Rivers

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  • Created by: megtucker
  • Created on: 15-05-16 15:18

Meanders

As the course of a river approaches its middle stages, it flows over flatter land

Lateral erosion deominates as the river swings in large bends known as meanders. Meanders constantly change their shape and position.

Water is pushed to the outer bend. This reduces friction with the bed and banks. So the river has more energy for transporting material which can erode the outside bank via abrasion

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Oxbow lakes

When the river floods it breaks through the thin meander neck and the river takes the easier straight course

This leaves the meander loop 'cut off' as an oxbow lake

Over time, the oxbow lake will become colonised by vegetation

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Floodplains

Floodplains and levees are both formed by deposition in time of river flood.

The river's load is composed of different sized particles.

When a river floods it deposits the heaviest of these particles first.

The larger particles, often pebble-sized, form the levees.

The sands, silts and clays are similarly sorted with the sands being deposited next, then the silts and finally the lightest clays.

Every time the river floods deposition bulids up the floodplain.

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Delta formation

Deltas are found at the mouth of a river, where the river meets the sea.

At this point the river is carrying too much load for the velocity and so depostion occurs/

The top of the delta is fairly flat surface.

This is where the coarset riverload is dropped.

The finer particles are carried into deeper water.

The silt is dropped to form a steepslope on the edge of the delta while the clay stays in suspension until it reaches the deeper water. 

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Upper course

  • Little water
  • Steep land
  • Waterfalls
  • Gorges
  • Tributairies
  • Large angular bedrock
  • Narrow and shallow river channels
  • Fast flowing
  • V-shaped valley
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Middle Course

  • Meanders
  • Smaller, rounder bedrock
  • Depens and widens 
  • Wider river channels 
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Lower course

  • Slow flowing
  • River mouth
  • Oxbow lakes
  • Sand and silt deposition
  • Delta
  • Levees
  • Flood plains
  • Flat land
  • Deepens and widens more
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River Environments

Factors:

  • Climate 
  • Rock type
  • Rock structure
  • Aspect
  • Geology
  • Slope / Gradient
  • Types of fow
  • Channel shape
  • Sea-level change 

Processes:

  • Erosion - abrasion, attrition, hydraulic action and solution
  • Transportation - traction, suspension, saltation and solution
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River Features

Erosional Features:

  • V-shaped valley
  • Interlocking spurs
  • Waterfalls
  • Gorges
  • Rapids
  • Potholes

Erosion and depositional features:

  • Meanders
  • Ox-bow lakes

Depositional features:

  • Deltas
  • Levees
  • Floodplains
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