The Amazon River is the second longest river in the world and one of the most important waterways on the planet. It contains more fresh water by volume than any other river, is home to the world’s largest species of river dolphins and hosts 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 River: bridges.
Given that the Amazon flows through three countries (Peru, Colombia and Brazil) and that more than 30 million people live in the river basin, according to the World Wildlife Fund (opens in new tab), it seems a bit unbelievable that no bridge crosses the river. So why is that the case? Are there fundamental difficulties with building such structures in a rainforest that contains garbage, large swamps, and deep, dense thickets? Are there financial barriers? Or is it simply not worth the effort?
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Amazon anomaly
Compared to some of the other most recognizable rivers in the world, the lack of bridges in the Amazon is strange. In Cairo alone there are about nine bridges over the Nile; more than 100 (opens in new tab) bridges have been completed in the last 30 years across the Yangtze, the main river of Asia; while the European Danube, which is only one third longer than the Amazon, has 133 bridge crossings (opens in new tab).
So what about Amazon?
“There is no urgent need for a bridge across the Amazon,” said Walter Kaufmann, president of Structural engineering (Concrete structures and bridge design) at the Swiss Federal Institute of Technology (ETH) Zurich, they told Live Science in an email.
The Amazon, for most of its 4,300 miles (6,920 kilometers), winds through sparsely populated areas, meaning it has very few major roads that can be connected to any bridge. And in cities and towns bordering the river, boats and ferries are established means of moving goods and people from coast to coast, meaning there is no real need to build bridges except to make travel somewhat faster.
“Of course, there are technical and logistical difficulties,” Kaufman noted.
According to Kaufman, Amazon is far from an ideal location for bridge builders, because it has a number of natural stumbling blocks that engineers and construction workers would have to overcome.
For example, its large swamps and soft soils would require very long access viaducts [a multi-span bridge crossing extended lower areas] and very deep foundations, “and that would require huge financial investments, Kaufman said. In addition, changing the position of the river flow across seasons, with “pronounced differences” in water depth, would make construction “extremely demanding”. This is partly due to the rise and fall of river water throughout the year and the soft sediment of river banks that erodes and shifts seasonally, according to Amazon Waters Initiative (opens in new tab).
Kaufman noted that while these specific problems are not unique to Amazon, “they are particularly serious” there.
“The environment on Amazon is certainly among the most difficult [in the world]”Bridges over the sea are also challenging if the water depth is deep, but at least you know that construction is possible with pontoons, for example.”
Pontoons, or floating structures, are not a solution that would work in most parts of the Amazon, Kaufman said, because the river is heavily influenced by seasonal variations, which adds an extra layer of complexity. For example, during the dry season - between June and November - the Amazon has an average width of between 2 and 6 miles (3.2 and 9.7 km), while in the wet season - from December to April - the river can be up to 30 miles wide. (48 km), and the water level can be 50 feet (15 meters) higher than during the dry season, according to the British (opens in new tab).
“This challenge would be unique,” Kaufman said.
So, in addition to the fact that there is no urgent need for a bridge across the Amazon, the processes involved in building the bridge would be significant.
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Bridge too far?
It is worth noting that, although there are no bridges crossing the Amazon, there is one that crosses the Negro River, its main tributary. Named the Ponte Rio Negro, the bridge, completed in 2011, connects Manaus and Irandubu, and to this day is the only major bridge to cross any tributary of the Amazon.
But while there are no specific plans for a bridge across the Amazon, “that doesn’t mean it won’t happen,” said Philip Fernside, an American biologist, scientist and conservationist who has spent most of his career in Brazil, he told Live Science.
Jair Bolsonaro, President of Brazil, 2019. stated that he wanted a bridge (opens in new tab) through Amazon, which will be built as part of his “Rio Branco Project”, but there is still no progress. “That would be very expensive compared to the economic benefits it would bring,” Fernside noted.
Following the completion of the Ponte Rio Negro bridge, temporary plans have been made for a bridge over the upper Amazon - known as the Solimoes River - in the municipality of Manakapuru, which would connect the BR-319 with Manaus and eliminate the need for a ferry crossing.
“BR-319 is a high political priority, but there is no economic justification,” Fernside said. “It is cheaper to transport products from factories in the Manaus free trade zone to Sao Paulo by water.
In addition, as noted in a 2020 commentary, Fearnside wrote for an environmental news site mongabai (opens in new tab) in connection with the proposed development of BR-319, the creation of such a bridge would “give cuts the forest access to about half of what is left of the Amazon forest in the country, so this is perhaps the most important conservation issue for Brazil today, ”Fearnside said.
So is there a chance that a bridge across the Amazon could be built in the near future?
“I think a bridge could only be built if need dominates over difficulties and costs,” Kaufman said. “Personally, I doubt that this will happen soon, unless there are unforeseen economic developments in the region.
Originally published on Live Science.