Alluvium in the context of Diluvium

A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it runs out of water, or only flow during certain seasons. Rivers are regulated by the water cycle, the processes by which water moves around the Earth. Water first enters rivers through precipitation, whether from rainfall, the runoff of water down a slope, the melting of glaciers or snow, or seepage from aquifers beneath the surface of the Earth.

Rivers flow in channeled watercourses and merge in confluences to form drainage basins, areas where surface water eventually flows to a common outlet. Drainage divides keep rivers separated from other courses of water and causes upstream water within the confines of the divide to fall into the downhill stream. Rivers have a great effect on the landscape around them. They may regularly overflow their banks and flood the surrounding area, spreading nutrients to the surrounding area. Sediment or alluvium carried by rivers shapes the landscape around it, forming deltas and islands where the flow slows down. Rivers rarely run in a straight line, instead, they bend or meander; the locations of a river's banks can change frequently. Rivers get their alluvium from erosion, which carves rock into canyons and valleys.

An alluvial plain is a plain (an essentially flat landform) created by the deposition of sediment over a long period by one or more rivers coming from highland regions, from which alluvial soil forms. A floodplain is part of the process, being the smaller area over which the rivers flood at a particular time. In contrast, the alluvial plain is the larger area representing the region over which the floodplains have shifted over geological time.

As the highlands erode due to weathering and water flow, the sediment from the hills is transported to the lower plain. Various creeks will carry the water further to a river, lake, bay, or ocean. As the sediments are deposited during flood conditions in the floodplain of a creek, the elevation of the floodplain will be raised. As this reduces the channel floodwater capacity, the creek will, over time, seek new, lower paths, forming a meander (a curved path). The leftover higher locations, typically natural levees at the margins of the flood channel, will be eroded by lateral stream erosion, local rainfall, and possibly wind transport if the climate is arid and does not support soil-holding grasses. These processes, over geologic time, will form the plain, a region with little relief (local changes in elevation) yet with a constant but slight slope.

The prehistory of Mesopotamia is the period between the Paleolithic and the emergence of writing in the area of the Fertile Crescent around the Tigris and Euphrates rivers, as well as surrounding areas such as the Zagros foothills, southeastern Anatolia, and northwestern Syria.

In general, Paleolithic Mesopotamia is poorly documented, with the situation worsening in southern Mesopotamia for periods prior to the 4th millennium BC. Geological conditions meant that most of the remains were buried under a thick layer of alluvium or submerged beneath the waters of the Persian Gulf. The Middle Paleolithic witnessed the emergence of a population of hunter-gatherers who lived in the caves of the Zagros and, seasonally, in numerous open-air sites. They were producers of a lithic industry of the Mousterian type, and their funerary remains, found in the cave of Shanidar, indicate the existence of solidarity and the practice of healing between the members of a group. During the Upper Paleolithic, the Zagros was probably occupied by modern man. The Shanidar cave contains only tools made of bone or antler, typical of a local Aurignacian called "Baradostian" by specialists.

The Ubaid period (c. 5500–3700 BC) is a prehistoric period of Mesopotamia. The name derives from Tell al-'Ubaid where the earliest large excavation of Ubaid period material was conducted initially in 1919 by Henry Hall, Leonard Woolley in 1922–1923, and later by Pinhas Delougaz in 1937. Excavations continue into the present day.

In Southern Mesopotamia, this period marks the earliest known human settlements on the alluvial plain, although it is likely earlier periods exist that are obscured under the alluvium. In the south it has a very long duration between about 5500 and 3800 BC when it is replaced by the Uruk period.

In geology, a placer deposit or placer is an accumulation of valuable minerals formed by gravity separation from a specific source rock during sedimentary processes. The name is from the Spanish word placer, meaning "alluvial sand". Placer mining is an important source of gold, and was the main technique used in the early years of many gold rushes, including the California Gold Rush. Types of placer deposits include alluvium, eluvium, beach placers, aeolian placers and paleo-placers.

Placer materials must be both dense and resistant to weathering processes. To accumulate in placers, mineral particles must have a specific gravity above 2.58.

A levee (/ˈlɛvi/ or /ˈlɛveɪ/), dike (American English), dyke (Commonwealth English), embankment, floodbank, or stop bank is an elevated ridge, natural or artificial, alongside the banks of a river, often intended to protect against flooding of the area adjoining the river. It is usually earthen and often runs parallel to the course of a river in its floodplain or along low-lying coastlines.

