Geography - Rivers



Factors needed;

  • Large bedload
  • Turbulent water flow
  • Upstream (GPE)
  • High Flow

1. Bedload is transported by traction. When flowing water encounters the bedload, it is forced over it and downcuts behind the bedload in swirling eddie currents. These currents erode the rivers bed and create small depressions in it

2. As depressions deepen, pebbles can become trapped in them. Vertical eddie currents drill into depressions making them more circular and deeper

3. Attrition rounds and smooths the pebbles caught in the hole and helps to reduce the size of the bedload

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1. Friction with the channel bed and banks causes turbulence in the water flow - this promotes the development of alternating bars of sediment along the channel

2. A helical flow is established and riffles (shallow areas) and pools (deeper areas) are created and extended. 

3. The outer bank is eroded as a result of a higher flow velocty, whereas deposition takes place on the inner bank and forms a point bar

  • Deposition of inner bend has less energy due to more friction, therefore it cannot transport load
  • Erosion occurs on outside of bend as water has more energy as it is deeper so there is less friction on the water
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Braided Stream

Factors needed;

  • Large amount of sediment
  • Variable flow
  • Sparse vegetation
  • Occurs when transported load contains alot of coarse material - sand and stone
  • Fluctuations in discharge levels, low river velocity and by the river loosing energy

1. During precipitation, streams move at higher velocity
2. Velocity carries lots of material
3. Water slows in wide sections with little downward slopes allowing sediment to settle
4. Sediment blocks stream causing lower velocity
5. Settled sediment forms sand banks
6. Streams overflow bank forming new channels
7. Streams split up until they meet at a certain point but they split again

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  • Occurs where a river is flowing very fast and looses energy ~(due to being at sea level) as it hits the sea - deposits material
  • Flocculation - water and salt water coagulate by chemical reaction (electrical charge) and become heavier and sink due to cohesion
  • Occur when rate of deposition exceeds the rate of sediment removal

Factors needed;

  • Sediment is large
  • Coast has a small tidal range and weak currents - limited wave action (mediterranean)

Topset beds = Large and heavier particles are the first to be deposited as river looses energy

Forset beds = Medium graded particles travel a little further before they are deposited

Bottomset beds = Very finest particles travel furthest into the lake before deposition

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