Sedimentary deposits of silt, sand, and gravel, that have been transported and then deposited by running water, usually a stream or river. Modern alluvial deposits are found in streambeds, river valleys, flood plains, deltas, and estuaries Many ancient geological formations are made up of alluvial sediments. Alluvial aquifers are important water sources.
See also Sand and Gravel Aquifers, Stratified Drift.