs only t o input t he upst ream dat a and t hen select Copy Up t o D ow n t o ent er t he downst ream dat a. As a final not e, t he low cord elevat ions t hat are concurrent wit h t he ground elevat ion were ent ered as a value lower t han t he ground elevat ion. The program will aut om at ically clip off and rem ove t he deck/ roadway area below t he ground. For exam ple, at st at ion 0, a low cord elevat ion of 0 feet was ent ered. However, t he act ual ground elevat ion at t his point is approxim at ely 13-8 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) 340 feet . Therefore, t he program will aut om at ically rem ove t he area of t he roadway below t he ground. Addit ionally, t he last st at ion was ent ered as a value of 5000 feet . This st at ioning ensured t hat t he roadway and decking ext ended int o t he lim it s of t he cross sect ion geom et ry. As described previously, t he program will clip off t he area beyond t he lim it s of t he cross sect ion geom et ry. Below t he deck st at ion and elevat ion dat a, t here are t wo fields t o ent er t he upst ream and downst ream em bankm ent side slopes. These values are used by t he WSPRO bridge analysis m et hod and for graphical represent at ion on t he profile plot . For t his exam ple, values of 2.0 ( horizont al t o 1 vert ical) were ent ered for bot h t he US Em ba n k m e n t SS a n d D S Em ba nk m e nt SS, as m easured from t he USGS At las. At t he bot t om of t he D e ck \ Roa dw a y D a t a Edit or , t here are t hree addit ional fields for dat a ent ry. The first is t he Max Allow a ble Subm e r ge n ce . This input is a rat io of downst ream wat er surface t o upst ream energy, as m easured above t he m inim um weir elevat ion. When t he rat io is exceeded, t he program will no longer consider t he bridge deck t o act as a weir and will swit ch t he com put at ion m ode t o t he energy ( st andard st ep) m et hod. For t his exam ple, t he default value of 0.95 ( 95 % ) was select ed. The second field at t he bot t om of t he edit or is t he M in W e ir Flow Ele va t ion. This is t he elevat ion t hat det erm ines when weir flow will st art t o occur over t he bridge. I f t his field is left blank ( as for t his exam ple) , t he program will default t o use t he lowest high cord value on t he upst ream side of t he bridge. Finally, t he last field at t he bot t om of t he edit or is t he select ion of t he weir flow subm ergence m et hod. This m et hod will det erm ine t he reduct ion of t he weir flow coefficient due t o subm ergence. For t his exam ple, a broad crest ed weir flow subm ergence m et hod was select ed. Upon ent ering all of t he above dat a, t he OK but t on was select ed t o exit t he D e ck / Roa dw a y D a t a Edit or . Br idge Pie r Ge om e t r y. To ent er t he pier dat a, t he Pie r icon was select ed from t he Br idge / Cu lve r t D a t a Edit or . This result ed in t he display shown in Figure 13.6. The m odeler should not include t he piers as part of t he ground or bridge deck/ roadway because pier- loss equat ions use t he separat e bridge pier dat a during t he com put at ions. 13-9 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-6: Bridge Pier Data Editor The program will est ablish t he first pier as pier num ber 1. As shown in Figure 13.6, t he upst ream and downst ream st at ions were ent ered for t he cent erline of t he first pier. The upst ream and downst ream st at ions were based on t he geom et ry of t he cross sect ions locat ed im m ediat ely upst ream ( cross sect ion 52.38) and im m ediat ely downst ream ( cross sect ion 52.36) of t he bridge. The user needs t o be caut ious placing t he pier cent erline st at ions because t he Xcoordinat es for t he upst ream and downst ream cross sect ion st at ioning m ay be different . This is t o ensure t hat t he piers “ line up” t o form t he correct geom et ry. For t his exam ple, t he 17 piers are placed 24 feet on cent er, wit h cent erline st at ioning from 2466 t o 2850. The piers are 1 foot wide for t heir ent ire height . The st art ing elevat ion is set below t he ground, and t he ending elevat ion is inside t he bridge decking. Wit h t hese elevat ions, t he program will “ clip off” t he excess pier height s. Aft er ent ering t he dat a, t he OK but t on was select ed. Sloping Abut m e nt s. The next icon on t he left side of t he Br idge / Culve r t D a t a Edit or is Sloping Abu t m e nt . This icon was select ed t o ent er t he abut m ent dat a, and is shown in Figure 13.7 for t he first ( left ) abut m ent . The user can view t he dat a for t he second ( right ) abut m ent by select ing t he down arrow on t he Sloping Abu t m e n t D a t a Edit or in t he HEC- RAS program . Aft er t he dat a were ent ered, t he OK but t on was select ed t o exit t he edit or and t he schem at ic of t he bridge/ deck, piers, and abut m ent s was displayed as is shown in Figure 13.8. ( Not e: The figure in t he t ext displays t he ineffect ive flow areas t hat will be added in t he next sect ion.) 13-10 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-7: Sloping Abutment Data Editor The cross sect ions shown in Figure 13.8 are developed by superim posing t he bridge dat a on t he cross sect ions im m ediat ely upst ream ( 52.38) and im m ediat ely downst ream ( 52.36) of t he bridge. The t op cross sect ion in Figure 13.8 reflect s t he geom et ry im m ediat ely inside t he bridge on t he upst ream side and t he bot t om cross sect ion reflect s t he geom et ry im m ediat ely inside t he bridge on t he downst ream side. While viewing t he bridge, t he m odeler can select t o view j ust t he upst ream , j ust t he downst ream , or bot h of t he cross sect ion views. This is perform ed by select ing Vie w and t hen t he required opt ion. Addit ionally, from t he Vie w m enu, t he user should select H igh ligh t W e ir , Ope n in g Lid a nd Gr ou nd as well as H ighlight Pie r s. These opt ions enable t he m odeler t o view what t he program will consider as t he weir lengt h, bridge opening, and pier locat ions. Any errors in t he dat a will appear as inconsist ent im ages wit h t hese opt ions. Also, t he zoom - in opt ion will allow t he user t o exam ine dat a det ails. Finally, t he Apply D a t a but t on was select ed t o accept t he dat a. ( Not e: To save t he dat a t o t he hard disk, t he user m ust select Sa ve Ge om e t r y D a t a under t he File m enu on t he Ge om e t r ic D a t a Edit or ) . Ineffective Flow Areas As a final st ep for t he bridge geom et ry, any ineffect ive flow areas t hat exist ed due t o t he bridge ( or any ot her obst ruct ion) were ent ered. I neffect ive flow is used t o define an area of t he cross sect ion in which t he wat er will accum ulat e but is not being act ively conveyed. At a bridge, ineffect ive flow areas norm ally occur j ust upst ream and downst ream of t he road em bankm ent , away from t he bridge opening. 13-11 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-8: Bridge/Culvert Data Editor for County Road Bridge #341 For t his exam ple, ineffect ive flow areas were included on bot h t he upst ream cross sect ion ( 52.38) and t he downst ream cross sect ion ( 52.36) , as well as on cross sect ion 52.29 ( t he cross sect ion in t he expansion reach) . To det erm ine an init ial est im at e for t he st at ioning of t he ineffect ive flow areas on eit her side of t he bridge, a 1: 1 rat io of t he dist ance from t he bridge t o t he cross sect ion was used. For t his exam ple, cross sect ion 52.38 is locat ed 26 feet upst ream of t he bridge. Therefore, t he left and right ineffect ive flow areas were set t o st art at 26 feet t o t he left and right of t he bridge opening. The left side of t he bridge opening is at st at ion 2444, which leads t o a left ineffect ive st at ion of 2444 - 26 = 2418. The right side of t he bridge opening is at st at ion 2864, which leads t o a right ineffect ive flow st at ion of 2864 + 26 = 2890. Sim ilarly, cross sect ion 52.36 is locat ed 27 feet downst ream from t he bridge and t he ineffect ive flow areas at t his cross sect ion were set at 27 feet t o t he left and right of t he bridge opening, at st at ions of 2417 ( = 2444 27) and 2891 ( = 2864 + 27) , respect ively. The init ial elevat ion of t he ineffect ive flow areas for t he upst ream cross sect ion was chosen as 340.8, a value slight ly lower t han t he lowest high cord elevat ion ( 341.0) . This ineffect ive flow elevat ion was chosen so t hat when 13-12 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) t he wat er surface becom es great er t han t his ineffect ive elevat ion, t he flow would m ost likely be weir flow and would be considered as effect ive flow. At t he downst ream cross sect ion, t he elevat ion of t he ineffect ive flow area was set t o be 339.0, slight ly lower t han t he low cord elevat ion ( 340.2) . This elevat ion was chosen so t hat when weir flow occurs over t he bridge, t he wat er level downst ream m ay be lower t han t he low cord, but yet it will cont ribut e t o t he act ive flow area. The ineffect ive flow areas were ent ered by first select ing t he Cr oss Se ct ion icon from t he Ge om e t r ic D a t a Edit or . Then, Opt ion s and I n e ffe ct ive Flow Ar e a s were chosen for cross sect ion 52.38 and t hen for cross sect ion 52.36. The ineffect ive st at ions and elevat ions as previously det erm ined were ent ered, as shown in Figure 13.9 for cross sect ion 52.38. Figure 13-9: Normal Ineffective Flow Areas for Cross Section 52.38 Since t he “ Norm al” t ype of ineffect ive flow was chosen, t hese ent ries im ply t hat all t he wat er t o t he left of t he left st at ion and t o t he right of t he right st at ion will be considered as ineffect ive flow unt il t he wat er level exceeds t he elevat ion of 340.8 feet . Cross sect ion 52.29 is in t he area of expanding flow and t herefore only a port ion of t he cross sect ional flow will be effect ive. A “ Norm al” t ype of ineffect ive flow areas were set at st at ions 1030 and 3800, bot h at an elevat ion of 338. These st at ions were det erm ined by t aking int o account t he dist ance of cross sect ion 52.29 from t he bridge ( 426 feet ) , as com pared t o t he t ot al dist ance of t he expansion reach lengt h ( 1956 feet ) . Wit h t hese dist ances, cross sect ion 52.29 is locat ed approxim at ely 25% ( = 426 / 1956 * 100% ) down t he expansion reach lengt h. As t he flow exit s t he bridge opening, it will init ially expand at a great er rat e t han it will furt her down st ream . An init ial est im at e of t he degree of expansion was assum ed t o be approxim at ely 60% at cross sect ion 52.29. Therefore, 60% of t he left overbank widt h was subt ract ed from t he left m ain channel bank st at ion t o det erm ine t he left ineffect ive flow st at ion. Sim ilarly, 60% of t he right overbank widt h was added t o t he right m ain channel bank st at ion t o det erm ine t he right ineffect ive flow st at ion. The elevat ion of 338 was chosen t o be great er t han t he wat er surface elevat ions. The OK but t on was select ed and t hen Apply D a t a was chosen t o accept t he dat a. The ineffect ive flow areas t hen appeared as t riangles, as shown 13-13 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) previously on Figure 13.8 for t he bridge cross- sect ions. Addit ionally, t he ineffect ive flow areas will appear on t he cross sect ions plot s. Finally, a not e will appear in t he box at t he bot t om of t he Cr oss Se ct ion D a t a Edit or t hat st at es an ineffect ive flow exist s for each cross sect ion t hat t his opt ion was select ed for, as shown in Figure 13.2. The ineffect ive flow areas could have been ent ered previously along wit h t he discussion of t he cross sect ion dat a ( X- Y coordinat es, reach lengt hs, et c.) . However, it is oft en easier t o ent er t he bridge dat a first and t hen t he ineffect ive flow dat a t o easily det erm ine where t he ineffect ive flow st at ions should be locat ed. Aft er t he st eady flow analysis was perform ed, t he ineffect ive flow areas were evaluat ed t o det erm ine if t hey were placed appropriat ely. This will be discussed near t he end of t his exam ple. Bridge Modeling Approach The bridge rout ines in HEC- RAS allow t he m odeler t o analyze t he bridge flows by using different m et hods wit h t he sam e geom et ry. The different m et hods are: low flow, high flow, and com binat ion flow. Low flow occurs when t he wat er flows only t hrough t he bridge opening and is considered as open channel flow ( i.e., t he wat er surface does not exceed t he highest point of t he low cord of t he bridge) . High flow occurs when t he wat er surface encount ers t he highest point of t he low cord of t he bridge. Finally, com binat ion flow occurs when bot h low flow or pressure flow occur sim ult aneously wit h flow over t he bridge. The m odeler needs t o select appropriat e m et hods for bot h t he low flow and for t he high flow m et hods. For t he com binat ion flow, t he program will use t he m et hods select ed for bot h of t he flows. From t he Ge om e t r ic D a t a Edit or , select t he Br idge / Cu lve r t icon and t hen t he Br idge M ode lin g Appr oa ch but t on. This will act ivat e t he Br idge M ode lin g Appr oa ch Edit or as shown in Figure 13.10. For t his exam ple, t here is only 1 bridge opening locat ed at t his river st at ion and t herefore t he bridge num ber was 1. The m odeler is referred t o Chapt er 6 of t he Use r ’s M a n u a l and Chapt er 5 of t he H ydr a u lic Re fe r e n ce M a nu a l for addit ional discussion on t he bridge m odeling approach edit or. Low Flow M e t hods. The m odeler needs t o select which low flow m et hods t he program should com put e and which m et hod t he program should use. The m odeler can select t o have t he program com put e part icular m et hods or all of t he m et hods. Then, t he m odeler needs t o select which m et hod t he program will use as a final solut ion. Alt ernat ively, t he m odeler can select t he com put at ion of several or all of t he m et hods, and t hen have t he program use t he m et hod wit h t he great est energy loss for t he final solut ion. 13-14 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-10: Bridge Modeling Approach Editor For t his exam ple, all four low flow m et hods were select ed t o be com put ed. For t he m om ent um m et hod, a drag coefficient Cd = 2.00 was ent ered for t he square nose piers. For t he Yarnell m et hod, a value of K = 1.25 was ent ered. Finally, t he WSPRO m et hod was select ed t o be used for t he solut ion. The m odeler is referred t o Exam ple 2 - Beaver Creek for an exam ple applicat ion t hat furt her discusses t he low flow m et hods of energy, m om ent um , and Yarnell. For t he WSPRO m et hod, t he user is required t o ent er addit ional dat a. This was perform ed by select ing t he W SPRO Va r ia ble s but t on from t he Br idge M ode lin g Appr oa ch edit or. This act ivat ed t he W SPRO D a t a Edit or , as shown in Figure 13.11. Most of t he dat a ent ered on t his edit or is used t o det erm ine t he “ Coefficient of Discharge” for t he WSPRO m et hod. The following discussion out lines t he WSPRO dat a t hat was ent ered for t his analysis. The user is referred t o Chapt er 6 of t he Use r ’s M a n u a l and t o Chapt er 5 of t he H ydr a u lic Re fe r e n ce M a n ua l for a m ore det ailed discussion of WSPRO m et hod. At t he t op of t he edit or, as shown in Figure 13.11, t he value of 341 feet was ent ered for t he left and right elevat ions of t he t op of t he em bankm ent s. The elevat ions for t he t oe of t he abut m ent s were ent ered as 323.6 and 330.5, for t he left and right abut m ent s, respect ively. Next , t he abut m ent t ype was select ing as t ype 3: sloping abut m ent s and sloping em bankm ent s. The average slope of t he abut m ent s was ent ered as 1 ( horizont al t o 1 vert ical) and t he t op widt h of t he em bankm ent was ent ered as 31 feet . All of t hese values were obt ained from t he USGS At las. 13-15 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-11: WSPRO Data Editor The cent roid st at ioning of proj ect ed bridge opening at t he approach cross sect ion was ent ered as a value of 2531 feet . To obt ain t his value, t he bridge opening widt h is proj ect ed ont o t he approach cross sect ion ( 52.46) . This proj ect ed widt h is sit uat ed ont o t he approach sect ion such t hat t he m ain channel is in t he sam e relat ive posit ion t o t he bridge opening widt h on t he approach sect ion as at t he bride opening. The widt h of t he proj ect ing bridge opening should em brace t he flow, which could pass t hrough t he act ual bridge opening wit hout cont ract ion. Then, t he cent roid of t he bridge opening widt h on t he approach sect ion was t hen det erm ined t o be at a st at ioning of 2531. The bot t om port ion of t he edit or is divided int o four sect ions. The first sect ion is t o describe t he W ing W a lls on t he abut m ent s. For t his exam ple, t here were no wing walls present . I f wing walls were present , t he user can select eit her “ Angular” or “ Rounded,” by depressing t he down arrow adj acent t o t his field. Then, t he appropriat e dat a would be ent ered for t he angle, lengt h and radius fields, pert aining t o t he t ype of wing wall