HYDROLOGICAL BASIN: CHARACTERISTICS, TYPES, FLORA, FAUNA, EXAMPLES - GEOGRAPHY - 2025

A watershed is a natural drainage system through which surface and groundwater flow to a single receiving site. This site can be the sea, the ocean or an endorheic lake, that is to say a lake that has no water outlet to another destination.

The hydrological basin is a very useful model for integrated territorial planning, since it allows to relate the natural and socioeconomic environment existing in an area. The characteristics of a hydrological basin are given by its relief, especially the maximum height that its peaks reach.

Amazon basin. Source: Kmusser / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0)

The peaks establish the limits of the basin, because it is in the mountain ranges where the water is distributed by gravity. These are the so-called watersheds and the water currents that feed the hydrological basin are born there.

Among them are those that give rise to the main river in the basin, that is, the receiver of all surface flow. This river is in charge of transporting this flow to the point of discharge or exit from the basin.

Other factors that define the characteristics of the basin are rainfall, runoff, evaporation rate and infiltration of water into the soil. In addition, a part of the water is lost through evapotranspiration due to the temperature and metabolism of the plants.

The vegetation cover that exists in a hydrological basin influences the losses due to transpiration and the decrease in erosion as well as the increase in infiltration. For its part, the water that infiltrates feeds the aquifers of the hydrological basin, that is, the groundwater.

The two largest hydrological basins in the world are the Amazon River Basin in South America and the Congo River Basin in Africa.

Characteristics of the

The elemental dynamics of a hydrological basin is the precipitation and the flow of the water determined by the force of gravity. The water precipitates on the earth from the highest points to the lowest point and the pattern of this displacement is given by the relief of the hydrological basin.

- relief

Every hydrological basin has elevated parts, generally mountain ranges whose peaks determine the limit of the basin. This is because at the summit line, rainwater will flow back and forth on the slopes of the mountain range.

These lines of the summits are called parts of water, since the water that flows up each slope goes to different basins. By gravity, the water goes to the lower parts of the basin, which are the valleys and plains.

- Water

Water enters through precipitation, so the higher the annual precipitation in a region, the greater the flow of the hydrological basin. This determines the outlet flow of the hydrological basin, that is, the amount of water that reaches the final discharge point.

In a hydrological basin, water moves both superficially and underground. In this sense, surface waters correspond to a hydrographic basin, while a hydrological basin is also taken into consideration groundwater.

Runoff and the hydrological network

As water rushes onto the ground in the watershed area, it can follow two basic paths. In one case it runs off the ground (runoff) and in the other it penetrates the ground (infiltration).

In the first case, most of the water flows superficially forming small channels, then streams and these constitute rivers. When the smaller rivers converge, they form larger courses until creating a main river that carries the water to the final discharge site of the basin.

This set of rivers, where some are tributaries or tributaries of other larger ones, forms a network called the fluvial network or the hydrological network of the basin. In the surface path of water, a part is lost through evaporation and the amount evaporated depends on the temperature.

Infiltration

Another portion of the water infiltrates between the cracks and pores in the soil, accumulating in the soil and forming underground deposits (aquifers). Of the infiltrated water, a portion is absorbed by plants or lost through evaporation.

The part of the water that goes to deeper layers can flow horizontally in underground rivers or remain accumulated.

Vegetation and water

The water absorbed from the soil by the plants will end up back in the atmosphere due to perspiration.

- Aquifers

The portion of the water that does not run off the surface and infiltrate can accumulate in subterranean layers at different depths. This occurs when the water infiltrates deeply and encounters an impermeable soil layer.

Groundwater. Source: Bluetelly / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

In this case, aquifers are formed, which can consist of a substrate soaked in water or cavities where true underground cisterns are formed. The latter happens in calcareous substrates where the water creates galleries and even underground rivers are formed.

Surge

The water in these aquifers can rise to the surface in so-called springs or, if heated by geothermal energy, can form geysers. In the latter the water comes out under pressure as hot liquid and water vapor.

These and the wells created by the human being are the discharge routes of the aquifers. While the recharges occur by rain or the contributions of surface rivers.

Wells

The human being accesses the water in the aquifers by building wells up to the water table, extracting the water using buckets or hydraulic pumps. On the other hand, there are cases where groundwater flows from a high point to a low point where the well is located.

Under these conditions the pressure will make the water in the well rise, even to the surface (artisan well).

