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Sec 2 rivers 2013
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- 2. What is ariver? • A river is a natural watercourse, usually freshwater, flowing towards the sea. • Without the hydrological cycle, rivers cannot be formed.
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- 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 – infiltratedwater 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
- 12. Waterfalls • Sudden, steepand vertical flow of fast- flowing water falling from great heights • Formed by river erosion
- 13. Niagara Falls onNiagara River, Canada and USA • formed by erosion of rock of different resistance
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- 15. Formation of Waterfalls •River flows across rocks of different resistance.
- 16. Formation of Waterfalls •River erodes the less resistant rock more rapidly • This cause a change in the gradient of the river course.
- 17. Formation of waterfalls •Over time, river plunges from a great height to hit the riverbed below, • This forms a waterfall.
- 18. Formation of plungepools • Repeated pounding of the river bed leads to a depression at the base of a waterfall • A plunge pool is formed.
- 19. Meander • A riverthat 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
- 20. Meander Note: Outer Bank =Concave Bank Note: Inner Bank = Concave Bank
- 21. River Cliff • Constant erosion (undercutting) erodesthe outer (concave) bank of the meander • forming a river cliff. Slip-off slope River cliff
- 22. Slip-off slope • Constant depositionat the outer (convex) bank deposits sediments • forming a slip- off slope. Slip-off slope River cliff
- 23. Floodplain Levees Floodplain Areas oflow-lying ground adjacent to a river at the lower course
- 25. Formation of Floodplainand Levee
- 26. Formation of Floodplainand Levee
- 27. Floodplain and Levee •During a heavy rainfall, river water overflows its bank. River loses speed as it encounters friction.
- 28. 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.
- 29. Formation of Floodplainand Levee
- 30. Floodplain and Levee •Overtime, the accumulation of fine sediments results in the formation of flat plains
- 31. • Coarser andheavier sediments are acculumated • Results in the formation of raised banks • Known as levees.
- 32. Formation of Delta •At the river mouth, a river loses energy and starts to deposit its sediments.
- 33. 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.
- 34. DistributariesDelta Over time, theaccumulated sediments that rise over the water and the distributaries form a delta.
- 35. Positive Impact ofriver • Rivers provide water for domestic purposes such as drinking, bathing and washing. • Rivers are a good source of food such as fish and prawns.
- 36. Positive Impact ofriver • Rivers are important waterways for transporting people and goods.
- 37. Negative Impact ofriver • River water overflows river bank cause lives to be lost and destroy property and crops. • .
- 38. Negative Impact ofriver • Consuming contaminated river water can cause people to fall ill • Eg contract diseases such as cholera.