rivers

• Lower course


  1. Gentle gradient

  2. Very wide and almost flat

  3. Very wide and deep channel
• Interlocking spurs


  • In the upper course of a river
  • Most of the erosion is vertical
  • Creates steep sided v-shaped valleys
  • Rivers lack the power to erode laterally sideways
  • They have enough power to wind around high heel sites that stick out into their paths on either side
  • The hillsides that interlock with each other like a zip as the river winds around them are called interlocking spurs
• Types of erosion


  • Vertical erosion
  • Lateral erosion
• Vertical erosion


  • Deepens the river valley and channel making it v-shaped
  • Dominant in the upper course of the river
  • High turbulence causes the rough and angular particles to be scraped along the riverbed causing intense downwards erosion
• Lateral erosion


  • Widens the river valley and channel during the formation of meanders
  • Dominant in the middle and lower courses of the river
• Vertical and lateral erosion can happen at the same time but one is usually dominant
• Hard engineering


  Man-made structures built to control the flow of rivers and reduce flooding
• Soft engineering


  Schemes set up using knowledge of river and its processes to reduce the effects of flooding
• Hard engineering methods


  • Dams and reservoirs
  • Channel straightening
  • Embankments
  • Flood relief channels
• Dams


  Barriers built across the river usually in the upper course
• Reservoir


  Artificial lake formed behind the dam
• Dams and reservoirs


  • Store water
  • Control water flow
  • Prevent floods happening downstream
  • Expensive to build and maintain
  • Cause material deposition in reservoir, making farmland less fertile
• Channel straightening


  Removing meanders by building straighter artificial channels
• Channel straightening


  • Water leaves quickly, limiting flood risk
  • Flood risk may happen downstream instead
• Embankments


  Raised walls built along riverbanks
• Embankments


  • River can hold more water, reducing frequent floods
  • Expensive
  • Severe risk of flooding
• Flood relief channels


  Channels built to divert water around built up areas or to divert excess water if river levels get too high
• Flood relief channels


  • Gates control release of water
  • Increased discharge where channel rejoins river
• Soft engineering strategies


  • Flood warning and preparation
  • Flood planned zoning
  • Planting trees
  • River restoration
• Flood warning and preparation


  Environmental agency issues flood warnings, buildings are modified, residents can prepare sandbags and floodboards
• Flood warning and preparation


  • Gives people time to move possessions, reduces flood impact
  • Doesn't prevent the flood
  • Modifying buildings is expensive
• Flood planned zoning


  Restrictions on buildings on different parts of a floodplain that are likely to be affected by a flood
• Flood planned zoning


  • Reduces flood risk and impact
  • Limits expansion of urban areas
• Planting trees


  Planting trees in the river valley to intercept rainwater and prevent discharge and flood risk downstream
• Planting trees


  • Prevents discharge, reduces flood risk
  • Land not available for farming and buildings
• River restoration


  Making the river more natural by removing man-made levees so the floodplain can flood naturally
• River restoration


  • Reduces discharge and flood risk
  • Little maintenance needed
  • Local flood risk can increase if nothing else is done