select ed. The second sect ion is t o describe t he Guide Ba nk s. For t his exam ple, t here were no guide banks. I f guide banks were present , t he opt ions are “ St raight ” or “ Ellipt ical” t o describe t he t ype and t hen t he user would ent er t he appropriat e dim ensions of lengt h, offset , and skew. The t hird sect ion at t he bot t om of t he edit or is Opt ional Cont ract ion and Expansion Losses. The WSPRO m et hod includes frict ion losses t hroughout t he bridge region for t he calculat ions. However, t he only cont ract ion or expansion loss t hat is included is an expansion loss from t he exit sect ion ( cross sect ion 52.29) t o t he cross sect ion im m ediat ely downst ream from t he bridge ( 52.36) . The user can include addit ional losses at t he approach 13-16 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) sect ion ( 52.46) , at t he guide banks, at t he upst ream out side cont ract ed sect ion ( 52.38) , at t he inside bridge upst ream sect ion ( 52.37 BU) , and at t he inside bridge downst ream sect ion ( 52.37 BD) . For t his exam ple, t here were no addit ional energy losses select ed. The final sect ion of t he edit or is used t o select opt ions for t he piers and frict ion slope m et hod. I f t he piers are cont inuous, t hen t he user should select Piers are cont inuous for t he widt h of t he bridge. This select ion will det erm ine a weight ing fact or in t he det erm inat ion of t he “ Coefficient of Q” discharge fact or. Finally, t he WSPRO m et hod t radit ionally ut ilizes t he geom et ric m ean equat ion t o det erm ine t he represent at ive frict ion slope bet ween t wo cross sect ions. I f t he Use Geom et ric Mean as Frict ion Slope Met hod is select ed, t hen t he program will use t his m et hod. I f it is not select ed, t hen t he program will use t he frict ion slope averaging m et hod t hat has been select ed by t he user. ( This is select ed in t he St eady Flow Analysis window by choosing Opt ion s, Fr ict ion Slope M e t hods, and t hen t he appropriat e choice. The default m et hod is Average Conveyance. The user is referred t o Chapt er 7 of t he Use r ’s M a n ua l and t o Chapt er 2 of t he H ydr a u lic Re fe r e n ce M a n ua l for m ore inform at ion on frict ion slope m et hods.) This com plet ed t he ent ry of t he dat a for t he WSPRO m et hod as t he low flow m et hod. The OK but t on at t he bot t om of t he edit or was select ed t o exit t he edit or. Next , t he high flow m et hod was select ed on t he Br idge M ode lin g Appr oa ch Edit or . H igh Flow M e t hods. High flows occur when t he wat er surface elevat ion upst ream of t he bridge is great er t han t he highest point on t he low cord of t he upst ream side of t he bridge. Referring t o Figure 13.10, t he t wo alt ernat ives for t he program t o com put e t he wat er surface elevat ions during t he high flows are: Energy Only ( St andard St ep) or Pressure and/ or Weir Flow. The Energy Only ( St andard St ep) m et hod regards t he flow as open channel flow and considers t he bridge as an obst ruct ion t o t he flow. The Pressure Flow com put at ions are divided int o t wo scenarios. The first is when only t he upst ream side of t he bridge deck is in cont act wit h t he wat er and t he second is when t he bridge const rict ion is flowing com plet ely full. The program will begin t o calculat e eit her t ype of pressure flow when t he com put ed low flow energy grade line is great er t han t he highest point of t he upst ream low cord. Weir Flow occurs when t he upst ream energy grade line elevat ion ( as a default set t ing) exceeds t he lowest point of t he upst ream high cord. For t his exam ple, t he high flow m et hod was select ed as energy. From t he dat a on t he USGS At las, t he observed wat er surface elevat ions did not encount er t he bridge deck, so t herefore a high flow m et hod of analysis was not ant icipat ed. The user is referred t o “ Exam ple 2 - Beaver Creek” for a bridge analysis t hat applied a high flow m et hod. At t his point , all of t he bridge dat a have been ent ered. The OK but t on was select ed t o close t he Br idge M ode lin g Appr oa ch Edit or and t he Apply D a t a but t on was depressed on t he Br idge / Culve r t D a t a Edit or before it was closed. Then, t he geom et ry dat a was saved as t he file “ Bridge Crossing near Johnst on St at ion” by select ing File and t hen Sa ve Ge om e t r y D a t a As from t he Ge om e t r ic D a t a Edit or . 13-17 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) As a final geom et ric com ponent , a pict ure of t he bridge has been included as a separat e file. The red square on t he river syst em schem at ic indicat es t hat a pict ure has been added for t hat cross sect ion. This pict ure was scanned from t he USGS At las and saved as t he file “ chit .bm p.” To view t his pict ure, t he user can select t he Vie w Pict u r e icon from t he left side of t he Ge om e t r ic D a t a Edit or . When river st at ion 52.37 is select ed, t he pict ure should appear. The user is referred t o Chapt er 6 of t he Use r ’s M a nua l for a discussion on adding and viewing pict ures t o t he river syst em schem at ic. Steady Flow Data From t he m ain program window, select Edit and t hen St e a dy Flow D a t a . This will display t he St e a dy Flow D a t a Edit or shown in Figure 13.12. For t his analysis on t he reach of Bogue Chit t o, t wo profiles were select ed t o be com put ed. The flow dat a were ent ered for river st at ion 56.97 ( t he upst ream cross sect ion) and t he flow values were 25000, and 31500 cfs. These flows will be considered cont inuous t hroughout t he reach so no flow change locat ions were used. Addit ionally, t he default profiles nam es of “ PF# 1 and “ PF# 2” were changed t o “ 50 yr” and “ 100 yr,” respect ively. This was perform ed by select ing Edit Pr ofile N a m e s from t he Opt ion s m enu, and t hen t yping in t he new t it le. Next , t he boundary condit ions were ent ered by select ing t he Re a ch Bounda r y Condit ion s but t on. This result ed in t he display shown in Figure 13.13. For t his exam ple, a subcrit ical analysis was perform ed. Therefore, a downst ream boundary condit ion was required for each flow value. The t ype of boundary condit ions were known wat er surface elevat ions, t herefore, Set boundary for one profile at a t im e was select ed. Wit h t his select ion, t he t able in t he cent ral port ion of t he edit or expanded t o show t wo rows, one for each of t he t wo profiles. Then, t he m ouse arrow was placed over t he downst ream field for profile one and t he box was select ed ( highlight ed) . The Know n W .S. but t on was chosen and t he dat a ent ry box appeared t hat request ed t he wat er surface elevat ion for t he first profile. A value of 325.7 feet was ent ered, and t he procedure was repeat ed for profile t wo, wit h a known wat er surface of 326.0 feet . These values were obt ained from t he USGS At las. The OK but t on was select ed t o exit t he boundary condit ions edit or. 13-18 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-12: Steady Flow Data Editor Figure 13-13: Steady Flow Boundary Conditions Data Editor For t he purposes of t he analysis, if t he downst ream boundary condit ions are not known, t hen t he m odeler should use an est im at ed boundary condit ion. However, t his m ay int roduce errors in t he region of t his est im at ed value. Therefore, t he m odeler needs t o have an adequat e num ber of cross sect ions downst ream from t he m ain area of int erest so t hat t he boundary condit ions do not effect t he area of int erest . Mult iple runs should be perform ed t o observe t he effect of changing t he boundary condit ions on t he out put of t he m ain area of int erest . For a det ailed explanat ion of t he t ypes of boundary condit ions, refer t o Chapt er 7 of t he Use r ’s M a n ua l and Chapt er 3 of t he H ydr a u lic Re fe r e n ce M a n ua l. 13-19 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) A final opt ional com ponent of t he st eady flow dat a was t o ent er t he observed wat er surface elevat ion dat a from t he USGS At las. This was perform ed by select ing Opt ions and t hen Obse r ve d W S ... from t he St e a dy Flow D a t a Edit or . This act ivat ed t he Obse r ve d W a t e r Su r fa ce D a t a Edit or, as shown in Figure 13.14. The River was select ed as “ Bogue Chit t o” and t he Reach was “ Johnst on St a.” The observed values were ent ered for each of t he t wo profiles, adj acent t o t he river st at ions t hat observed dat a was available for, as shown in Figure 13.14. The OK but t on was t hen select ed t o exit t he edit or. Figure 13-14: Observed Water Surface Elevations This com plet ed t he ent ry for t he st eady flow dat a. The Apply D a t a but t on was select ed on t he St e a dy Flow D a t a Edit or and t he flow dat a was t hen saved as “ 50 and 100 year flows.” Steady Flow Analysis From t he m ain program window, select Ru n and t hen St e a dy Flow Ana lysis. This will act ivat e t he St e a dy Flow Ana lysis W in dow as shown in Figure 13.15. First , t he geom et ry file and st eady flow file t hat were previously developed should appeared in t he select ion boxes on t he right side of t he window. Then, for t his sim ulat ion, a subcrit ical flow analysis was select ed. Addit ionally, from t he St e a dy Flow Ana lysis window, Opt ion s and t hen Cr it ica l D e pt h Ou t pu t Opt ion was select ed. An “ x” was placed beside t he opt ion for Cr it ica l Alw a ys Ca lcu la t e d. This m ay require addit ional com put at ion t im e during program execut ion, but t hen t he user can view t he crit ical dept h line during t he review of t he out put for t he cross sect ions. Select Opt ion s and t hen ensure t hat t here is a check m ark “ ” in front of Che ck da t a be for e e x e cu t ion. This will cause t he program t o check all of t he input dat a t o ensure t hat all pert inent inform at ion was ent ered. Next , a Short I D was ent ered as “ wspro plan” and t hen t he opt ions were saved as a plan ent it led “ WSPRO Bridge Analysis.” Finally, COM PUTE was select ed at t he bot t om of t he window. 13-20 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-15: Steady Flow Analysis Window Review of Output Aft er t he program has com plet ed t he analysis, t he last line should read “ Finished St eady Flow Sim ulat ion.” Click t he Close but t on at t he bot t om of t he window t o close it . This review of t he out put will include discussions on t he wat er surface profiles, profile sum m ary t ables, and det ailed out put t ables. Water Surface Profiles From t he m ain program window, select Vie w and t hen W a t e r Sur fa ce Pr ofile s. This will act ivat e t he wat er surface profile plot as shown in Figure 13.16. As shown in Figure 13.16, only t he second profile was select ed t o be displayed, for clarit y. This was accom plished by select ing Opt ion s, Pr ofile s, and t hen profile 2. Addit ionally, t he variables of Wat er Surface, Energy Grade Line, Crit ical Dept h, and Observed Wat er Surface were select ed t o be displayed, by select ing Opt ion s and t hen Va r ia ble s. The user can select addit ional profiles, variables, and t he zoom feat ure under t he Opt ions m enu when viewing t he profile plot in t he program . Figure 13.16 displays a solid line for t he wat er surface profile and a  for t he observed dat a, as shown in t he legend. The wat er surface agrees well wit h t he observed dat a. Addit ionally, it can be seen t hat t he profile occurred in t he subcrit ical flow regim e. This ensures t hat for t he low flow analysis, Class A low flow ( subcrit ical flow) was occurring t hrough t he bridge. ( This also occurred for t he first profile.) To furt her review t he out put , t he profile t ables will be discussed next . 13-21 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Bogue Chitto, MS - Example 13 WSPRO Bridge Analysis Geom: Bridge Crossing near Johnston Station Johnston Sta 350 Flow: 50 and 100 year flows Legend EG 100 yr 340 Elevation (ft) WS 100 yr Crit 100 yr 330 Ground Obs WS 100 yr 320 310 300 0 5000 10000 15000 20000 25000 30000 35000 40000 Main Channel Distance (ft) Figure 13-16: Water Surface Profile #2 for Bogue Chitto Profile Tables The profile t ables are used t o display t he dat a for all of t he river st at ions sim ult aneously. One t ype of profile t able is t he St andard Table 1 ( Figure 3.17) . This t able can be act ivat ed by select ing from t he m ain program window View, Profile Sum m ary Table, and t hen St d. Tables, and St andard Table 1. This t able displays t he wat er surface elevat ion and energy grade line elevat ion ( am ong ot her variables) for all t he cross sect ions, and can be used t o com pare t he calculat ed values t o t he observed wat er surface elevat ions. By select ing Opt ions and Define Table, t he addit ional colum n heading of “ Obs WS” can be insert ed prior t o t he “ W.S. Elev.” colum n. Wit h t hese values displayed on t he t able, t he user can easily com pare t he observed t o t he calculat ed values. 13-22 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-17: Standard Profile Table 1 Anot her t ype of profile t able is t he Br idge On ly t able. This t able is act ivat ed from t he St d. Ta ble s m enu and is shown in Figure 13.18, displaying t he result s for bot h profiles. The first row is for t he first profile and t he second row is for t he second profile. The result s in t he t able show t he calculat ed values of t he energy grade line at t he cross sect ion im m ediat ely upst ream from t he bridge ( EG US) are 336.85 and 338.19 feet for t he first and second profiles, respect ively. The colum n heading Min El Prs shows a value of 340.20, which is t he highest elevat ion of t he low cord on t he upst ream side. I f t he energy grade line value had exceeded t his elevat ion, t hen pressure flow would have been calculat ed. The Min Top Rd colum n shows t he m inim um elevat ion of t he high cord on t he upst ream side. I f t he energy grade line had exceeded t his value, t hen weir flow would have been calculat ed. Since t he energy grade line for eit her profile did not exceed t he low cord elevat ion, pressure flow, nor weir flow developed. This is also apparent since t here are no values in t he pressure only wat er surface ( Prs O WS) or t he weir flow ( Q Weir) colum ns. The user is referred t o “ Exam ple 2 - Beaver Creek” for an exam ple where pressure and weir flow occurred. 13-23 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-18: Bridge Only Profile Table To det erm ine t he m et hod t hat was used for t he final energy grade line value at t he bridge, t he Br idge Com pa r ison t able was act ivat ed from t he St d. Ta ble s m enu, and is shown in Figure 13.19. The t wo rows display t he result s for each of t he t wo flow profiles, in ascending order. The river st at ion in t he second colum n is set at 52.37 ( t he only bridge locat ion for t his reach) . The sixt h t hrough nint h colum ns show t he result s of t he low flow m et hods t hat were chosen t o be com put ed : Energy, Mom ent um , Yarnell and WSPRO m et hods, respect ively. The values of t he energy grade line t hat t he program used is shown in t he t hird colum n. As shown in Colum n five, t he program used t he result from t he WSPRO m et hod, as had been select ed in t he Br idge M ode lin g Appr oa ch Edit or . Finally, t he fourt h colum n shows t he wat er surface elevat ion t hat coincides wit h t he energy elevat ion used by t he program . ( Not e: There were no result s in t he last t wo colum ns for t he high flow m et hods since only low flow occurred t hrough t he bridge opening.) The result s of t he WSPRO m et hod were only slight ly great er t han t he result s of t he energy m et hod. Bot h t he m om ent um and Yarnell m et hods ret urned valid result s since t he wat er surface did not encount er t he low cord of t he deck. The user can adj ust t he input param et ers of t he WSPRO m et hod t o det erm ine t he significance of t he values on t he out put , such as slope of t he abut m ent s and t he inclusion of wing walls or guide banks. Figure 13-19: Bridge Comparison Table The final profile t able t hat will be discussed is t he Six XS Br idge t able, which is also select ed from t he St d. Ta ble s m enu. This t able is shown in Figure 13.20, for profile 2. This t able is specifically designed t o show t he dat a for t he six cross sect ions t hat are used in t he hydraulic com put at ions t hrough t he bridge. The wat er surface and energy grade line values are shown in t he first 13-24 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) t wo colum ns of dat a, and are used t o det erm ine t he wat er surface profile t hrough t he bridge. The C&E Loss colum n of t he t able shows t he cont ract ion or expansion losses. As shown in t he figure, t he only river st at ion ( wit hin t he six bridge cross sect ions) t hat had an expansion or cont ract ion loss was river st at ion 52.36 ( t o river st at ion 52.29) . This is because t he WSPRO m et hod, by default , only includes an expansion loss bet ween t he exit sect ion and t he cross sect ion im m ediat ely downst ream from t he bridge. The user can include addit ional cont ract ion/ expansion losses by select ing t he losses on t he W SPRO D a t a Edit or. For t his exam ple, no addit ional energy losses were select ed, so no addit ional cont ract ion or expansion losses appeared on t he t able. Figure 13-20: Six XS Bridge Table for Profile 2 Detailed Output Tables I n addit ion t o t he profile t ables, t he user can view det ailed out put t ables, which provide inform at ion at each specific cross- sect ions. A t ype of det ailed out put t able t hat displays result s for t he bridge is shown in Figure 13.21. This t able was act ivat ed from t he m ain program window by select ing Vie w , D e t a ile d Ou t pu t Ta ble , t hen Type and Br idge . The River and Reach were select ed as “ Bogue Chit t o” and “ Johnst on St a.” , and t he river st at ion was 52.37 ( t he only river st at ion t hat had a bridge) . The Profile was select ed as “ 2” and t he Opening was “ Bridge # 1” ( t he only opening at t his cross sect ion) . The t able shows dat a for t he cross sect ions inside t he bridge, as well as t he cross sect ion j ust upst ream from t he bridge. As t he user select s t he different t able fields, t he descript ion for t he variables will appear at t he bot t om of t he t able. At t he bot t om of t he left side of t he t able, t he field Br Sel Mt hd shows t hat t he “ WSPRO” result s were used for t he bride analysis. Addit ionally, t he Coef of Q field shows t hat t he WSPRO coefficient of Q value was calculat ed as 0.72 for t he second profile. 