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L4 Levees And Floodplains
1. levees and flood plains. To explain the causes of river deposition To describe and explain the formation of levees To describe and explain the formation of floodplains NT pg 106 B&P pg 85 CGP pg44
9. What are they? Often several metres higher than the river’s floodplain, they are high natural embankments of silt situated close to the river channel. Where are they found? They are most commonly found in the lower course of a river where there is a floodplain, along rivers that flood periodically, have a slow flow and carry large amounts of load.
12. A broken artificial levee on the Mississippi river, USA A broken natural levee in New Orleans, USA Both natural and artificial levees can be broken by natural force.
13. How are they formed? The river before the flood at regular height. The river whilst flooding
14. There is an increase in friction between the water leaving the channel and the floodplain when a river overflows. The water is shallower on the river banks and valley floor, thus this is why deposition of load occurs. After repeated flooding causing the deposition of silt onto the banks, this eventually settles which over time builds up to form a levee. The coarser material is deposited first, and is positioned closer to the river. After repeated flooding, the river bed and levees are raised due to the constant process of the deposition of silt. Over time, this eventually causes the river to rise above level of flood plain. This is called an ‘aggraded bed’.
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