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IB Geography: Drainage Basins: Bradshaw Model
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IB Geography: Drainage Basins: Bradshaw Model

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  • 1. Bradshaw Model
  • 2. Upstream Downstream Discharge Occupied channel width Channel depth Average velocity Load quantity Load particle size Channel bed roughness Slope angle (gradient)
  • 3.  
  • 4.  
  • 5. Discharge
    • The volume of water that passes through a cross-section per unit of time.
    • Cubic metres per second.
    • Increases due to the input from a greater amount of the river basin above that point.
    Upstream Downstream Discharge Occupied channel width Channel depth Average velocity Load quantity Load particle size Channel bed roughness Slope angle (gradient)
  • 6. Occupied Channel Width
    • Distance across the actual channel, measured at the water surface.
    • Increases due to increase in discharge, input from tributaries etc.
    Upstream Downstream Discharge Occupied channel width Channel depth Average velocity Load quantity Load particle size Channel bed roughness Slope angle (gradient)
  • 7. Channel Depth
    • The height from the water surface to the stream bed.
    • Increase downstream as does the size of the river.
    • Line connecting places of greatest depth is called the thalweg .
    Upstream Downstream Discharge Occupied channel width Channel depth Average velocity Load quantity Load particle size Channel bed roughness Slope angle (gradient)
  • 8.  
  • 9. Average Velocity
    • Is the speed of water flow (distance travelled per unit of time).
    • Steady increase downstream.
    • How can it be so if the gradient is deceasing? (imagine 2 slides – one steep, one less so).
    Upstream Downstream Discharge Occupied channel width Channel depth Average velocity Load quantity Load particle size Channel bed roughness Slope angle (gradient)
  • 10.
    • Downstream the river becomes more efficient with proportionally less contact with its bed and banks.
    • Shown by higher Hydraulic Radius and lower Channel Bed Roughness.
  • 11.  
  • 12. Load Quantity
    • Capacity of the river.
    • Total load of all sizes.
    • Increases with discharge and velocity.
    Upstream Downstream Discharge Occupied channel width Channel depth Average velocity Load quantity Load particle size Channel bed roughness Slope angle (gradient)
  • 13.  
  • 14. Load Particle Size
    • Decreases considerably downstream.
    • Angular pebbles become more rounded.
    • Attrition.
    Upstream Downstream Discharge Occupied channel width Channel depth Average velocity Load quantity Load particle size Channel bed roughness Slope angle (gradient)
  • 15.  
  • 16.  
  • 17. Channel Bed Roughness
    • Decreases because of fewer stones etc, small load particle size etc.
    Upstream Downstream Discharge Occupied channel width Channel depth Average velocity Load quantity Load particle size Channel bed roughness Slope angle (gradient)
  • 18.  
  • 19.  
  • 20. Slope Angle
    • Decreases.
    Upstream Downstream Discharge Occupied channel width Channel depth Average velocity Load quantity Load particle size Channel bed roughness Slope angle (gradient)
  • 21.  
  • 22.