riverplain

A riverplain, sometimes referred to as a floodplain or alluvial plain, is a broad, flat or gently sloping land area that lies adjacent to a river. It forms as sediment carried by the river is deposited during floods and over time the accumulated material builds up a wide plain alongside the channel.

Formation and geomorphology

Riverplains develop through repeated flooding, when the river loses velocity and drops sand, silt, and clay. This sediment builds up layers that create fertile soils and a flattened landscape. Meandering rivers often widen their plains over time as new channels form and old ones abandon, leaving oxbow lakes and remnants of former courses. Levees can develop along the river channel from repeated sediment build-up, while terrace steps may appear if the land uplifts or the river drops to lower levels.

Soils and ecology

Alluvial soils on riverplains are typically rich in nutrients, supporting productive agriculture and a range of riparian habitats. Vegetation often reflects seasonal flooding and proximity to water, from wetlands to forested banks. The hydrologic regime—frequency and depth of floods—shapes both soil properties and ecosystems.

Human use and hazards

Riverplains are commonly settled and farmed areas because of their fertile soils. They are, however, prone to flooding and waterlogging, requiring management such as levees, drainage systems, and land-use planning to mitigate risks. In some regions, riverplains are important for biodiversity and provide important ecosystem services, including groundwater recharge and flood attenuation.

Global distribution and distinction

Riverplains occur along many of the world’s rivers, from large alluvial plains to smaller floodplains. They are distinct from deltas, which form at river mouths where sediment enters standing bodies of water, and from higher river terraces formed by long-term vertical changes in the landscape.