Alluvial Systems

An alluvial system consists of sediments eroded, transported, and deposited by water flowing in rivers or streams. The sediments, known as alluvium, can range from clay-sized particles less than 0.002 mm in diameter to boulders greater than 64 mm in diameter, depending on their source and the sediment transport capacity of streams in the system. The term alluvial is closely related to the term fluvial, which refers to flowing water. Thus, alluvial systems are the result of fluvial processes.

Modern alluvial systems can create flat and fertile valley bottoms that are attractive for farming because of their rich soils, which are replenished during frequent floods. The same floods that replenish soils, though, can become hazardous when homes are built on floodplains. Ancient alluvial systems that now lie below Earth's surface can be exceptionally good aquifers and petroleum reservoirs.

This delta formed downstream of a break in a natural levee. Note the marsh growth that developed along the banks of the distributaries. Photograph by Dan Guravich. Photo Researchers, Inc. Reproduced by permission.