The work of rivers


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The work of rivers

  1. 1. The Work of RiversThe erosional work of streams/rivers carves and shapes the landscape through which they flow.3 functions of riversc. Erosiond. Transportatione. Deposition
  2. 2. The Work of RiversA. Erosion•A river may erode in 4 ways3.Abrasion/corrasionLoad carried by a river will grind against itsbed and sides.This process slowly wears the bed and sidesaway.
  3. 3. The Work of RiversA. Erosion2. AttritionWhen thrown against the sides and bed ofrivers, the load gets broken into smallerpieces.
  4. 4. The Work of RiversA. Erosion3. Hydraulic actionThe work of turbulence in the water.Running water causes friction in the joints ofrocks in a stream channelJoints may be enlargedLoosened fragments of rocks get swept away.
  5. 5. The Work of RiversA. Erosion4. Solution/CorrosionCertain minerals in rocks like limestone canbe dissolved in water.Rocks are then eroded.
  6. 6. The Work of RiversRelationship of velocity and sediment size toerosion
  7. 7. The Work of RiversB. Transportation (4 ways)
  8. 8. The Work of RiversB. Transportation (4 ways)•TractionLarger and heavier rocks/gravels are dragged orrolled along the bed.
  9. 9. The Work of RiversB. Transportation (4 ways)2. Saltation (saltim: by leaps/jumps)Smaller and lighter rock fragments and sandhop and bounce along the river bed.At times, the distinction between traction andsaltation may be difficult to determine.
  10. 10. The Work of RiversB. Transportation (4 ways)3. SuspensionSome of the load like silt and clay (fine-grained) will float along.They may only be deposited when streamvelocity reaches near 0.Turbulence in the water is crucial in holding aload of sediments.
  11. 11. The Work of RiversB. Transportation (4 ways)4. SolutionSome minerals are transported in dissolvedform.Especially chemical solution derived fromminerals like limestone or dolomite.
  12. 12. The Work of RiversC. DepositionA river will drop its load when:c. Volume decreasesd. Speed decreases
  13. 13. The Work of RiversC. DepositionA river’s volume decreases when• Dry season• Dry region with high evaporation• Presence of permeable rocks• Receding flood waters
  14. 14. The Work of RiversC. DepositionA river’s speed decreases when• It enters a lake• It enters a calm sea• It enters a gently sloping plain
  15. 15. The Work of RiversThe work of a river depends on its energyEnergy a function ofc. Volume of waterd. Speed of water flow (dependent on gradient)
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