Nomenclature

The main river is usually defined as the course with the greatest water flow (average or maximum) or with the greatest length or greatest drainage area. This concept of a main river, like that of the birth of a river or the distinction between a main river and a tributary, are subjective.

In many cases, doubts arise about the name and route of the rivers, especially in hydrographic basins with heterogeneous relief and great extension, in which there has not been a common criterion about the dimensions of the main river and its tributaries. In other cases, there are several names for the same river, along its length. Examples of rivers whose names have been discussed in relation to where we can fix their source or with more important tributaries than the main river we can point out:

• - The Amazon River, with three important tributaries in its upper part (Marañón, Ucayali, Huallaga) although in this case, the Ucayali has been taken, along the course of the Apurímac River, whose sources are in Misti, Arequipa, Peru, as the true Amazon.[12]​.

• - The Nile, formed by the confluence of the White Nile and the Blue Nile.[13]​.

• - The Orinoco, with a tributary longer than the Orinoco itself at the point of its confluence, the Guaviare.[14]​.

• - The Miño, with a longer and mightier tributary at the point of its confluence, the Sil.

• - The Mississippi-Missouri, the tributary (the Missouri) being longer than the main river, although not larger, at the point of its confluence.

• - The Guadalquivir, formed by the upper part of the river with this name at its confluence with the Guadiana Menor, whose length is greater.

In other cases, the same river has different names along its course, especially in cases where arms or channels are formed from a channel and each of these arms takes a different name. This is the case of Apure (Apure Seco, Apure Viejo and Apurito). The Magro could also be included in this case (rambla de la Torre, Magro river, Alcalá, rambla de Algemesí, among others.).

Guys

Rivers can be classified from various points of view, among which the following stand out:

• - Depending on the period of activity, in perennial, seasonal, transient or allochthonous rivers.[15]​.

• - According to its geometry or morphology, a river or a certain stretch can be classified in the following categories: rectilinear, sinuous, meandering, anastomosing, with islands, in estuaries, in swamps or mangroves, in deltas.[16]​.

• - According to its age, it is classified as young, mature or old rivers.[17]​.

• - Depending on its stability condition, a section of channel can be considered with static, dynamic stability, with dynamic instability or with morphological stability.[18]​.

• - Its sections can be classified as high mountain, mountain, mountain slope, intermediate and plain.[19]​.

• - According to its degrees of freedom, it can be classified as having one, two or three degrees of freedom.[20]​.

• - Depending on the material of the margins and the bottom, they can be considered as cohesive, non-cohesive, armored materials, well graded or with extended granulometry, poorly graded or with uniform granulometry.[21]​.

• - Depending on the conditions of solid transport, three types of channels can be considered: stable, erodible and depositional.[22]​.

Algunos ríos cortos y torrentes "Torrente (hidrografía)") pueden fluir desde su cabecera inicio hasta el mar sin convertirse en afluentes o tributarios de otro mayor, ni recibir agua de otros ríos. En general, un río forma parte de una red de drenaje (o sistema fluvial) ocupando una cuenca hidrográfica "Cuenca (accidente geográfico)"). Algunas cuencas abarcan pocos km², en cambio la cuenca del Amazonas se extiende a lo largo de 6,14 millones de km² (véase la lista de las principales cuencas).

Las cuencas de los ríos y sus redes de drenaje pueden cambiar de forma natural en periodos relativamente cortos de tiempo como consecuencia de capturas fluviales.

Rivers and landscapes

Rivers erode rocks and sediments, opening channels and valleys, modeling the landscape in what is called fluvial modeling. The deep channel of the Colorado River has cut in some places to a depth of 1.5 km, forming the Grand Canyon. And the canyon of the Majes River or Camaná River, in Peru, is even deeper, about 3 km deep.

River valleys are generally V-shaped, especially in mountainous areas of recent uplift, but this shape is modified along the course of the river, also expanding its size, slope, transverse profile, sediment transport capacity and many other characteristics.[23]​.

