HYDROGRAPHIC SLOPES: CHARACTERISTICS AND LIST IN LATIN AMERICA - GEOGRAPHY - 2025

The hydrographic slopes are a group of basins that flow into the same body of water. The size and shape of the slopes is determined by the relief of the area where they are formed.

The symmetry of the watersheds can vary, depending on whether the basins are evenly distributed or not. When there are a greater number of basins to one side of the watershed divide, it is considered as asymmetric.

Río de la Plata flowing into the Atlantic. Source: Earth Sciences and Image Analysis Laboratory, NASA Johnson Space Center

In Spain there are three hydrographic slopes, of which the most important is the one that flows into the Atlantic. In this slope, some of the most important rivers are the Tagus and the Duero.

For Mexico there are also three slopes defined by the great mountain ranges of the country. On the Pacific side, the Colorado River stands out, while on the Caribbean side the most important is the Rio Grande.

Colombia has four main slopes, highlighting the Atlantic with the Magdalena-Cauca system, which has a large navigable part. The slopes of the Amazon and the Orinoco flow into these two great rivers.

In Argentina, the Atlantic slope is the most important as it is the Río de la Plata basin. In this basin, the most important contribution is made by the Paraná River with an area of ​​2,800,000 km².

Characteristics of watersheds

A watershed is defined as the group of basins that flow into the same sea or river. Watersheds can vary in size and shape. Also, they are defined by some characteristics, such as symmetry and watershed.

Symmetry

This concept refers to the way in which the different basins of the slope are distributed, in relation to the center of it. If the slope is divided into two parts of similar dimensions, it is considered to be symmetrical.

The symmetry of a slope will be influenced mainly by the relief of the region. The distribution of mountain ranges and other orographic features will determine the way in which the basins are arranged in a slope.

Continental watershed

The so-called water or drainage dividers establish the boundaries between contiguous hydrographic basins. They are natural borders that separate the river system that make up two or more basins.

Water dividing lines have been used in many cases to define boundaries. A continental divide is one that divides the great slopes of the seas or oceans in a continent.

The layout of continental divisions can be very simple when there are geographical features such as mountain ranges that define it. In other cases, when the terrain is flatter, the boundaries are not so clearly defined.

Hydrographic slopes of Spain

The rivers that make up this slope are generally quite short and very large. These originate in mountainous areas that are very close to the Cantabrian coast.

The difference in level between the source and the mouth of these rivers is quite large, so they have a great erosive force. Erosion capacity is dampened by vegetation associated with rivers.

On the other hand, these rivers receive a large amount of precipitation throughout the year, which contributes to increasing their flow. Due to their characteristics, the rivers on this slope are very useful to be used in hydroelectric projects.

The rivers that make up the Cantabrian slope are not very numerous and the Bidasoa, Eo, Nalón, Navia and Nervión can be highlighted.

Atlantic slope

The Atlantic slope is the largest in Spain, with 69% of the basins flowing into this ocean. Most of the rivers that make up the basins of this slope are born in the Central Plateau.

Rivers tend to be long and gently sloping, running through plains and peneplains before reaching the Atlantic. The shortest rivers are those that make up the Andalusia and Galicia basins.

These rivers have a low erosive force and are mighty because they receive numerous tributaries. The precipitation regime is irregular and because they are subject to a Mediterranean climate, the flow decreases from north to south.

On the Atlantic slope, the Miño River (which rises in the Sierra de Meira, Galicia) and those that originate in the Central Plateau stand out. Among the longest we have the Tajo, Duero, Guadalquivir and Guadiana.

Mediterranean slope

It is made up of rivers of unequal size, the Ebro being the longest. The other rivers are much shorter and form small, low-flow basins.

The Ebro is the river with the highest flow, mainly due to the contributions it receives from its many tributaries. The shorter rivers originate in mountainous areas and have a great erosive force.

In general, the rivers of the Mediterranean slope have a fairly irregular water regime and are subject to significant seasonal floods. Some streams are seasonal and dry for most of the year and are known as ramblas.

In addition to the Ebro, which forms the most important basin on the Atlantic slope, we have the Llobregat, Turía, Jucar and Segura, among others.

