An ALLUVIAL plain is a flat landform created by the deposition of sediment over time by rivers and streams. It is typically composed of SILT, MUD, and other materials left behind by flowing water. The term 'ALLUVIAL' comes from the Latin word for 'FLOOD, ' and a DELTA is a triangular-shaped deposit of sediment at the mouth of a river. SILT is a fine-grained material that is often found in rivers and streams, and SILT can be deposited on an ALLUVIAL plain to form a silty layer. MUD is a mixture of water and soil particles, and it can also be deposited on an ALLUVIAL plain.