The flora and fauna of rivers is different from that found in the oceans because the water has different characteristics, especially salinity.[24]​[25]​ The species that inhabit rivers have had to adapt to currents and unevenness. However, there are numerous exceptions, such as the case of the salmon "Salmo (genus)") that spawn in the upper or mountainous basins of the rivers,[26] or the freshwater sharks of Nicaragua, and also in the case of marine species that penetrate the ocean deltas carried by the high tide of the tides and ocean currents, as happens in the Orinoco and Amazon deltas. The same happens with river estuaries, although in this case, the entry of marine species into the rivers is usually momentary during the flow or high tide, which is due to the fact that they are emptied during the ebb or low tide, while in the deltas, what changes during the tides is the greater or lesser salinity of their waters.

Some freshwater fish are:

• - Eel: they are born in the Sargasso Sea. The larvae migrate to European and North African rivers, where they reach three years of age (eels). They will spend between 4 and 10 years in the rivers, at which time they begin their reproductive migration to the place where they were born. Adults die after reproducing.

• - Catfish, in Central and South America;.

• - Barbel, in central Europe.

• - Bream "Bream (fish)"): lives in gentle flowing waters;

• - Caribbean or piranha, in the rivers of South America;.

• - Cachama, in South America;.

• - Large tent;.

• - Escardinio"): lives in calm waters full of vegetation;

• - Sturgeon, a large Eurasian fish, whose eggs are used to make caviar;

• - Goby;.

• - Rodeo");.

• - Rutile: adapts to muddy waters although it prefers clear ones;

• - Salmon "Salmo (genus)"): is born in mountain rivers with fast-flowing waters and stony bottoms. At three years old it migrates to the sea and returns to the river to reproduce.

• - Tarpon;.

• - Trembler, gymnoto or electric eel (South America);

• - River trout: lives in clear, cold waters, rich in oxygen;

Some mammals whose habitat is freshwater are:

• - Beaver; in the rivers of North America and Eurasia.

• - Pink dolphin; in the Amazon River and its tributaries.

• - Hippo; in central and southern Africa.

• - Amazonian manatee; in the Amazon River and its tributaries.

• - Platypus; in eastern Australia.

• - Water supply: Rivers are vital sources of fresh water for life on Earth. They provide water for human consumption, agriculture, livestock and industry. Many communities and cities depend on rivers as their main source of water supply.

• - Biodiversity and habitat: Rivers are home to a great diversity of plant and animal species. Riparian and aquatic ecosystems provide essential habitats for many species, including fish, birds, mammals and amphibians. Rivers also function as ecological corridors, allowing the movement of species and contributing to the connectivity of ecosystems.

• - Water cycle: Rivers play a key role in the water cycle. They act as drainage pathways for surface runoff, collecting and transporting precipitation water to the oceans. In addition, rivers recharge underground aquifers and contribute to maintaining the water balance in the environment.

• - Flood Control: Rivers have the ability to mitigate floods by acting as natural conduits for the flow of water. During periods of heavy rainfall, rivers can absorb and redirect excess water, helping to prevent flooding in inhabited areas and reducing the risk of damage to property and human life.

• - Recreation and tourism: Rivers[27] offer numerous recreational and tourist opportunities. Activities such as sport fishing, canoeing, rafting and boating are popular on the rivers. Additionally, many scenic rivers and river landscapes attract tourists, providing opportunities for nature tourism, wildlife viewing, and enjoyment of natural beauty.

Water is a renewable resource in danger due to human activity. All pure water from rain, before reaching the ground, receives its first polluting load, when it dissolves chemical substances such as carbon dioxide, sulfur oxide and nitrogen oxide, which convert it into acid rain.[28] Once in the soil, the water runs along the surface or filters into underground layers. When crossing the fields, the river water is loaded with pesticides and when it passes through cities it carries products such as gasoline, automobile oils, organic waste, heavy metals, etc. Rivers show a certain capacity to get rid of pollutants, but to do so they need to have a very long stretch in which bacteria can carry out their purifying work. In a river contaminated by organic matter, three zones are distinguished from the point of contamination:

• - Polysaprobic zone"): It is the most contaminated area, it has a high population of bacteria.[29]​.

• - Mesosaprobic zone"): Its level of contamination is medium, because the bacteria have already eliminated much of the organic contamination.[30]​.

