Alluvium are sediments deposited by erosion processes, usually by streams. They are generally formed in an extensive process throughout the shallow end of rivers and create delta floodplain. Alluvium has a likelihood to be released during any stage of when the river overflows or sudden drops in the rapid flow rate of a river, such as when it comes into contact with a lake.

Alluvium is spread on a great range of soil, especially residing along the bottom zones of many regions. It is made up of various organic substances, including sand, gravel, silt, and clay. For this reason, it usually produces extremely fertile soils as seen in some of the deltas located at the Nile, Huang, Tigris-Euphrates, Indus, Ganges-Brahmaputra, and Yellow rivers. Most regions contain alluvium remains that consist of gemstones, tin ore, platinum, and gold.