WATER ON THE LAND

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  • WATER ON THE LAND
    • A river is usually split into three courses: upper, middle and lower course.
      • Upper course: narrow valley with steep sides. Waterfalls and rapids. Velocity is low because high friction. Vertical corrosion in upper course.
      • Middle course: valley is wider with more gentle slopes. Greater velocity with lateral (and some vertical) erosion occurring. Meanders and oxbow lakes.
      • Lower course: wide valley, extremely gentle slopes. Velocity can be lower than middle course (low gradient). flood plains (with alluvium) and levees. Deposition key process.
    • Rivers can be looked at in either long profile or cross profile diagrams.
      • Long profile shows river from source to mouth. Shows the gradient if the river. Split into the three stages. Normal shape is concave and with a decreasing gradient.
      • Cross profile shows a view across the river and valley. For example, more of a V shape in the upper stage, but gets wider and flatter in lower stages.
    • Rivers erode in 4 main ways.
      • Hydraulic action: the force of the water against the rocks.
      • Corrosion: dissolving of the rocks through a chemical reaction.
      • Abrasion: when the river bashes against the bed with it's load.
      • Attrition:when the boulders and sediment bash into each other.
    • Rivers transport material in 4 ways.
      • Traction: when boulders roll along the bottom of the river bed.
      • Saltation: when boulders bounce along the bottom of the river bed.
      • Suspension: some material is light enough to be carried along in the current.
      • Solution: when the material dissolves in the water (for example calcium carbonate)
    • Features of rivers include waterfalls, gorges, meanders, levees and oxbow lakes.
      • Waterfalls forms due to differential erosion. Plunge pool created. Gorge formed as waterfall retreats.
      • Meanders are thought to form due to a series of riffles and pools (shallows and deeps). Cause uneven flow, therefore erosion and deposition occur, causing bend.
      • Oxbow lake forms when the loop of a meander becomes bigger and the neck smaller. A river cliff develops on outside, slip off slope on inside bend.
      • Levees are natural embankments that develop on the bank of the river when the river has flooded.As velocity decreases, it deposits material forming the levee.

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