River mouth

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The port and city are the southern terminus of the Suez Canal which flows through Egypt and debouches into the Mediterranean Sea near Port Said. Iss016e019375.jpg
The port and city are the southern terminus of the Suez Canal which flows through Egypt and debouches into the Mediterranean Sea near Port Said.

A river mouth is the part of a river where the river debouches into another river, a lake, a reservoir, a sea, or an ocean. [1]

River Natural flowing watercourse

A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and northeast England, and "beck" in northern England. Sometimes a river is defined as being larger than a creek, but not always: the language is vague.


In the geography of rivers, streams, and glaciers, a debouch, or debouche, is a place where runoff from a small, confined space emerges into a larger, broader space. The term is of French origin and means to cause to emerge. The term also has a military usage.

Lake A body of relatively still water, in a basin surrounded by land

A lake is an area filled with water, localized in a basin, that is surrounded by land, apart from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, and therefore are distinct from lagoons, and are also larger and deeper than ponds, though there are no official or scientific definitions. Lakes can be contrasted with rivers or streams, which are usually flowing. Most lakes are fed and drained by rivers and streams.


Water motion

The water from a river can enter the receiving body in a variety of different ways. [1] The motion of a river is influenced by the relative density of the river compared to the receiving water, the rotation of the earth, and any ambient motion in the receiving water, such as tides or seiches. [2]

If the river water has a higher density than the surface of the receiving water, the river water will plunge below the surface. The river water will then either form an underflow or an interflow within the lake. However, if the river water is lighter than the receiving water, as is typically the case when fresh river water flows into the sea, the river water will float along the surface of the receiving water as an overflow.

The density, or more precisely, the volumetric mass density, of a substance is its mass per unit volume. The symbol most often used for density is ρ, although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume:

Alongside these advective transports, inflowing water will also diffuse. [1]

In the field of physics, engineering, and earth sciences, advection is the transport of a substance or quantity by bulk motion. The properties of that substance are carried with it. Generally the majority of the advected substance is a fluid. The properties that are carried with the advected substance are conserved properties such as energy. An example of advection is the transport of pollutants or silt in a river by bulk water flow downstream. Another commonly advected quantity is energy or enthalpy. Here the fluid may be any material that contains thermal energy, such as water or air. In general, any substance or conserved, extensive quantity can be advected by a fluid that can hold or contain the quantity or substance.


At the mouth of a river, the change in flow condition can cause the river to drop any sediment it is carrying. This sediment deposition can generate a variety of landforms, such as deltas, sand bars, spits, and tie channels. [3]

Sediment Particulate solid matter that is deposited on the surface of land

Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand and silt can be carried in suspension in river water and on reaching the sea bed deposited by sedimentation and if buried, may eventually become sandstone and siltstone.

Landform A natural feature of the solid surface of the Earth or other planetary body

A landform is a natural feature of the solid surface of the Earth or other planetary body. Landforms together make up a given terrain, and their arrangement in the landscape is known as topography. Typical landforms include hills, mountains, plateaus, canyons, and valleys, as well as shoreline features such as bays, peninsulas, and seas, including submerged features such as mid-ocean ridges, volcanoes, and the great ocean basins.

River delta Silt deposition landform at the mouth of a river

A river delta is a landform that forms from deposition of sediment that is carried by a river as the flow leaves its mouth and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or another river that cannot carry away the supplied sediment. The size and shape of a delta is controlled by the balance between watershed processes that supply sediment, and receiving basin processes that redistribute, sequester, and export that sediment. The size, geometry, and location of the receiving basin also plays an important role in delta evolution. River deltas are important in human civilization, as they are major agricultural production centers and population centers. They can provide coastline defense and can impact drinking water supply. They are also ecologically important, with different species' assemblages depending on their landscape position.

Cultural influence

Many places in the United Kingdom take their names from their positions at the mouths of rivers, such as Plymouth (i.e. mouth of the Plym River), Sidmouth (i.e. mouth of the Sid River), and Great Yarmouth (i.e. mouth of the Yare River); in Celtic, the term is Aber or Inver.

