(ORDO NEWS) — The answer to the question “What is the longest river in the world?” may seem simple you just need to find the source of the river, its mouth and measure the length.
But the subjectivity of the measurement does not make it so easy. This is such a complex issue that several hydrologists have explained that the length of a river is no longer considered a fair measure. So, what is the longest river in the world?
How long is the river?
According to Laurel Larsen, assistant professor of geography at the University of California at Berkeley, “the length of a particular river is the maximum possible continuous distance along the thalweg from the headwaters (first-order stream) to the mouth of the river.”
To explain these terms, a thalweg is “a line connecting the lowest or deepest points along the course of a river or valley”. But the flow of the first order is more complicated.
There are two main ways to classify the order of streams, but Strahler’s method is the most common. In this method, streams without tributaries flowing into them streams that just start in a river are of the first order.
When two first order flows join together, they form a second order flow, and when two second order flows join, they form a third order flow (but if a first order flow intersects with a second order flow, the main river remains a second order flow). Here is a mindfulness puzzle.
In this case, the source of the river is considered the furthest distance to the source of a stream that has no tributaries although in practice this can be extremely difficult to determine. And it’s not a perfect system.
About the mouth this is also debatable. For some rivers, the mouth is relatively easy to determine. But for large streams entering the ocean, such as the Amazon, the location of the mouth can make a big difference.
What is the longest river?
As a rule, the Nile River has always been considered the longest river, with the Amazon ranked second. But in 2007, a group of Brazilian scientists announced that a new analysis had put the Amazon in first place.
They got this result by identifying a new source and, more importantly, a new mouth of the great river. Traditionally, the source of the Amazon was located on the northern side of the island of Marajo.
A new study has shown that the river circles the south side of the island to the Para River and then flows into the ocean.
Which side of the island the estuary is on may not seem all that important, but Marajo Island is the size of Switzerland. The new source plus the new mouth eventually enlarged the Amazon and made it longer than the Nile.
But this result is rather controversial. The Para River is usually associated with the Tocantins River and not the Amazon.
And more recent research has tended to say that while it does have some Amazonian water, Para is different from the Amazon. This means that for the time being, the championship in the issue of the longest river in the world remains with the Nile.
But there is another, more fundamental problem with measuring a river: what does length even mean?
What is the length of a river?
Early 20th century mathematician Lewis Fry Richardson observed that Spain and Portugal disagreed about the length of their border. Spain stated that it was 987 km, and Portugal – 1214 km.
The disagreement didn’t boil down to disputed territories or anything like that: Richardson explained that it was the length of the measuring stick. As the ruler gets smaller, it can more accurately capture curves and nuances of twists and turns in complex boundaries.
The same problem is observed in the case of measuring rivers. Rivers have small bends, but if you zoom in, more small bends can appear in the thalweg.
This is known as the coastline paradox: the length of something complex is basically impossible to determine because the length continues to increase as the scale of measurement decreases.
Both for this reason and because of the inherent difficulty of determining its length, several researchers have said that the length of the river is of little importance.
What really matters is the catchment area that is, the area of land from which water enters the river. Unlike the length of a river, multiple height measurements make this metric much easier to calculate.
Using this metric, the Amazon is the largest river in the world, with a catchment area of 6.3 million square kilometers. If it were a country, its drainage basin would be the seventh largest country in the world – right after Australia.
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