13-25 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) Figure 13-21: Bridge Type Detailed Output Table At t his t im e, t he user can select t o view t he dat a for t he first profile as well as viewing t he cross sect ion t ables for t he cross sect ions. This com plet ed t he review of t he out put for t he cross sect ion t ables. Next , t he locat ions of t he cross sect ions in relat ion t o t he bridge were evaluat ed, by using t he inform at ion present ed in t he various t ables t hat were previously discussed. Evaluation of Cross Section Locations As st at ed previously, t he locat ions of t he cross sect ions and t he values select ed for t he expansion and cont ract ion coefficient s in t he vicinit y of t he bridge are crucial for accurat e predict ion of t he energy losses t hrough t he bridge st ruct ure. For t his exam ple, t he locat ions of t he cross sect ions and t he energy loss coefficient s were evaluat ed for t he second profile. The following analysis is based on dat a t hat were developed for low flow event s occurring t hrough bridges and t he m odeler should use caut ion when applying t he 13-26 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) procedure for ot her t han low flow sit uat ions. Each of t he reach lengt h and coefficient evaluat ion procedures are discussed in t he following sect ions. Expansion Reach Length The expansion reach lengt h, Le, is defined as t he dist ance from t he cross sect ion placed im m ediat ely downst ream of t he bridge t o t he cross sect ion where t he flow is assum ed t o have fully expanded. For t his exam ple, t his dist ance is from cross sect ion 52.36 t o cross- sect ion 52.00. I nit ially, t he expansion reach lengt h was est im at ed using t he t able values present ed in Appendix B of t he H ydr a u lic Re fe r e n ce M a n ua l. Aft er t he analysis, t he m odeler can evaluat e t he init ial est im at e of t he expansion reach lengt h. For t he analysis, it is recom m ended t o use t he regression result s from t he Arm y Corps of Engineers st udy [ HEC- 1995] , which are sum m arized in t he sam e Appendix B. The result s of t he st udy suggest t he use of Equat ion 13- 1 t o evaluat e t he expansion reach lengt h. This equat ion is valid when t he m odeling sit uat ion is sim ilar t o t he dat a used in t he regression analysis. ( I n t he docum ent , alt ernat ive expressions are present ed for ot her sit uat ions.) The equat ion is: ⎛F Le = ER (Lobs ) = −298 + 257⎜⎜ 52.36 ⎝ F52.00 where: Le = ER = ⎞ ⎟⎟ + 0.918 Lobs + 0.00479Q ⎠ ( 13- 1) expansion reach lengt h, ft expansion rat io F52.36 = m ain channel Froude num ber at t he cross sect ion im m ediat ely downst ream of t he bridge ( cross sect ion 52.36 for t his exam ple) F52.00 = m ain channel Froude num ber at t he cross sect ion of fully expanded flow ( init ially cross sect ion 52.00 for t his exam ple) Lobs = average lengt h of obst ruct ion caused by t he t wo bridge approaches, ft Q t ot al discharge, ft 3/ s = ( Not e: The subscript s used in Equat ion 13- 1 and all subsequent equat ions reflect t he river st at ion num bering for t his exam ple.) From t he field dat a, t he average lengt h of t he obst ruct ion is approxim at ely 1770 feet and t he t ot al discharge, Q, is 31500 cfs for t he high flow event . From t he init ial analysis, t he value of t he Froude num ber at cross- sect ion 52.36 was 0.40 and at cross sect ion 52.00 was 0.27 ( as shown on St a n da r d Ta ble 1 ) . Subst it ut ing t he values int o Equat ion 13- 1 yielded t hat t he expansion reach lengt h, Le, was approxim at ely 1874 feet . This equat ion has a st andard error of 96 feet , which yields an expansion reach lengt h range from 1778 t o 1970 feet t o define t he 68% confidence band. The dist ance 13-27 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) used for t he expansion reach lengt h ( t he dist ance from cross sect ion 52.36 t o cross sect ion 52.00) was set t o be 1956 feet in t he m ain channel, which is approxim at ely equal t o t he calculat ed dist ance of 1874 feet . Therefore, t he expansion reach lengt h was det erm ined t o be set appropriat ely. I f t he reach lengt hs were not accept able, t hen t he m odeler has t he opt ion t o adj ust t he lengt h so t hat it is wit hin t he calculat ed range. Then, aft er a new analysis, t he new Froude num bers should be used t o calculat e a new expansion reach lengt h. I f t he geom et ry is not changing rapidly in t his region, t hen only 1 or 2 it erat ions should be necessary t o obt ain a const ant expansion reach lengt h value. Contraction Reach Length The cont ract ion reach lengt h, Lc, is defined as t he dist ance from t he cross sect ion locat ed im m ediat ely upst ream of t he bridge ( 52.38) t o t he cross sect ion t hat is locat ed where t he flow lines are parallel and t he cross sect ion exhibit s fully effect ive flow ( 52.46) . To evaluat e t his reach lengt h, t he regression result s ( shown as Equat ion 13- 2 below) from t he Arm y Corps of Engineers st udy [ HEC- 1995] was used. The equat ion is: ⎛F Lc = CR (Lobs ) = 263 + 38.8⎜⎜ 52.36 ⎝ F52.00 where: Lc = ⎞ ⎛Q ⎟⎟ + 257⎜⎜ ob ⎝ Q ⎠ 2 ⎛n ⎞ ⎟⎟ − 58.7⎜⎜ ob ⎠ ⎝ nc ⎞ ⎟⎟ ⎠ 0.5 + 0.161Lobs ( 13- 2) cont ract ion reach lengt h, ft CR = cont ract ion rat io F52.36 = m ain channel Froude num ber at t he cross sect ion im m ediat ely downst ream of t he bridge ( cross sect ion 52.36 for t his exam ple) F52.00 = m ain channel Froude num ber at t he cross sect ion of fully expanded flow ( cross sect ion 52.00 for t his exam ple) Qob = discharge conveyed in t he t wo overbanks at cross sect ion 52.46, cfs Q = t ot al discharge, ft 3/ s nob = Manning n value for t he overbanks at sect ion 52.46 nc = Manning n value for t he m ain channel at sect ion 52.46 From t he field dat a and t he result s of t he init ial analysis, t he Froude num bers at sect ions 52.36 and 52.00 were 0.40 and 0.27, respect ively, t he t ot al over bank flow at cross sect ion 52.46 was approxim at ely 25773 cfs ( 15697 + 10076) , t he t ot al flow was 31500 cfs, t he weight ed n value for bot h of t he overbanks was 0.13, t he n value for t he m ain channel was 0.05 ( from t he Cr oss Se ct ion Type t able) , and t he average lengt h of t he obst ruct ion was 13-28 Exam ple 13 Bogue Chit t o - Single Bridge ( WSPRO) 1770 feet . Subst it ut ion of t hese values int o Equat ion 13- 2 yielded t he cont ract ed reach lengt h of 685 feet . This equat ion has a st andard error of 31 feet which result s in a cont ract ion reach lengt h range from 716 t o 654 feet t o define t he 68% confidence band. For t his exam ple, t he dist ance from cross sect ion 52.38 t o cross sect ion 52.46 was set at 380 feet along t he m ain channel. An addit ional analysis was perform ed wit h t he cont ract ion reach lengt h set at 685 feet and no appreciable difference was observed in t he result s. Therefore, t he cont ract ion reach lengt h of 380 feet considered as appropriat e for t his exam ple. Expansion and Contraction Coefficients For t he WSPRO m et hod, only an expansion loss is used from t he river st at ion im m ediat ely downst ream of t he bridge ( 52.36) t o t he river st at ion of expanded flow ( 52.29) . This expansion loss, as was shown in Figure 13.20, is det erm ined from Equat ion 5- 7 and is discussed in Chapt er 5 of t he H ydr a u lics Re fe r e n ce M a n ua l. Addit ionally, t he HEC- RAS WSPRO rout ine allows t he m odeler t he opt ion of adding addit ional expansion and cont ract ion energy losses. These losses would be com put ed using t he absolut e value of t he difference of t he velocit y heads t im es t he appropriat e coefficient . For t his exam ple, no addit ional energy losses were added. The user is referred t o Chapt er 3 of t he H ydr a u lics Re fe r e n ce M a n ua l for a furt her discussion on expansion and cont ract ion coefficient s. I n sum m ary, t he above recom m endat ions for t he expansion and cont ract ion reach lengt hs represent an im provem ent in t he general m et hodology behind t he predict ion of t hese values. The m odeler is recom m ended t o apply t hese new crit eria as a m ore subst ant ial m et hod for det erm ining t he required values. As a final not e, aft er t he init ial analysis, t he expansion and t he cont ract ion reach lengt hs as well as t he expansion and cont ract ion coefficient s should be evaluat ed sim ult aneously. Then, adj ust m ent s should be m ade t o t he reach lengt h and coefficient values before a subsequent analysis is perform ed. Finally, t he new dat a should be used t o reevaluat e all of t he reach lengt hs and coefficient s. This procedure will ensure t hat t he m odeler is always using t he current flow dat a for t he analysis. Summary This exam ple dem onst rat ed t he use of t he WSPRO rout ines in HEC- RAS t o calculat e wat er surface profiles along a river reach t hat cont ained a bridge crossing. The WSPRO rout ines are used for low flow analysis, and have been adapt ed t o t he HEC- RAS m et hodology of cross sect ion locat ions around and t hrough a bridge. The user has t he opt ions t o include addit ional energy losses, as well as account for t he t ype of abut m ent s and t he presence of wing walls and guide banks in t he WSPRO rout ines. By adj ust ing t hese input param et ers, t he m odeler can det erm ine t he im pact on t he calculat ed coefficient of discharge value and t he result ing wat er surface profiles. 13-29 Exam ple 14 I ce- Covered River CH APT ER 1 4 Ice-Covered River Purpose This exam ple, which dem onst rat es t he analysis of an ice- covered river, focuses on describing a river ice cover and a river ice j am in HEC- RAS. The wat er surface elevat ions result ing from t he presence of an ice cover or an ice j am can t hen be com pared t o t he equivalent open wat er case. The est im at ed ice j am t hicknesses can also be com pared t o t he m easured j am t hickness1 . An ice cover changes t he effect ive channel geom et ry. This m eans t hat separat e geom et ry files m ust be creat ed for t he open wat er case, t he ice cover case, and t he ice j am case. The best approach is t o creat e a separat e plan for each. See Chapt er 5 of t he Use r ’s M a n u a l and Exam ple 7 of t he Applica t ion M a n u a l for a furt her discussion on working wit h proj ect s and a discussion of t he files t hat const it ut e a plan. The dat a for t his exam ple were ent ered in m et ric unit s. To review t he dat a files for t his exam ple, select File from t he m ain program window and t hen Ope n Pr oj e ct . Select t he proj ect labeled “ Tham es River I ce Jam - Exam ple XX.” This will open t he proj ect and act ivat e t he following files: Plan: “ Tham es River Open Wat er Analysis” Geom et ry: “ Tham es River Open Wat er Dat a” Flow: “ Est im at ed Tham es River Flow” 1 Belt aos, S., and W.J. Moody ( 1986) Measurem ent s of t he Configurat ion of a Breakup Jam . NWRI Cont ribut ion 86- 123. Nat ional Wat er Research I nst it ut e, Canada Cent er for I nland Wat ers, Burlingt on, Ont ario, Canada L7R 4A6 14-1 Exam ple 14 I ce- Covered River Plan: “ Tham es River I ce Cover Analysis” Geom et ry: “ Tham es River I ce Cover Dat a” Flow: “ Est im at ed Tham es River Flow” Plan: “ Tham es River I ce Jam Analysis” Geom et ry: “ Tham es River I ce Jam Dat a” Flow: “ Est im at ed Tham es River Flow” Open Water Analysis Three geom et ry files are creat ed for t his proj ect , and all are based on t he sam e channel geom et ry and channel propert ies. Only t he ice cover descript ion varies am ong plans. Open Water Geometry A geom et ry file was creat ed t hat m odeled t he exist ing condit ions for a reach of t he Tham es River. This reach is a nat ural channel where an ice j am occurred. To view t he river syst em schem at ic, select Edit and t hen Ge om e t r ic D a t a from t he m ain program window. This will act ivat e t he Ge om e t r ic D a t a Edit or and display t he river syst em schem at ic. This is a very sim ple schem at ic wit h a single st raight channel. The river is t he Tham es River and it has only a single reach: I ce Jam Sect ion. The river reach is defined by 22 river st at ions. The user can view t he geom et ric dat a for each river st at ion by select ing t he Cr oss Se ct ion icon from t he Ge om e t r ic D a t a Edit or . The dat a for each river st at ion com prises X and Y coordinat es, downst ream reach lengt hs, Manning’s n values, m ain channel bank st at ions, and cont ract ion and expansion coefficient s. There was no out - of- channel flow during t he ice j am event . As a result , overbank areas are not included. There are no st ruct ures in t his sect ion of channel. Aft er all geom et ric dat a were ent ered, t he geom et ry file was saved using t he t it le “ Tham es River Open Wat er Dat a.” Steady Flow Data Next , t he st eady flow dat a file was creat ed by select ing Edit and St e a dy Flow D a t a from t he m ain program window. This act ivat ed t he St e a dy Flow D a t a Edit or . The profile select ed t o be analyzed corresponds t o t he est im at ed flow during t he ice j am event . The flow value of 261 cubic m et ers per second ( CMS) was ent ered at river st at ion 42000 ( t he upst ream river st at ion) , and a known downst ream wat er surface elevat ion of 177.64 m et ers 14-2 Exam ple 14 I ce- Covered River was ent ered by select ing t he Boun da r y Condit ions icon. Next , t he observed wat er surface elevat ions during t he ice j am event were ent ered by select ing Opt ion s and t hen Obse r ve d W S using t he St e a dy Flow D a t a Edit or . The observed wat er levels at nine river st at ions were t hen ent ered. Aft er all st eady flow dat a were ent ered, t he st eady flow file was saved using t he t it le “ Est im at ed Tham es River Flow.” Open Water Plan Aft er t he geom et ric dat a and st eady flow dat a were ent ered and saved, a plan ent it led “ Tham es River Open Wat er Analysis” was creat ed by first select ing Ru n and t hen St e a dy Flow Ana lysis from t he m ain program window. The plan it self was creat ed in t he St e a dy Flow Ana lysis W indow . Again, see Chapt er 5 of t he Use r ’s M a nua l and Exam ple 7 of t he Applica t ion M a n ua l for furt her discussion of t he files t hat const it ut e a plan. A subcrit ical analysis was chosen as t he Flow Re gim e and t hen File and Sa ve Pla n As were select ed. The t it le “ Tham es River Open Wat er Analysis” was ent ered and t he OK but t on select ed. The Shor t I D for t his plan was set as “ open_wat er.” Aft er t he plan was saved, t he Com pu t e but t on was select ed t o execut e t he program . Not e t hat t he calculat ion required only one it erat ion t o solve t he st eady flow equat ions for t he ent ire channel. Open Water Output The rat her st raight forward open wat er out put will not be reviewed here. Not e t hat t he wat er surface elevat ions calculat ed assum ing open wat er do not m at ch t he observed ice j am elevat ions at all, as would be expect ed. Ice Cover Analysis To analyze t he case of a cont inuous ice cover, an ice cover wit h a const ant t hickness and roughness will be placed on t he channel. To do t his analysis, t he geom et ry file was m odified t o reflect t he presence of t he ice cover. Then a new plan was creat ed wit h t he new geom et ry file and t he original st eady flow file. This procedure is out lined below. Ice Cover Geometry To add t he ice cover, t he geom et ry file “ Tham es River Open Wat er Dat a” was act ivat ed. At t his point , t he m odeler has t he opt ion of ent ering t he ice cover propert ies cross sect ion by cross sect ion, by select ing t he Cr oss Se ct ion icon from t he Ge om e t r ic D a t a Edit or , or by select ing Ta ble s and t hen I ce Cove r from t he Ge om e t r ic D a t a Edit or . I n t his case, t he Ta ble s opt ion was used. First , t