RIVERS

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Waterfall and Gorges

 

  • The soft rock is eroded quicker than the hard rock and this creates a step.
  • As erosion continues, the hard rock is undercut forming an overhang.
  •  Abrasion and hydraulic actionerode to create a plunge pool.
  • Over time this gets bigger, increasing the size of the overhang until the hard rock is no longer supported and it collapses.
  • This process continues and the waterfall retreats upstream.
  • A steep-sided valley is left where the waterfall once was. This is called a gorge
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Interlocking spurs

  • In the upper course there is more vertical erosion 
  • The river cuts down into the valley. If there are areas of hard rock which are harder to erode, the river will bend around it.
  • This creates interlocking spurs of land which link together like the teeth of a zip.
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Meanders

  • As a river goes around a bend, most of the water is pushed towards the outside, this causes increased speed and therefore increased erosion (through hydraulic action and abrasion).
  • The lateral erosion on the outside bend causes undercutting of the bank to form a river cliff
  • Water on the inner bend is slower, causing the water to slow down and deposit the eroded material, creating a gentle slope.
  • The build-up of deposited sediment is known as a slid-off-slope(or sometimes river beach).
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Oxbow lake

  • Due to erosion on the outside of a bend and deposition on the inside, the shape of a meander will change over a period of time
  • Erosion narrows the neck of the land within the meander and as the process continues, the meanders move closer together
  • When there is a very high discharge(usually during a flood), the river cuts across the neck, taking a new, straighter and shorter route
  • Deposition will occur to cut off the original meander, leaving a horseshoe-shaped oxbow lake
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Flood plains

  • They form due to both erosion and deposition
  •  Erosionremoves any interlocking spurs, creating a wide, flat area on either side of the river
  • During a flood, material being carried by the river is deposited (as the river loses its speed and energy to transport material)
  • Over time, the height of the floodplain increases as material is deposited on either side of the river
  • Floodplains are often agricultural land, as the area is very fertile because it's made up of alluvium (deposited silt from a river flood)
  • The floodplain is often a wide, flat area caused by meanders shifting along the valley
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Levees

  • Levees occur in the lower course of a river when there is an increase in the volume of water flowing downstream and flooding occurs.
  • Sediment that has been eroded further upstream is transported downstream.
  • When the river floods, the sediment spreads out across the floodplain.
  • When a flood occurs, the river loses energy. The largest material is deposited first on the sides of the river banks and smaller material further away.
  • After many floods, the sediment builds up to increase the height of the river banks, meaning that the channel can carry more water (a greater discharge) and flooding is less likely to occur in the future.
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Deltas

Deltas are found at the mouth of a river, as it enters a sea or lake. The sediments the river has been transporting by bedloadand suspended load are deposited as velocity decreases as the river flows into the sea. Deltas are usually made up of three types of deposit:

  • The larger and heavier sediments are the first to be deposited as the river loses its energy. These form the topset beds.
  • Medium-sized sediments travel little further before they are deposited, forming the forset beds
  • The finest sediments travel furthest into the lake before deposition and form the bottomset beds
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River Tees- (case study)

The River Tees is located in the north of England. The source of the River Tees is located in the Pennines and it flows east to its mouth where the river joins the North Sea.

Upper course:

  • The upper coursehas hard impermeable rocks. Here, vertical erosion has formed a V-shaped valley.
  • High Force, the UK's largest waterfall,at 21 metres high, is located in the upper course. An area of hard rock, called Whin Sill (or Whinstone), is located above a layer of soft rocks (sandstone and shale) and together they create this impressive waterfall.
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River Tees 2

Middle course:

  • As the River Tees starts to erode sideways (lateral erosion), it forms meanders,these can be identified in the middle coursenear Barnard Castle.

Lower course:

  • Near Yarm, the meanders in the lower courseare much larger, and oxbow lakeshave formed. In this area there are also leveeswhich have formed when the river has flooded.
  • The River Tees has a very large estuarywith mudflats and sandbanks which supports wildlife in the area. Sites such as Seal Sands are protected areas.
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