• - Oligosaprobic zone"): The water is in conditions similar to those it had before the contamination occurred.[30]​.

It is difficult to measure the exact length of a river due to the properties of the terrain through which it flows. The 10 largest rivers in the world with approximate length are listed below:[note 1]​.

1. • Amazon River (7062 km).

2. • Nile River (6670 km)[34]​.

3. • Yangtze River (6380 km)[34]​.

4. • Mississippi-Missouri River (6275 km)[35]​.

5. • Río Madeira / Mamoré / Grande "Río Grande (Bolivia)") (5908 km).

6. • Yellow River or Huang He River (China) (5464 km)[34]​.

7. • Obi River (5400 km)[36]​.

8. • Paraná River-Río de la Plata (4880 km)[37]​.

9. • Amur River (4410 km)[38]​.

10. • Congo River (4380 km or 4670 km, depending on where it is born)[38]​[39]​.

Every state exercises territorial sovereignty over the course or portion of the course of a river that is part of its territory.[40]​.

There are two categories of rivers:

• - Interior or national rivers, which have their course in the territory of a State.

• - Rivers that in their course separate or cross the territory of more than one State, also called binational or multinational. These rivers can be border or successive, or both at the same time, as is the case of the Danube and many others.

Internationalized rivers are those in which there is freedom of navigation, which, depending on whether it is more or less extensive, may be in favor of all flags or only of the riverside rivers.

The police and administration of a river open to free navigation raises numerous problems: the customs regime, pilotage, port regulations, taxes, etc.

The general rule is that in principle the administration of each sector of the river is exercised by the respective riverside manager.

A formula that has managed to avoid problems, especially in European rivers where the concentration of navigation is very great, consists of the establishment of international river administration commissions.

Fountains and rivers had a special cult in Greece, as can be seen in the graphic representations. Fountains and rivers are generally symbolized by a robust man, with some resemblance to Jupiter "Jupiter (mythology)"). Some coins are known that represent them in the guise of a woman, and in others the rivers appear with the figure of a naked young man half-length, in the water, extending his arms in an attitude of swimming: this is how they are seen on the coins of Campania and Cilicia. Sometimes rivers are shown with antlers or horns, perhaps because, when they collide, their waves are reminiscent of the lowing of an ox.

The fountains and rivers that are specially represented in the monuments have been:

• - Acragas, Girgenti Vechio, in Sicily.

• - Alfeo in Arcadia, a region of Greece in the center of the Peloponnese, Morea.

• - Amenano, Guidicello, near Mount Etna.

• - Arethusa, fountain on the island Ortigia, near Syracuse.

• - Asines, Falconara, in Sicily.

• - Callirrohe, that is, "peaceful waves", source in Aetolia, near Calidon.

• - Caístro, Kitchek-Meinder or the little Meander in Lydia.

• - Euphrates, which has its origin in Caranitide, a province of Eastern Armenia.

• - Indo, Sind or Pliny's Sindus.

• - Ister, Danube.

• - Lico, in Vindelicia, part of the circles of Suavia and Bavaria.

• - Meander, Meinder, in western Phrygia, near Celenes, in Asia Minor.

• - Nile, with his so-called children Memphis and Anchirroha.

• - Sagaris or Sangarius, Sakarya, who is born in the confines of Galatia and Phrygia, in Asia Minor.

• - Scamandro or Xanto, Kirke-Keuzler, on Mount Ida in the Trocada.

• - Strimon, Stryma Marmari or Rendina, on Mount Hemus in Thrace.

• - Tiber, in the Apennines, towards the borders of southern Umbria in Italy.[41]​.

Potamology") is the study of river waters (from the Greek Ποταμός potamós = 'river'), which covers concepts such as its flow, its channel, its basin, its course or current, the fluvial regime, the fluvial dynamics, its profiles (longitudinal and transversal), its tributaries and their importance, ecology, flora, fauna, water and hydroelectric resources") or navigation river, among others. It is considered part of hydrography.[42][43]​.

• - Wikimedia Commons hosts a multimedia gallery about river.

• - Wiktionary has definitions and other information about river.