he Ch a n I ce Thick ne ss colum n was highlight ed by dragging t he m ouse over t he ent ire lengt h of t he colum n. Then t he Se t Va lu e s icon was clicked and t he value of 0.5 m et ers was ent ered. This value corresponds t o a reasonable, end- of- wint er ice t hickness t hat result s from t herm al growt h. I t 14-3 Exam ple 14 I ce- Covered River was not necessary t o ent er ice t hicknesses for eit her overbank, as no overbank areas were included in t his sim ulat ion. I n a sim ilar way, t he Manning’s n value was set for t he channel ice cover by ent ering t he Manning n value in t he Cha n ice M a nn n colum n using t he Se t Va lu e s icon. I n t his case a value of 0.03 was used, t ypical for a float ing sm oot h ice cover. Aft er all of t he ice cover dat a were ent ered, t he geom et ry file was saved using t he Geom et ric Dat a edit or by select ing File and t he Sa ve Ge om e t r y D a t a As. The t it le ent ered was “ Tham es River I ce Cover Dat a.” Steady Flow Data The st eady flow analysis of t he ice- covered channel will use t he sam e flow dat a used in t he open wat er geom et ry. Therefore, t here were no adj ust m ent s m ade t o t he st eady flow dat a in t he file “ Est im at ed Tham es River Flow.” Ice Cover Plan A new plan was creat ed from t he geom et ry file wit h t he ice cover and t he st eady flow dat a file. This plan was creat ed by first select ing Run and t hen St e a dy Flow An a lysis from t he m ain program window. The plan it self was creat ed in t he St e a dy Flow Ana lysis W indow . A Sh or t I D for t his plan was set as “ ice_covered.” The geom et ry file “ Tham es River I ce Cover Dat a” and t he st eady flow file “ Est im at ed Tham es River Flow” were select ed by using t he down arrows on t he right side of t he window. A subcrit ical analysis was chosen as t he Flow Re gim e , and t hen File and Sa ve Pla n As were select ed. The t it le “ Tham es River I ce Cover Analysis” was ent ered and t he OK but t on select ed. Aft er t he plan was saved, t he Com pu t e but t on was select ed t o execut e t he program . Not e t hat t he calculat ion required only one it erat ion t o solve t he st eady flow equat ions for t he ent ire channel. Ice Cover Output The rat her st raight forward ice- covered channel out put will not be reviewed here. I t can be not ed t hat t he wat er surface elevat ions calculat ed by assum ing an ice cover do not m at ch t he observed ice j am elevat ions at all, as would be expect ed. Ice Jam Analysis To analyze t he case of an ice j am , an ice j am sim ulat ion will be select ed for t he channel. To do t his analysis, t he geom et ry file was m odified t o reflect t he presence of t he ice j am . Then a new plan was creat ed wit h t he new geom et ry file and t he original st eady flow file. This procedure is out lined below. 14-4 Exam ple 14 I ce- Covered River Ice Jam Geometry To add t he ice j am , t he geom et ry file “ Tham es River Open Wat er Dat a” was act ivat ed. At t his point , t he m odeler has t he opt ion of ent ering t he ice j am propert ies cross sect ion by cross sect ion, by select ing t he Cr oss Se ct ion icon from t he Ge om e t r ic D a t a Edit or , or by select ing Ta ble s and t hen I ce Cove r from t he Ge om e t r ic D a t a Edit or . I n t his case, t he Ta ble s opt ion was used. First , t he Ch a n I ce Thick ne ss colum n was highlight ed by dragging t he m ouse over t he ent ire lengt h of t he colum n. Then t he Se t Va lu e s icon was clicked and t he t hickness value of 0.5 m et er was ent ered. I n fact , HEC- RAS will est im at e t he j am t hickness, but t hese ent ered values will represent t he m inim um allowable ice t hickness in t he j am . This t hickness was select ed on t he basis of field observat ions, which showed t hat no cross sect ion had a m inim um t hickness less t han 0.5 m . This m inim um j am t hickness value will vary from river reach t o river reach, and it is probably wort h t rying several m inim um j am t hickness values at any locat ion. Next , it was necessary t o indicat e t o HEC- RAS t hat t his sim ulat ion should be t reat ed as an ice j am and not an ice cover wit h fixed t hickness. This is done in t he I ce Ja m Cha n colum n of t he I ce Cove r Ta ble by changing t he default value of n ( no) t o y ( yes) for each river st at ion where t he ice j am is t hought t o have occurred. ( Not e t hat t his m ust be done for each river sect ion individually, as t he Set Va lu e s icon will not work for yes/ no input .) I n t his case, it is not necessary t o change t he default values of n in t he colum n I ce Ja m OB, as t here is no overbank flow. I t is necessary t o fix t he ice t hickness in t he sect ions im m ediat ely upst ream and downst ream of t he j am , because a cross sect ion wit h known ice t hickness is required at t he upst ream and downst ream lim it s of t he j am . I n t his case, a t hickness of 0.5 m was set for t he upst ream and downst ream river st at ion of t he I ce Jam Reach, and t he value in t he I ce Ja m Ch a n colum n was set t o n for t hese t wo river st at ions. I t is im port ant t o rem em ber t hat for every ice j am , t here m ust be an n set in t he I ce Ja m Ch a n colum n im m ediat ely upst ream and downst ream of t he j am . The nom inal Manning’s n value was set for t he channel ice cover by ent ering t he Manning n value in t he Cha n ice M a nn n colum n using t he Se t Va lu e s icon. However, in t his case, it is desired t hat HEC- RAS est im at e t he Manning’s n of t he j am using t he procedure out lined in t he H ydr a u lic Re fe r e nce M a n u a l. I t is necessary t o indicat e t o HEC- RAS t hat t his sim ulat ion should est im at e t he Manning’s n of t he ice j am and not use t he value ent ered in t he Ch a n ice M a n n n colum n. This is done in t he Fix e d M a nn n colum n by changing t he default value of y t o n . The default value of y was ent ered for t he upst ream and downst ream river st at ions of t he I ce Jam Reach, because t hese st at ions are considered t o have a known roughness as well as a known t hickness. The ot her param et ers, which describe t he ice j am m at erial propert ies, such as t he frict ion angle, porosit y, and st ress rat io, were all left at t heir default values. I n m ost cases, it will not be necessary t o m odify t hese values from t heir default values. Aft er all of t he ice cover dat a were ent ered, t he geom et ry file was saved using t he Geom et ric Dat a edit or by select ing File and t he Sa ve Ge om e t r y D a t a As. The t it le ent ered was “ Tham es River I ce Jam Dat a.” 14-5 Exam ple 14 I ce- Covered River Steady Flow Data The st eady flow analysis of t he ice j am will use t he sam e flow dat a as t he open wat er geom et ry. Therefore t here were no adj ust m ent s m ade t o t he st eady flow dat a in t he file “ Est im at ed Tham es River Flow.” Ice Jam Plan A new plan was creat ed from t he geom et ry file wit h t he ice cover and t he st eady flow dat a file. This plan was creat ed by first select ing Sim u la t e and t hen St e a dy Flow Ana lysis from t he m ain program window. The plan it self was creat ed in t he St e a dy Flow Ana lysis W indow . A Shor t I D for t his plan was set as “ ice_j am .” The geom et ry file “ Tham es River I ce Jam Dat a” and t he st eady flow file “ Est im at ed Tham es River Flow” were select ed by using t he down arrows on t he right side of t he window. A subcrit ical analysis was chosen as t he Flow Re gim e and t hen File and Sa ve Pla n As were select ed. The t it le “ Tham es River I ce Jam Analysis” was ent ered and t he OK but t on select ed. Aft er t he plan was saved, t he Com pu t e but t on was select ed t o execut e t he program . Not e t hat t he calculat ion required a num ber of it erat ions t o solve t he st eady flow equat ions and t he ice j am force balance equat ion for t he ent ire reach. The calculat ions it erat e unt il t he calculat ed j am t hicknesses and wat er surface elevat ions converge t o a const ant value wit hin t he m inim um t olerances. See t he H ydr a u lic Re fe r e n ce M a n ua l sect ion on ice j am calculat ions for m ore inform at ion on t he convergence crit eria. Ice Jam Output The ice j am result s are shown in a graphical profile plot in Figure 14.1. The calculat ed ice j am t hickness along t he channel, t he wat er surface elevat ions, and t he observed wat er surface elevat ions at select ed cross sect ions are shown. Not e t hat t he calculat ed ice j am wat er surface elevat ions m at ch t he observed wat er surface elevat ions reasonably well. 14-6 Exam ple 14 I ce- Covered River Figure 14-1: Ice Jam Profile Plot Comparison of Open Water, Ice Cover, and Ice Jam Results To com pare t he out put from t he t hree plans, t he user can view t he result s graphically and in t abular form at . I n t he int erest of brevit y, not all t he graphical plot s t hat are available will be illust rat ed here. Profile Plot At t his point , t he result s of all t hree plans can be com pared. The profile plot of t he ice j am , t he river ice cover, and t he open wat er result s can be seen in Figure 14.2 I t is also possible t o graphically display com parisons of t he result s in Cross Sect ion Plot s, and X- Y- Z- Perspect ive Plot s. 14-7 Exam ple 14 I ce- Covered River Figure 14-2: Profile Plot displaying the ice jam, ice cover, and open water results Ice Table I n addit ion t o graphical displays, it is possible t o com pare t he out put in t abular form . From t he m ain program window, select Vie w and t hen Pr ofile Sum m a r y Ta ble . By select ing I ce Cove r under t he St d. Ta ble s m enu, a t able wit h t he ice result s will be shown. This t able includes t he ice t hickness ( if any) at each river sect ion, t he calculat ed wat er surface elevat ions at each sect ion, t he cum ulat ive ice volum e in t he channel and overbanks, and t he calculat ed weight ed Manning’s n at each sect ion. This t able can be used t o com pare t he result s from each plan. An exam ple ice t able is shown in Figure 14.3. 14-8 Exam ple 14 I ce- Covered River Figure 14-3: Tabular Ice Output Table 14-9 Exam ple 15 Lat eral Weir and Gat ed Spillway CH APT ER 1 5 Split Flow Junction with Lateral Weir/Spillway Purpose This exam ple dem onst rat es t he use of HEC- RAS t o opt im ize t wo different split flow problem s: a lat eral weir wit h gat ed spillway and a looped net work. I n bot h sit uat ions, t he program uses an it erat ive procedure t o com put e t he flows and energies at a given point ( eit her t he lat eral weir or t he upst ream j unct ion of t he looped net work) . To perform t he analysis, t he user m ust ent er t he geom et ric dat a for t he lat eral weir and gat es, along wit h t he geom et ry of t he river reach syst em . Then, t he user m ust ent er t he opening height of each gat e group for each flow profile in t he St e a dy Flow Edit or . Finally, t he user should set t he split flow opt im izat ion flag ( t o perform t he it erat ive procedure) for t he lat eral weir and for t he j unct ion at t he upst ream end of t he looped net work. The m odeler is referred t o Chapt er 6 of t he Use r ’s M a n ua l for discussion on ent ering t he geom et ric dat a for t he weir and gat ed spillways and j unct ions and m ult iple reaches, Chapt er 7 of t he Use r ’s M a n ua l for ent ering t he gat e opening flow dat a, and Chapt er 8 of t he H ydr a ulic Re fe r e nce M a nu a l for t he hydraulic analysis procedures for analyzing t he flow t hrough t he gat e openings and over t he weir. To review t he dat a files for t his exam ple, from t he m ain program window select File and t hen Ope n Pr oj e ct . Select t he proj ect labeled “ Split Flow Junct ion wit h Lat eral Weir - Exam ple 15.” This will open t he proj ect and act ivat e t he following files: Plan: “ Split Flow” Geom et ry: “ Lat eral Weir wit h Full Looped Net work” Flow: “ 3 Flow Profiles” Geometric Data To view t he geom et ric dat a for t he river syst em , from t he m ain program window select Edit and t hen Ge om e t r ic D a t a . This will act ivat e t he Ge om e t r ic D a t a Edit or and display t he river syst em schem at ic as shown in Figure 15.1. The schem at ic displays t he 24 river st at ions of t he rivers “ Spruce Creek” and “ Bryon Creek,” wit h river st at ion 1278 as t he upst ream cross sect ion and 0 as t he downst ream cross sect ion. 15-1 Exam ple 15 Lat eral Weir and Gat ed Spillway Figure 15-1: River System Schematic for Split Flow Example Stream Junction Data There are four different river reaches in t he river syst em schem at ic. Spruce Creek is divided int o t hree different reaches: Upper River, Middle River, and Lower River. Bryon Creek is t he fourt h reach. Bryon Creek and Middle River, t oget her form a closed loop bet ween t he Meadows river j unct ion and t he Pot t sville river j unct ion. The j unct ion edit or for t he Meadows river j unct ion is shown in Figure 15.2 Meadows is t he upst ream j unct ion. This is where t he flow split s int o t he t wo different rivers. This will be discussed in m ore det ail lat er. 15-2 Exam ple 15 Lat eral Weir and Gat ed Spillway Figure 15-2: Meadows Junction Cross Section Data The cross sect ion dat a consist s of t he X- Y coordinat es, Manning’s n values, cont ract ion and expansion coefficient s, et c. The user can view t his dat a for each river st at ion by select ing t he Cr oss Se ct ion icon on t he left side of t he Ge om e t r ic D a t a Edit or . For t his exam ple, a lat eral weir was added at river st at ion 1150 and will be discussed in t he next sect ion. Figure 15.3 displays t he reach lengt hs in t he vicinit y of t he weir and was act ivat ed by select ing Ta ble s and t hen Re a ch Le ngt hs from t he Ge om e t r ic D a t a Edit or . Figure 15-3: Reach Lengths in Upper River Lateral Structure To add a lat eral weir and gat ed spillways, t he La t e r a l St r uct u r e icon was select ed from t he left side of t he Ge om e t r ic D a t a Edit or . This act ivat ed t he La t e r a l St r u ct u r e Edit or as shown in Figure 15.4. First , t he river “ Spruce Creek” and t he reach “ Upper River” were select ed. Then, Add a La t e r a l St r u ct ur e was select ed from t he Opt ion s m enu, and river st at ion 1150 was 15-3 Exam ple 15 Lat eral Weir and Gat ed Spillway ent ered as t he locat ion for t he weir. By ent ering t he river st at ion, t he upst ream end of t he lat eral weir is aut om at ically placed bet ween t he cross sect ion wit h t he next highest river st at ion upst ream and t he next lowest river st at ion downst ream . The schem at ic will display a profile plot of t he lat eral weir and any gat es. When t he lat eral weir is first added, t he schem at ic will be blank because t he dat a have not yet been ent ered. For t his exam ple, a descript ion of t he weir was ent ered as “ Lat eral Weir and Spillway in Upper River.” Underneat h t he descript ion box, is t he Posit ion box. By clicking on t he down arrow, t he m odeler can choose t o place t he lat eral weir in t he right or left overbank, or t he right or left side of t he channel. For t his problem , t he weir has been placed in t he right overbank. Figure 15-4: Lateral Weir Data Editor To ent er t he dat a for t he weir, t he W e ir / Em ba n k m e nt icon was select ed from t he left side of t he La t e r a l W e ir D a t a Edit or . This act ivat ed t he La t e r a l W e ir / Em ba n k m e nt Edit or as shown in Figure 15.5. This edit or is som ewhat sim ilar t o t he deck/ roadway edit or used for bridges and culvert s. 15-4 Exam ple 15 Lat eral Weir and Gat ed Spillway Figure 15-5: Lateral Weir/Embankment Editor The right side of t he edit or has t wo colum ns for t he st at ion and elevat ion dat a. These dat a point s define t he t op of t he lat eral weir and t hey are ent ered in t he upst ream t o t he downst ream direct ion. Sim ilar t o cross sect ion dat a, t he st at ioning for t he dat a can be based on any horizont al dat um . I n t his exam ple, t he weir st art s at an elevat ion of 90 feet at an arbit rary horizont al st at ion of 100 feet . Fift y feet downst ream , t he weir drops t o an elevat ion of 78 feet . Aft er fort y feet , it ret urns t o an elevat ion of 90 feet at st at ion 190. The weir cont inues at an elevat ion of 90 feet unt il t he final st at ion of 200. The left side of t he edit or has four fields. The t op field is t he Dist ance t o Upst ream Cross Sect ion. The upst ream cross sect ion is t he first norm al cross sect ion im m ediat ely upst ream of t he lat eral weir based on river st at ioning. ( Bet ween t wo norm al river cross sect ions, t here can be t wo or m ore lat eral weirs.) I n t his exam ple, t he upst ream cross sect ion is 1188 and t he upst ream end of t he lat eral weir is 10 feet from t his cross sect ion. So t he Dist ance has been ent ered as 10 feet . The program will com put e t he dist ances t o downst ream cross sect ions based on where t he lat eral weir is locat ed. I n t his exam ple, t he Posit ion of t he lat eral weir has been specified as t he right overbank ( see above) . This m eans t hat t he program will use t he right overbank reach lengt hs. The right overbank lengt h ( bet ween cross sect ions 1188 and 1108) is 90 feet . Therefore, t he lat eral weir int ersect s t he downst ream cross sect ion ( river st at ion 1108) t went y feet from t he downst ream end of t he lat eral weir. I t should be not ed t hat t he lat eral weir cannot cross m ore t han eight cross sect ions. I f t his happens, t he user should eit her increase t he cross sect ion spacing ( so t hat t here are only eight cross sect ions t hat t he weir act ually crosses) , or alt ernat ely, t he user can break t he lat eral weir int o t wo or m ore weirs t hat are physically adj acent . The lat t er opt ion would generally be preferred. However, breaking t he lat eral weir int o t wo or m ore weirs m ight cause t he program t o t ake longer t o converge during t he it erat ive process. 