Sec 2 rivers 2013

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Sec 2 rivers 2013

  1. 1. Rivers SEC ONE TEXTBOOK PAGE 101
  2. 2. What is a river? • A river is a natural watercourse, usually freshwater, flowing towards the sea. • Without the hydrological cycle, rivers cannot be formed.
  3. 3. HYDROLOGICal CYCLE
  4. 4. HYDROLOGICAL CYCLE SURFACE RUNOFF INFILTRATION CONDENSATION TRANSPIRATION AND EVAPORATION PRECIPITATION
  5. 5. HYDROLOGICAL CYCLE • Precipitation – water from clouds come to the Earth’s surface as rain, snow and hail • Transpiration – plants release water vapour into atmosphere
  6. 6. HYDROLOGICAL CYCLE •Surface Run-off – rain that falls on Earth’s surface flows over land • Condensation – water vapour rises, cools and changes into tiny water droplets
  7. 7. HYDROLOGICal CYCLE • Infiltration – water that soaks into the soil subsurface • Percolation – water moves further down into the underlying soil after infiltration
  8. 8. HYDROLOGICal CYCLE •Throughflow – infiltrated water that flows sideways in the soil subsurface • Interception – water is absorbed by trees
  9. 9. RIVER SYSTEM • Source – the starting point of a river • Mouth – the ending point of a river • Drainage Basin – The area drained by a river and its tributaries
  10. 10. RIVER SYSTEM •Confluence – the point at which a tributary joins the main river • Watershed – The boundary formed by the edges of the drainage basin
  11. 11. Waterfalls • Sudden, steep and vertical flow of fast- flowing water falling from great heights • Formed by river erosion
  12. 12. Niagara Falls on Niagara River, Canada and USA • formed by erosion of rock of different resistance
  13. 13. Formation of Waterfalls
  14. 14. Formation of Waterfalls • River flows across rocks of different resistance.
  15. 15. Formation of Waterfalls • River erodes the less resistant rock more rapidly • This cause a change in the gradient of the river course.
  16. 16. Formation of waterfalls • Over time, river plunges from a great height to hit the riverbed below, • This forms a waterfall.
  17. 17. Formation of plunge pools • Repeated pounding of the river bed leads to a depression at the base of a waterfall • A plunge pool is formed.
  18. 18. Meander • A river that follows a winding course, usually forming hoop-like bends. • River may meander because Lower gradient  lower speed  lower river energy river turns to avoid obstacles
  19. 19. Meander Note: Outer Bank = Concave Bank Note: Inner Bank = Concave Bank
  20. 20. River Cliff • Constant erosion (undercutting) erodes the outer (concave) bank of the meander • forming a river cliff. Slip-off slope River cliff
  21. 21. Slip-off slope • Constant deposition at the outer (convex) bank deposits sediments • forming a slip- off slope. Slip-off slope River cliff
  22. 22. Floodplain Levees Floodplain  Areas of low-lying ground adjacent to a river at the lower course
  23. 23. Formation of Floodplain and Levee
  24. 24. Formation of Floodplain and Levee
  25. 25. Floodplain and Levee • During a heavy rainfall, river water overflows its bank. River loses speed as it encounters friction.
  26. 26. Floodplain and Levee • Deposition occurs as river’s energy decreases. • Coarser and heavier sediments are deposited nearer to the river bank. • Finer and lighter sediments are deposited further away.
  27. 27. Formation of Floodplain and Levee
  28. 28. Floodplain and Levee • Overtime, the accumulation of fine sediments results in the formation of flat plains
  29. 29. • Coarser and heavier sediments are acculumated • Results in the formation of raised banks • Known as levees.
  30. 30. Formation of Delta • At the river mouth, a river loses energy and starts to deposit its sediments.
  31. 31. Formation of Delta • As the sediments build up, the mouth will be blocked • The river also split into several small channels called distributaries to flow to the sea.
  32. 32. DistributariesDelta Over time, the accumulated sediments that rise over the water and the distributaries form a delta.
  33. 33. Positive Impact of river • Rivers provide water for domestic purposes such as drinking, bathing and washing. • Rivers are a good source of food such as fish and prawns.
  34. 34. Positive Impact of river • Rivers are important waterways for transporting people and goods.
  35. 35. Negative Impact of river • River water overflows river bank cause lives to be lost and destroy property and crops. • .
  36. 36. Negative Impact of river • Consuming contaminated river water can cause people to fall ill • Eg contract diseases such as cholera.

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