Managing Floods + Rivers

• Meanders

  A winding, looping curve in the course of a river on soft, flat flood plain
• The outside of a meander bend is …

  • Fast and erodes,
  • river cliff
• The inside of a meander bend is …

  • Slow and deposits,
  • slip off slope
• Oxbow lake formation

  1. Outer banks of a meander continue eroded through processes (hydraulic action and abrasion)

  2. Neck of the meander becomes narrower

  3. Two outer bends meet and the river cuts through usually during a flood event (when the energy in the river is at its highest)

  4. Water now takes its shortest route

  5. Deposition gradually seals off old meander bend forming a new straighter river channel
• Oxbow lake

  Old meander bend left isolated from main channel
• Oxbow lake evolution

  1. Old meander bend may fill up with sediment

  2. May gradually dry up

  3. When the water dries up, the feature left behind is known as a meander scar
• V-Shaped Valley

  Valleys eroded due to fast flowing water often found in upland areas
• V shaped valley formation

  • river erodes vertically down and it leaves behind valley sides shaped like a V
  • because as it erodes straight down it leaves very steep valley sides
  • that are then attacked by weathering processes such as freeze thaw and biological weathering.
  • This weakens the valley sides which may collapse or move down slope due to mass movement processes such as slumping
  • The river can then erode this material and move it away, leaving behind the characteristic V shape.
• Interlocking spurs

  series of ridges projecting out on alternate sides of a valley and around which a river winds its course.
• Interlocking spurs formation

  1. upper course of a river most erosion is vertically downwards. This creates steep sided, V shaped valleys
  2. The rivers aren't powerful enough to erode laterally (sideways) - they have to wind around the high hillsides that stick out into their paths on either side
  3. hillsides that interlock with each other as the river winds around them are called interlocking spurs
• Dams and reservoirs description

  A ealk built across a river which majes an artificial lake called a reservoir
• Dams and reservoirs advantages

  Boost tourism

  Provides hydroelectric power
• Dams and reservoirs disadvantages

  Alter the ecosystem

  Reduce sediment load

  Very expensive

  Can trigger earthquakes and landslides
• Channel straightening description

  A meander section of river is straightened and deepened
• Channel straightening advantages

  Improves navigation + trade

  Increases homeowner confidence

  (encourages people to invest in property)
• Channel straightening disadvantages

  - pushes MORE water downstream

  
  

  - not SOLVING problem, just moving it LOWER down the stream

  - Damaged ecosystems
• Embankments description

  An artificially raised bank
• Embankments advantages

  Cheap with a one-off cost

  Allows for flood water to be contained within the river.

  Creates walking routes
• Embankments disadvantages

  Looks unnatural.

  Cant fish or boat

  High maintenance
• Flood relief channels

  The floodwater flows into the relief channel and is taken either to an area where it can be absorbed, or re-enters the river further down its course.
• Flood relief channels advantages

  Removes excess water from the river channel to reduce flooding.
• Flood relief channels disadvantages

  Expensive to build.

  If water levels continue to rise, the relief channel may also flood.
• Flood warnings and preparation

  The environmental agency monitors rivers and issues warnings via newspapers, TV, radio and the internet when they are likely to flood so people can prepare.
• Flood warnings and preparations advantages

  People have time to protect their properties

  Possessions can be saved, fewer insurance claims
• Flood warnings and preparation disadvantages

  Some people may not be able to access the warnings.

  Flash floods may happen too quickly for a warning to be effective.

  They do not stop land from flooding - they just warn people that a flood is likely.
• flood plain zoning


  Only certain land has uses on flood plain

  Important buildings placed further away
• flood plain zoning advantages

  Reduces flood risk to important buildings

  Less damage caused
• flood plain zoning disadvantages

  - Not always possible to change existing land uses.

  - Planners have to decide what type of flood to plan for.
• Planting trees

  Planting trees near the river so they soak up the water
• Planting trees advantages

  Low cost option

  enhances the environment
• Planting trees disadvantages

  Less land is available for farming

  Trees take a while to grow
• River restoration

  Restoring rivers to more natural course by taking away embankments and restoring meanders. This allows rivers to flood but slows them down. However you may still need flood banks.
• River restoration advantages

  - Little maintenance

  - Creates habitats
• River restoration disadvantages

  Local flood risk can increase