Levées and Floodplains

Look at the image below which shows the part of the floodplain of the River Dee, Wales. What land uses can you see?

A floodplain is a wide, flat area of land on either side of a river in its lower course. Both the processes of erosion and deposition form the floodplain.

Lateral erosion is caused by meanders and their associated river cliffs and the slow migration of meanders downstream.

Deposition occurs on the slip-off slope (the sediment deposited on the inside of a meander) and when the river floods and the increase in friction causes the flood waters to deposit the sediments they are carrying.

Levées are natural embankments of sediment along the banks of a river. They are formed along rivers that carry a large load and periodically flood.

Sometimes natural levées are heightened and reinforced by humans to protect settlements, industry and infrastructure on the floodplain from floods.

1. What is a floodplain?
2. Give four reasons why floodplains usually have high population densities.
3. Describe how fluvial erosion is involved in the formation of a floodplain [4 marks]
4. Describe how fluvial deposition is involved in the formation of a floodplain [4 marks]
5. What is a levée?
6. Describe the formation of a natural levee. You answer should include the following terms: sediment, velocity, energy, deposition, friction, and flood.
7. Give five reasons why humans create artificial levees.

NewScientist - Air-dropped dams could fix levee breaches [31 August 2007]

8. Read the article ‘Air-dropped dams could fix levee breaches’ and watch the YouTube video.
9. What is a levee breach?
10. Why do levee breaches need to be fixed quickly?
11. What happened when the levees broke in New Orleans due to Hurricane Katrina?
12. What emergency management strategies is being suggested to deal with levee breaches?
13. Why are natural defences such as beaches and wetlands a ‘better’ long-term protection?

Produce a three box story board to show the formation of a natural levée. Can you add labels to your story board? Including the words: friction, deposition, bankfull and floodplain (at least!).