15-5 Exam ple 15 Lat eral Weir and Gat ed Spillway The next field down is t he Weir Widt h. This is widt h of t he weir in t he direct ion of flow over t he weir ( perpendicular t o t he flow in t he river cross sect ion) . I t is not used for hydraulic com put at ions, but is used by t he GUI for graphical purposes. I n t his exam ple, it has been set t o 10 feet . The next lower field is Weir Flow Reference. By left clicking on t he down arrow, t he m odeler can t oggle bet ween “ Energy Grade” and “ Wat er Surface.” Based on t his swit ch, t he program will com put e t he flow over t he weir ( and t hrough any gat es) , using eit her t he energy grade or t he wat er surface when calculat ing t he head ( i.e. t he dept h of flow) on t he weir. I n t his exam ple, since t he lat eral weir is locat ed in t he overbank, t he energy m et hod was select ed. The bot t om field is t he Weir Coefficient ( Cd) . I t is a coefficient t hat is used in t he com put at ion of weir flow. I t has been ent ered as 3.0. Finally, under Weir Crest Shape t he user should select eit her “ Broad Crest ed” or “ Ogee” weir. For t his exam ple, broad crest ed has been select ed. I f t he Ogee had been select ed, t wo addit ional fields and a !Cd but t on would have popped up allowing t he user t o ent er a Spillway Approach Height and a Design Energy Head. For t he Ogee weir, t he user can eit her ent er a weir coefficient or have t he program com put e a weir coefficient by clicking on t he !Cd but t on. Gated Spillway To ent er t he dat a for t he gat es, t he Ga t e icon was select ed from t he La t e r a l St r u ct ur e D a t a Edit or ( Figure 15.4) . This act ivat ed t he Ga t e Edit or as shown in Figure 15.6. For t his exam ple, 3 sluice gat es were ent ered. The t hree gat es are always t o be opened ( or closed) t he sam e am ount , so t hey were defined as a single gat e group for ease of operat ion. I f t he gat es were t o be opened or closed individually, t hen each gat e would be defined separat ely. This will be discussed furt her when t he opening height s are set in t he st eady flow dat a edit or. Aft er t he Ga t e Edit or is act ivat ed, t he gat e dat a can be ent ered. The Height , Widt h, and I nvert for t he gat es were ent ered as 5, 5, and 73 feet , respect ively. On t he right side of t he edit or, t he cent erline st at ions for t he t hree gat es were ent ered as shown in Figure 15.6. As t hese values were ent ered, t he count er field # Openings increased t o represent t he t ot al num ber of gat es ( 3 for t his exam ple) . By default , t he first , and in t his exam ple t he only, gat e group is labeled as “ Gat e # 1.” This label could have been changed by clicking on t he Renam e but t on. 15-6 Exam ple 15 Lat eral Weir and Gat ed Spillway Figure 15-6: Lateral Gate Editor The rem aining port ion of t he edit or is divided int o t wo sect ions, one for t he gat e dat a and one for weir dat a. The gat e dat a are used when t he wat er surface upst ream of t he gat e is great er t han 1.25 t im es t he gat e opening ( as m easured from t he gat e invert ) . At t his wat er surface elevat ion, t he gat e is in cont act wit h t he wat er and is cont rolling t he flow rat e. The weir dat a are used when t he upst ream wat er surface is less t han or equal t o t he gat e opening. At t his wat er surface elevat ion, t he weir under t he gat e is cont rolling t he flow t hrough t he gat e opening ( i.e., t he wat er is not in cont act wit h t he gat e) . I n bet ween t hese t wo elevat ions, t he flow is in a t ransit ion zone. For t he gat e dat a, t he Discharge Coefficient was ent ered as 0.6. This coefficient is used when t he gat e is experiencing sluice flow ( downst ream end of t he gat e is not subm erged) . The next field is t he Gat e Type. By select ing t he down arrow, t he t ype “ Sluice” was chosen. When t he gat e t ype was select ed, t he Trunnion Exponent , Opening Exponent , and Head Exponent values were aut om at ically set t o 0.0, 1.0, 0.5 respect ively. Since a sluice gat e has been select ed, t he Trunnion Height field has been grayed out . The orifice coefficient of 0.8 was ent ered for full flow condit ions ( t his is used when t he t ailwat er elevat ion on t he gat e causes it t o be subm erged) . 15-7 Exam ple 15 Lat eral Weir and Gat ed Spillway For t he weir dat a, t he Shape was select ed as “ Broad Crest ed.” The weir coefficient was left as 3. This inform at ion appears in t he weir dat a area at t he bot t om of t he Ga t e Edit or . This com plet ed t he dat a ent ry for t he gat es. The OK but t on was select ed at t he bot t om of t he Ga t e Edit or and t he gat es appeared on t he La t e r a l St r u ct ur e D a t a Edit or as shown in Figure 15.4. At t his point , t he user should zoom in on t he gat e openings t o ensure t hat t hey do not overlap and appear as int ended. The La t e r a l St r u ct ur e D a t a Edit or was t hen closed. Steady Flow Data The flow dat a consist ed of t hree com ponent s: t he flow rat es for each profile; t he boundary condit ions; and t he gat e elevat ion set t ings. Each of t hese com ponent s are described in t he following sect ions. Flow Profiles To ent er t he flow dat a, t he St e a dy Flow D a t a Edit or ( as shown in Figure 15.7) was act ivat ed from t he m ain program window by select ing Edit and t hen St e a dy Flow D a t a . For t his exam ple, t he num ber of flow profiles was select ed as 3. When t his num ber was ent ered, t he t able in t he cent ral port ion of t he edit or expanded t o provide t hree colum ns for dat a ent ry, one for each profile. The t able init ially creat ed four rows, one for each of t he four river reaches ( Bryon, Upper, Middle, and Lower Spruce) . For each reach, t he upst ream m ost cross sect ion is list ed under RS ( t he river st at ion) . An init ial flow m ust be given at t he upst ream end of each reach. An addit ional flow change was added t o t he Middle Spruce reach t o m odel a t ribut ary t hat ent ers t his reach at st at ion 730. ( Since t he wat er surfaces and energies in t his t ribut ary are not needed, t he t ribut ary was not included in t he river schem at ic.) The flow change was added by clicking t he appropriat e down arrow t o select t he River “ Spruce Creek,” Reach “ Middle River,” and River St at ion “ 730.” As shown in Figure 15.7, t he flow at t he upst ream m ost cross sect ion ( RS 1278 in Upper River) is 1500 cfs for t he first profile. This 1500 cfs split s at t he Meadows j unct ion int o reach Middle River and Bryon Creek. The upst ream end of Bryon Creek has 1200 cfs. The upst ream end of Middle River has t he rem aining 300 cfs. The program will use t he 1200 cfs and t he 300 cfs as t he init ial guess for t he flow split at t he Meadows j unct ion. For profile 1 at river st at ion 730 ( in Middle River) t he flow is list ed as 350 cfs. This m eans t hat a t ribut ary flow of 50 cfs ent ers at t his point . Even t hough t he final flow in t he Middle river will be different aft er t he flow opt im izat ion, t he program will m aint ain t he 50 cfs addit ion at t his point . This will be discussed m ore fully under t he Ou t pu t Ana lysis sect ion below. Finally, t he flow for t he t op of t he Lower River has been ent ered as 1550. This represent s t he 1200 cfs com ing from Bryon Creek and t he 350 cfs ( aft er t he t ribut ary) com ing from Middle River. 15-8 Exam ple 15 Lat eral Weir and Gat ed Spillway Figure 15-7: Steady Flow Data Editor Boundary Conditions Aft er t he flow dat a were ent ered, t he boundary condit ions were ent ered by select ing t he Bou nda r y Con dit ion s but t on at t he t op of t he St e a dy Flow D a t a Edit or . This act ivat ed t he Bou nda r y Con dit ion s Edit or as shown in Figure 15.8. For t his exam ple, a subcrit ical analysis was perform ed. Therefore, an ext ernal boundary condit ion was only needed at t he downst ream m ost cross sect ion in reach Lower River. The field under Downst ream was select ed and t hen Norm al Dept h was chosen. A value of S = .001 was ent ered. Since t he Set boundary for all profiles has been clicked, t he norm al slope of 0.001 will be used for all t hree profiles. The upst ream field of Upper River is blank, since t his is a subcrit ical only analysis. All t he rem aining fields represent int ernal connect ions bet ween different reaches and do not require any addit ional input from t he user. 15-9 Exam ple 15 Lat eral Weir and Gat ed Spillway Figure 15-8: Boundary Condition Data Editor Gate Openings The final dat a ent ry for t he analysis was t he gat e opening height s. To ent er t his dat a, from t he St e a dy Flow D a t a Edit or , select Opt ion s and t hen I n lin e / La t e r a l Spillw a y Ga t e Ope n ings. This act ivat ed t he I n lin e / La t e r a l Spillw a y Ga t e Ope n ings Edit or as shown in Figure 15.9. Figure 15-9: Lateral Spillway Gate Data Editor At t he t op port ion of t he edit or, t he River “ Spruce Creek,” Reach “ Upper River” and t he River St at ion “ 1150” were select ed. The Descript ion is t he sam e as was ent ered in t he La t e r a l Spillw a y D a t a Edit or ( Figure 15.4) . The # Gat e Groups field shows t hat t here is only 1 gat e group at t his river st at ion. The t able in t he cent ral port ion of t he edit or has a single row for t he one and only gat e group. The first colum n list s t he descript ion for t he gat e group, as it was nam ed in t he Ga t e Edit or ( Figure 15.6) . The second colum n displays t he num ber of gat e openings for t he gat e group ( 3) . The t hird colum n displays t he m axim um gat e height for t he gat e group ( 5 feet for t his exam ple) . 15-10 Exam ple 15 Lat eral Weir and Gat ed Spillway The rem aining port ion of t he edit or consist s of ent ry fields for t he num ber of gat es opened and t he opening height s of t he gat es for each flow profile. For t he Lat eral weir, all of t he gat es in a gat e group m ust be operat ed t oget her. For t his exam ple, for profile 1, t he t hree gat es were opened 3 feet . To close t he gat es, t he user could set t he num ber of gat es opened t o zero, or, alt ernat ely, t he gat e height could have been set t o zero. However, if t he user ent ers a non- zero ( i.e. posit ive) num ber for t he num ber of gat es and t he gat e height , t hen t he program will open all of t he gat es in t he gat e group t o t hat height ( t he field for t he num ber of gat es is set up for t he I nline weir where it is possible t o only open part of t he gat es in a gat e group) . This m eans t hat if one gat e is opened four feet , t hen all of t he gat es will be opened four feet . I f t he user want ed t o only open one gat e, t hen t hat gat e would have t o be defined as a separat e gat e group. A Lat eral Weir can have a m axim um of t en gat e groups. So t en gat es ( or groups of gat es) could be operat ed independent ly. I f m ore t han t en gat e groups are needed, t he lat eral weir could be defined as t wo or m ore part s. For inst ance, a t housand foot long lat eral weir could be defined as t wo 500 foot long lat eral weirs. Each “ weir” would have t o be ent ered separat ely wit h it s own river st at ion and dat a. By choosing t he appropriat e Dist ance t o upst ream cross sect ion, t he t wo weirs could be placed im m ediat ely adj acent t o each ot her. This would allow for t went y different gat e groups t o be operat ed independent ly. The user can t oggle across t he t able t o view t he num ber of gat es open and t he gat e opening height s for all of t he profiles. During t he analysis of t he out put , t he various gat e set t ings will be discussed. This concludes t he dat a ent ry for t his exam ple. At t his point , t he OK but t on at t he bot t om of t he edit or was select ed and t he flow dat a was saved as “ 3 Flow Profiles.” Steady Flow Analysis Aft er all of t he geom et ric and flow dat a had been ent ered, t he St e a dy Flow Ana lysis W in dow was act ivat ed from t he m ain program window by select ing Ru n and t hen St e a dy Flow Ana lysis. I t is shown in Figure 15.10. First , t he Short I D was ent ered as “ Split Flow.” Next , t he flow opt im izat ion flags were t urned on. This was done by select ing Opt ions and t hen Split Flow Opt im iza t ion s. This act ivat ed t he Split Flow Opt im iza t ion Edit or as shown in Figure 15.11. The t ab for t he lat eral weir was select ed by clicking on it . Aft er clicking on it , t he user can t oggle bet ween t urning opt im izat ion on or off by checking t he box under t he “ opt im ize” colum n. I f t he opt im izat ion flag had been left off, t he program would st ill calculat e t he flow over t he lat eral weir. However, t his flow would not be rem oved from t he river syst em ( t his will be discussed m ore lat er) . 15-11 Exam ple 15 Lat eral Weir and Gat ed Spillway Figure 15-10: Steady Flow Analysis Editor Figure 15-11: Optimization Data Editor for Lateral Weirs Next , opt im izat ion for t he j unct ion was t urned on. This was done by clicking on t he Junct ion t ab, which changes t he Opt im iza t ion Edit or as shown in Figure 15.12. Opt im izat ion at t he Meadows j unct ion can t hen be t oggled like it was for t he lat eral weir. Flow opt im izat ion can only be perform ed at j unct ions t hat have m ore t han one downst ream reach. For t his reason, t he Edit or does not display t he Pot t sville j unct ion. I f t he opt im izat ion flag at t he Meadows j unct ion had been left off, t he program would not opt im ize t he flow split . Rat her, t he program would m aint ain t he sam e flow rat io in each reach. For inst ance, assum e t hat for t he first profile, t he j unct ion opt im izat ion is off and t hat t he upst ream lat eral weir has an out flow of 500 cfs. This m eans t hat t here would be 1,000 cfs flowing int o t he Meadows j unct ion inst ead of 1,500 cfs. The program would t hen proport ionat ely reduce t he flow in each reach. Middle River would be 200 cfs ( inst ead of 300 cfs) and Bryon Creek would be 800 cfs ( inst ead of 1,200 cfs) . 15-12 Exam ple 15 Lat eral Weir and Gat ed Spillway Figure 15-12: Optimization Data Editor for Junctions Now t hat t he opt im izat ion flags have been t urned on, t he files for t his plan can be nam ed and saved. First , t he geom et ry file was select ed as “ Lat eral Weir wit h Full Looped Net work” and t he flow file was “ 3 Flow Profiles.” Next , t he Flow Regim e was select ed as “ Subcrit ical.” Then, File and Sa ve Pla n As were chosen and t he inform at ion was saved as t he plan “ Split Flow.” This plan nam e t hen appeared on t he St e a dy Flow Ana lysis W indow , as well as on t he m ain program window. Finally, t he COM PUTE but t on was clicked t o perform t he analysis. Output Analysis For t he analysis of t he out put , t he wat er surface profiles, t he lat eral weir t ype cross- sect ion t able, t he lat eral weir only t ype profile t able, t he j unct ions t able, and t he st andard profile t able will be reviewed. Each of t hese is described in t he following sect ions. Water Surface Profiles The wat er surface profiles are shown in Figure 15.13. This figure was act ivat ed from t he m ain program window by select ing Vie w and t hen W a t e r Su r fa ce Pr ofile s. The figure shows all t hree of t he flow profiles. I t shows all t hree of t he reaches t hat m ake up Spruce Creek, but it does not show t he Bryon Creek reach. As can be seen from t he figure, t he lat eral weir has no flow for t he first profile, flow t hrough j ust t he gat es for t he second profile, and flow t hrough t he gat es and over t he weir for t he t hird profile. 