- Main river and tributaries

The backbone of a basin is its main river, which generally corresponds to the river with the greatest flow or the longest length. However, it is not always easy to establish this in a watershed.

Every river is formed by a source, a high course, a medium one, a low one and finally the mouth. So the main river collects all the surface water of the basin, as other rivers that are called tributaries converge in it.

In turn, these tributaries of the main river collect the waters of their own tributaries, in such a way that a network is formed. This network begins in the highest parts of the basin with small streams and streams.

- Factors that affect the flow of the hydrological basin

The factors that determine how much water will flow through the basin (flow) and at what speed it will flow out, are diverse and complex. The amount of water that enters and flows through the basin is defined by both precipitation and evapotranspiration.

Then it is necessary to know how much water remains stored in underground reservoirs, for which it is necessary to know the infiltration and the dynamics of the aquifers.

While the speed at which it runs depends on runoff, influenced by the type of soil, the slope and the vegetation cover. In a basin with high slopes (steep slopes of the land) and bare vegetation, runoff is high and infiltration is low.

Sedimentation

The amount of sediment carried by the water in a hydrological basin is another very relevant factor. This has to do with erosive processes, which also increase with the slope and the scarce vegetation.

The entrained sediments can clog river beds and reduce their transport capacity, causing flooding.

Watershed types

The types of hydrological basins can be classified by their size or relief or by the final destination of the evacuation or discharge of their waters.

Exoreic basin

This is the most common type and includes hydrological basins whose waters drain into the sea or directly into the ocean. As for example, the basins of the Amazon, the Orinoco, the Mississippi, the Congo, the Ganges, the Nile and the Guadalquivir.

Endorheic basin

In this case, the final destination of the water in the basin is a closed inland lake or sea, returning by evapotranspiration to the atmosphere. These endorheic basins do not have any type of communication with the sea.

Endorheic basin of the Caspian Sea. Source: Jeff Schmaltz, MODIS Rapid Response Team, NASA / GSFC / Public domain

For example, the Lake Eyre basin in Australia, which is the largest endorheic basin in the world. The Caspian Sea, which is the largest endorheic lake on the planet, is also an endorheic basin.

Arreica basin

In this type there is no receiving surface water body, no major river, no lake, nor does its waters reach the sea. The waters that flow through the basin simply end up infiltrating or evaporating.

This generally occurs in arid or semi-arid areas, where precipitation is low, evaporation is high, and soils are highly permeable. For example, the Qattara depression in the Libyan desert, as well as in Patagonia, present basins of this type.

Flora and fauna

All the terrestrial species of the world inhabit some hydrological basin, being distributed according to their climatic affinities and dispersal capacity. In this sense, there are species of wide distribution that are located in different basins of the world while others have more restricted distribution.

For example, the jaguar (Panthera onca) inhabits hydrological basins from southern Mexico to the southern cone of America. While the Tepuihyla rimarum frog is exclusive to the Ptari tepui, a tabular mountain in Venezuelan Guiana, belonging to the Orinoco hydrological basin.

Endemic species

These are species that only inhabit a restricted geographical area, some only a certain watershed. For example, the Iberian desman (Galemys pyrenaicus) a species of semi-aquatic insectivorous rodent endemic to the basins of the Iberian Peninsula.

Mexican axolotl (Ambystoma mexicanum). Source: Emőke Dénes / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

While in Mexico you can find the Mexican axolotl (Ambystoma mexicanum) a peculiar salamander endemic to its basins.

On the other hand, among the plants we can point out the water lily called Victoria amazónica, typical of the Amazon basin. While in the basins of the Atlantic forest in Brazil the national tree of this country is located, the Brazilian wood or pernambuco (Caesalpinia echinata).

Migration

On the other hand, there are migratory species, that is, they move from one region to another, being able to move from one basin to another.

For example, many migratory birds such as the stork (Ciconia ciconia) migrate. They spend the summer in the basins of southern Europe and in winter they go to the sub-Saharan basins of Africa.

Parts of the

The parts of a watershed are determined by the relationship between sediment carry and deposition, as well as by elevation levels. In this way, you have the upper, middle and lower basin.

Upper basin

It corresponds to the highest elevations of the basin, from the source of the main river to the lower levels of the mountains. In this part the erosion and the carry of materials is greater due to the slope that gives greater force to the water currents.

Middle basin

It extends from the foothills, running through the middle elevations of the terrain, with a lower speed of the water. The erosive power is lower, with a balance occurring between the material deposited by the river (sedimentation) and that which it draws towards the lower basin (erosion).

