Levees A levee is a build-up of alluvium on the banks of a river and is a feature of the old stage river. Levees are caused by floods and are a feature of deposition.
They can be seen in the lower course of the River Liffey and the River Moy, Co. Mayo.
River bed During flood Flood-stage water level
Formation 1
2
During times of low flow in a river, the load that is being carried by the river is dropped onto the river bed. This raises the height of the bed.
During times of flood, the water flows out more easily over the top of the channel and onto the surrounding land. As it does this, it loses energy and deposits its load.
3 4
The heavy coarse material is deposited on the river banks. The finer silt is deposited further away onto the flood plain.
After many floods, the river builds up a bank on either side.
Thickest and coarsest sediments deposited at channel edges
After many floods Natural levees built up by many floods
Thin and fine sediments deposited over outer parts of flood plain
River bank
This levee provides a natural walkway. Levees can also be called dikes or embankments.
