region on which rivers have deposited sediment
Floodplain (centre) within the alluvial plain of the Waimakariri River, New Zealand (part of the Canterbury Plains). A small, incised alluvial plain from Red Rock Canyon State Park (California).
An alluvial plain is a plain (an essentially flat landform) created by the deposition of sediment over a long period by one or more rivers coming from highland regions, from which alluvial soil forms. A floodplain is part of the process, being the smaller area over which the rivers flood at a particular time. In contrast, the alluvial plain is the larger area representing the region over which the floodplains have shifted over geological time.
Discovered by embedding cosine similarity (sentence-transformers MiniLM, 384-dim).