Sediment consisting of mud, sand, silt, gravel, and other unconsolidated detrital matter that is carried along and deposited by flowing water: The largest alluvia tend to accumulate within the water channel itself while particles of clay, silt, and fine sand are small enough to be suspended as the water continues to flow.

When the watercourse overflows its banks, these alluvia can be distributed across a valley floor where such an overbank or flood deposits have become the most common areas in which buried archaeological sites are found.

Some valley-stream areas are composed of deposits of alluvia and those are the places where researchers often find buried archaeological treasures.