When there is heavy rain and the amount of water in the river channel is more than the amount that can be contained, the water overflows the banks and floods the surrounding areas.

Once out of the channel, the water encounters more friction because of a larger wetted perimeter formed by the large flat low land. The increase in friction reduces the energy of the water and slows down its speed. This results in deposition.

The larger and coarser materials are deposited first because they are heavier. They are deposited at the river banks. The smaller and finer materials are carried further away because they are lighter and deposited further away from the river. The coarser materials at the river banks form raised embankments called leeves while the finer materials form the flood plain.