Low basin

It is the lowest part of the basin in order to reach the mouth of the main river. Here the relationship is in favor of sedimentation, forming alluvial plains, where the derivations of the river leave much of its sediments.

Examples of basins in the world

- The Amazon basin (South America)

The Amazon River basin is the largest hydrological basin in the world with more than 6,000,000 km ² and is located in the center of South America. Additionally, this basin has the peculiarity of being connected with the Orinoco basin, the third in extension in South America, through the Casiquiare arm.

Hydrological basin of the Amazon. Source: Contains modified Copernicus Sentinel data {{{year}}} / CC BY-SA 3.0-IGO (https://creativecommons.org/licenses/by-sa/3.0-igo)

In this case, the Casiquiare constitutes an effluent from the Orinoco River, draining part of this basin to the Negro River of the Amazon basin. For what some refer to it as the Amazon-Orinoco basin.

Its main river, the Amazon, originates in the Peruvian Andes and empties into the Atlantic Ocean off the Brazilian coast with a flow of up to 300,000 m ³ / sec. On the other hand, this hydrological basin has two water discharge systems, one superficial which is the Amazon River and the other underground.

Hamza River

The underground water flow system is named after the Hamza River, although some do not really consider it a river. This is because the water does not flow through galleries but through the pores of the rocks at a much slower speed.

The Hamza “river” is twice the width of the Amazon, but its speed is only 3,090 m ³ / sec.

Water cycle

The Amazon jungle plays a fundamental role in regulating the planetary climate, due to its contribution to the water cycle. Not only because of the flow of water that the river discharges into the Atlantic Ocean, but also because of the evapotranspiration contributions that the jungle makes to the atmosphere.

Native species

This basin is home to the highest concentration of biological diversity on the planet, forming an extensive tropical rainforest. Among the unique animal species of the Amazon basin are the hyacinth macaw (Anodorhynchus hyacinthinus) and the Orinoco black caiman (Melanosuchus niger).

While some species of plants native to this hydrological basin are the yucca or cassava (Manihot esculenta) and the pineapple or pineapple (Ananas comosus).

- The Congo Basin (Africa)

Map of the route of the Congo River. Rzeka_Kongo.jpg: Demis, Radosław Botevderivative work: Osado / CC BY 2.5 PL (https://creativecommons.org/licenses/by/2.5/pl/deed.en)

It is the second largest hydrological basin in the world and the first in Africa, with an area of ​​3,700,000 km ². The main river is the Congo River which is born in the East Rift Mountains of Africa and the Tanganyika and Mweru lakes.

This river first flows northwest and then drifts southwest to empty into the Atlantic Ocean to the west. This basin drains about 41,000 m ³ / sec, that is, it has 5 times less flow than the Amazon.

Native species

It is home to the second largest tropical rain forest on the planet after the Amazon. Endangered species such as the mountain gorilla (Gorilla gorilla gorilla) and the coastal gorilla (Gorilla gorilla diehli) inhabit it.

As well as the jungle elephant (Loxodonta cyclotis) and the okapi (Okapia johnstoni), a relative of giraffes. Among the plants, the species of the genus Raphia stand out, whose fibers are used in the textile industry.

References

1. Calow P (Ed.) (1998). The encyclopedia of ecology and environmental management.
2. Carranza-Valle, J. (2011). Hydrological evaluation of the Peruvian Amazon basins. National Meteorology and Hydrology Service. Peru.
3. Cotler-Ávalos, H., Galindo-Alcántar, A., González-Mora, ID, Raúl Francisco Pineda-López, RF and Ríos-Patrón, E. (2013). Watersheds: Fundamentals and perspectives for their management and management. Environmental disclosure notebooks. SEMARNAT.
4. Margalef, R. (1974). Ecology. Omega editions.
5. Miller, G. and TYLER, JR (1992). Ecology and Environment. Grupo Editorial Iberoamérica SA de CV
6. Odum, EP and Warrett, GW (2006). Fundamentals of ecology. Fifth edition. Thomson.
7. Ordoñez-Gálvez, JJ (2011). What is a hydrological basin? Technical primer. Geographical Society of Lima.
8. Ordoñez-Gálvez, JJ (2011). Groundwater - Aquifers.. Technical primer. Geographical Society of Lima.
9. Secretariat of the Convention on Biological Diversity and the Central African Forest Commission (2009) Biodiversity and Forest Management in the Congo Basin, Montreal.