Unit 1 topic 2

• 1. Level Geography, Unit 1 - Hydrology and Fluvial Geomorphology, Unit 1.2 - Rivers and Flooding, X923

  
• Unit Objectives


  On completion of this topic, you should be able to:
• Describe and explain the main types of river processes of:


  1. Erosion (abrasion/corrasion, solution, cavitation, hydraulic action)

  2. Load transport (traction, saltation, suspension and solution)

  3. Deposition and sedimentation
• Describe and understand where and when erosion, transportation and deposition operate


  (knowledge of the hjülstrom curve)
• Characteristics of river flow

  • Velocity and discharge
• Describe the patterns of river flow


  Laminar, turbulent and helicoidal

  
• Thalweg


  Reasons for differences in flow patterns
• Draw, describe and understand the types of channel patterns in a plan

  Straight, braided, meandering
• Draw, describe and understand in cross-section describe and explain a range of features:


  Inside the channel, including meander (river cliffs, point bars, oxbow lakes), riffle and pool sequences

  
• Draw, describe and understand landforms along a river


  Waterfalls, gorges, bluffs, levée, floodplains, and deltas

  
• Understand the following about floods and flooding:


  Causes; impacts, predicting flood risk and recurrence intervals, methods of preventing and ameliorating floods through: forecasts and warnings; hard engineering (dams, straightening, levées, and diversion spillways; soft engineering
• Case studies required for this topic are: You need to know about a recent river flood event and have details about the causes of the flood (human and physical causes), the impact on people, the impact on the environment evaluating the attempts to reduce the impact of the flood.
• Long profile of a river


  A diagram showing the river's height and steepness, showing changes in gradient from source to mouth

  
• Changes along the long profile


  • Gradient changes from steep to gentle, size of sediment decreases, discharge (amount of water flowing) increases, velocity (speed) increases
• Cross profile of a river


  A diagram showing the river's width and depth, highlighting the channel shape and valley shape

  
• How a river valley changes as you go downstream


  Steep sided V-shaped valley in upper course, wider valley with floodplain in middle course, very wide and flat with large floodplain in lower course

  
• Vertical erosion


  Downwards erosion, erodes the bed and deepens the river, occurs mainly in the upper course
• Lateral erosion


  Sideways erosion, erodes the banks and widens the river, occurs mainly in the lower course
• River processes


  • Vertical erosion
  • Lateral erosion
  • Attrition
  • Solution
  • Hydraulic action
  • Abrasion
• Abrasion


  Rocks collide and scrape along the bed and banks wearing it away
• Attrition


  Rocks collide with each other, they become smaller and rounder
• Hydraulic action


  Water is forced into cracks which makes them larger
• Solution


  Acids in the water dissolve rock (especially limestone)
• Transportation processes


  • Solution
  • Saltation
  • Traction
  • Suspension
• Saltation


  Small pebbles bounce along the riverbed
• Suspension


  Small particles are carried in the river water
• Solution


  Dissolved materials are carried in the river water
• Deposition


  When a river drops the eroded material it is transporting, happens when a river slows down (loses velocity)
• Hjülstrom curve


  An area graph which shows the relationship between sediment size, erosion, transportation and deposition
• Types of river flow


  • Laminar
  • Turbulent
  • Helicoidal
• Laminar flow


  Smooth, straight channel with a low velocity, water flows in sheets or laminae parallel to the channel bed
• Turbulent flow


  Disorderly flow that occurs when there are higher velocities and an increase in bed roughness, associated with hydraulic action (cavitation)
• Helicoidal flow


  A 'corkscrewing' motion, associated with alternating pools and riffles in the channel bed where the river carries large amounts of material
• Types of river channels


  • Straight
  • Meandering
  • Braided
• Activity One: Study the photograph and


  Name the type of river channel shown

  2. Draw a cross-section of the river channel and label the main features

  3. Suggest reasons for the formation of the channel types

  4. Explain how turbulent flow causes erosion in river channels

  
• Erosional upper course landforms


  • Steep-sided V-shaped valleys
  • Interlocking spurs
  • Rapids
  • Waterfalls
  • Gorges

  
• How interlocking spurs form


  Vertical erosion caused the river to cut down, creating a steep valley. Weathering on the sides widens the valley into a V Shape. The river winds around the areas of hard rock, resulting in projections of highlands on alternate sides of the valley.

  
• How waterfalls and gorges form


  Soft rock is eroded quicker than hard rock. Abrasion and hydraulic action undercut the hard cap rock above, causing it to collapse. The collapsed material erodes the river's bed by abrasion, forming a deep plunge pool. This process continues causing the waterfall to retreat upstream, leaving a steep-sided gorge downstream.
• Activity Two: Study the photograph and


  Name the landform A shown

  2. Describe the landscape features

  3. Explain how the landscape features have formed

  
• Middle course river features


  • Wider, shallower valleys
  • Meanders
  • Oxbow lakes