15-13 Exam ple 15 Lat eral Weir and Gat ed Spillway Figure 15-13: Water Surface Profiles for Spruce Creek Lateral Structure Detailed Output Table To review t he det ailed hydraulic result s for t he lat eral st ruct ure t he Lat eral St r u ct ur e t ype D e t a ile d Ou t pu t Ta ble was act ivat ed and is show in Figure 15.14. This t able was act ivat ed from t he m ain program window by select ing Vie w , D e t a ile d Out put Ta ble , Type , and t hen La t e r a l St r uct ur e . At t he t op of t he t able, River was select ed as Spruce Creek, t he Reach was select ed as “ Upper River” and t he river st at ion was 1150 ( t he node for t he lat eral weir) . The profile was select ed as “ 3.” The t able shows t he energy grade and wat er surface at t he upst ream and t he downst ream end of t he weir. For t his profile, t he energy grade at t he st art of t he lat eral st ruct ure is 85.97 feet and 85.78 feet at t he downst ream end. The t ot al flow upst ream of t he lat eral st ruct ure is 15000 cfs. The t ot al flow in t he river downst ream of t he lat eral st ruct ure is 12387 cfs ( t he lat eral st ruct ure is spilling 2599 cfs or 17.42% of t he flow) . The program shows t hat t he flow over t he t op of t he weir is 1374.61 cfs and t hrough t he gat es is 1224 cfs for a t ot al of 2599 cfs. I n order t o perform t he backwat er com put at ions ( and get t he wat er surfaces and energies in t he vicinit y of t he weir) , t he program m ust know t he am ount of flow in t he river. To do t his, it assum es t he am ount of flow t hat will be divert ed by t he lat eral weir. This is based on t he previous it erat ion ( for t his exam ple, for t he final it erat ion, a flow of 2613 cfs was assum ed t o be divert ed) . Aft er t he backwat er calculat ions have been perform ed, t he 15-14 Exam ple 15 Lat eral Weir and Gat ed Spillway program can com put e a flow for t he lat eral weir based on wat er surfaces and energies ( in t his case, 2599 cfs) . I f t hese t wo num bers are wit hin t he default t olerance of 2% ( 2% of t he assum ed 2613 cfs or 52 cfs) , t hen t he lat eral weir is assum ed t o have converged. The default t olerances can be changed from t he St e a dy Flow Edit or by choosing Opt ions and t hen select ing Se t Ca lcu la t ion Tole r a n ce s ( t his edit or is not shown) . Figure 15-14:Lateral Weir Output Table for Profile 3 Lateral Structure Profile Summary Table The La t e r a l St r u ct ur e On ly Pr ofile Sum m a r y Ta ble is shown in Figure 15.15. This figure was act ivat ed from t he m ain program window by select ing Vie w , Pr ofile Sum m a r y Ta ble , St d. Ta ble s, and t hen La t e r a l St r u ct u r e . The figure displays t he wat er surface elevat ions, energy grade line, and t ot al weir and gat e flows for each of t he profiles. This t able shows t hat gat e flow occurred for t he last t wo profiles and weir flow occurred only for t he last profile. I t can be used t o assist in t he det erm inat ion of t he gat e set t ings t o adj ust t he am ount of weir flow and gat e flow. 15-15 Exam ple 15 Lat eral Weir and Gat ed Spillway Figure 15-15: Lateral Weir Profile Table Junctions Profile Summary Table The Ju n ct ion s On ly Pr ofile Ta ble is shown in Figure 15.16. This figure was act ivat ed from t he m ain program window by select ing Vie w , Pr ofile Sum m a r y Ta ble , St d. Ta ble s, and t hen Ju nct ion s. The figure displays t he wat er surface elevat ions, energy grade lines, and t ot al flows for each river cross- sect ion im m ediat ely bounding t he j unct ion. This t able m akes it easy t o check if t he split flow at t he j unct ion converged. ( For a given profile, t he energy grade lines for t he cross sect ions j ust downst ream of t he j unct ion should be approxim at ely t he sam e. The default t olerance for j unct ions is 0.02 feet ) . I t also m akes it easy t o see how m uch flow is going int o each reach. Figure 15-16: Junctions Profile Table 15-16 Exam ple 15 Lat eral Weir and Gat ed Spillway Standard Profile Summary Table The St a n da r d Ta ble 1 is shown in Figure 15.17. This figure was act ivat ed from t he m ain program window by select ing Vie w , Pr ofile Sum m a r y Ta ble , St d. Ta ble s, and t hen St a n da r d Ta ble 1 . For t his t able, only t he t hird profile is being displayed. The flow at river st at ion 1188, upst ream of t he lat eral st ruct ure, is 15000 cfs. The flows at river st at ions 1108 and 1028 are 12736 cfs and 12387 cfs. This represent s t he flow divert ed by t he lat eral st ruct ure. River st at ion 1108 int ersect s t he m iddle of t he lat eral weir. So for t he t hird profile, part of t he flow is divert ed bet ween river st at ions 1188 and 1108 and t he rest is divert ed bet ween 1108 and 1028. Not e also t he 500 cfs increase in flow bet ween river st at ion 810 and 730 ( from 4302 cfs t o 4802 cfs) in t he Middle River reach. This represent s t he 500 cfs inflow t ribut ary ( t he t ribut ary is not shown on t he river schem at ic) . I n t he St e a dy Flow Edit or , t he flow at river st at ion 730 was ent ered as 4500 cfs for t he t hird profile. However, due t o t he flow diversion from t he lat eral st ruct ure and t he flow split at t he Meadows j unct ion, t he flow in t he Middle River is not const ant . I n t his sit uat ion, t he program will keep t rack of t he relat ive flow change. The 4500 cfs at river st at ion 730 is 500 cfs great er t han t he 4000 cfs flow at t he st art of t he Middle River reach. Hence, t he program adds 500 cfs flow at t his river locat ion. Figure 15-17: Profile Standard Table 1 15-17 Exam ple 15 Lat eral Weir and Gat ed Spillway Additional Adjustments Now t hat t he dat a have been ent ered and t he program has been run, adj ust m ent s can be m ade t o t he init ial flow split assum pt ions. Making adj ust m ent s can reduce t he num ber of it erat ions t hat t he program requires and hence speed up t he com put er run. This will usually be t rue even if ot her m odificat ions are being m ade t o t he geom et ry file ( e.g. a bridge is being added t o one of t he river reaches) . I n som e cases, a dat a set t hat is not converging can be m odified t o one t hat will converge. Junction Flow Split Figure 15.16. above, shows t he flow split at t he Meadows j unct ion. For t he t hird profile, Middle River has 4302 cfs and Bryon Creek has 8085 cfs. The 4302 cfs is around 35% of t he t ot al flow at t he Meadows j unct ion. However, t he original dat a, in t he St e a dy Flow Edit or , shows t hat Middle River has 4000, which is around 25% of t he original 15000 cfs flow at Meadows ( Bryon Creek has t he rem aining 11000 cfs) . Adj ust ing t his flow t o be closer t o 35% of t he t ot al will speed up t he convergence process. I n t his case a value of 5000 cfs for Middle River and 10000 cfs for Bryon Creek would im prove t he run t im e ( and increase t he chances of successful convergence) . Not e t hat it would be incorrect t o sim ply ent er t he 4302 cfs for Middle River and 8085 cfs for Bryon Creek in t he St e a dy Flow Edit or. I f t his were done, t hen t he program would assum e t hat a flow loss was t aking place at t he Meadows j unct ion. Not e also t hat if t he flow in t he Middle River is changed t o 5000, t hen t he flow at 730 should be changed t o 5500 t o m aint ain t he 500 cfs increm ent . Lateral Structure Flow Split The user can also ent er a first guess for t he am ount of flow t hat will be divert ed by t he lat eral st ruct ure. As in t he case of a j unct ion, t his can im prove t he run perform ance. To ent er t his dat a, from t he St e a dy Flow D a t a Edit or , Opt ion s and t hen I nit ia l Split Flow Va lu e s were select ed. This act ivat ed t he I n it ia l La t e r a l Flow Split s Edit or as shown in Figure 15.18. By clicking under t he I nit ial Flow field for t he appropriat e profile, a first guess for t he lat eral weir flow can be ent ered. The program will t hen assum e t hat t his m uch flow is divert ed when it perform s t he first it erat ion of t he backwat er calculat ions. 15-18 Exam ple 15 Lat eral Weir and Gat ed Spillway Figure 15-18: Initial Lateral Flow Split Data Editor Summary This exam ple com put ed 3 flow profiles for t he Bryon Creek and Spruce Rivers. I t included a lat eral weir wit h gat es and a fully looped river net work bet ween t he Meadows and Pot t sville j unct ion. By reviewing t he lat eral weir and j unct ion t ables and t he wat er surface profiles and t ables, t he user can det erm ine t he am ount of flow being divert ed by t he lat eral weir and t he am ount of flow being split int o t he t wo reaches downst ream of t he Meadows j unct ion. The La t e r a l W e ir / Spillw a y Ou t pu t t able provides det ailed out put for t he lat eral weir, for a given profile. The Ju n ct ion s t able provides flow split out put for one or m ore profiles. The user can also adj ust t he init ial st art ing condit ions t o im prove t he run perform ance of t he com put er com put at ions. 15-19 Exam ple 16 Channel Modificat ion CH APT ER 1 6 Channel Modification Purpose This exam ple dem onst rat es t he use of HEC- RAS t o perform a channel m odificat ion on an exist ing channel geom et ry using a series of t rapezoidal cut s. Wat er surface profiles result ing from a channel m odificat ion can be com pared t o wat er surface profiles result ing from t he exist ing channel geom et ry. The user is referred t o Chapt er 12 of t he Use r ’s M a n ua l for discussion on m odifying t he exist ing geom et ric dat a, im plem ent ing t he new channel geom et ry, and com paring exist ing and m odified condit ions. To review t he dat a files for t his exam ple, from t he m ain program window select File and t hen Ope n Pr oj e ct . Select t he proj ect labeled “ Channel Modificat ion - Exam ple 16.” This will open t he proj ect and act ivat e t he following files: Plan: “ Exist ing Condit ions” Geom et ry: “ Base Geom et ry Dat a” Flow: “ 100 Year Profile” Geometric Data To view t he geom et ric dat a for t he river syst em , from t he m ain program window select Edit and t hen Ge om e t r ic D a t a . This will act ivat e t he Ge om e t r ic D a t a Edit or and display t he river syst em schem at ic as shown in Figure 16.1. Channel Modification Data To perform a m odificat ion on t he channel, select Cha nne l M odifica t ion from t he Tools m enu of t he Ge om e t r ic D a t a Edit or . This will act ivat e t he 16- 1 Exam ple 16 Channel Modificat ion window shown in Figure 16.2. The dat a displayed in Figure 16.2 is not present upon ent ering a new channel m odificat ion window. The dat a shown in t he left hand colum n of Figure 16.2 is used t o const ruct t he cut s for each cross sect ion. Figure 16-1: River System Schematic for Base Geometry Data The channel m odificat ion began wit h t he Rive r set t o “ Crit ical Creek” and t he Re a ch set t o “ Upper Reach.” The St a r t in g Rive r St a t ion was set by default t o 12 and t he Endin g Rive r St a t ion was changed t o a value of 1, t he downst ream end of t his part icular reach. The Pr oj e ct cu t fr om uppe r RS a t slope opt ion was ent ered as 0.01. This opt ion proj ect s a cut using t he specified slope from t he invert elevat ion of t he St a r t ing Rive r St a t ion. 16- 2 Exam ple 16 Channel Modificat ion Once t he correct river st at ions were set , t he first cut was est ablished. The Ce n t e r Cu t s ( y/ n ) colu m n in t he Se t Ra n ge of Va lu e s t able was ent ered as “ y.” This set t he cent erline for t he first cut at t he cent erline of t he m ain channel. Next , “ 100” was ent ered in t he Bot t om W idt h colum n t o set t he widt h of t he first cut t o 100 feet along t he cent erline. The I n ve r t Ele va t ion colum n was left blank for t he first cut , which default s t he program t o t he exist ing invert elevat ion of t he St a r t in g Rive r St a t ion. Bot h side slopes for t he banks were ent ered as 2 ( 2 horizont al t o 1 vert ical) . The Cu t n / K colum n for t he new Manning’s n- value was ent ered as 0.025. Figure 16-2: Channel Modification Window The second cut was also done on t he exist ing cent erline of t he m ain channel. A Bot t om W idt h of 400 feet and an I nve r t Ele va t ion of 1810 feet were ent ered. The ent ry init iat ed t he second cut at an elevat ion of 1810 feet , at t he St a r t ing Rive r St a t ion. The cut will t hen proj ect wit h t he specified slope from t his elevat ion. The slopes were again ent ered wit h a value of 2 and Manning’s n- value was ent ered as 0.03. Aft er t he dat a was ent ered, t he 16- 3 Exam ple 16 Channel Modificat ion Apply Cu t s t o Se le ct e d Ra nge but t on was pressed t o com put e t he dat a shown in t he lower t able of Figure 16.2. An opt ion available t o t he user is Cu t cr oss se ct ion u nt il cu t da yligh t s. For t his part icular exam ple t his opt ion was select ed. As t he program perform s t he cut t ing of t he t rapezoidal channel, t he left and right banks of t he channel will init iat e at t he invert elevat ion and cut t hrough t he ground unt il t hey reach open air, t hen t he cut t ing will st op. I f t his opt ion is t urned off, t he left and right banks of t he t rapezoid will be proj ect ed t o infinit y, cont inually cut t ing any ground t hat lies above t hem . Performing the Channel Modifications Aft er t he Apply Cut s t o Se le ct e d Ra nge was select ed, t he Com pu t e Cu t s but t on was pressed. This applied all of t he channel m odificat ion dat a from t he lower t able t o t he graphic, updat ing t he inform at ion. Addit ionally, t he Cu t a n d Fill Ar e a s but t on was pressed t o display Figure 16.3 The Cut and Fill Dat a displays t he area and volum e of each individual cut for t he left overbank, m ain channel, and right overbank. The t able also displays t he t ot al area and volum e for each individual cut as well as t he t ot al volum e for t he ent ire reach. Figure 16-3: Cut and Fill Areas Saving the Channel Modifications Aft er t he com plet ion of all channel m odificat ions a new geom et ry file was creat ed. From t he Ch a n n e l M odifica t ion s D a t a W in dow , Figure 16.2, t he t it le “ Modified Geom et ry” was ent ered in t he upper right hand window. Next , 16- 4 Exam ple 16 Channel Modificat ion t he but t on Cr e a t e M odifie d Ge om e t r y was pressed and t he file was saved. Finally, t he original geom et ry file was saved t o t he hard disk by select ing Sa ve Ge om e t r y D a t a from t he Ge om e t r ic D a t a Edit or . This st ep was needed because t he dat a ent ered in t he Ch a nn e l M odifica t ion D a t a W indow is saved in t he base geom et ry file and not t he m odified geom et ry file. Hence, when t he m odified geom et ry file was saved, t he m odificat ions which were used t o creat e t hat file had not yet been saved. Steady Flow Analysis Aft er saving all t he geom et ric dat a, t he st eady flow dat a file was creat ed. From t he m ain program window, Edit and t hen St e a dy Flow D a t a were select ed. This act ivat ed t he St e a dy Flow D a t a W indow shown in Figure 16.4. Profiles were select ed wit h flows of 9000 cfs at river st at ion 12 and 9500 cfs at river st at ion 8. The upst ream and downst ream boundary condit ions were est ablished as “ Norm al Dept h = 0.01.” This st eady flow dat a file is ident ical t o t he file produced in Exam ple 1. The user is referred t o Exam ple 1 for a furt her discussion on developing a st eady flow dat a file. Figure 16-4: Steady Flow Data Window 16- 5 Exam ple 16 Channel Modificat ion Comparing Existing and Modified Conditions Plans for t he different geom et ry files m ust be m anufact ured before a com parison can be analyzed. Once t he plans are creat ed t he user can view t he graphical and t abular result s. Steady Flow Analysis A new plan was creat ed by select ing Run and t hen St e a dy Flow Ana lysis from t he m ain program window. This act ivat ed t he St e a dy Flow Ana lysis W indow shown in Figure 16.5. The Ge om e t r y File was select ed as “ Base Geom et ry Dat a” and t he St e a dy Flow File was select ed as “ 100 Year Profile.” Next , a new plan was creat ed by select ing N e w Pla n from t he File m enu. The t it le was ent ered as “ Exist ing Condit ions,” and t he Shor t I .D . was ent ered as “ Exist Cond.” A m ixed Flow Re gim e was select ed and t he file was saved by choosing File and t hen Save Plan. Finally, t he Com put e but t on was select ed t o perform t he st eady flow analysis. Figure 16-5: Steady Flow Analysis Window This procedure was repeat ed for t he m odified channel geom et ry. On t he St e a dy Flow An a lysis W in dow t he Ge om e t r y File was select ed as “ Modified Geom et ry” and t he St e a dy Flow File rem ained “ 100 Year Profile.” The Flow Re gim e was changed t o “ Supercrit ical.” The t it le was ent ered as “ Modified Condit ions Run” and t he Shor t I .D . was ent ered as “ Modified.” The file was saved and t hen t he Com pu t e but t on was select ed. 16- 6 Exam ple 16 Channel Modificat ion Water Surface Profiles Aft er t he sim ulat ion was com plet ed, W a t e r Su r fa ce Pr ofile s was select ed from t he Vie w m enu on t he m ain program window. To com pare t he different profiles for t he exist ing and m odified channel geom et ry, Opt ion s and t hen Pla n s was select ed from t he profile plot . This displayed t he Pla n Se le ct ion W indow . From t his window t he check box Com pa r e Ge om e t r y a s w e ll a s Ou t pu t was select ed and t he exist ing and m odified geom et ry plans were select ed for com parison, as shown on Figure 16.6. Figure 16-6: Plan Selection Window Aft er pressing t he OK but t on on t he Pla n Se le ct ion W indow , Figure 16.7 was displayed. The figure shows t he t wo plans for t he exist ing channel geom et ry and t he m odified channel geom et ry. I t can be seen from t he profile t hat t he exist ing channel geom et ry had a flow t hat was m ixed bet ween t he subcrit ical and supercrit ical regim e. The m odified channel geom et ry alt ered t he flow t o be exclusively supercrit ical for t his reach. 