What geographical feature forms when a river floods its banks?

When a river floods its banks, it spreads out over the surrounding land, creating a flat area known as a floodplain. Floodplains are formed through the accumulation of sediment and materials deposited by the river during floods. This allows for fertile soil to develop, making floodplains important for agriculture and ecosystems surrounding rivers.

In contrast, a meander refers to a bend in the river's path rather than an area formed by flooding. An ox-bow lake is a crescent-shaped lake formed when a meander is cut off from the river, which occurs due to erosion and sediment deposition, not directly from flooding. A delta is a landform created at the mouth of a river, where it meets a body of water, and is characterized by sediment deposited by the river over time as it slows down, rather than as a direct result of flooding.

Thus, floodplain is the specific feature formed by a river overflowing its banks, making it the correct choice.