Rivers

• Parts of the water (hydrological) cycle

  • Precipitation
  • Interception
  • Surface runoff
  • Infiltration
  • Transpiration
• Precipitation


  Moisture falling from clouds as rain, snow or hail
• Interception


  Vegetation prevent water reaching the ground
• Surface runoff


  Water flowing over surface of the land into rivers
• Infiltration


  Water absorbed into the soil from the ground
• Transpiration


  Water lost to the atmosphere from plants
• River discharge


  The volume of water that flows in a river
• Hydrographs


  Show discharge at a certain point in a river as it changes over time in relation to rainfall
• Hydrographs

  • Peak discharge is the highest discharge over a period of time
  • Lag time is the delay between peak rainfall and peak discharge
  • Rising limb is the increase in river discharge
  • Falling limb is the decrease in river discharge to normal level
• Formation of waterfalls (upper course)

  1. River flows over alternative types of rocks

  2. River erodes soft rock faster creating a step

  3. Further hydraulic action and abrasion form a plunge pool beneath

  4. Hard rock above is undercut leaving cap rock which collapses providing more material for erosion

  5. Waterfall retreats leaving steep sided gorge
• Formation of floodplains and levees (middle and lower course)

  1. Floodplains are created by migrating meanders creating a wide flat areas of land either side of the river

  2. When a river floods, fine silt/alluvium is deposited on the valley floor

  3. Closer to the river's banks, the heavier materials build up to form natural levees
• Estuary


  Where the river meets the sea, affected by tides, waves and rivers, main process is deposition
• River management schemes

  • Soft engineering: Afforestation, Wetland and flood storage areas, Floodplain zoning, River restoration
  • Hard engineering: Straightening Channel, Artificial Levees/embankments, Flood relief channels, Dams and reservoirs
• Upper Course


  • Steep narrow valleys
  • Mountains and hill
  • Small river channel
  • Lots of energy
  • Vertical erosion
• Middle Course


  • Gradient gets gentle, so the water has less energy and moves more slowly
  • The river will begin to erode laterally (sideways) making the river wider
  • Channel is wider and deeper
• Lower Course

  • Near the river's mouth, the river widens further and becomes flatter
  • Material transported is deposited
• How are ox-bow lakes created?

  1. Erosion of outer bank forms river cliff

  2. Deposition inner bank forms slip off slope

  3. Further hydraulic action and abrasion of outer banks, neck gets smaller

  4. Erosion breaks through neck, so river takes the fastest route, redirecting flow

  5. Evaporation and deposition cuts off main channel leaving an oxbow lake
• Physical causes of flooding

  • Prolonged heavy rainfall causes the ground to become saturated leading to runoff
  • Steep-sided valleys channels water to flow quickly into rivers causing greater discharge
  • Impermeable rocks causes surface runoff to increase river discharge
• Human causes of flooding

  • Urbanisation - Tarmac and concrete are impermeable. This prevents infiltration & causes surface runoff
  • Deforestation – when trees are removed, water flows rapidly into rivers
  • Agriculture – exposed soil can lead to surface runoff