16- 7 Exam ple 16 Channel Modificat ion Figure 16-7: Water Surface Profiles showing existing and modified geometry Cross Section Plots From t he m ain program window, select Vie w and t hen Cr oss Se ct ion . The sam e m et hod illust rat ed in t he previous sect ion was used for select ing t he exist ing and m odified plans. The cross sect ion plot illust rat ed in Figure 16.8 displays t he exist ing and m odified channel geom et ry along wit h t he wat er surface profiles for bot h plans. As seen from t he figure, t he channel m odificat ion lowered t he wat er surface for t he 100- year event . For t he m odified geom et ry t he wat er surface level was lowered enough t o cont ain t he 100- year flow in t he m ain channel. I n addit ion, t he channel m odificat ions changed t he t ype of flow from subcrit ical t o supercrit ical at t his part icular cross sect ion. 16- 8 Exam ple 16 Channel Modificat ion Figure 16-8: Cross Section showing existing and modified geometry X-Y-Z Perspective Plot From t he m ain program m enu select Vie w and t he X- Y- Z Pe r spe ct ive Plot s. Figure 16.9 displays t he 3D plot from river st at ion 12 t o river st at ion 1. The user can select various azim ut h and rot at ion angles t o obt ain differing views of t he reach. The figure shows t he difference in lat eral dist ribut ion of t he wat er surfaces for t he exist ing and m odified channel geom et ry for t he given flow dat a. 16- 9 Exam ple 16 Channel Modificat ion Figure 16-9: X-Y-Z Perspective Plot Standard Table I n addit ion t o graphical display, t he user can com pare t he out put in t abular form . From t he m ain program window, select Vie w and t hen Pr ofile Sum m a r y Ta ble . By select ing St a n da r d Ta ble 1 , t he t able shown in Figure 16.10 is displayed. The first t wo colum ns of t he t able display t he river reach and river st at ion. The t hird colum n ident ifies which plan corresponds t o t he dat a. The ident ifiers in t his colum n are obt ained from t he Sh or t I D ent ered in t he St e a dy Flow D a t a Edit or . The rem aining port ion of t he t able displays inform at ion about t ot al flow, energy grade line elevat ion, wat er surface elevat ion, et c. 10 Exam ple 16 Channel Modificat ion As shown in t he t able t he m odificat ions lowered t he wat er surface by approxim at ely 5 feet . The t able also shows t he t ransform at ion of flow from t he subcrit ical regim e, for t he exist ing condit ions, t o a supercrit ical regim e for t he m odified condit ions. This corresponds wit h t he increase in velocit y. Figure 16-10: Profile Output Table Summary The geom et ry of Exam ple 1 was m odified t o prevent t he flow from t he 100year event from overflowing t he channel. This was accom plished by m odifying t he exist ing channel condit ions t o include t wo cut s down t he cent erline of t he channel. By reviewing t he wat er surface profiles and t ables, t he user can det erm ine t he benefit s of a specific channel m odificat ion for a given flow. 11 Exam ple 17 Unst eady Flow Applicat ion CH APT ER 1 7 Unsteady Flow Application Purpose This exam ple dem onst rat es t he use of HEC- RAS t o perform an unst eady flow analysis on a net work of reaches cont aining j unct ions, st orage areas, bridges, culvert s, and hydraulic connect ions. The geom et ric dat a const ruct ed for t his exam ple illust rat es m ult iple unst eady flow applicat ions in HEC- RAS. The geom et ric dat a used in t his exam ple is not a specific reference t o any exist ing st ream net work. This exam ple focuses on m odeling and evaluat ing st orage areas, hydraulic connect ions, and hydraulic param et ers in an unst eady flow environm ent . The user is referred t o previous exam ples for discussion on m odeling bridges, culvert s, m ult iple reaches, and j unct ions. To review t he dat a files for t his exam ple, from t he m ain program window select File and t hen Ope n Pr oj e ct . Select t he proj ect labeled “ Unst eady Flow Applicat ion.” This will open t he proj ect and act ivat e t he following files: Plan: “ Diam ond River Base Plan” Geom et ry: “ Diam ond River Base Geom et ry” Unst eady Flow: “ Unst eady Flow” Geometric Data To view t he geom et ric dat a for t he river syst em , from t he m ain program window select Edit and t hen Ge om e t r ic D a t a . This will act ivat e t he Ge om e t r ic D a t a Edit or and display t he river syst em schem at ic as shown in Figure 17.1. 17- 1 Exam ple 17 Unst eady Flow Applicat ion General Description The Geom et ric Dat a consist s of a net work of channels connect ed by j unct ions. Four st orage areas are included in t he geom et ry ( Pyram id Lake, Eagle Lake, Upper Angora, and Lower Angora) . Pyram id Lake is connect ed by t wo reaches ( East and West ) and by Eagle Lake, via a culvert and a weir. Eagle Lake is hydraulically connect ed t o River St at ion 1.9 on t he Sout heast Reach and t o t he previously m ent ioned Pyram id Lake. Upper Angora is connect ed t o t he Sout hwest Reach via a lat eral weir locat ed bet ween cross sect ions 1.99 and 1.9. Lower Angora is hydraulically connect ed t o Upper Angora via a culvert and a weir. Figure 17-1: River System Schematic for Diamond River Base Geometry 17- 2 Exam ple 17 Unst eady Flow Applicat ion I n addit ion t o t hese feat ures, a culvert is locat ed at River St at ion 3.395 on t he Nort hwest Reach and a bridge is locat ed at River St at ion 1.895 on t he Sout h Reach. The cross sect ion geom et ry is prism at ic wit h lit t le change in elevat ion wit h dist ance except for t he Nort h Reach. The level t opography provides an excellent environm ent t o exam ine unst eady flow for such aspect s as flow reversal. This exam ple assum es t hat t he user has sufficient experience const ruct ing t he following river syst em feat ures and all at t ribut es associat ed wit h each feat ure. • Reaches • Cross Sect ion Geom et ry • Junct ions • Bridges and Culvert s Consult wit h previous exam ples for inform at ion pert aining t o t he above m ent ioned feat ures. The following descript ion com m ences wit h t he creat ion of st orage areas. 17- 3 Exam ple 17 Unst eady Flow Applicat ion Figure 17-2: Initial Geometry for Development Creating Storage Areas I n t he Ge om e t r ic D a t a Edit or, t he st art ing geom et ry for t his exam ple is shown in Figure 17.2. On t he Tools t oolbar in t he Ge om e t r ic D a t a Edit or t he icon for St or a ge a r e a was select ed. The point er was t hen placed bet ween t he East and West reaches and t he st orage area was drawn by single clicking and dragging t he m ouse for each desired point for t he st orage area. The final point for t he st orage area was select ed by double clicking t he m ouse. Upon double clicking t he m ouse, a dialog box appears request ing a st orage area nam e. The nam e “ Pyram id Lake” was ent ered. Point s on a st orage area m ay be added or rem oved by using t he Add Point s t o a Reach or SA and Rem ove Point s t o a Reach or SA opt ions found in t he Edit m enu. 17- 4 Exam ple 17 Unst eady Flow Applicat ion I t is im port ant t hat t he program recognizes t he connect ion of Pyram id Lake t he East and West reaches. The connect ion m ay be m ade in t wo different ways. The first opt ion is t o draw t he st orage area so t he end of each reach included wit hin t he st orage area polygon. The second opt ion is t o drag and drop t he end of each reach wit hin t he st orage area polygon by using t he M ove Obj e ct t ool found in t he Edit m enu of t he Ge om e t r ic D a t a Edit or . bot h cases t he reach and st orage area are connect ed if a black dot appears t he int ersect ion of t he reach and t he side of t he st orage area. to is In at Figure 17-3: Geometry with Storage Areas The rem aining t hree st orage areas were creat ed in t he sam e m anner as Pyram id Lake wit hout any connect ions t o reaches. Figure 17.3 displays t he com plet ed st orage areas in t he Ge om e t r ic D a t a Edit or before t he addit ion 17- 5 Exam ple 17 Unst eady Flow Applicat ion of t he hydraulic connect ions. The hydraulic connect ions for each st orage area are discussed in im pending sect ions. Entering Data for a Storage Area Aft er t he st orage area was drawn in t he Ge om e t r ic D a t a Edit or t he surface area for st orage was ent ered. The dat a was ent ered in t he St or a ge Ar e a Edit or , displayed in Figure 17.4, found by select ing t he St or a ge a r e a icon on t he Edit or s t oolbar. For Pyram id Lake t he Ar e a t im e s de pt h m e t h od was select ed. An area of 1000 acres wit h a m inim um elevat ion of 0 feet was ent ered. This m et hod com put es t he product of a const ant area and change in wat er surface elevat ion t o calculat e st orage volum e. Figure 17-4: Storage Area Editor for Pyramid Lake An addit ional opt ion for calculat ing st orage volum e is t he Ele va t ion ve r su s volu m e cur ve m et hod, shown in Figure 17.5 for Eagle Lake. For t his m et hod t he init ial elevat ion was ent ered as 0 feet wit h a volum e of 0 acre- feet . Dat a was t hen ent ered in increm ent s of 2 feet for t he cum ulat ive volum e of st orage produced at each increm ent . I t is im port ant t o not e t hat t he user is not ent ering t he surface area of st orage at each increm ent but t he cum ulat ive volum e of st orage at each increm ent . 17- 6 Exam ple 17 Unst eady Flow Applicat ion Figure 17-5: Storage Area Editor for Eagle Lake Lateral Structure Connected to a Storage Area A lat eral st ruct ure was placed on t he Sout hwest Reach by select ing t he La t e r a l St r u ct u r e icon from t he Edit or s t oolbar in t he Ge om e t r ic D a t a Edit or . Aft er select ing t he icon, t he La t e r a l St r u ct u r e D a t a Edit or appears, as shown in Figure 17.6. Wit h t he reach select ed as Sout hwest , under t he Opt ions m enu, Add a La t e r a l St r uct u r e was select ed. The locat ion of t he st ruct ure was ent ered at 1.95. This placed t he beginning of t he st ruct ure bet ween river st at ions 1.99 and 1.9. To ent er dat a for t he st ruct ure, t he W e ir / Em ba n k m e nt icon was select ed from t he La t e r a l St r u ct u r e D a t a Edit or . The dat a was ent ered as shown in Figure 17.7 on t he La t e r a l W e ir Em ba n k m e n t W in dow . The weir is broad crest ed wit h a widt h of 10 feet , placed 10 feet from t he upst ream river st at ion 1.99. The weir flow reference m et hod was chosen as “ wat er surface.” Ret urning t o t he La t e r a l St r u ct u r e D a t a Edit or , t he “ right overbank” was select ed from t he pull- down posit ion m enu. Last ly, a connect ion was m ade t o t he st orage area by select ing t he Se t SA but t on. A window will t hen popup, allowing t he user t o select a st orage area t o connect t o. On t he pull- down m enu “ Upper Angora” was select ed. 17- 7 Exam ple 17 Unst eady Flow Applicat ion Anot her lat eral st ruct ure was added from t he sout heast reach t o t he Eagle lake st orage area. This lat eral st ruct ure was added in t he sam e m anner as t he previous one, except it had a culvert in addit ion t o t he overflow weir. Figure 17-6: Lateral Weir Data Editor 17- 8 Exam ple 17 Unst eady Flow Applicat ion Figure 17-7: Lateral Weir Embankment Window Storage Area Connections St orage area connect ions are used t o connect st orage areas t o ot her st orage areas. To m ake a connect ion from Pyram id Lake t o Eagle Lake, t he St or a ge Ar e a Con ne ct ion icon was select ed from t he Edit or s t oolbar in t he Ge om e t r ic D a t a Edit or . This brought up t he St or a ge Ar e a Conn e ct ion edit or shown in Figure 17.8. The st orage areas were select ed by pressing t he Se t SA but t ons next t o t he Fr om and To locat ion fields. Pyram id Lake was select ed as t he Fr om locat ion, and Eagle lake as t he To locat ion. Next t he W e ir / Em ba n k m e nt icon was select ed. A 500 ft long broad crest ed weir was ent ered at an elevat ion of 16.5 feet . 17- 9 Exam ple 17 Unst eady Flow Applicat ion Figure 17-8: Storage Area Connection Editor for Pyramid to Eagle Lakes An opening in t he em bankm ent was placed along t he cent erline of t he weir by select ing t he Cu lve r t icon on t he St or a ge Ar e a Con ne ct ion D a t a Edit or . This select ion displayed t he Cu lve r t D a t a Edit or shown on Figure 17.9. A circular culvert wit h a diam et er of 5 feet and an invert elevat ion of 11.5 feet was ent ered for t his hydraulic connect ion. Addit ional param et ers ent ered are shown in Figure 17.9. One addit ional st orage area connect ion ( Upper t o Lower lake) was const ruct ed in t he sam e m anner t o connect t hose t wo st orage areas. 17- 10 Exam ple 17 Unst eady Flow Applicat ion Figure 17-9: Culver Data Editor for RS 1.9 to Eagle Parameters for Hydraulic Tables Hydraulic st ruct ures, such as bridges and culvert s, are convert ed int o fam ilies of rat ing curves t hat describe t he st ruct ure as a funct ion of t ailwat er, flow, and headwat er. The user can set param et ers t o define t he curves by select ing H Ta b Pa r a m e t e r s from t he Br idge a n d Cu lve r t Edit or or from t he St or a ge Ar e a Conn e ct ion Edit or . For t his exam ple, t he culvert s in st orage area connect ions, t he culvert locat ed on t he Nort hwest Reach, and t he bridge locat ed on t he Sout h Reach m ay have t heir param et ers adj ust ed. For t he bridge locat ed on t he Sout h Reach t he Br idge / Culve r t icon on t he Edit or t oolbar in t he Ge om e t r ic D a t a Edit or was select ed. I n t he Br idge Cu lve r t D a t a t he Sout h Reach was select ed and t he H Ta b Pa r a m icon was depressed bringing up t he Pa r a m e t e r s for H ydr a u lic Pr ope r t ie s Ta ble s shown in Figure 17.10. Default values were used for t he num ber of point s on a free flow curve, t he num ber of subm erged curves, and t he num ber of point s on each subm erged curve. Lim it s on t he ext ent of t he curves were defined by set t ing t he m axim um headwat er and t ailwat er elevat ions at 19 feet . For addit ional inform at ion on HTAB Param et ers refer t o Chapt er 8 of t he User’s Manual, Perform ing an Unst eady Flow Analysis. 17- 11 Exam ple 17 Unst eady Flow Applicat ion Figure 17-10: Parameter for Hydraulic Property Tables Cross Section Table Parameters I n HEC- RAS, cross sect ions are processed int o t ables of elevat ion versus hydraulic propert ies of areas, conveyances, and st orage. The user is required t o set an int erval for spacing t he point s in t he cross- sect ion t ables. I n t he Ge om e t r ic D a t a Edit or t he icon H t a b Pa r a m e t e r s was select ed under t he Edit or s t oolbar. This displays t he Cr oss Se ct ion Ta ble Pa r a m e t e r s W indow shown in Figure 17.11. The st art ing elevat ion, t able increm ent , and num ber of point s colum ns are aut om at ically filled by t he program but m ay be changed by t he user. The program aut om at ically st art s t he t able for each cross sect ion 1 foot above t he channel invert . The program chooses a t able increm ent and num ber of point s by first at t em pt ing t o use 20 point s, and choosing an increm ent t hat will put t he t able up t o t he t op of t he cross sect ion. I f t his result s in t oo large of an increm ent ( great er t han 1.0 foot ) t he program will use a one foot increm ent and add addit ional point s t o get t he t able t o t he t op of t he cross sect ion. The increm ent for t his exam ple was set t o 1 for “ All Reaches” by highlight ing t he increm ent colum n and select ing t he Se t Va lu e s but t on. The user can set individual values for each cross sect ion if it is deem ed necessary. W a r n in g: Alw a ys e n su r e t h a t your cr oss se ct ion t a ble s e n com pa ss t he com ple t e r a nge of st a ge s t ha t w ill be m ode le d. I f t he t ables do not go up t o a high enough elevat ion, t he program will have t o ext rapolat e during t he com put at ions. More oft en t han not , t he ext rapolat ion causes inst abilit ies in t he result s. To visualize t he ext ent of t he t ables, a graphic of individual cross sect ions is shown on t he right hand side of t he window. The graphic displays t he cross sect ion corresponding t o t he row in which you cursor lies in t he t able. 17- 12 Exam ple 17 Unst eady Flow Applicat ion Figure 17-11: Cross Section Table Parameters Unsteady Flow Data The user is required t o ent er boundary condit ions and init ial condit ions for t he syst em at t he beginning of t he sim ulat ion period. For addit ional inform at ion on unst eady flow dat a refer t o Chapt er 8 of t he User’s Manual, Perform ing an Unst eady Flow Analysis. The Un st e a dy Flow D a t a Edit or , shown in Figure 17.12, was select ed from t he m ain program window under t he Edit m enu. Boundary Conditions Boundary condit ions are required for t he fart hest upst ream and downst ream cross sect ions. Upon ent ering t he Un st e a dy Flow D a t a Edit or t he fart hest upst ream and downst ream cross sect ions will be locat ed in t he boundary condit ions colum n. I n t his case, t he user will see River St at ion 6.0 on t he Nort h Reach and River St at ion 0.0 on t he Sout h Reach. Boundary condit ions are set by highlight ing t he adj acent cell under Bounda r y Condit ion Type . When a cell is highlight ed, not all boundary condit ions are available. The program will aut om at ically gray out all irrelevant boundary condit ion t ypes. I nt ernal boundary condit ions m ay be added by select ing t he desired cross sect ion in t he Un st e a dy Flow D a t a Edit or and pressing t he Add a Bou nda r y Condit ion Loca t ion but t on. 17- 13 Exam ple 17 Unst eady Flow Applicat ion Figure 17-12: Unsteady Flow Data Editor Upstream Boundary Condition For River St at ion 6.0 a flow hydrograph was select ed by highlight ing t he cell and pressing t he Flow H ydr ogr a ph but t on. The window for a Flow H ydr ogr a ph is shown in Figure 17.13. For t his exam ple t he flow hydrograph was m anually ent ered by select ing t he En t e r Ta ble radio but t on. The D a t a Tim e I n t e r va l was set t o t hree hours and t he radio but t on Use Sim u la t ion Tim e was select ed. The Use Sim u la t ion Tim e opt ion st art s t he hydrograph at t he beginning of t he sim ulat ion t im e window, which is discussed in an upcom ing sect ion. The hydrograph was t hen m anually ent ered wit h a baseflow of 100 cfs and a floodwave t hat peaked at 5000 cfs. 17- 14 Exam ple 17 Unst eady Flow Applicat ion Figure 17-13: Flow Hydrograph for Upstream Boundary Condition The user m ay also select t o read hydrograph dat a from a DSS file. To do t his t he user presses t he but t on Se le ct D SS file and Pat h. When t his but t on is pressed a DSS file and pat hnam e select ion screen will appear as shown in Figure 17.14. The user first select s t he desired DSS file by using t he browser but t on at t he t op. Once a DSS file is select ed, a list of all of t he DSS pat hnam es wit hin t hat file will be displayed in t he t able. The user can use t he pat hnam e filt ers t o reduce t he num ber of pat hnam es shown in t he t able. When t he desired DSS pat hnam e is found t he user closes t he window and t he filenam e and pat hnam e will be recorded in t he Flow H ydr ogr a ph W indow . 