Floodplains are large, flat expanses of land that form on either side of a river. The floodplain is the area that a river floods onto when it exceeds bank-full capacity. Increased friction as the river breaks its banks reduces the river’s efficiency to transport material resulting in increased levels of deposition. The deposited load on the floodplain is known as alluvium. Alluvium is rich in nutrients and leads to floodplains often being used for farming.
Floodplains become wider when there is a significant amount of meander migration as the width of the floodplain is determined by the sinuosity of the river and the amount of meander migration that takes place.