Detrital debris carried by a river and generally deposited along its course, either in the riverbed or on the floodplain. Weathered material moved by gravity, such as on scree slopes, is referred to as colluvial. Eluvial material is weathered material that is still at or near its site of creation. Examples include rock slides and dust clouds, which are transported by wind or water and then settle over large areas. Alluvial fans and deposits form when sediment-laden waters flow across flat surfaces such as open plains and deserts. As the water reaches the end of the flat area, it spreads out forming shapes like crescent moons or half-moons. These sediment-rich bodies of water may be small canyons or wide valleys. Alluvial soil develops where these muddy waters reach the end of their journey and drain away.
Alluvial soil is made up of very fine particles that are easily washed away by rain or melted snow. The amount of alluvium in an area determines how much soil will be produced and destroyed by natural processes. Areas with more frequent flooding or intense precipitation will change more rapidly than those with less severe conditions. Flooding also has the effect of moving some alluvium down stream, where it can become re-deposited in another location.
The type of climate in an area influences how much alluvium will be produced.
Alluvial material is that which is moved and deposited by water, whereas fluvial material is that which is moved and deposited by a river or stream. Alluvium can include sand, silt, gravel, and clay; fluvial material can include branches, logs, and rocks.
Fluvial geology is the study of rivers and their effects on Earth's surface. Alluvial geologists study the composition of sediments discharged into lakes and oceans as well as those transported by rivers. They also study how rivers change the shape of surrounding land. Fluvial geology has many applications including mining, oil and gas production, flood control, and recreation.
Fluvial processes have been important in the formation and modification of landscapes throughout history. They still play an important role in modern times with the construction of dams, levees, and other human interventions having significant effects on sediment supply and distribution.
Fluvial environments are characterized by large fluctuations in water level and flow rate. This can have significant effects on the size and distribution of suspended particles in the water. Large amounts of sediment may be carried away from its origin in a single event called a flood or deposited back into its area of origin during periods of low water called ebbs.
Moving water bodies, such as rivers and streams, deposited alluvial (or fluvial) parent materials. Finer particles (sand and silt) are deposited when water velocity falls, whereas fine silt and clay particles are deposited by slow-moving water, such as those found around deltas. The amount of sand in the soil depends on how far the river has flowed since it last changed course or was blocked by a dam. Clays can also be transported by rivers and deposited hundreds of miles away from their source. These clays become part of the alluvial fan and are responsible for much of the fertility of tropical forests.
Alluvial fans are large areas of flat land formed by the deposition of sediment carried by rivers. Alluvial fans may be composed of silts, clays, or both. They can be as wide as 200 miles but most are much smaller than that. The width of an alluvial fan is generally related to the distance that the river flows without changing direction. For example, if a river flows west for 100 miles then turns south for 100 more miles before it reaches its destination, the bed of the river will have turned 360 degrees - hence the name "alluvial fan".
An important aspect of alluvial soil development is the role that floodplains play in transporting sediment downstream. Floodplains are the areas within reach of every stage of the water cycle (precipitation, runoff, and flooding).
Canals, both alluvial and non-alluvial Alluvial soil: Alluvial soil is soil that is generated over time by the movement and deposition of silt by the action of water. Alluvial canals are canals that are dug through such soils. The term "alluvial canal" is also used as a generic term for any large river channel. Examples include the Ganges River in India and the Yangtze River in China.
Non-alluvial soil: Non-alluvial soil is soil that does not flow like silt but instead is composed of hardpan rock or some other stable material. Canals through non-alluvial soil serve only to drain water away from buildings or other structures.
Alluvial soil consists mainly of sand mixed with silt. The depth of an alluvial soil profile varies depending on how much sediment was deposited by rain or rivers over time. It may be as shallow as 10 feet (3 m) across broad valleys where there were no rocks to prevent erosion. In areas where rocks do accumulate, the alluvial soil can become deeper than 100 feet (30 m).
The main type of canal used for drainage purposes in urban areas throughout the world is the storm sewer, which usually runs under public streets at grade with the ground surface. Some storm sewers discharge their contents into larger waterways called creeks or rivers.