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  • Insert cover image for Chapter 17 (p. 460)
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Transcript

  • 1. Chapter 17: Fluvial Processes and Landforms Physical Geography Ninth Edition Robert E. Gabler James. F. Petersen L. Michael Trapasso Dorothy Sack
  • 2. Fluvial Processes and Landforms
  • 3. Fluvial Processes and Landforms
    • Fluvial geomorphology
      • Study of flowing water as a land-shaping process
      • Stream
        • General term for natural, channelized flow
      • Interfluve
      • Floods
      • Long-term effects
  • 4. 17.1 Surface Runoff
    • Surface runoff
    • Infiltration capacity
    • Interception
    • Amount of runoff depends on:
      • Intensity and duration of storm
      • Surface features
      • Infiltration & evap.
      • Deep soil, soil type, slope
  • 5. 17.1 Surface Runoff
    • Surface runoff
      • Sheet wash (unchannelized)
        • Rills
        • Gullies
        • Ephemeral flow
      • Perennial flow
      • Intermittent flow
      • Base flow
  • 6. 17.2 The Stream System
    • Small perennial streams join to make larger perennial streams
      • Tributaries
      • Trunk stream
  • 7. 17.2 The Stream System
    • Drainage Basins (or watersheds)
      • Expanse of land from which it received runoff
      • Drainage area
      • Subbasins
      • Drainage divide
        • Continental divide
  • 8. 17.2 The Stream System
    • Drainage Basins (or watersheds)
      • Source
      • Stream order
        • First-order stream
        • Second-order stream
        • Third-order stream
        • Mississippi River (10 th order stream)
  • 9. 17.2 The Stream System
    • Drainage Basins (or watersheds)
      • Mouth
      • Exterior drainage
      • Interior drainage
      • Base level
  • 10. 17.2 The Stream System
    • Drainage Density and Patterns
      • Drainage density (D d )
        • Length of channels per unit area
        • Highly erodible and impermeable rocks tend to have higher D d
        • Slope and vegetation affects D d
  • 11. 17.2 The Stream System
    • Drainage Patterns
      • Dendritic
      • Trellis
      • Multiple channels
      • Centripetal
      • Rectangular
      • Deranged
  • 12. 17.2 The Stream System
    • Drainage Patterns
      • Transverse stream
      • Antecedent stream
        • Examples: Columbia River, Cumberland Gap
        • Also called superimposed
  • 13. 17.3 Stream Discharge
    • Amount of stream discharge (Q) depends on:
      • Recent weather
      • Drainage basin
        • Size
        • Relief
        • Climate
        • Vegetation
        • Rock type
        • Land-use
    • Q = Volume of water in a given cross section per unit of time
  • 14. 17.3 Stream Discharge Ten Largest Rivers of the World
  • 15. 17.3 Stream Discharge
    • Q = wdv
      • w = width
      • d = channel depth
      • v = average stream velocity
  • 16. 17.4 Stream Energy
    • Kinetic energy
    • Stream gradient
    • Channel roughness
      • Friction
      • 95% of energy is consumed in overcoming friction
  • 17. 17.4 Stream Energy
    • Stream load
    • Stream competence and Stream capacity
      • Both increase in response to small increases in velocity
      • If velocity doubles, sediment load may go up 6-8 times
    • Graded stream
  • 18. 17.5 Fluvial Processes
    • Stream Erosion
      • Fluvial erosion
      • Degradation
      • Aggradation
      • Corrosion
        • Also called solution
      • Hydraulic action
      • Turbulence
      • Plunge Pools
      • Q: Why do deep plunge pools form at the base of most waterfalls?
  • 19. 17.5 Fluvial Processes
    • Stream Erosion
      • Abrasion (more powerful than hydraulic)
      • Potholes
        • Originate below waterfalls, swirling rapids, structural weakness
      • Attrition
      • Headward erosion
  • 20. 17.5 Fluvial Processes
    • Stream Transportation
      • Solution
        • Minerals that are dissolved in water
      • Suspension
        • Finest solid particles carried
      • Saltation
        • Particles that are heavier and “bounce” along stream bed
  • 21. 17.5 Fluvial Processes
    • Stream Transportation
      • 3 Main Types of Stream Load:
        • Dissolved load (Ions of rock material in solution)
        • Suspended load (small clastic in suspension)
        • Bed load (large particles that saltate or move in traction along streambed)
      • Relative proportion of these vary with drainage
  • 22. 17.5 Fluvial Processes
    • Stream Transportation
      • Relative proportion of these vary with drainage
        • Humid regions
          • Higher rates of weathering
          • Suspended loads
          • Muddy river
          • e.g. Yellow River, China
        • Arid regions
          • Limited weathering
          • Bed load
  • 23. 17.5 Fluvial Processes
    • Stream Deposition
      • A decrease in stream velocity will reduce its load through deposition
      • Bar (accumulation of sediment, channel bend)
      • Alluvium (fluvial deposits)
        • Characteristic of sorting and/or rounding
  • 24. 17.5 Fluvial Processes
    • Stream Deposition
      • Natural levees
      • Floodplains
      • Vertical accretion
      • Lateral accretion
      • Q: What would the river floodwaters leave behind is flooded homes after the water recedes?