River Plym river in Devon, England

The River Plym is a river in Devon, England. It runs from Dartmoor in the centre of the county southwest to meet the River Meavy, then south towards Plymouth Sound. The river is popular with canoeists, and the Plym Valley Railway runs alongside a section of the river.

River Sid river in the United Kingdom

The River Sid is a minor river in East Devon. It flows for 6.5 miles (10.5 km) southwards from a source in Crowpits Covert at a height of 206 metres above sea level. The source is at the head of a goyle or small ravine.

River Yare river in the United Kingdom

The River Yare is a river in the English county of Norfolk. In its lower reaches it is one of the principal navigable waterways of The Broads and connects with the rest of the network.

See also

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Sedimentary rock Rock formed by the deposition and subsequent cementation of material

Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of mineral or organic particles on the floor of oceans or other bodies of water at the Earth's surface. Sedimentation is the collective name for processes that cause these particles to settle in place. The particles that form a sedimentary rock are called sediment, and may be composed of geological detritus (minerals) or biological detritus. Before being deposited, the geological detritus was formed by weathering and erosion from the source area, and then transported to the place of deposition by water, wind, ice, mass movement or glaciers, which are called agents of denudation. Biological detritus was formed by bodies and parts of dead aquatic organisms, as well as their fecal mass, suspended in water and slowly piling up on the floor of water bodies. Sedimentation may also occur as dissolved minerals precipitate from water solution.

Estuary A partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea

An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea.

Lagoon A shallow body of water separated from a larger body of water by barrier islands or reefs

A lagoon is a shallow body of water separated from a larger body of water by barrier islands or reefs. Lagoons are commonly divided into coastal lagoons and atoll lagoons. They have also been identified as occurring on mixed-sand and gravel coastlines. There is an overlap between bodies of water classified as coastal lagoons and bodies of water classified as estuaries. Lagoons are common coastal features around many parts of the world.

Alluvial fan A fan- or cone-shaped deposit of sediment crossed and built up by streams

Alluvial fans are triangular-shaped deposits of water-transported material, often referred to as alluvium. They are an example of an unconsolidated sedimentary deposit and tend to be larger and more prominent in arid to semi-arid regions. These alluvial fans typically form in elevated or even mountainous regions where there is a rapid change in slope from a high to low gradient. The river or stream carrying the sediment flows at a relatively high velocity due to the high slope angle which is why coarse material is able to remain in the flow. When the slope decreases rapidly into a relatively plain or plateau, the stream loses the energy it needs to move its sediment. Deposition subsequently occurs and the sediment ultimately spreads out, creating an alluvial fan. Three primary zones occur within an alluvial fan which includes the proximal fan, medial fan, and the distal fan.

Fluvial processes Processes associated with rivers and streams

In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluvioglacial is used.

Shoal A natural landform that rises from the bed of a body of water to near the surface and is covered by unconsolidated material

In oceanography, geomorphology, and earth sciences, a shoal is a natural submerged ridge, bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body of water to near the surface. Often it refers to those submerged ridges, banks, or bars that rise near enough to the surface of a body of water as to constitute a danger to navigation. Shoals are also known as sandbanks, sandbars, or gravelbars. Two or more shoals that are either separated by shared troughs or interconnected by past or present sedimentary and hydrographic processes are referred to as a shoal complex.

Longshore drift Sediment moved by the longshore current

Longshore drift from longshore current is a geological process that consists of the transportation of sediments along a coast parallel to the shoreline, which is dependent on oblique incoming wind direction. Oblique incoming wind squeezes water along the coast, and so generates a water current which moves parallel to the coast. Longshore drift is simply the sediment moved by the longshore current. This current and sediment movement occur within the surf zone.

Antarctic bottom water A cold, dense, water mass originating in the Southern Ocean surrounding Antarctica

The Antarctic bottom water (AABW) is a type of water mass in the Southern Ocean surrounding Antarctica with temperatures ranging from −0.8 to 2 °C (35 °F), salinities from 34.6 to 34.7 psu. Being the densest water mass of the oceans, AABW is found to occupy the depth range below 4000 m of all ocean basins that have a connection to the Southern Ocean at that level.

