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VI. River Engineering And Geomorphology For Transportation Design

VI. River Engineering And Geomorphology For Transportation Design. VI. River Engineering And Geomorphology For Transportation Design. Lecture Overview A Sedimentation and Scour B Dynamic Nature of Streams in the Arid West C Sediment Transport Models Next Lecture

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VI. River Engineering And Geomorphology For Transportation Design

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  1. VI. River Engineering And Geomorphology For Transportation Design

  2. VI. River Engineering And Geomorphology For Transportation Design Lecture Overview A Sedimentation and Scour B Dynamic Nature of Streams in the Arid West C Sediment Transport Models Next Lecture • Section VII – Effects of Transportation Structures on Stream Systems

  3. VI. River Engineering And Geomorphology For Transportation Design A.1. Sedimentation And Scour: Basic Sediment Transport Theory a) Sediment Continuity b) Sediment Transport Capacity c) Sediment Load d) Sediment Transport Functions e) Sediment Yield

  4. VI. River Engineering And Geomorphology For Transportation Design A.1. Basic Sediment Transport Theory a)Sediment ContinuityEquation • Storage change = erosion or deposition • Streams naturally balance sediment load • Imbalances cause adjustments to occur • Fixing one problem may cause another Sediment in – Sediment out = Storage Change

  5. VI. River Engineering And Geomorphology For Transportation Design A.1. Basic Sediment Transport Theory c) Sediment Transport Capacity • The amount of sediment a stream can move Basic Principles: • Streams carry as much sediment as they can • Streams deprived of sediment will find some • Streams with excess will lose some • There are several types of sediment transport

  6. VI. River Engineering And Geomorphology For Transportation Design A.1. Basic Sediment Transport Theory c) Sediment Load • Types of Sediment load • Bed-material load • Wash load • Total load • Types of Sediment Movement • Sliding, rolling, saltation, suspension, solution

  7. Wash Load Wash Load Suspended Load T O T A L L O A D Suspended Bed-Material Load Bed-Material Load Bed Load Bed Load VI. River Engineering And Geomorphology For Transportation Design A.1. Basic Sediment Transport Theory c) Sediment Load: Classification Sediment Load Classification Schemes. (After SCS, 1983, Figure 4-2.)

  8. VI. River Engineering And Geomorphology For Transportation Design A.1. Basic Sediment Transport Theory d) Sediment Transport Equations Key References: • ADWR, 1985 – Design Manual for Engineering Analysis of Fluvial Systems • ASCE Publications • Sediment Transport Textbooks Variables: shown on next slide

  9. Some Variables Affecting River Behavior and River Characteristics That Can Change With Time Variable Variable Subgroup River Characteristics Hydrology Dominant Discharge Mean Annual Discharge Flow Duration Statistics Variation with Season Diversions and Storage Flow Source Channel Width Channel Depth Bank Height Bank Slope Bank Materials Bank Stratification Stream Pattern Bed Forms Meander Amplitude Meander Wavelength Sinuosity Floodplain Width Depth of Floodplain Flow Stream Terraces Channel Slope Aggradation Degradation Local Scour Bed Sediment Bar Sediment Pool & Riffle Sequence Armoring Bedrock Outcrop & Control Human Modifications Bank Protection Grade Control Roadway Crossings Utility Crossings Flow Width Depth Hydraulic Radius Friction Factor Velocity Topwidth Turbulence Temperature Transmission Losses Flood Characteristics Magnitude (peak) Duration (flashy?) Ratio of Peak to Base Flow Ratio of Rare to Frequent Floods Channel Capacity Losses Reservoirs/Flood Storage Mean Diameter Size Distribution Armoring Potential Cohesion Stratigraphy Streambed and Bank Sediment Climate Precipitation Type (snow?) Precipitation Intensity Precipitation Duration Seasonal Distribution Temperature/Evaporation Time Scale Engineering (short-term) Geologic (long-term) Channel Vegetation Vegetation Type Root Depth Root Density Branch/Foliage Density Trunk Pliability Growth Rate Germination Cycle Grazing Practices Watershed Characteristics Vegetation Cover Slope Drainage Area Elevation Geology Valley Slope Sediment yield Human Impacts – Urbanization Grazing Practices

  10. VI. River Engineering And Geomorphology For Transportation Design A.1. Basic Sediment Transport Theory d) Sediment Transport: Typical Equation • Zeller-Fullerton (Einstein/Meyer-Peter Muller) • Qs = W n1.77 V4.32 G0.45 Y-0.3 D 50-0.61 • Einstein’s suspended bed-material integration • Meyer-Peter, Muller bedload equation • Total bed-material discharge

  11. VI. River Engineering And Geomorphology For Transportation Design A.1. Basic Sediment Transport Theory d) Sediment Transport: Function Considerations • Type of Load • Variability • Spatial variation • Within channel, along stream • Geographic regions • Temporal • Flow rates during hydrograph • Seasonal • Initiation of Sediment Movement • Source Data for Empirical Equations

  12. VI. River Engineering And Geomorphology For Transportation Design A.1. Basic Sediment Transport Theory d) Sediment Transport: Yield • Definitions • Erosion: soil loss • Delivery: sediment yield • Factors Influencing Sediment Yield Climate, geology, vegetation, land use, topography, soils, runoff, channel conditions

  13. Sediment Yield Over Time

  14. VI. River Engineering And Geomorphology For Transportation Design A.1. Basic Sediment Transport Theory e) Sediment Yield: Methodologies • PSIAC • Planning Level • Average Annual Yield (Delivery) • Total Load • MUSLE/USLE/RUSLE • Soil Loss • Event Based Model (MUSLE/RUSLE) • Suspended Load

