Levees:
● Levees = naturally raised river banks found on either or both sides of a river channel prone to flooding
→ Characteristics:
● Raised river banks (2 – 8 metres)
● Composed of gravel, stones and alluvium
● Coarsest sediment closest to river channel
● Steep-sided → steeper on channel side than land side
● Flat top covered with grass
→ Formation:
1. When a river bursts its banks, friction with land reduces
velocity and causes deposition
○ Heavy sediment is deposited closest to the river
○ Size of sediment becomes progressively smaller
with increased distance
2. With each flood, banks are built up higher
3. Levees do not reduce risk of flooding → river develops
thicker layer of sediment which raises river in its channel
Floodplains:
● Floodplain = large area of flat land either side of a river
prone to flooding
→ Characteristics:
● River bluff (area of slightly higher land along edge of floodplain)
● Reeds and marsh plants
● Oxbow lakes
● Levee
● Meander scar
● Layers of alluvium cover the floodplain
→ Formation:
● Formed by combination of erosion and deposition
● Width of floodplain is due to meander migration and lateral
erosion over 100s of years
○ Meander position gradually moves downstream
○ Cutting a wider valley
● When floods have receded , flood plain is higher and more fertile
○ Alluvium and silt are deposited
○ Alluvial deposits infill old meander scars