Nomenclature

The main river is usually defined as the course with the greatest water flow (average or maximum) or with the greatest length or greatest drainage area. This concept of a main river, like that of the birth of a river or the distinction between a main river and a tributary, are subjective.

In many cases, doubts arise about the name and route of the rivers, especially in hydrographic basins with heterogeneous relief and great extension, in which there has not been a common criterion about the dimensions of the main river and its tributaries. In other cases, there are several names for the same river, along its length. Examples of rivers whose names have been discussed in relation to where we can fix their source or with more important tributaries than the main river we can point out:

• - The Amazon River, with three important tributaries in its upper part (Marañón, Ucayali, Huallaga) although in this case, the Ucayali has been taken, along the course of the Apurímac River, whose sources are in Misti, Arequipa, Peru, as the true Amazon.[12]​.

• - The Nile, formed by the confluence of the White Nile and the Blue Nile.[13]​.

• - The Orinoco, with a tributary longer than the Orinoco itself at the point of its confluence, the Guaviare.[14]​.

• - The Miño, with a longer and mightier tributary at the point of its confluence, the Sil.

• - The Mississippi-Missouri, the tributary (the Missouri) being longer than the main river, although not larger, at the point of its confluence.

• - The Guadalquivir, formed by the upper part of the river with this name at its confluence with the Guadiana Menor, whose length is greater.

In other cases, the same river has different names along its course, especially in cases where arms or channels are formed from a channel and each of these arms takes a different name. This is the case of Apure (Apure Seco, Apure Viejo and Apurito). The Magro could also be included in this case (rambla de la Torre, Magro river, Alcalá, rambla de Algemesí, among others.).

Guys

Rivers can be classified from various points of view, among which the following stand out:

• - Depending on the period of activity, in perennial, seasonal, transient or allochthonous rivers.[15]​.

• - According to its geometry or morphology, a river or a certain stretch can be classified in the following categories: rectilinear, sinuous, meandering, anastomosing, with islands, in estuaries, in swamps or mangroves, in deltas.[16]​.

• - According to its age, it is classified as young, mature or old rivers.[17]​.

• - Depending on its stability condition, a section of channel can be considered with static, dynamic stability, with dynamic instability or with morphological stability.[18]​.

• - Its sections can be classified as high mountain, mountain, mountain slope, intermediate and plain.[19]​.

• - According to its degrees of freedom, it can be classified as having one, two or three degrees of freedom.[20]​.

• - Depending on the material of the margins and the bottom, they can be considered as cohesive, non-cohesive, armored materials, well graded or with extended granulometry, poorly graded or with uniform granulometry.[21]​.

• - Depending on the conditions of solid transport, three types of channels can be considered: stable, erodible and depositional.[22]​.

Algunos ríos cortos y torrentes "Torrente (hidrografía)") pueden fluir desde su cabecera inicio hasta el mar sin convertirse en afluentes o tributarios de otro mayor, ni recibir agua de otros ríos. En general, un río forma parte de una red de drenaje (o sistema fluvial) ocupando una cuenca hidrográfica "Cuenca (accidente geográfico)"). Algunas cuencas abarcan pocos km², en cambio la cuenca del Amazonas se extiende a lo largo de 6,14 millones de km² (véase la lista de las principales cuencas).

Las cuencas de los ríos y sus redes de drenaje pueden cambiar de forma natural en periodos relativamente cortos de tiempo como consecuencia de capturas fluviales.

Rivers and landscapes

Rivers erode rocks and sediments, opening channels and valleys, modeling the landscape in what is called fluvial modeling. The deep channel of the Colorado River has cut in some places to a depth of 1.5 km, forming the Grand Canyon. And the canyon of the Majes River or Camaná River, in Peru, is even deeper, about 3 km deep.

River valleys are generally V-shaped, especially in mountainous areas of recent uplift, but this shape is modified along the course of the river, also expanding its size, slope, transverse profile, sediment transport capacity and many other characteristics.[23]​.

