Ch. 10 - Rivers

• River Basin

  The area drained by a river and its tributaries
• Watershed

  The high ground that separates two river basins
• River Course

  The journey the river takes to the sea
• Source

  Where the river begins, high up in the mountain
• Interlocking Spurs


  criss-crossing hills that form as the river erodes the softer rock
• Tributaries

  smaller rivers that join a larger river at a confluence
• Confluence

  the point where a tributary joins a larger river
• Oxbow lakes

  form when meanders are cut off
• Mouth of a River

  Where the river enters the sea
• Estuary

  The part of the river affected by tides. Sometimes a delta will be deposited here.
• Waterfalls

  vertical drops in the upper course of a river formed by vertical erosion
• Meanders

  bends that form in the middle course of a river due to greater lateral erosion
• Levees

  ridges of sediment deposited on the banks of the river in the lower course
• Hydraulic Action

  • Hydraulic action is erosion by the power of moving water.
  • The faster the water moves, the more it erodes.
  • The material that is eroded is carried along by the river and is called its load.
• Abrasion

  • Abrasion is a type of erosion caused by the river's load striking the bed and banks of the river.
  • The load is carried by the flowing water.
  • If the channel is made up of hard rock, it takes longer to erode.
• Attrition

  • Attrition happens when rock and stones carried by the river strike off each other.
  • As a result, they are worn down and become smooth and round.
• Solution

  • Solution happens when the water slowly dissolves parts of the river channel.
  • For example, limestone is dissolved when carbonic acid is in the water.
• Erosion

  Erosion is the wearing away of the bed and banks of a river.
• Transportation

  A river transports, or carries, its load as it moves towards the sea.

  Material is moved by a river in a number of ways, especially in times of flooding.
• Rolling (Traction)

  Larger, heavier particles, for example pebbles and stones, are rolled along the riverbed by the force of the water.
• Bouncing (Saltation)


  Smaller particles, for example small pebbles and sand, are bounced along the riverbed.
• Suspension

  The lightest particles of silt and clay are carried along while suspended in the water.
• Solution

  Salts are dissolved in the water and are invisible.
• Deposition

  Deposition occurs when a river drops its bedload. There are a few reasons for this.
• Causes of Deposition

  1. Decrease in Speed: When a river slows down, the river has less energy to carry the bedload. This can happen when a river enters a lake or the sea, and when the slope (gradient) becomes gentler.
• Causes of Deposition pt. 2

  2. Decrease in Volume: If the volume of water in the river decreases, bedload will be deposited.

  This can happen during summer, when there is less rainfall, or through drought caused by climate change.
• Causes of Deposition pt. 3

  3. Increase in Bedload: If the sediment in a river increases, the river may not have enough energy to carry it. For example, during a flood there is more bedload in the river. After the flood, this extra bedload cannot be carried, so the river deposits