Sediment transport The movement of solid particles, typically by gravity and fluid entrainment

Sediment transport is the movement of solid particles (sediment), typically due to a combination of gravity acting on the sediment, and/or the movement of the fluid in which the sediment is entrained. Sediment transport occurs in natural systems where the particles are clastic rocks, mud, or clay; the fluid is air, water, or ice; and the force of gravity acts to move the particles along the sloping surface on which they are resting. Sediment transport due to fluid motion occurs in rivers, oceans, lakes, seas, and other bodies of water due to currents and tides. Transport is also caused by glaciers as they flow, and on terrestrial surfaces under the influence of wind. Sediment transport due only to gravity can occur on sloping surfaces in general, including hillslopes, scarps, cliffs, and the continental shelf—continental slope boundary.

Depositional environment The combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment

In geology, depositional environment or sedimentary environment describes the combination of physical, chemical and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be formed after lithification, if the sediment is preserved in the rock record. In most cases the environments associated with particular rock types or associations of rock types can be matched to existing analogues. However, the further back in geological time sediments were deposited, the more likely that direct modern analogues are not available.

In sedimentary geology and fluvial geomorphology, avulsion is the rapid abandonment of a river channel and the formation of a new river channel. Avulsions occur as a result of channel slopes that are much less steep than the slope that the river could travel if it took a new course.

Wax Lake

Wax Lake was a lake in St. Mary Parish, Louisiana that was converted into an outlet channel to divert water from the Atchafalaya River to the Gulf of Mexico.

Bar (river morphology) An elevated region of sediment in a river that has been deposited by the flow

A bar in a river is an elevated region of sediment that has been deposited by the flow. Types of bars include mid-channel bars, point bars, and mouth bars. The locations of bars are determined by the geometry of the river and the flow through it. Bars reflect sediment supply conditions, and can show where sediment supply rate is greater than the transport capacity.

An alluvial river is a river in which the bed and banks are made up of mobile sediment and/or soil. Alluvial rivers are self-formed, meaning that their channels are shaped by the magnitude and frequency of the floods that they experience, and the ability of these floods to erode, deposit, and transport sediment. For this reason, alluvial rivers can assume a number of forms based on the properties of their banks; the flows they experience; the local riparian ecology; and the amount, size, and type of sediment that they carry.

A contourite is a sedimentary deposit commonly formed on continental rise to lower slope settings, although they may occur anywhere that is below storm wave base. Countourites are produced by thermohaline-induced deepwater bottom currents and may be influenced by wind or tidal forces. The geomorphology of contourite deposits is mainly influenced by the deepwater bottom-current velocity, sediment supply, and seafloor topography.

The Amazon Canyon is a submarine canyon within the Amazon Fan in the Atlantic Ocean, located approximately 200 mi (322 km) from the mouth of the Amazon River, near South America. It covers an area of 2,250 km2 (870 sq mi). It was formed in the mid to late Miocene period. The canyon is believed to have formed through mass failures, and subsequently evolved through underwater erosion. Because of its relatively small size, the canyon has been extensively mapped.


Overdeepening is a characteristic of basins and valleys eroded by glaciers. An overdeepened valley profile is often eroded to depths which are hundreds of metres below the deepest continuous line along a valley or watercourse. This phenomenon is observed under modern day glaciers, in salt-water fjords and fresh-water lakes remaining after glaciers melt, as well as in tunnel valleys which are partially or totally filled with sediment. When the channel produced by a glacier is filled with debris, the subsurface geomorphic structure is found to be erosionally cut into bedrock and subsequently filled by sediments. These overdeepened cuts into bedrock structures can reach a depth of several hundred metres below the valley floor.


  1. 1 2 3 Charles, Hogg, (2014-06-12). "The flow of rivers into lakes: Experiments and models". doi:10.17863/cam.32.
  2. Ma, Yanxia (2009). Continental Shelf Sediment Transport and Depositional Processes on an Energetic, Active Margin: the Waiapu River Shelf, New Zealand. pp. 2, 19.
  3. Rowland, J. C.; Dietrich, W. E.; Day, G.; Parker, G. (2009). "Formation and maintenance of single‐thread tie channels entering floodplain lakes: Observations from three diverse river systems". Journal of Geophysical Research. 114 (F2). doi:10.1029/2008JF001073.