Hydrographic slopes of Mexico

In Mexico the hydrographic network is defined by its relief, which is characterized by large mountain ranges near the coast. Likewise, there are frequent large (closed) endorheic basins towards the interior of the country that are known as pockets.

The rivers of Mexico tend to be short and of variable flow depending on their geographical location. The basins of the north of the country have less mighty rivers and often sporadic. The southern rivers receive abundant rainfall and have a greater flow.

Bravo River. Source: Bob Palin

The continental divisions define three hydrographic slopes:

Western or Pacific slope and Gulf of California

In this slope the rivers are generally short and with very fast currents. This watershed receives water from 32 rivers with a significant flow, which together discharge 81,781 million hm³ of water / year.

The longest river that makes up the Pacific slope is the Colorado River, which has a total extension of 2,500 km. However, this river is shared with the United States and in Mexican territory they only run 160 km.

The basin with the largest surface area on this slope is that of the Balsas River, which occupies 117,406 km². It is one of the longest rivers facing the Pacific, with a length of 770 km and contributes 16,587 hm³ / year of water.

Other important rivers are the Culiacán, which is 875 km long, but the surface of its basin is barely 15,731 km². The Santiago (572 km) and Yaquí (410 km) rivers have basins with surfaces greater than 70,000 km².

Eastern or Gulf slope and Caribbean Sea

The basins of this slope give towards the Atlantic region, ending in the Gulf of Mexico and the Caribbean Sea. Sixteen important rivers flow towards this area, which together have a total water runoff of 248,572 million hm3 / year.

The water supply of this slope is more than three times higher than that of the Pacific slope. The longest river that flows into the Gulf of Mexico is the Rio Grande with 3,034 km in length.

The Rio Grande is shared with the United States and its basin covers an area of ​​225,242 km². However, the river that contributes the greatest runoff on this slope is the Grijalva-Usamacinta, which is one of the largest and longest in Mexico.

The Grijalva-Usamacinta river has a length of 1,521 km and its basin has an area of ​​83,553 km². The water supply of this basin is 115,536 hm³ / year, greater than the set of 32 main rivers on the Pacific slope.

Other important basins that face the Gulf slopes are the Pánuco (510 km), San Fernando (400 km) and the Papaloapán (354 km).

South or interior slope

This slope is characterized because its rivers flow into interior lagoons. Therefore, the basins that make it up are endorheic.

These rivers are generally short and have a small flow. The basin with the largest surface area is that of the Nazas-Aguanaval rivers, which are shared by the states of Durango, Zacatecas and Coahuila.

The Nazas River is born in Durango and originally flowed into the Laguna de Mayran, in San Pedro, Coahuila. However, at present the river has been channeled and various dams have been built to use its waters for agricultural activities.

The Aguanaval River originates in the Sierra de Zacatecas and later flows into the lagoon region of the state of Coahuila. Likewise, it is associated with the formation of different dams.

As a whole, the Nazas-Aguanaval basin has a surface area of ​​89,239 km² and a length of 1,081 km. The water supply is 2,085 hm³ / year and there are 8 dams along its route.

Another important basin on the inland slope is the river Lerma. This river has a length of 708 km and its basin covers an area of ​​47,116 km².

This river is born in the state of Mexico and runs through Querétaro, Guanajuato and Michoacán until it empties into the Chapala lagoon in Jalisco.

Hydrographic slopes of Colombia

In Colombia, the hydrographic system is quite extensive and part of its territory overlooks the Pacific and another has the influence of the Atlantic.

The occurrence of these different slopes is influenced by the relief of the country. Thus, the longest rivers make their way through the Llanos area to flow into the Amazon and Orinoco rivers.

Magdalena river. Source: Jimmy Gómez N

Pacific slope

This slope is made up of more than 200 rivers and occupies an approximate area of ​​88,000 km². Most of its rivers are born in the mountainous area of ​​the Western Cordillera and contribute 10% of the total flow of the rivers of Colombia.

The rivers of this slope are generally short and very large, since the precipitations are high, of up to 9,000 mm per year. In addition, there is a great unevenness between the source and the mouth, so the erosive force is high.

