Rivers

• Green spaces to protect and enhance wildlife
• Type of erosion


  River Landscapes
• Hydric action


  The force of the water on the bed and banks causes material to be removed and worn away
• Abrasion


  The material carried by the river rubs against the river beds and banks, wearing them away. This causes the most erosion in rivers
• Attrition


  The load that is carried in the river collides and wears down into smaller, smoother pieces of sediment
• Solution


  Some rock minerals dissolve in the slightly acidic river water e.g. limestone and chalk are most affected
• Types of transportation


  • Traction: The large boulders and rocks are rolled along the river bed
  • Saltation: The small pebbles and stones are bounced along the river bed
  • Suspension: The fine light material such as silt is carried along in the water
  • Solution: Minerals which have been dissolved in the water are carried along in solution
• Types of mass movement

  • Sliding: Saturated rock slides down unsaturated rock along a flat slip plane. It occurs quickly.
  • Slumping: Saturated rock slides down unsaturated rock along a concave slip plane. It occurs slower than sliding.
  • Soil creep: Individual particles of soil move slowly down a slope due to expansion and contraction.
• Types of weathering


  • Biological: Animals and the roots of plants penetrate cracks in rocks on the river valley causing them to split apart
  • Chemical: Slightly acidic rainwater reacts with minerals in the rocks and dissolves them
  • Mechanical (Freeze-thaw): Rainwater enters cracks in the rock. Pressure is continually exerted on the rock as water freezes during cold temperatures (expanding in volume by 9%) and then melts. Eventually the crack widens and blocks of rock break off.
• Deposition occurs when material (load) is put down by a river. This occurs when the river's energy decreases and it can no longer transport the sediment.
• River Teesdale


  Located in north-east England, it flows eastwards from the source in the Pennines to the mouth where it flows into the North Sea
• Changes in river characteristics downstream

  • Gradient: Decreases
  • Discharge: Increases
  • Velocity: Increases
  • Width: Increases
  • Depth: Increases
• In the middle and lower sections, floodplains and levees also form as a result of repeated flooding of the areas
• Deposition


  • The dropping off of sediment in a low energy environment
  • Floodplains: A flat area of land either side of a river in its lower course
  • Levees: Natural embankments of sediments formed along the banks of rivers that carry large loads and flood
  • Estuaries: Where the river meets the sea, large deposits of sediment form mudflats and salt marshes
• Storm hydrograph


  Shows changes in the discharge of a river caused by a rainstorm
• Components of a storm hydrograph

  • Rainfall (mm)
  • Discharge (cumecs)
  • Rising limb
  • Peak flow
  • Falling limb
  • Lag time
• Flood management methods


  • Hard engineering: Embankments, Channelisation, Dams and Reservoirs, Flood relief channels
  • Soft engineering: Changing land use, Flood warning and preparation, Floodplaining, River restoration
• Hard engineering


  • Structures built to defend areas from floodwaters
  • Advantages: Stop water from spreading, Cheap and low maintenance, Allow water to flow more quickly, Can store large volumes of water, Can be used for recreation, Long-lasting
  • Disadvantages: Flood water may go over the top, Can burst under pressure, Dredging needs to be done yearly, Concrete lining looks unnatural, Increases flood risk downstream, Expensive to build, Disrupts natural processes
• Soft engineering


  • Adaptations to flood risks and allowing natural processes to deal with rainwater
  • Advantages: Cheap, look more natural, allow natural processes, provide habitats
  • Disadvantages: Take longer to implement, may not be suitable for all areas, can restrict access