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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

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