The flora and fauna of rivers is different from that found in the oceans because the water has different characteristics, especially salinity.[24]​[25]​ The species that inhabit rivers have had to adapt to currents and unevenness. However, there are numerous exceptions, such as the case of the salmon "Salmo (genus)") that spawn in the upper or mountainous basins of the rivers,[26] or the freshwater sharks of Nicaragua, and also in the case of marine species that penetrate the ocean deltas carried by the high tide of the tides and ocean currents, as happens in the Orinoco and Amazon deltas. The same happens with river estuaries, although in this case, the entry of marine species into the rivers is usually momentary during the flow or high tide, which is due to the fact that they are emptied during the ebb or low tide, while in the deltas, what changes during the tides is the greater or lesser salinity of their waters.

Some freshwater fish are:

• - Eel: they are born in the Sargasso Sea. The larvae migrate to European and North African rivers, where they reach three years of age (eels). They will spend between 4 and 10 years in the rivers, at which time they begin their reproductive migration to the place where they were born. Adults die after reproducing.

• - Catfish, in Central and South America;.

• - Barbel, in central Europe.

• - Bream "Bream (fish)"): lives in gentle flowing waters;

• - Caribbean or piranha, in the rivers of South America;.

• - Cachama, in South America;.

• - Large tent;.

• - Escardinio"): lives in calm waters full of vegetation;

• - Sturgeon, a large Eurasian fish, whose eggs are used to make caviar;

• - Goby;.

• - Rodeo");.

• - Rutile: adapts to muddy waters although it prefers clear ones;

• - Salmon "Salmo (genus)"): is born in mountain rivers with fast-flowing waters and stony bottoms. At three years old it migrates to the sea and returns to the river to reproduce.

• - Tarpon;.

• - Trembler, gymnoto or electric eel (South America);

• - River trout: lives in clear, cold waters, rich in oxygen;

Some mammals whose habitat is freshwater are:

• - Beaver; in the rivers of North America and Eurasia.

• - Pink dolphin; in the Amazon River and its tributaries.

• - Hippo; in central and southern Africa.

• - Amazonian manatee; in the Amazon River and its tributaries.

• - Platypus; in eastern Australia.

• - Water supply: Rivers are vital sources of fresh water for life on Earth. They provide water for human consumption, agriculture, livestock and industry. Many communities and cities depend on rivers as their main source of water supply.

• - Biodiversity and habitat: Rivers are home to a great diversity of plant and animal species. Riparian and aquatic ecosystems provide essential habitats for many species, including fish, birds, mammals and amphibians. Rivers also function as ecological corridors, allowing the movement of species and contributing to the connectivity of ecosystems.

• - Water cycle: Rivers play a key role in the water cycle. They act as drainage pathways for surface runoff, collecting and transporting precipitation water to the oceans. In addition, rivers recharge underground aquifers and contribute to maintaining the water balance in the environment.

• - Flood Control: Rivers have the ability to mitigate floods by acting as natural conduits for the flow of water. During periods of heavy rainfall, rivers can absorb and redirect excess water, helping to prevent flooding in inhabited areas and reducing the risk of damage to property and human life.

• - Recreation and tourism: Rivers[27] offer numerous recreational and tourist opportunities. Activities such as sport fishing, canoeing, rafting and boating are popular on the rivers. Additionally, many scenic rivers and river landscapes attract tourists, providing opportunities for nature tourism, wildlife viewing, and enjoyment of natural beauty.

Water is a renewable resource in danger due to human activity. All pure water from rain, before reaching the ground, receives its first polluting load, when it dissolves chemical substances such as carbon dioxide, sulfur oxide and nitrogen oxide, which convert it into acid rain.[28] Once in the soil, the water runs along the surface or filters into underground layers. When crossing the fields, the river water is loaded with pesticides and when it passes through cities it carries products such as gasoline, automobile oils, organic waste, heavy metals, etc. Rivers show a certain capacity to get rid of pollutants, but to do so they need to have a very long stretch in which bacteria can carry out their purifying work. In a river contaminated by organic matter, three zones are distinguished from the point of contamination:

• - Polysaprobic zone"): It is the most contaminated area, it has a high population of bacteria.[29]​.

• - Mesosaprobic zone"): Its level of contamination is medium, because the bacteria have already eliminated much of the organic contamination.[30]​.

