Aerial view of the Amazon - - - (Image Source: Wikimedia Commons)

Although lists of the longest rivers in the world are often easy to find, they do not tell the reader much about how much water is discharged by the rivers.

This list details the five rivers in the world with the largest average discharge that is recorded at the mouth.

5) Madeira River, South America – 1.1 million cubic feet (31,200 m3) per second

Flowing through the southern Amazon Rainforest, the Madeira River is a major waterway that is fed by a large watershed of over 500,000 square miles (1.3 million km2) in area.

Fed by a myriad of rivers, the Madeira flows into the River Amazon around 150 km to the east of Manaus with an average discharge of 1.1 million cubic feet (31,200 m3) per second.

The large water volume of the Madeira River is due to a few reasons:

Firstly, the size of the watershed, which contains a myriad of rivers that feed into the Madeira, and the fact that its western side drains part of the Andes Mountains.
However, the most important reason is due to the excessive rainfall within the region – being a tropical environment, extremely high rainfall totals occur over the Amazon rainforest.
Within the Madeira basin, the mean annual precipitation is around 78 inches (2,000mm), which provides the river with a massive amount of water all year round.

The Madeira River is the largest tributary of the Amazon River, with the largest catchment area, water volume, and sediment flow among its tributaries.

4) Orinoco River, South America – 1.31 million cubic feet (37,000 m3) per second

The Orinoco River is the fourth most voluminous river in the world, with a discharge rate of 1.31 million cubic feet (37,000 m3) per second recorded at its mouth, where it flows into the Atlantic Ocean.

It has a vast watershed that covers four-fifths of Venezuela and a quarter of Colombia – the southern section of the watershed is located within the northern reaches of the Amazon Rainforest.

The intense tropical rainfall which falls in the Orinoco Basin is the main reason for such a high river water volume - although the dense rainforest reduces water runoff rates to some degree, much of it ends up draining into the River Orinoco.

The large watershed size also contributes to its high river volume – with a vast 366,000 square mile (948,000 km2) watershed, there is plenty of intense rainfall that can run off into the Orinoco.

Furthermore, although the southern parts of the watershed consist of dense rainforest, the northern side tends to be of a more savannah-like landscape – the lack of trees allows high runoff rates to occur during periods of high rainfall.

The Orinoco River, near Puerto Ayacucho airport, Venezuela (Image Source)

3) Ganges River, Asia – 1.34 million cubic feet (38,100 m3) per second

Flowing from the Himalayan Mountains, the Ganges crosses northern India, and meets the Indian Ocean via the Ganges delta, which straddles both India and Bangladesh.

With a length of 1,560 miles (2,510 km)], despite the Ganges being relatively shorter than a number of the world’s most renowned rivers, it is the river with the third highest discharge in the world.

Its large watershed is the main reason for this – draining one fourth of India, there is a vast area of land over which rainfall runoff can run into the river. To the south, large areas of land are used for agricultural purposes – with a lack of trees, rainfall quickly runs off towards the river.
The Himalayan Mountains – which lie to the north of the Ganges – also contribute to its high discharge. Many rivers that flow southwards from the mountains reach the Ganges, which therefore accumulates runoff from both precipitation and glacier meltwater.

Although rainfall rates are seasonal along the watershed, the intense monsoon rainfall – which occurs between June and September, also increases the discharge massively, which peaks towards the end of this period.

2) Congo River, Africa – 1.45 million cubic feet (41,200 m3) per second

The second highest river in the world by volume, the Congo flows for 2,900 miles (4,700 km) through a large section of western and central Africa – rising in north-eastern Zambia and discharging into the Atlantic Ocean.

Much of its course runs through the Democratic Republic of the Congo, and it has a vast watershed that includes the Congo Basin rainforest, and a large portion of the highlands of the East African Rift system.

The size and nature of the watershed is partly responsible for the high discharge – with an area of 1,335,000 miles2 (3,457,000 km2) being drained by one river, and an area that includes drainage from vast savannah and highland areas that are often not forested, it is little surprise that the volume of water flowing through the mouth of the Congo is so large.

Congo River. Kisangani, Democratic Republic of Congo (Image Source: Flickr)

In addition, incredibly high rainfall rates – related to the fact that the river is located almost wholly within a tropical climate zone – also amplify the Congo’s discharge. The Congo Basin receives an average of 60 inches (1,500 mm) of rainfall per year – a great amount of this drains into the Atlantic.

1) Amazon River, South America – 7.38 million cubic feet (209,000 m3) per second

Although the Amazon is the second longest river in the world, it is also – by a considerable amount – the largest river in the world by water volume and has over 4 times the discharge of the Congo River, the world’s second largest river.

Aerial view of the Amazon Rainforest, near Manaus, the capital of the Brazilian state of Amazonas, Brazil. (Image Source: Flickr)

The Amazon empties 7 million cubic feet of water in the ocean every second, which is more than the volume of water discharged by the next six largest rivers combined
- The daily discharge at the mouth of the Amazon averages 4 billion gallons of water each and everyday
16 - 18% of the world’s runoff to the oceans is discharged from the Amazon River
Not a single bridge crosses the Amazon
The Mississippi River, the largest river in North America, has 10 times less water volume than the Amazon
4 of the 10 largest rivers on Earth in terms of water discharge and drainage area are located in the Amazon River Basin

The Amazon River Basin - - - (Image Source: Montanher et al.)

The Amazon flows for 4,000 miles (6,400 km) across much of South America, rising in southern Peru, in the Andes Mountains, and traveling westwards through the Amazon Basin for most of its route, after which it drains into the Atlantic Ocean in the east.

With an incredibly large 2.7 million square miles (7 million km2) drainage basin, that covers much of the Amazon Rainforest, and drains other areas (such as parts of the Andes Mountains), this is a large reason that explains such a high discharge at the mouth of the river.
The tropical climate of the region also contributes massively to this – with much of the Amazon Rainforest receiving between around 60 and 120 inches (1,500 and 3,000 mm) of rainfall per year, there is a constant supply of runoff water which drains from the Amazon watershed – the only outlet channel for this is the mouth of the Amazon River.

Valentina is a guide for Pedal Chile and is our resident badass. Valentina was born and raised in La Patagonia, which probably explains her affinity for adventuring. When Valentina isn’t crushing some poor dude’s soul, you can find her shredding down Rucapillán. Favorite season: Austral Summer

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