A river mouth is where a

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, 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 ...

flows into a larger

body of water A body of water or waterbody is any significant accumulation of water on the surface of Earth or another planet. The term most often refers to oceans, seas, and lakes, but it includes smaller pools of water such as ponds, wetlands, or more rare ...

, such as another river, a

lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...

reservoir A reservoir (; ) is an enlarged lake behind a dam, usually built to water storage, store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of wa ...

, a

bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a ''gulf'', ''sea'', ''sound'', or ''bight''. A ''cove'' is a small, ci ...

gulf A gulf is a large inlet from an ocean or their seas into a landmass, larger and typically (though not always) with a narrower opening than a bay (geography), bay. The term was used traditionally for large, highly indented navigable bodies of s ...

, a

sea A sea is a large body of salt water. There are particular seas and the sea. The sea commonly refers to the ocean, the interconnected body of seawaters that spans most of Earth. Particular seas are either marginal seas, second-order section ...

, or an

ocean The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...

. At the river mouth,

sediments Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

are often deposited due to the slowing of the current, reducing the carrying capacity of the water. The water from a river can enter the receiving body in a variety of different ways. 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 Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

seiches A seiche ( ) is a standing wave in an enclosed or partially enclosed body of water. Seiches and seiche-related phenomena have been observed on lakes, reservoirs, swimming pools, bays, harbors, caves, and seas. The key requirement for formation of ...

. If the river water has a higher

density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...

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 In hydrology, interflow is the lateral movement of water in the unsaturated zone, or vadose zone, that returns to the surface or enters a stream. Interflow is sometimes used interchangeably with throughflow; however, throughflow is specifically the ...

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. Alongside these advective transports, inflowing water will also

diffuse Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical p ...

Landforms

At the mouth of a river, the change in flow conditions can cause the river to drop any sediment it is carrying. This

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

deposition can generate a variety of

landform A landform is a land feature on the solid surface of the Earth or other planetary body. They may be natural or may be anthropogenic (caused or influenced by human activity). Landforms together make up a given terrain, and their arrangement ...

s, such as

deltas A river delta is a landform, wikt:archetype#Noun, archetypically triangular, created by the deposition (geology), deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or ...

sand bar In oceanography, geomorphology, and geoscience, 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 close to the surface or ...

s, spits, and tie channels. Landforms at the river mouth drastically alter the geomorphology and ecosystem. Along coasts, sand bars and similar landforms act as barriers, sheltering sensitive ecosystems that are enriched by nutrients deposited from the river. However, the damming of rivers can starve the river of sand and nutrients, creating a deficit at the river's mouth.

Cultural influence

As river mouths are the site of large-scale sediment deposition and allow for easy travel and ports, many towns and cities are founded there. 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 corresponding terms are Aber or Inver, from which come numerous place names such as

Aberdeen Aberdeen ( ; ; ) is a port city in North East Scotland, and is the List of towns and cities in Scotland by population, third most populous Cities of Scotland, Scottish city. Historically, Aberdeen was within the historic county of Aberdeensh ...

Abercrombie Abercrombie may refer to: People * Abercrombie Lawson (1870–1927), botanist and professor * Abercrombie (surname) (list of people with the family name Abercrombie) Places Antarctica * Abercrombie Crests, rock summits in Antarctica Australia ...

, and Abernethy, as well as

Inverness Inverness (; ; from the , meaning "Mouth of the River Ness") is a city in the Scottish Highlands, having been granted city status in 2000. It is the administrative centre for The Highland Council and is regarded as the capital of the Highland ...

Inverkip Inverkip (; ) is a village and parish in the Inverclyde council area and historic county of Renfrewshire in the west central Lowlands of Scotland, southwest of Greenock and north of Largs on the A78 trunk road. The village takes its name from ...

, and

Inveraray Inveraray ( or ; meaning "mouth of the Aray") is a town in Argyll and Bute, Scotland. Located on the western shore of Loch Fyne, near its head, Inveraray is a former royal burgh and known affectionately as "The Capital of Argyll." It is the ...

. Due to rising sea levels as a result of climate change, the coastal cities are at heightened risk of flooding. Sediment starvation in the river compounds this concern.

References

{{Authority control Fluid dynamics Fluvial landforms

Mouth A mouth also referred to as the oral is the body orifice through which many animals ingest food and animal communication#Auditory, vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also t ...

Landforms

Cultural influence

See also

References