17- 15 Exam ple 17 Unst eady Flow Applicat ion Figure 17-14: DSS Pathname and Filename Downstream Boundary Condition For River St at ion 0.0 of t he Sout h Reach t he boundary condit ion select ed was norm al dept h. Again, t he corresponding cell for t hat part icular river st at ion was highlight ed and t he N or m a l D e pt h but t on was select ed. The window shown in Figure 17.15 is t hen displayed and a value of 0.0000947 was ent ered. This m et hod requires t he user t o ent er a frict ion slope for t he reach in t he vicinit y of t he boundary condit ion, t he slope of t he wat er surface is oft en a good est im at e of t he frict ion slope. Figure 17-15: Normal Depth for Downstream Boundary Initial Conditions I nit ial condit ions consist of flow and st age inform at ion at each of t he cross sect ions, as well as elevat ions for any st orage areas defined in t he syst em . Dat a for init ial condit ions is est ablished by select ing t he I nit ia l Condit ion s 17- 16 Exam ple 17 Unst eady Flow Applicat ion t ab on t he Un st e a dy Flow D a t a Edit or . Aft er select ing t he t ab, Figure 17.16 will be displayed. Figure 17-16: Unsteady Flow Data Initial Conditions Flow dat a was ent ered for each reach so t he program could perform a st eadyflow backwat er run t o com put e t he corresponding st ages at each cross sect ion. As shown on Figure 17.16, t he Nort h Reach has an init ial flow of 100 cfs, corresponding t o t he baseflow of t he hydrograph ent ered as t he upst ream boundary condit ion. The ot her various reaches t hen split t he 100 cfs of flow down t o t he Sout h Reach where t he flow com bines t o 80 cfs. I n addit ion t o flow dat a, init ial elevat ion for each st orage area is needed. I nit ial elevat ions were set t o 11, 10, 12, and 10 feet for Pyram id Lake, Eagle Lake, Lower Angora, and Upper Angora, respect ively. The dat a was t hen saved in t he Un st e a dy Flow D a t a Edit or and t he window was closed. 17- 17 Exam ple 17 Unst eady Flow Applicat ion Unsteady Flow Analysis Aft er t he geom et ry and unst eady flow dat a have been com plet ed an unst eady flow analysis m ay be init iat ed. Under t he m ain program window Unst e a dy Flow Ana lysis was select ed under t he Ru n m enu. This will display t he Un st e a dy Flow Ana lysis W indow shown in Figure 17.17. A plan was defined by select ing t he Geom et ry File “ Diam ond River Base Geom et ry” and t he Unst eady Flow File “ Unst eady Flow.” Under t he File m enu, Sa ve Pla n As was select ed and t he plan t it le was ent ered as “ Diam ond River Base Plan.” Aft er ent ering t he t it le of t he plan a short ident ifier was ent ered as “ Base” and t he plan was saved. Figure 17-17: Unsteady Flow Analysis Window Simulation Time Window The sim ulat ion t im e window, locat ed on Figure 17.17, requires a beginning and ending dat e and t im e for sim ulat ion. The dat e m ust have a four digit year and can be ent ered in eit her of t he t wo following form at s: 01Jan1990 or 17- 18 Exam ple 17 Unst eady Flow Applicat ion 01/ 01/ 1990. For t his applicat ion t he dat e was saved in t he lat t er form at . The t im e field is ent ered in m ilit ary t im e ( i.e. 1 p.m . is ent ered as 1300) . For t his applicat ion t he sim ulat ion t im e began and ended at 0800. Computation Settings The com put at ion set t ings in t he Un st e a dy Flow Ana lysis W in dow cont ain t he following: t he com put at ional int erval; hydrograph out put int erval; inst ant aneous profiles int erval; and t he nam e and pat h of t he out put DSS file. For t his exam ple t he com put at ion int erval was set t o 15 m inut es. The com put at ion int erval should be sm all enough t o accurat ely describe t he rise and fall of t he floodwave. The hydrograph out put int erval was set t o 1 hour. This int erval defines t he out put of com put ed st age and flow hydrographs writ t en t o HEC- DSS. The det ailed out put int erval was set t o 6 hours, specifying t he int erval at which det ailed hydraulic out put will be com put ed by t he post processor. I t is suggest ed t hat t his int erval rem ain fairly large t o reduce t he am ount of post processing and st orage required. The pat h select ed for t he out put t o DSS was “ C: \ HEC\ RAS\ Unst eady\ Diam ond.dss.” Location of Stage and Flow Hydrographs The user has t he opt ion of specifying locat ions t o have hydrographs com put ed and available for display. The user m ay select individual cross sect ions, groups of cross sect ions, or ent ire reaches. From t he Opt ion s m enu on t he Un st e a dy Flow Ana lysis W indow , t he St a ge a n d Flow Ou t pu t Loca t ion s opt ion was select ed, displaying Figure 17.18. For t his exam ple “ All Reaches” was select ed. This opt ion will com put e hydrographs at every cross sect ion in t he dat a set . I f t he user is working wit h an ext rem ely large dat a set , com put at ion t im e and dat a st orage can be reduced by only select ing t he m ost essent ial cross sect ions for out put . 17- 19 Exam ple 17 Unst eady Flow Applicat ion Figure 17-18: Stage and Flow Output Locations Unsteady Flow Simulation There are t hree com ponent s used in perform ing an unst eady flow analysis wit hin HEC- RAS: t he geom et ric dat a preprocessor ( HTAB) ; t he unst eady flow sim ulat or ( UNET) ; and an out put post processor. Geometry Pre-processor (HTAB) The geom et ry pre- processor is used t o speed up t he unst eady flow calculat ions by processing t he geom et ric dat a int o a series of hydraulic propert y t ables and rat ing curves. I t is highly recom m ended and illust rat ed in t his exam ple t hat t he user run t he geom et ry pre- processor and exam ine hydraulic out put for anom alies before running t he unst eady flow sim ulat or and t he post - processor. The Geom et ry Pr e - pr oce ssor box under “ Program s t o Run” was select ed in t he Un st e a dy Flow Ana lysis W indow , Figure 17.17. The Unst e a dy Flow Sim u la t ion and Post - Pr oce ssor boxes were unselect ed ( no checkm arks) and t he Com put e but t on was depressed. Aft er t he geom et ry pre- processor finished processing t he dat a, H ydr a u lic Pr ope r t y Plot s was select ed from t he Vie w m enu on t he m ain program m enu. Figure 17.19 displays a t ypical cross sect ion plot of hydraulic propert ies for t his exam ple. Cross sect ions are processed int o t ables of elevat ions versus hydraulic propert ies of areas, conveyances, and st orage. Viewing t hese plot s for anom alies is a good diagnost ic t ool t o search for cross sect ions wit h irregular geom et ry. 17- 20 Exam ple 17 Unst eady Flow Applicat ion Figure 17-19: Hydraulic Properties for a Cross Section The geom et ry pre- processor evaluat es hydraulic st ruct ures such as bridges and culvert s and relat es t he st ruct ures as a funct ion of t ailwat er, flow, and headwat er. From t he Type m enu in t he H ydr a u lic Pr ope r t ie s Ta ble s, I n t e r na l Bou nda r ie s was select ed. Next , t he Sout h Reach was select ed displaying Figure 17.20, t he fam ily of rat ing curves for t he bridge locat ed at RS 1.895. On t he plot t he free flow rat ing funct ion describes t he flow if t ailwat er subm ergence does not occur, such as free flow over a weir. Above t he free- flow rat ing funct ion is a fam ily of subm erged flow rat ing curves, one for each t ailwat er elevat ion. 17- 21 Exam ple 17 Unst eady Flow Applicat ion Figure 17-20: Family of Rating Curves for Bridge Located on the South Reach As shown in Figure 17.20 t here is a t ransit ional area t o left of t he free flow curve bet ween 10 and 12 feet of elevat ion where t he lines of const ant t ailwat er ext end vert ically. This occurs because at t his wat er elevat ion flow begins t o cont act t he upst ream side of t he bridge, causing backwat er. This is a t ransit ion zone where free surface flow changes t o orifice flow. This t ype of flow is unpredict able because t he flow is changing from free surface flow t o a “ sluice gat e t ype” of pressure flow and t hen possibly t o a full flowing orifice flow. Unsteady Flow Simulation and the Post-Processor Aft er t he hydraulic propert y t ables were exam ined t he Ge om e t r y Pr e pr oce ssor box was unselect ed on t he Un st e a dy Flow Ana lysis W indow and t he Unst e a dy Flow Sim u la t ion and Post - Pr oce ssor boxes were select ed. Then t he Com pu t e but t on was depressed. 17- 22 Exam ple 17 Unst eady Flow Applicat ion The out put from t he sim ulat ion can be viewed from m any different t ables and graphs. The m ost int erest ing out put for t his exam ple is found by viewing t he st age and flow hydrographs. From t he m ain program window, Vie w and t hen St a ge a nd Flow H ydr ogr a ph was select ed. By select ing t he Type m enu on t he St a ge a n d Flow H ydr ogr a ph W in dow t he user can view st age and flow hydrographs for cross sect ions, bridges, culvert s, inline st ruct ures, lat eral st ruct ures, st orage areas, st orage area connect ions, and pum p st at ions. Figure 17-21: Stage and Flow Hydrograph for the West Reach First , t he “ Cross Sect ion” opt ion was select ed from t he Type m enu and t he reach was set t o West , displaying Figure 17.21. As seen from t he figure, t he flow was init ially negat ive, denot ing t hat at t he beginning of t he sim ulat ion t im e flow was m oving away from Pyram id Lake. As t he floodwave progressed t he flow changed t o posit ive, im plying a reversal in t he direct ion of flow t owards Pyram id Lake. Aft er t he floodwave passed, t he direct ion of flow ret urned t o flowing away from Pyram id Lake. The st age and flow can also be viewed as t abular out put by select ing t he Ta ble t ab locat ed on t he St a ge a n d Flow H ydr ogr a ph W indow . The out put will be displayed in t he 17- 23 Exam ple 17 Unst eady Flow Applicat ion increm ent set on t he hydrograph out put int erval locat ed in t he Un st e a dy Flow Ana lysis W indow . Figure 17-22: Stage and Flow Hydrograph for Southwest Reach The geom et ric dat a set was const ruct ed wit h relat ively no slope t o em phasize t he abilit y of RAS t o m odel unst eady flow, including flow reversals. As seen in Figure 17.22 for t he Sout hwest Reach, t he flow reverses direct ion during t he peak of t he floodwave. This flow reversal occurs because wat er is divert ed t o t he West Reach and t o t he lat eral weir on t he Sout hwest Reach. These diversions decrease t he flow in t he Sout hwest Reach com pared t o t he flow in t he Sout heast Reach. The discrepancy in flows bet ween t he t wo reaches causes a significant difference in wat er surface elevat ions at t he Lower Junct ion. The difference in wat er surface elevat ion forces wat er t o m ove upst ream on t he Sout hwest Reach during t he floodwave. Next , t he La t e r a l St r uct u r e opt ion was select ed from t he Type m enu and t he reach was set t o Sout hwest , displaying Figure 17.23. As shown in Figure 17.23, t he lat eral weir is affect ed by t he flow reversal on t he Sout hwest 17- 24 Exam ple 17 Unst eady Flow Applicat ion Reach. Addit ionally, t he t ailwat er st age for t he lat eral weir rises above t he headwat er st age t wice during sim ulat ion, causing flow t o ent er t he reach from t he lat eral weir. Figure 17-23: Stage and Flow Hydrograph for Lateral Structure Located on the Southwest Reach I n addit ion t o viewing out put direct ly from t he St a ge a nd Flow H ydr ogr a ph W indow t he user can open t he Ge om e t r ic D a t a Edit or and select t o view out put by clicking on t he desired feat ure. From t he Ge om e t r ic D a t a Edit or t he st orage area “ Pyram id” was select ed by clicking on it wit h t he m ouse. Plot St a ge a n d Flow H ydr ogr a ph was select ed, displaying Figure 17.24. As shown in Figure 17.24, t he st age of t he st orage area st eadily decreases because flow is leaving t he st orage area unt il t he floodwave passes t hrough, causing t he st age t o increase. The st age of t he st orage area t hen begins t o decrease again aft er t he floodwave. 17- 25 Exam ple 17 Unst eady Flow Applicat ion Figure 17-24: Stage and Flow Hydrograph for Pyramid Lake Finally, from t he Ge om e t r ic D a t a Edit or t he st orage are connect ion “ Pyram id t o Eagle” was select ed, displaying Figure 17.25. I nit ially, t here is no flow in t his connect ion. This occurs because t he st age is below t he low invert elevat ion of t he culvert at 11.5 feet . When t he st age increases t o over 11.5 feet t he flow rat e st eadily increases, as shown on Figure 17.25. 17- 26 Exam ple 17 Unst eady Flow Applicat ion Figure 17-25: Stage and Flow Hydrograph for Hydraulic Connection – Pyramid to Eagle Summary The concept of unst eady flow analysis wit hin a net work of channels and st orage areas was discussed. This exam ple dem onst rat es t he abilit y of HECRAS t o rout e a hydrograph t hrough a net work of channels cont aining j unct ions, culvert s, bridges, st orage areas, lat eral weirs, and hydraulic connect ions. Unst eady flow analysis can be ext rem ely difficult com pared t o st eady flow analysis because input param et ers can cause inst abilit ies in calculat ions. I nst abilit ies can cause t he program t o fail t o converge on a solut ion. I t is highly recom m ended t hat t he user have experience wit h unst eady flow m odeling. Refer t o Chapt er 8 of t he User’s Manual for addit ional inform at ion on unst eady flow analysis. 17- 27 Appendix A References APPEN D I X A References Barkau, Robert L., 1992. UNET, One- Dim ensional Unst eady Flow Through a Full Net work of Open Channels, Com put er Program , St . Louis, MO. Federal Highway Adm inist rat ion, 1995. Evaluat ing Scour at Bridges, Hydraulic Engineering Circular No. 18, U.S. Depart m ent of Transport at ion, Washingt on D.C. Federal Highway Adm inist rat ion, 1990. User’s Manual for WSPRO - A com put er m odel for wat er surface profile com put at ions, Publicat ion No. FHWA- I P- 89- 027, 177 p. Federal Highway Adm inist rat ion, 1985. Hydraulic Design of Highway Culvert s, Hydraulic Design Series No. 5, U.S. Depart m ent of Transport at ion, ( Sept em ber) Washingt on D.C. Federal Em ergency Managem ent Agency, 1985. “ Flood I nsurance St udy Guidelines and Specificat ions for St udy Cont ract ors,” FEMA 37, Washingt on, D.C. Hydrologic Engineering Cent er, 1995. Flow Transit ions in Bridge Backwat er Analysis, RD- 42, U.S. Arm y Corps of Engineers, Davis, CA. Hydrologic Engineering Cent er, 1996. HEC- RAS River Analysis Syst em , Hydraulic Reference Manual, U.S. Arm y Corps of Engineers, Davis, CA. Hydrologic Engineering Cent er, 1996. HEC- RAS River Analysis Syst em , User’s Manual, U.S. Arm y Corps of Engineers, Davis, CA. Hydrologic Engineering Cent er, 1995. UNET, A One- Dim ensional Unst eady Flow Through a Full Net work of Open Channels, User’s Manual, U.S. Arm y Corps of Engineers, Davis, CA. King, H.W. and E.F. Brat er, 1963. Handbook of Hydraulics, Fift h Edit ion, McGraw Hill Book Com pany, New York. Shearm an, J.O., 1990. User’s Manual for WSPRO - A com put er m odel for wat er surface profile com put at ions, Federal Highway Adm inist rat ion, Publicat ion No. FHWA- I P- 89- 027, 177 p. Unit ed St at es Geological Survey, 1979. Backwat er at Bridges and Densely Wooded Flood Plains, Beaver Creek Near Kent wood, Louisiana, Hydrologic At las No. HA- 601. Yarnell, D.L., 1934. Bridge Piers as Channel Obst ruct ions, Technical Bullet in 442, U.S. Depart m ent of Agricult ure, Washingt on, D.C. A-1 Appendix A References A-2