• - Oligosaprobic zone"): The water is in conditions similar to those it had before the contamination occurred.[30]​.

It is difficult to measure the exact length of a river due to the properties of the terrain through which it flows. The 10 largest rivers in the world with approximate length are listed below:[note 1]​.

1. • Amazon River (7062 km).

2. • Nile River (6670 km)[34]​.

3. • Yangtze River (6380 km)[34]​.

4. • Mississippi-Missouri River (6275 km)[35]​.

5. • Río Madeira / Mamoré / Grande "Río Grande (Bolivia)") (5908 km).

6. • Yellow River or Huang He River (China) (5464 km)[34]​.

7. • Obi River (5400 km)[36]​.

8. • Paraná River-Río de la Plata (4880 km)[37]​.

9. • Amur River (4410 km)[38]​.

10. • Congo River (4380 km or 4670 km, depending on where it is born)[38]​[39]​.

Every state exercises territorial sovereignty over the course or portion of the course of a river that is part of its territory.[40]​.

There are two categories of rivers:

• - Interior or national rivers, which have their course in the territory of a State.

• - Rivers that in their course separate or cross the territory of more than one State, also called binational or multinational. These rivers can be border or successive, or both at the same time, as is the case of the Danube and many others.

Internationalized rivers are those in which there is freedom of navigation, which, depending on whether it is more or less extensive, may be in favor of all flags or only of the riverside rivers.

The police and administration of a river open to free navigation raises numerous problems: the customs regime, pilotage, port regulations, taxes, etc.

The general rule is that in principle the administration of each sector of the river is exercised by the respective riverside manager.

A formula that has managed to avoid problems, especially in European rivers where the concentration of navigation is very great, consists of the establishment of international river administration commissions.

Fountains and rivers had a special cult in Greece, as can be seen in the graphic representations. Fountains and rivers are generally symbolized by a robust man, with some resemblance to Jupiter "Jupiter (mythology)"). Some coins are known that represent them in the guise of a woman, and in others the rivers appear with the figure of a naked young man half-length, in the water, extending his arms in an attitude of swimming: this is how they are seen on the coins of Campania and Cilicia. Sometimes rivers are shown with antlers or horns, perhaps because, when they collide, their waves are reminiscent of the lowing of an ox.

The fountains and rivers that are specially represented in the monuments have been:

• - Acragas, Girgenti Vechio, in Sicily.

• - Alfeo in Arcadia, a region of Greece in the center of the Peloponnese, Morea.

• - Amenano, Guidicello, near Mount Etna.

• - Arethusa, fountain on the island Ortigia, near Syracuse.

• - Asines, Falconara, in Sicily.

• - Callirrohe, that is, "peaceful waves", source in Aetolia, near Calidon.

• - Caístro, Kitchek-Meinder or the little Meander in Lydia.

• - Euphrates, which has its origin in Caranitide, a province of Eastern Armenia.

• - Indo, Sind or Pliny's Sindus.

• - Ister, Danube.

• - Lico, in Vindelicia, part of the circles of Suavia and Bavaria.

• - Meander, Meinder, in western Phrygia, near Celenes, in Asia Minor.

• - Nile, with his so-called children Memphis and Anchirroha.

• - Sagaris or Sangarius, Sakarya, who is born in the confines of Galatia and Phrygia, in Asia Minor.

• - Scamandro or Xanto, Kirke-Keuzler, on Mount Ida in the Trocada.

• - Strimon, Stryma Marmari or Rendina, on Mount Hemus in Thrace.

• - Tiber, in the Apennines, towards the borders of southern Umbria in Italy.[41]​.

Potamology") is the study of river waters (from the Greek Ποταμός potamós = 'river'), which covers concepts such as its flow, its channel, its basin, its course or current, the fluvial regime, the fluvial dynamics, its profiles (longitudinal and transversal), its tributaries and their importance, ecology, flora, fauna, water and hydroelectric resources") or navigation river, among others. It is considered part of hydrography.[42][43]​.

• - Wikimedia Commons hosts a multimedia gallery about river.

• - Wiktionary has definitions and other information about river.