Floodplains and levees

• What is a floodplain?

  A flat area of land surrounding a river, formed due to erosion and deposition.
• How is a floodplain formed by erosion?

  Lateral erosion will remove any kind of interlocking spurs creating a wide flat area around a river
• Under what conditions will a river deposit its load? (Give 2)

  • In flood conditions : when a river overflows onto its floodplain
  • Where there is shallow water : eg on the inside bend of meander
• What happens to river load during a flood?

  It is deposited in the floodplain
• Why is river load deposited in the flood plain during a flood?

  Because the river looses its speed and energy to transport materieal
• What is the deposited material called in the floodplain?

  Alluvium
• When will a river deposit its load?

  As the rivers velocity and ability to carry something decreases
• What are stratified river deposits?

  Where larger sediments are deposited first (they are heavier) and the smaller sediments are deposited last (they are lighter)
• Why are larger sediments deposited first and smaller sediments deposited last?

  Because the larger sediments are heavier so the river cannot carry them far, and the smaller sediments are light enough to be carried long distances
• What is a levee?

  A raised embankment that can be naturally formed due to stratified deposition on the sides of rivers after flooding
• How are levees formed?

  During a flood event when the river level rises above its bank, it deposits its largest sediments first (closest to bank) and smallest last (furthest from bank) then the river retreats back to normal levels