The Amazon is the second longest river in the world and one of the most important waterways on earth. It contains more fresh water than any other river, is home to the world’s largest river dolphin species, and is home to 100 species of electric fish and up to 60 species of piranhas.
Yet despite its many and varied qualities, there is something that cannot be found on the Amazon: Bridges.
As the Amazon flows through three countries (Peru, Colombia and Brazil) and more than 30 million people live in the river basin, according to the World Wildlife Fund (opens in new tab), it seems somewhat unlikely that there is no bridge spanning the river. Why is that? Are there fundamental difficulties in building such structures in a rainforest with mixed forests, extensive wetlands, and deep, dense undergrowth? Are there financial hurdles? Or is it just not worth the effort?
Related: What is the longest bridge in the world?
The Amazon anomaly
Compared to some of the other most famous rivers in the world, the Amazon’s lack of bridge crossings is an oddity. There are about nine Nile bridges in Cairo alone; more than 100 (opens in new tab) bridges across the Yangtze, Asia’s most important river, have been completed in the past 30 years; while Europe’s Danube River is only a third the length of the Amazon 133 bridge crossings (opens in new tab).
So what’s up with the Amazon?
“There isn’t a sufficiently urgent need for a bridge across the Amazon,” said Walter Kaufmann, chairman of Structural mechanical engineering (concrete construction and bridge construction) at the Swiss Federal Institute of Technology (ETH) Zurich, Live Science announced in an email.
For much of its 6,920-kilometer length, the Amazon meanders through areas that are sparsely populated, meaning there are very few major roads to which a bridge can connect. And in the towns and cities that border the river, boats and ferries are an established means of moving goods and people from bank to bank, so no real bridges need to be built except to make the journeys a little faster.
“Of course there are also technical and logistical difficulties,” says Kaufmann.
According to Kaufmann, the Amazon is not an ideal location for bridge builders because it harbors numerous natural stumbling blocks that engineers and construction workers would have to overcome.
For example, its extensive swamps and soft soils would require “very long access viaducts”. [a multi-span bridge crossing extended lower areas] and very deep foundations,” said Kaufmann, which would require high financial investments seasons, with “pronounced differences” in water depth, would make construction “extremely challenging”. This is partly due to the fact that the river’s water level rises and falls throughout the year and that the soft sediments of the river banks erode and shift seasonally Amazon Waters Initiative (opens in new tab).
Kaufmann noted that while these particular problems are not unique to the Amazon, they are “particularly severe” there.
“The environment on the Amazon is certainly one of the most difficult [in the world]”, said Kaufmann. “Bridges over straits are also a challenge when the water depth is deep, but at least you know that you can build with pontoons, for example.”
Pontoons or floating structures aren’t a solution that would work in most parts of the Amazon, Kaufmann said, because the flow is heavily influenced by seasonal variations, adding an extra layer of complexity. For example, during the dry season — between June and November — the Amazon River averages between 2 and 6 miles (3.2 and 9.7 km) wide, while during the wet season — December through April — the river can be as wide as 30 miles ( 48 km), and water levels can be 50 feet (15 meters) higher than during the dry season, to Britannica (opens in new tab).
“This challenge would be unique,” said Kaufmann.
Aside from the fact that there is no immediate need for a bridge across the Amazon, the processes involved in building a bridge would be significant.
Related: What is the largest freshwater fish in the world?
A bridge too far?
It is worth noting that although no bridge crosses the Amazon, there is one that crosses the Negro River, its main tributary. Completed in 2011, the bridge named Ponte Rio Negro connects Manaus and Iranduba and is to date the only major bridge that crosses a tributary of the Amazon.
But while there are no concrete plans for a bridge across the Amazon, “that doesn’t mean it won’t happen,” said Philip Fearnside, an American biologist, scientist, and conservationist who has spent much of his career in Brazil. said LiveScience.
In 2019, Brazil’s President Jair Bolsonaro stated he wanted a bridge (opens in new tab) to be built across the Amazon as part of his “Rio Branco Project” but so far there has been no progress. “It would be very expensive compared to the economic benefits it would bring,” Fearnside noted.
After the completion of the Ponte Rio Negro, preliminary plans were drawn for a bridge across the upper Amazon – known as the Solimões River – in the municipality of Manacapuru, which would connect the BR-319 highway to Manaus and eliminate the need for a ferry crossing.
“BR-319 has high political priority, but there is no economic justification,” Fearnside said. “It’s cheaper to transport products from the factories in the Manaus Free Zone to São Paulo by water.”
As noted in a 2020 comment, Fearnside also wrote for the environmental news site Mongabay (opens in new tab) In relation to the proposed development of the BR-319, the creation of such a bridge would “give deforester Access to about half of what remains of the country’s Amazon forest and is therefore perhaps the most important conservation issue facing Brazil today,” Fearnside said.
So is there a chance that a bridge could be built across the Amazon in the near future?
“I think a bridge is only built when the need outweighs the difficulties and costs,” said Kaufmann. “Personally, I doubt that will happen anytime soon unless there are unforeseen economic developments in the region.”
Originally published on Live Science.
https://www.livescience.com/why-no-bridges-over-amazon-river Why are there no bridges over the Amazon River?