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  • 1. Rivers SEC ONE TEXTBOOK PAGE 101
  • 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.
  • 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. 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. HYDROLOGICal CYCLE • Infiltration – water that soaks into the soil subsurface • Percolation – water moves further down into the underlying soil after infiltration
  • 8. HYDROLOGICal CYCLE •Throughflow – infiltrated water that flows sideways in the soil subsurface • Interception – water is absorbed by trees
  • 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. 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. Waterfalls • Sudden, steep and vertical flow of fast- flowing water falling from great heights • Formed by river erosion
  • 12. Niagara Falls on Niagara River, Canada and USA • formed by erosion of rock of different resistance
  • 13. Formation of Waterfalls
  • 14. Formation of Waterfalls • River flows across rocks of different resistance.
  • 15. Formation of Waterfalls • River erodes the less resistant rock more rapidly • This cause a change in the gradient of the river course.
  • 16. Formation of waterfalls • Over time, river plunges from a great height to hit the riverbed below, • This forms a waterfall.
  • 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. 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. Meander Note: Outer Bank = Concave Bank Note: Inner Bank = Concave Bank
  • 20. River Cliff • Constant erosion (undercutting) erodes the outer (concave) bank of the meander • forming a river cliff. Slip-off slope River cliff
  • 21. Slip-off slope • Constant deposition at the outer (convex) bank deposits sediments • forming a slip- off slope. Slip-off slope River cliff
  • 22. Floodplain Levees Floodplain  Areas of low-lying ground adjacent to a river at the lower course
  • 23. Formation of Floodplain and Levee
  • 24. Formation of Floodplain and Levee
  • 25. Floodplain and Levee • During a heavy rainfall, river water overflows its bank. River loses speed as it encounters friction.
  • 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. Formation of Floodplain and Levee
  • 28. Floodplain and Levee • Overtime, the accumulation of fine sediments results in the formation of flat plains
  • 29. • Coarser and heavier sediments are acculumated • Results in the formation of raised banks • Known as levees.
  • 30. Formation of Delta • At the river mouth, a river loses energy and starts to deposit its sediments.
  • 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. DistributariesDelta Over time, the accumulated sediments that rise over the water and the distributaries form a delta.
  • 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. Positive Impact of river • Rivers are important waterways for transporting people and goods.
  • 35. Negative Impact of river • River water overflows river bank cause lives to be lost and destroy property and crops. • .
  • 36. Negative Impact of river • Consuming contaminated river water can cause people to fall ill • Eg contract diseases such as cholera.