Rivers

• What is a River?

  A freshwater source flowing across the surface of land usually to the sea or another large body of water.
• What is a Drainage Basin?

  A Drainage Basin is an area of land drained by a river and its tributaries.
• What is a Confluence?

  The point at which two rivers meet.
• Describe a Tributary.

  A smaller river that joins the main channel.
• What is a Watershed?


  The high land that divides two drainage basins.
• How does Deposition occur in a River?


  Deposition occurs when a river loses its energy and velocity falls.
• When does Deposition occur in a River?


  When a river enters a shallower area (when it floods) this increases friction with the surface area and slows water down.
• What is the order of Deposition?


  )Boulder

  (Cobbles

  )Pebbles

  (Sand

  )Salt

  (Clay
• Give an example of Soft Engineering in Rivers.


  Plant more vegetation (afforestation)
• Give and example of Hard Engineering in Rivers.

  Dams and Reservoirs.
• Tributary

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

  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
• Suspension


  Transports the largest material
• Saltation

  Transports medium-sized material
• Traction

  Transports the smallest material
• Solution

  Transports dissolved material
• Upper course of river


  • Mainly vertical erosion
  • Steep gradient
  • Large boulders deposited
  • Large boulders rolled
• Middle course of river


  • Lots of deposition on inside of meanders
  • Begins to erode laterally
  • Deeper channels
  • Smaller particle size due to attrition
• Lower course of river

  • Lateral erosion continues
  • 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 called discharge
• Discharge increases downstream as tributaries join the main channel
• Velocity increases downstream, giving the river 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 and soft rock

  2. Soft rock eroded faster by hydraulic action, abrasion and solution

  3. Undercutting creates overhang of hard rock and plunge pool

  4. Overhang collapses

  5. Attrition acts on rocks in plunge pool

  6. Waterfall retreats upstream, leaving a gorge downstream
• Bed load

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

  Area of deposited material on inside of meander
• Gabions


  Metal cages filled with rocks, used to reinforce river banks
• Gabions are a form of hard engineering for river banks
• Disadvantages of gabions: 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
  • Can be expensive to install and maintain
  • Can be dangerous and unsightly when broken
• Formation of an oxbow lake


  1. Meander neck erodes over time until very narrow

  2. Flood enables water to break through meander neck

  3. Flooding subsides but most water follows new shorter channel

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

  5. Further deposition cuts off old meander completely creating oxbow lake
• Hard engineering strategies for rivers

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

  • Flood plain zoning
• Advantages of hard river engineering

  • Creates recreational/tourist value
  • Protects property and creates economic savings