River flow and channel types

• What are the three types of river flow?

  Laminar, turbulent, helicoidal
• What factors control the velocity of river flow?

  Gradient, volume, shape, roughness
• How does discharge affect a river's efficiency?

  It alters the water level in the channel
• What is required for laminar flow to occur?

  A smooth, straight channel
• Where is laminar flow most commonly found?

  In the lower course of rivers
• What human actions can force laminar flow?

  Interference with the river's natural state
• What characterizes turbulent flow?

  Higher velocities and complex channels
• What are eddies in turbulent flow?

  Erratic horizontal and vertical spirals of flow
• How do eddies affect the channel sides?

  They trap air and increase pressure
• What is the result of vertical eddies in a riverbed?

  They create hollows and lead to potholes
• What processes deepen the channel in turbulent flow?

  Cavitation and vertical abrasion
• What is helicoidal flow associated with?

  Horizontal eddies and corkscrew-like flow
• Where is helicoidal flow commonly found?

  On river bends with large material
• What is the thalweg in a river?

  Line of maximum velocity in a river
• How does the thalweg travel in meanders?

  From outside bank to inside bank
• What does the thalweg help transport?

  Material from outer to inner bank
• What is sinuosity in river channels?

  • Length of a stream channel ratio
  • Low sinuosity: value of 1 (straight)
  • High sinuosity: value above 4.4 (meandering)
• What are the three types of river channels?

  Straight, braided, meandering
• What characterizes straight channels?

  Sinuosity less than 1.5
• What causes braided channels to form?

  Divisions by islands or bars of material
• What happens to the thalweg in straight channels?

  It moves side to side
• What conditions lead to braided channels?

  Steep gradient and coarse material
• What happens when a river cannot transport its load?

  Deposited material forms stable islands
• What characterizes meandering channels?

  Wavelength depends on channel width and discharge
• What factors influence the wavelength of meanders?

  Channel width, discharge, nature of banks
• Where do meanders develop best?

  On shallow slopes near bankfull state
• What causes meandering to occur?

  Combination of slope, discharge, and load
• What role do sandbars play in meander development?

  They promote development in the channel
• How do meanders change over time?

  They migrate downstream and erode banks
• What happens to meanders as they become exaggerated?

  They lead to oxbow lakes formation
• What does it mean for a meander to become entrenched?

  It becomes ingrown or deeply cut into the landscape