Among the most important basins on this slope is that of the Patía River with 24,000 km². This river has a length of 400 km and more than 90 km are navigable, being the longest of this slope.

The San Juan river basin is the second most important (20,000 km²) and the river has a length of 380 km. It is the largest river on this slope, with 1,300 cm3 / second.

Another important basin is that of the Mira River (11,000 km²) that originates in Ecuador and has a route of 88 km in Colombian territory. Finally, the Baudo basin (8,000 km²) stands out, which rises at a height of 1,810 meters above sea level and has a length of 150 km.

Atlantic slope

In this slope we will include the so-called slopes of the Caribbean Sea and Catatumbo, because both are of Atlantic influence, so they can be considered the same region.

The basins that flow directly into the Caribbean Sea are formed in the three mountain ranges of the Andes and later run through the inter-Andean valleys. This part of the Atlantic slope has an approximate area of ​​363,878 km² and corresponds to 23% of the total flow.

The basin with the largest surface area on this slope is the one formed by the Magdalena-Cauca system (270,000 km²). The Magdalena has an extension of 1,558 km with a navigable length of 1,290 km, being the longest inter-Andean river in South America.

The Magdalena River originates from the Páramo de las Papas (3,685 masl) and receives more than 500 tributaries. The Cauca River, with a length of 1,350 km, is the most important tributary of the Magdalena.

Other important basins are those of the Atrato River (750 km) and the Sinú River (345 km). The Santa Marta basin is made up of short rivers that originate at 4,000 meters above sea level and run for 40 km until they reach the sea.

The rivers that drain into Lake Maracaibo (Venezuela) are known as the Catatumbo slope. These rivers are generally short, they originate in Colombia and end in Venezuela.

This slope has an area of ​​18,700 km² and the most important rivers are the Catatumbo (450 km), Zulia (310 km) and the Táchira (87 km).

Amazon slope

The Orinoco River is born in Venezuela, it is the fourth longest in South America (2,140 km) and the third most important for its flow. This slope is made up of more than 436 rivers with a surface area of ​​990,000 km².

The rivers of Colombia that flow into the Orinoco, are born mainly in the Eastern mountain range and run through the area of ​​the plains. The Orinoco slope in Colombian territory occupies an area of ​​328,000 km².

The most important basin is the Guaviare river (140,000 km²), which forms the boundary between the jungle region and the plains. This river originates from the Eastern Cordillera, being the longest tributary of the Orinoco (1,350 km).

Other relevant basins are those of the Meta River, the Vichada River and the Arauca River. The Meta basin (804 km) has a total area of ​​112,000 km², while the others are smaller.

Hydrographic slopes of Argentina

In Argentina there are two large slopes, one that flows into the Atlantic Ocean and the other towards the Pacific.

Parana River. Source: Ari Luiz de Castro

Atlantic slope

This is the most important slope in Argentina, the most important basin being the Río de la Plata.

The Río de la Plata basin contributes 11% of the flow that empties into the Atlantic and has an area of ​​3,200,000 km². The most important tributaries of this basin are the Paraná, Uruguay, Iguazú, Paraguay Salado and the Río de la Plata rivers.

In addition, other rivers that flow down from the Puna, the Pampa and Chacó mountain ranges, as well as the Andean system, drain into this basin.

The Paraná river is the most important in this basin, it has its origin in Brazil and also runs through Paragua and the northeast of Argentina. Its total length is 4,880 km and the basin covers an area of ​​2,800,000 km².

Other important rivers are the Paraguay (2,621 km), which is a tributary of the Paraná, and the Uruguay (1,838 km). The Río de la Plata is one of the smallest (320 km), but the other great rivers flow into it to go out to the Atlantic.

Other basins that supply the Atlantic slope are formed by the rivers that run through Patagonia. The rivers that form this basin receive water from the rains in winter and from the melting of snows in the spring.

The most important river in this basin is the Negro River, which is 730 km long and has no tributaries. The Negro river reaches the Atlantic through the Cóndor spa (Neuquén province).

Another Patagonian river is the Chubut, which has its source in the Andes with a length of 810 km. The Chubut basin covers an area of ​​53,800 km² and its flow is highly dependent on rainfall, varying between 4 - 50 m3 / second.

Pacific slope

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