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L1 River Processes


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L1 River Processes

  1. 1. River processes <ul><li>Hydrological cycle </li></ul><ul><li>The shape of river valleys changes as rivers flow downstream due to the dominance of different processes </li></ul><ul><li>Know the processes of erosion: hydraulic action, abrasion, attrition, solution, vertical and lateral erosion </li></ul><ul><li>Processes of transportation – traction, saltation, suspension and solution </li></ul><ul><li>Deposition and the reasons for it </li></ul><ul><li>Long profile </li></ul><ul><li>Changing cross profile </li></ul><ul><li>NT page 100 – 103 B&P pg 80-81, CGP pg 42-43 </li></ul>
  2. 2. The Water Cycle
  3. 4. Hydrological Cycle Key terms <ul><li>Evaporation </li></ul><ul><li>Transpiration </li></ul><ul><li>Condensation </li></ul><ul><li>Precipitation </li></ul><ul><li>Surface run off </li></ul><ul><li>Interception </li></ul><ul><li>Infiltration </li></ul><ul><li>Throughflow </li></ul><ul><li>Percolation </li></ul><ul><li>Groundwater flow </li></ul>
  4. 6. Your task <ul><li>Use Geog.1 page to make a copy of the hydrological diagram </li></ul><ul><li>Produce a table of definitions for each of the terms: </li></ul><ul><ul><ul><li>Evaporation </li></ul></ul></ul><ul><ul><ul><li>Transpiration </li></ul></ul></ul><ul><ul><ul><li>Condensation </li></ul></ul></ul><ul><ul><ul><li>Precipitation </li></ul></ul></ul><ul><ul><ul><li>Surface run off </li></ul></ul></ul><ul><ul><ul><li>Interception </li></ul></ul></ul><ul><ul><ul><li>Infiltration </li></ul></ul></ul><ul><ul><ul><li>Throughflow </li></ul></ul></ul><ul><ul><ul><li>Percolation </li></ul></ul></ul><ul><ul><ul><li>Groundwater flow </li></ul></ul></ul>
  5. 7. This is the same river… what is different about it in these two locations? Why? Afon Glaslyn, Wales
  6. 9. Erosion <ul><li>Total river energy depends on: </li></ul><ul><li>weight of water - the greater the weight of water the more energy the river will have due to gravity </li></ul><ul><li>The higher the source of the river the more energy it has </li></ul><ul><li>The steepness of the channel - this controls the speed of the river which determines how much kinetic energy it has ( the energy due to its movement) </li></ul><ul><li>Energy is lost through: </li></ul><ul><li>Friction </li></ul><ul><li>Turbulence within the flow of the river </li></ul>
  7. 10. Erosion 1 <ul><li>Abrasion </li></ul><ul><li>Scraping scouring of material (load) along the river bed </li></ul><ul><li>Effective in short turbulent periods when the river is full </li></ul><ul><li>Hydraulic action </li></ul><ul><li>Caused by the force of flowing water </li></ul><ul><li>Movement of loose unconsolidated material due to the frictional drag of moving water on sediment lying on channel bed </li></ul><ul><li>As speed of river increases the turbulent flow lifts the grains </li></ul><ul><li>Effective at removing loose material on outer banks of meanders leading to undercutting of river cliffs and collapse </li></ul>
  8. 11. Erosion 2 <ul><li>Corrosion (=solution) </li></ul><ul><li>most active on rocks that contain carbonates – limestone and chalk </li></ul><ul><li>Minerals in the rock are dissolved by weak acids in the river water and carried away in solution </li></ul><ul><li>Attrition </li></ul><ul><li>Reduction in size of particles within a river </li></ul><ul><li>Pebbles collide and become smoother, smaller and more rounded as they move along the river </li></ul>
  9. 12. Source: Juicy Geography website
  10. 14. River Transport <ul><li>River obtains its load from: </li></ul><ul><li>Material washed or fallen into the river from the valley sides </li></ul><ul><li>Material that has been eroded by the river itself </li></ul><ul><li>Traction </li></ul><ul><li>large stones and boulders are rolled along the bed. </li></ul><ul><li>Occurs during periods of high discharge </li></ul><ul><li>Saltation </li></ul><ul><li>small stones bounce along the channel bed </li></ul><ul><li>occurs during high energy conditions </li></ul><ul><li>small particles bounce up from the bed of the river only to fall back to the bottom again further downstream. As these particles land they dislodge other particles upwards causing more bouncing to take place </li></ul>
  11. 15. <ul><li>Suspension </li></ul><ul><li>very small particles of sand and silt are carried along by the flow of the river </li></ul><ul><li>material is carried and picked up due to turbulence </li></ul><ul><li>main cause of why rivers appear brown in colour </li></ul><ul><li>Solution </li></ul><ul><li>dissolved minerals are transported within the moving water </li></ul>
  12. 16. Deposition <ul><li>This is when the river dumps its load </li></ul><ul><li>It deposits the largest material first as this is heaviest </li></ul><ul><li>The smaller the load, the further it can be transported. </li></ul><ul><li>Large boulders are found in the upper course whereas smaller particles are found downstream </li></ul><ul><li>The river deposits its load when there is a fall in the speed of the water, or the volume of water is less </li></ul><ul><li>This occurs when the gradient changes at the foot of a mountain or when a river enters a lake or the sea. </li></ul>
  13. 17. The long profile of a river
  14. 18. The changing shape and characteristics of the channel
  15. 19. River Processes Terms <ul><li>Channel </li></ul><ul><li>Hydraulic action </li></ul><ul><li>Abrasion </li></ul><ul><li>Attrition </li></ul><ul><li>Solution </li></ul><ul><li>Load </li></ul><ul><li>Traction </li></ul><ul><li>Saltation </li></ul><ul><li>Suspension </li></ul><ul><li>Long profile </li></ul><ul><li>Cross profile </li></ul>