Rivers geo

• Tributary


  A small stream feeding into the main river channel
• Drainage basin


  Also known as the catchment area, the area of land that is drained by one river and its tributaries
• Confluence


  Where two or more rivers join together
• Source


  Where the river starts its journey, typically in highland areas
• Mouth


  Where the river reaches the sea
• Watershed


  The area of highland that separates two drainage basins
• Processes of erosion


  • Hydraulic action
  • Abrasion
  • Attrition
  • Solution
• Hydraulic action


  The force of water hitting the riverbank and squeezing air into cracks, weakening the rocks
• Abrasion


  The force of sediment and rocks in the water scratching and scraping away at the riverbank and bed
• Attrition


  Rocks hitting each other and breaking into smaller rocks as they are transported
• Solution


  Chemical reaction between river water and minerals in rocks, causing the rocks to dissolve
• Processes of transportation


  • Traction
  • Saltation
  • Suspension
  • Solution
• Traction


  Heavy rocks and boulders rolled along the riverbed
• Saltation


  Small stones and pebbles bouncing on the riverbed
• Suspension


  Very small particles of sand or clay suspended in the water
• Solution

  Material dissolved in the water, invisible and not colouring the water
• Features of the upper course

  • Mainly vertical erosion
  • Steep gradient
  • Large boulders deposited
  • Large boulders rolled
• Features of the middle course

  • Lots of deposition on inside of meanders
  • Begins to erode laterally
  • Deeper channels, greater discharge and volume
  • Concave gradient, smaller particle size due to attrition
• Features of the lower course

  • Lateral erosion continuing
  • Fine sediment dropped, building up floodplain
  • Large load but tiny particles
  • Greatest discharge and velocity, almost flat gradient
• The volume of water passing through a river at a given point is not the same as velocity
• The river's volume increases downstream as tributaries join the main channel
• The river's velocity increases downstream, giving it greater power to erode
• Lateral erosion broadens out the river valley in the middle and lower course
• Formation of a waterfall

  1. River flows over hard rock and soft rock

  2. Waterfall begins to form as soft rock eroded faster by hydraulic action, abrasion and solution

  3. Undercutting creates overhang of hard rock and plunge pool

  4. Overhang collapses, attrition acts on rocks in plunge pool

  5. Waterfall retreats upstream, leaving gorge downstream
• Bed load


  Rocks and rock fragments carried along by river water
• Slip-off slope


  Area of deposited material on inside of meander, also called a point bar
• Gabions


  Metal cages filled with rocks, used to reinforce riverbanks
• Gabions are a form of hard engineering for river banks
• Disadvantages of using gabions

  • Can be expensive to install and maintain
  • Can be dangerous
  • Unsightly when broken
• Gabions


  Metal cages filled with rocks used to reinforce river banks
• Gabions


  • Used in hard engineering to reinforce river banks
  • Also seen at the coast
• Formation of an oxbow lake

  1. Meander neck erodes over time until very narrow

  2. Flood occurs, enabling water to break through meander neck

  3. Deposition occurs at side of new channel, reducing flow around old meander

  4. Further deposition cuts off old meander, creating oxbow lake
• Hard engineering strategies for river management

  • Dams and reservoirs
  • Floodgates
  • Embankments
  • Dredging channels
• Soft engineering strategies for river management

  • Flood plain zoning
• Hard river engineering


  • Advantages: Creates recreational/tourist value, Protects property
  • Disadvantages: Expensive to install and maintain, Environmentally damaging, Unpopular appearance, Downstream problems
• Interlocking spurs are found in the upper course of rivers
• The inside of a river bend has the lowest velocity
• Hydrograph


  Chart showing the relationship between precipitation and discharge
• Lag time is the difference between peak rainfall and peak discharge
• Features found at the mouth of the River Ganges

  • Delta
  • Braided channels