  15. VI. River Engineering And Geomorphology For Transportation Design A.1. Basic Sediment Transport Theory e) Sediment Yield: Methodologies • Reservoir Data • BUREC Equation (Design of Small Dams) • Total Load • Average Annual • Sediment Delivery • Many Regional Methodologies • Total Load • Average Annual • Sediment Delivery

  16. VI. River Engineering And Geomorphology For Transportation Design A.1. Basic Sediment Transport Theory e) Sediment Yield: Implementation Rules • Real World: Yield Varies Widely • Rules of Thumb • Average annual is poor predictor in Arizona • For larger watersheds, use transport methods • Sediment delivery is generally underestimated • 10% sediment concentration

  17. VI. River Engineering And Geomorphology For Transportation Design A.2. Scour and Erosion a) Types of Scour b) Scour Prediction c) Scour Equation d) Scour Mitigation

  18. VI. River Engineering And Geomorphology For Transportation Design A.2. Scour and Erosion a) Types of Scour • Short-Term Scour • Scour is “lowering of a channel bed.” City of Tucson Manual, p. 6.07 • “Short-term changes in channel bed elevation.” • Long-Term Scour • Lateral Erosion

  19. VI. River Engineering And Geomorphology For Transportation Design A.2. Scour and Erosion a) Types of Scour • Components of scour • General • Bend • Thalweg • Bed form • Local • [Long-term]

  20. Scour Components

  21. Scour Components

  22. 2 1 4 3 Example of Scour During a Flood San Juan River Near Bluff, UT

  23. Natural Local Scour

  24. Field Evidence of Scour Depth

  25. Local Scour (PHOTO)

  26. VI. River Engineering And Geomorphology For Transportation Design A.2. Scour and Erosion a) Types of Scour (CONTINUED) • Long-Term Scour (Degradation) • Time Scale • Causes • Geologic forces • Hydrologic regime change • Sediment supply • Slope adjustments • Change in erodibility • PROCESS-BASED

  27. VI. River Engineering And Geomorphology For Transportation Design A.2. Scour and Erosion b) Scour Prediction: Factors That Influence Scour • Hydraulics • Velocity, Depth, Slope • Bend angle • Obstructions • Piers, walls, natural – shape, width, encroachment • Other factors • Flow rate • Material characteristics

  28. VI. River Engineering And Geomorphology For Transportation Design A.2. Scour and Erosion c) Scour Equations: Estimating Long-Term Scour • Arroyo Evolution Model (AMAFCA Manual) • Equilibrium Slope (ADWR and COT Manuals) • State Standard 5-96 • Field and Historical Data

  29. Field Evidence Of Scour

  30. Field Evidence OfLong-Term Scour

  31. Field Evidence Of Long-Term Scour

  32. Field Evidence Of Long-Term Scour

  33. Field Evidence Of Long-Term Scour

  34. VI. River Engineering And Geomorphology For Transportation Design A.2. Scour and Erosion d) Scour Mitigation Measures • Resistant Materials • Non-Transportable Materials • Change Hydraulics • Monitor and Maintenance • References: • Highways in Riverine Environment • HEC-18/HEC-20

  35. VI. River Engineering And Geomorphology For Transportation Design A.3. Recurrence Intervals • Small flows • Large floods • Sediment transport • Scour • Lateral erosion • Peak vs. Volume

  36. VI. River Engineering And Geomorphology For Transportation Design B. Dynamic Nature of Streams in the Arid West 1. Humid vs. Arid Environments 2. Alluvial Streams 3. Ephemeral vs. Perennial Streams 4. Lateral Erosion, Avulsion and Meandering 5. Aggradation/Degradation 6. Flash Floods 7. Flood Ratios, Flood Volume 8. Alluvial Fans

  37. Humid Region Streams Perennial Low Flood Ratio Long Durations Small Floods Dominate Meandering Slow Erosion Fast Recovery Free Flowing Low Sediment Load Resistant to Change Arid Region Streams Ephemeral High Flood Ratio Short Durations Large Floods Dominate Braided, Straight Fast Erosion Slow Recovery Dams and Diversions High Sediment Load Sensitive to Change B.1. Humid vs. Arid Environments

  38. VI. River Engineering And Geomorphology For Transportation Design B.2. Alluvial Streams • Formed by Materials it Carries • Boundaries Subject to Transport • Balance Between Transport/Deposition • Change the Boundaries, Change the Stream

  39. Perennial Equilibrium Non-flood recovery Defined banks Well vegetated Environmental protection Ephemeral Non-equilibrium Work only in floods Poorly defined banks Poorly vegetated Less environmental protection B.3. Ephemeral vs. Perennial

  40. VI. River Engineering And Geomorphology For Transportation Design B.4. Lateral Erosion • Bank Erosion • Widening • Meandering • Avulsion

  41. Mechanisms Of Bank Erosion

  42. Bank Erosion

  43. Bank Erosion

  44. Bank Erosion

  45. Widening Of Braided Streams

  46. Meandering

  47. ChannelAvulsion

  48. VI. River Engineering And Geomorphology For Transportation Design B.5. Aggradation/Degradation • Aggradation – Bed Elevation Increases • Some braided streams • Alluvial fans • Obstructions • Degradation – Bed Elevation Decreases • Urban rivers • Encroachment • In-stream mining

  49. Field Techniques: Terraces/Headcuts

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