river landforms 

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  • Created by: parker123
  • Created on: 29-12-17 15:36
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  • river landforms
    • meanders
      • formation of a meander.
        • fast flowing water
          • 1--water on the outside back causes lateral erosion through abrasion & hydraulic action, which undercuts the bank & forms a river cliff.
          • 2--helicoidal flow is a corkscrew movement. top part of flow hits the outside bank & erodes it. flow then 'corkscrews' to next bend. where deposits its load as friction slow the flow.
          • 3--fast flow causes vertical erosion on outside bend. this deepens river bed, resulting inn asymmetrical cross profile.
          • sand & pebbles are deposited on inside bank where current is slower, forming gentle slip-off slope.
      • characteristics of meanders
        • inside bank
          • curved, beach like feature.
          • gentle, convex slope
          • sediment consists of sand, gravel are smoothed and rounded by attrition
        • outside bank
          • steep drop down into river
          • unconsolidated material at base.
          • can be serval meters high
    • oxbow lakes
      • formation of oxbow lakes
        • 1-- an oxbow lake is a very small, horseshoe-shaped lake that is located serval metres from straight stretch of river. in lower/ middle courses.
        • 2-- meander loop becomes very large, only narrow ***** of land separates river channel (meander neck). neck becomes increasingly narrow.
        • 3--river floods , so main flow cuts across neck, this 'jshortcut'begins to break down banks & carve new channel.
        • 4--flood recede, so river reverts to normal meandering  channel. floods repeat and process happens again then bed channel becomes established by continued lateral & vertical erosion so becomes main channel.
        • 5--loop of old river is increasingly detached as no longer receiving water.
        • 6--flooding causes deposition on new river bed, this aids the detachment of old loop, marsh land colonise the area which widens the gap.
        • only far end of meander loop is left sometimes serval metres away from main channel. this is oxbow lake.
      • characteristics of a oxbow lake
        • inside - gentle slip-off slope into lake
        • marsh land colonises edges
        • outside- deepest waters, steep drop to lake
        • stagnant water evaporation reduces water.
    • levees
      • formation of levees
        • 1--levees are naturally raised banks found on wither or both sides of a river channel that is prone to flooding, in the lower/ middle course & landforms of fluvial deposition.
        • 2--when river burst its banks, friction with the land reduces velocity & causes deposition.
        • 3--heavy sediment is deposited closet to river. the size of sediment then becomes smaller with increased distance from river.
        • 4--with each successive flood the banks are built up higher
        • 5--now it many seem that levees make is more difficulty flood next time but no because over time the bed of river develops a thicker layer of sediment, which raises the river in its channel.
      • characteristic of levees
        • raised river banks (2-8m high)
        • composed of gravel,stones & alluvium
        • steep-sided but steeper sided on channel side.
        • grading of sediment with the coarsest  closet to river channel
    • flood plain
      • formation of a flood plain
        • 1--a flood palin is a large area of flat land either side of a river that is prone to flooding.
        • 2--the width of the flood plain is due to meander migration where outside bends erodes laterally into the edges of the valley.
        • 3--their position is gradually moving downstream, eventually this cuts a wider valley
        • 4--when floods have receded, the flood plain is slightly higher & more fertile due to deposits of silt caused by flooding.
        • 5--alluvial deposits also infill olds meander scars.
      • characteristics of a flood plain
        • reeds and marsh plants
        • river bluff (areas of slightly higher land along edge of flood plain)
        • meander scar, levees, oxbow lakes
        • layers of alluvium cover flood plain

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