Wanderlust World Wanderlust World The loose, solid material transported and deposited by flowing water is called alluvium (from Latin alluvius, "washed against"). It encompasses the full range of particle sizes that a river can move: silt, clay, sand, gravel, and cobbles.
Alluvium is the raw material of floodplains, deltas, alluvial fans, and river terraces. As a river loses energy—on a floodplain, at its mouth, or where gradient flattens—it drops its alluvial load, sorting it by size: coarse gravel and sand near the channel, fine silt and clay farther out.
Historically, the term was used in Roman law for land formed by river deposits (especially along the Tiber). Today, "alluvial" describes soils, aquifers, gold deposits (placer), and ecosystems shaped by this dynamic process.