Naturally occurring levees form on river floodplains following flooding. Sediment and alluvium are deposited on the banks and settle, forming a ridge that increases the river channel's capacity. Alternatively, levees can be artificially constructed from fill, designed to regulate water levels. In some circumstances, artificial levees can be environmentally damaging.

Narta Lagoon (Albanian: Laguna e Nartës) is a lagoon of the Adriatic Sea on the Mediterranean Sea in the central coast of Albania. The lagoon extends north of the Bay of Vlorë on the eastern shore of the Strait of Otranto and is separated from the sea by a narrow littoral strip, consisting of an alluvial dune. It has a surface area of 41.8 km (16.1 sq mi) with a maximal depth of 1.5 m (4.9 ft).

It is situated within the boundaries of the Vjosa Wild River National Park, and has been recognised as an important Bird and Plant Area of international importance. As of May 2020, it is home to 3,000 flamingos. It is formed by the constant accumulation of solid flow of the Vjosa River, which originates within the Pindus Mountains close to the border between Albania and Greece.

India is a union consisting of 28 states and 8 union territories. As of 2024, with an estimated population of 1.484 billion, India is the world's most populous country. India occupies 2.4% of the world's area and is home to 17.5% of the world's population. The Indo-Gangetic Plain has one of the world's biggest stretches of fertile not-deep alluvium and are among the most densely populated areas of the world. The eastern and western coastal regions of Deccan Plateau are also densely populated regions of India. The Thar Desert in western Rajasthan is one of the most densely populated deserts in the world. The northern and north-eastern states along the Himalayas contain cold arid deserts with fertile valleys. These states have relatively low population density due to indomitable physical barriers.

A point bar is a depositional feature made of alluvium that accumulates on the inside bend of streams and rivers below the slip-off slope. Point bars are found in abundance in mature or meandering streams. They are crescent-shaped and located on the inside of a stream bend, being very similar to, though often smaller than, towheads, or river islands.

Point bars are composed of sediment that is well sorted and typically reflects the overall capacity of the stream. They also have a very gentle slope and an elevation very close to water level. Since they are low-lying, they are often overtaken by floods and can accumulate driftwood and other debris during times of high water levels. Due to their near flat topography and the fact that the water speed is slow in the shallows of the point bar they are popular rest stops for boaters and rafters. However, camping on a point bar can be dangerous as a flash flood that raises the stream level by as little as a few inches (centimetres) can overwhelm a campsite in moments.

A ponor is a natural opening where surface water enters into underground passages; they may be found in karst landscapes where the geology and the geomorphology is typically dominated by porous limestone rock. Ponors can drain stream or lake water continuously or can at times work as springs, similar to estavelles. Morphologically, ponors come in forms of large pits and caves, large fissures and caverns, networks of smaller cracks, and sedimentary, alluvial drains.

Gold mining is the extraction of gold by mining.

Historically, gold mining from alluvial deposits used manual separation processes, such as gold panning. The expansion of gold mining to ores that are below the surface has led to more complex extraction processes such as pit mining and gold cyanidation. In the 20th and 21st centuries, large corporations produce the vast majority of the gold mined. However, as a result of the increasing value of gold, there are also millions of small, artisanal miners in many parts of the Global South.

Placer mining (/ˈplæsər/) is the mining of stream bed deposits for minerals. This may be done by open-pit mining or by various surface excavating equipment or tunneling equipment.

Placer mining is frequently used for precious metal deposits (particularly gold) and gemstones, both of which are often found in alluvial deposits—deposits of sand and gravel in modern or ancient stream beds, or occasionally glacial deposits. The metal or gemstones, having been moved by stream flow from an original source such as a vein, are typically only a minuscule portion of the total deposit. Since gems and heavy metals like gold are considerably denser than sand, they tend to accumulate at the base of placer deposits.

Entisols are soils, as defined under USDA soil taxonomy, that do not show any profile development other than an A-horizon (or “A” horizon). Entisols have no diagnostic horizons, and are unaltered from their parent material, which could be unconsolidated sediment, or rock. Entisols are the most common soils, occupying about 16% of the global ice-free land area.

Because of the diversity of their properties, suborders of entisols form individual Reference Soil Groups in the World Reference Base for Soil Resources (WRB): psamments correlate with arenosols, and fluvents with fluvisols. Many orthents belong to regosols or leptosols. Most wassents and aquic subgroups of other suborders belong to the gleysols.