Changing River Shape

• All rivers have long and cross profiles
• Long profile


  Shows the changes in the river gradient from the source to the mouth
• Typical long profile


  • Source is in an upland area
  • Upper course has steep, uneven surfaces
  • Middle course gradient decreases
  • Lower section gradient decreases further until almost flat
• Cross profile


  Cross-sections from one bank to another
• Upper course characteristics


  • Shallow
  • Steep valley sides
  • Narrow
  • Low velocity
  • Large bedload
  • Rough channel bed
  • High levels of friction
  • Vertical erosion
• Middle course characteristics


  • Deeper than upper course channel
  • Gentle valley sides
  • Wider than upper course channel
  • Greater velocity than upper course channel
  • Material in river decreases in size
  • Smoother channel bed
  • Lower levels of friction than upper course channel
  • Lateral erosion
• Lower course characteristics


  • Deeper than middle course channel
  • Flat floodplains
  • Wider than middle course channel
  • Greater velocity than the middle course channel (apart from as the river enters the mouth)
  • Material carried mainly sediment and alluvium
  • Smooth channel bed
  • Lowest friction
  • Deposition is dominant
• Valley shape and river shape are not the same thing
• Erosion


  The wearing away of surfaces
• Erosion processes


  • Hydraulic action
  • Abrasion
  • Attrition
  • Corrosion (solution)
• Vertical erosion


  Dominant in the upper course, increases the depth of the river and valley
• Lateral erosion


  Dominant in the middle and lower course, increases the width of the river and valley
• Transportation processes


  • Traction
  • Saltation
  • Suspension
  • Solution
• Deposition


  When a river does not have enough energy to carry its material and it drops it
• Bedload


  The heaviest material deposited first
• Alluvium

  The lighter materials, gravel, sand and silt, carried further downstream