Río de la Plata estuary

Estuary mouth located in Darwin, Northern Territory, Australia

An estuary is a semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea. The Río de la Plata ( Spanish: " Silver River" &mdash which is often referred to in English-speaking countries as the River Plate For a topic outline on this subject see List of basic Australia topics. The coast is defined as the part of the land adjoining or near the Ocean. Water is a common Chemical substance that is essential for the survival of all known forms of Life. "Riverine" redirects here For the use of that term in Maritime geography, see there A stream is a body of Water with a current, confined within a bed and stream-banks This article is about the body of water For other uses see SEA and Seas. ^[1] Estuaries are often associated with high rates of biological productivity.

An estuary is typically the tidal mouth of a river (aestus is Latin for tide), and estuaries are often characterized by sedimentation or silt carried in from terrestrial runoff and, frequently, from offshore. "Riverine" redirects here For the use of that term in Maritime geography, see there Sedimentation describes the motion of Molecules in Solutions or particles in suspensions in response to an external force such as gravity Silt is Soil or rock derived Granular material of a Grain size between sand and clay They are made up of brackish water. Estuaries are more likely to occur on submerged coasts, where the sea level has risen in relation to the land; this process floods valleys to form rias and fjords. Submergent coastline s are stretches along the coast that have been inundated by the sea due to a relative rise in sea levels In Geology, a valley (also called a vale, dale, glen or strath and near or in Appalachia, a draw) is A ria is a Landform, often referred to as a drowned river valley. A fjord or fiord (fjɔːd|fiːɔːd or fiːɔːd is a long narrow Inlet with steep sides created in a valley carved by glacial activity. These can become estuaries if there is a stream or river flowing into them. Large estuaries, like Chesapeake Bay and Puget Sound, often have many streams flowing into them and can have complex shapes. The Chesapeake Bay is the largest Estuary in the United States. Puget Sound (ˈpjuːʤᵻt is an arm of the Pacific Ocean, connected to the rest of the Pacific by the Strait of Juan de Fuca, in the Pacific Northwest Estuaries are often given names like bay, sound, fjord, etc. Headlands and bays are two related features of the coastal environment In Geography a sound or seaway is a large sea or ocean Inlet larger than a bay, deeper than a bight, wider than a Fjord A fjord or fiord (fjɔːd|fiːɔːd or fiːɔːd is a long narrow Inlet with steep sides created in a valley carved by glacial activity. The terms are not mutually exclusive. Where an enormous volume of river water enters the sea (as, for example, from the Amazon into the South Atlantic) its estuary could be considered to extend well beyond the coast. Estuarine circulation is common in estuaries; this occurs when fresh or brackish water flows out near the surface, while denser saline water flows inward near the bottom. Anti-estuarine flow is its opposite, in which dense water flows out near the bottom and less dense water circulates inward at the surface. These two terms, however, have a broader oceanographic application that extends beyond estuaries proper, such as in describing the circulation of nearly-closed ocean basins. Oceanography (from the greek words Ωκεανός meaning Ocean and γράφω meaning to write also called oceanology or Estuaries are marine environments, whose pH, salinity, and water level are varying, depending on the river that feeds the estuary and the ocean from which it derives its salinity (oceans and seas have different salinity levels). pH is the measure of the acidity or alkalinity of a Solution. Salinity is the Saltiness or dissolved salt content of a body of Water. The time it takes an estuary to completely cycle is called flushing time. As ecosystems, the estuaries are under great threat from human activities. They are small, in demand, impacted by events far upstream or out at sea, and concentrate materials such as pollutants and sediments^[2].

Classes of estuary

Salt wedge 

River output greatly exceeds marine input; there is little mixing, and thus a sharp contrast between fresh surface water and saline bottom water.

Highly stratified 

River output and marine input are more even, with river flow still dominant; turbulence induces more mixing of salt water upward than the reverse.

Slightly stratified 

River output is less than the marine input. Here, turbulence causes mixing of the whole water column, such that salinity varies more longitudinally rather than vertically.

Vertically mixed 

River output is much less than marine input, such that the freshwater contribution is negligible; longitudinal salinity variation only.

Inverse estuary 

Located in regions with high evaporation, there is no freshwater input and in fact salinity increases inland; overall flow is inward at the surface, downwells at the inland terminus, and flows outward subsurface.

Intermittent estuary 

Estuary type varies dramatically depending on freshwater input, and is capable of changing from a wholly marine embayment to any of the other estuary types. Headlands and bays are two related features of the coastal environment ^[3]

Grouped by structure rather than circulation, there are other types of estuaries. Bar-built estuaries are effectively synonymous with barrier island lagoons, such as Texas's Laguna Madre. A shoal or sandbar (also called sandbank) is a somewhat Linear Landform within or extending into a body of Water, A lagoon is a body of comparatively shallow salt or Brackish water separated from the deeper Sea by a shallow or exposed sandbank, coral Texas ( is a state geographically located in the South Central United States and is also known as the Lone Star State. The Laguna Madre is the name of two long shallow bays along the western coast of the Gulf of Mexico in the United States and Mexico Tectonic estuaries form when the sea floods a geologically subsident region, coastal plain estuaries are flooded river valleys, and fjords are submerged glacier-eroded valleys. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit In Geology, Engineering, and Surveying, subsidence is the motion of a surface (usually the Earth's surface as it shifts downward relative to A fjord or fiord (fjɔːd|fiːɔːd or fiːɔːd is a long narrow Inlet with steep sides created in a valley carved by glacial activity. "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. ^[4]

See also

• Ria
• Bay mud
• Brackish water
• Firth
• Liman
• List of waterways
• River Delta
• Coastal and Estuarine Research Federation

The Moore River estuary, a seasonally closed estuary in Western Australia

References