Levees
Levees can be natural or artificial. The artifial levees are built as banks to prevent the flood of water over the floodplain.
Levees are very important in built up residential areas where more precautions against flooding are taken- normally within the boundaries of the rivers 'flood plain' however you would expect this area to flood hense its name.
Natural levees
When a river floods over its banks, the water spreads out and the velocity slows. Due to this, its load of sediment is deposited. Frequent flooding causes the banks to be built up over time - above the level of the floodplain.
Levees animation (click play)
Some rivers reach the sea in deltas, which form as the rivers mouth becomes choked with sediment. This causes the main river channel to split into hundreds of smaller channels known as distrutaries.
Delta's form when the river sediment (silt mud and shingle) is deposited faster than it can be transported away due to the rivers loss of energy.