  • 25. 17.6 Channel Patterns
    • Straight channels
      • Exist for short distances
    • Braided river
      • Coarse sediment input is high
      • Downstream of glaciers
        • Yukon River, Canada
        • Brahmaputra River, Tibet
  • 26. 17.6 Channel Patterns
    • Meandering channels
      • Most common in humid climates (e.g. Missouri River)
      • May swing back and forth across valley
  • 27. 17.7 Land Sculpture by Streams
    • Idealized river
      • Gradient diminished downstream
      • Does not always occur
        • e.g. Mississippi River
    • Longitudinal Profile
      • Actual stream gradient from source to mouth
      • Upper, middle and lower
  • 28. 17.7 Land Sculpture by Streams
    • Features of the Upper Course
      • Usually flows on contact with bedrock
      • Steep gradient high above its base level
      • Erosion creates steep sided valley, gorge
      • This is called a V-shaped valley
  • 29. 17.7 Land Sculpture by Streams
    • Features of the Upper Course
      • Differential erosion
      • Many spill from lake to lake (e.g., Niagara Falls) or gorges
  • 30. 17.7 Land Sculpture by Streams
    • Features of the Middle Course
      • Moderate gradient
      • Moderately smooth channel
      • Cut bank
      • Point bar
      • Lateral migration
      • Floodplain good for farming but a flood hazard
  • 31. 17.7 Land Sculpture by Streams
    • Features of the Lower Course
      • Minimal gradient
      • Low stream energy
      • Lateral shifting of channel
      • Large depositional plain
      • Natural levees
      • Alluvial plain
  • 32. 17.7 Land Sculpture by Streams
    • Features of the Lower Course
      • Meander cut-offs
      • Oxbow lakes
      • Artificial levees
        • Raised level of channel (e.g. Yuba river, CA)
        • Flooding is a high risk
        • Yazoo streams
  • 33. 17.8 Deltas
    • Deltas
      • A stream flowing into a large body of water
      • Current expands in width, reducing flow velocity
      • Sediment may begin to settle out
      • Distinctive landform, a Delta forms
      • Slow going process
      • Distributaries
      • Example:
        • Ganges River
        • Mississippi River
  • 34. 17.8 Deltas
    • Deltas
  • 35. 17.9 Base-Level Changes and Tectonism
    • Base Level change
      • Due primarily from climate change (glaciers advancing, sea levels decrease)
      • Drop: downcutting and rejuvenated stream
      • Rise: deposition
    • New Uplift
      • Entrenched
  • 36. 17.9 Base-Level Changes and Tectonism
    • Stream Terraces
      • Older, higher valley floors preserved
      • Caused by varying:
        • Base-level
        • Stream equilibrium
        • Tectonism Q: How many terraces can you identify in this photo?
  • 37. 17.10 Stream Hazards
    • Flooding is a significant risk
      • Stream channel can withstand 1 or 2 year flow
      • 5, 10, 100 year flood overflows the channel
      • Olivehurst, CA (Feather River)
  • 38. 17.10 Stream Hazards
    • Stream Hydrograph
      • Record of changes in Q over time
      • Used to indicate how high/fast water level is
  • 39. 17.10 Stream Hazards
    • Stream Hydrograph
      • Rising limb
      • Peak flow
      • Receding limb
      • Recurrence interval
      • Q: Why would such a time lag occur between the rainfall and rise in the river?
  • 40. 17.10 Stream Hazards
    • Stream Hydrograph
      • Urbanization and suburbanization
        • Increases impermeable cover
        • Amount and rate of runoff increases
      • Q: What features of the urbanized landscape shown here enhance runoff?
  • 41. 17.11 The Importance of Surface Waters
    • Streams
      • Historical
        • Settlement and growth via Mississippi River
        • Exploration
        • Power for mills
      • Inexpensive transportation
      • Hydroelectricity
      • Irrigation water
      • Alluvial soils produce excellent farmland
      • Source of food and water
  • 42.
    • Reservoirs
      • Artificial lakes impounded by dams
      • Flood control
      • Store large amounts of water to make available during dry seasons or drought
        • Tennessee River
        • Lake Mead
        • Willamette River, OR
    17.11 The Importance of Surface Waters
  • 43.
    • Lakes
      • Inland water
      • Most hold surface water temporarily along stream systems
        • Lake Superior
        • Lake Victoria
      • Closed basins (salty)
        • Caspian Sea
        • Dead Sea
        • Great Salt Lake
    17.11 The Importance of Surface Waters
  • 44.
    • Lakes
      • Formation:
        • Most are products of glaciation
        • Rivers, groundwater, volcanism (e.g. Crater lake)
      • Sedimentation and other processes lead to the destruction of most lakes
      • Importance:
        • Recreation
        • Affect weather (moderate temperature/lake effect)
        • Water supply
        • Fishing
    17.11 The Importance of Surface Waters
  • 45. 17.12 Quantitative Fluvial Geomorphology
    • Objective analysis of fluvial systems
    • Used by scientists including:
      • Climatologists
      • Geomorphologists
      • Hydrologists
      • Soil scientist
    • Provide better understanding and improved prediction of water supply, floods, soil erosion, and pollution.
  • 46. Physical Geography End of Chapter 17: Fluvial Processes and Landforms