What is the term for the flat, low-lying land on either side of a river that floods?

The term for the flat, low-lying land on either side of a river that floods is known as a floodplain. Floodplains are important geographical features that develop over time through the sediment deposition by the river during flood events. When rivers overflow their banks due to increased rainfall or melting snow, the floodplains absorb this excess water, mitigating potential flood damage and providing a rich habitat for diverse ecosystems.

In contrast, a dune refers to a mound or ridge of sand formed by wind, often found in desert or coastal regions, and does not relate to river dynamics. A delta is the landform created at the mouth of a river where it meets a body of water, forming as sediment is deposited as the river slows down, which is significantly different from the areas adjacent to the river that flood. Wetlands encompass areas that are saturated with water but do not specifically refer to the flat lands beside rivers; they can include marshes and swamps in various contexts. Thus, the floodplain is the most accurate term to describe the specific geographic feature associated directly with river flooding.