Wednesday, June 7

The reason why there are no bridges that cross the Amazon along its 6,000 kilometers

The Amazon is impressive. No palliatives, no half measures. It is because of its size, which allows it to dispute the title of the longest river in the world with the Nile. Because of its flow. For its biodiversity. And even for the secrets that its surroundings still hide, such as the lost civilization that a team of archaeologists has just discovered in the Amazon Rainforest of Bolivia. Along its channel, however, it hides some new surprises. Perhaps a little more prosaic, but certainly just as curious.

For example: there are no bridges across the Amazon.

And that, in a river that crosses several countries, welcomes more than 30 million people in its basin and has a length of at least 6,400 km, is almost as striking as its size or flow.

How is it possible?

Very different from other big rivers. The Amazon is long, very long. Whether it takes the cake is however something subject to debate. Determining which is the longest river in the world may seem easy —and even more so today— but first we should settle an important debate that has been on the table since the 20th century: where exactly does the Amazon rise. Most scientists believe it is at least 6,400 km long, which would put it below the 6,650 km of the Nile. In 2007, a group of researchers made a new—and controversial—calculation that puts it closer to 6,900 km.

…and “allergic” to bridges. Whether one or another fact is taken into account, the unquestionable thing is that the Amazon is a Rare avis among rivers of its size. livescience He points out that in Cairo alone the Nile is crossed by almost a dozen bridges. In 2019, in fact, Egypt inaugurated a huge one more than 67 m wide and half a dozen lanes in each direction in the capital. The Danube adds 133 and the Yangtze, the great river of Asia, has incorporated more than a hundred in three decades.

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The key: population and roads. Yes, more than 30 million people live in the Amazon basin, spread over nine countries, but they are not spread out homogeneously. Not much less. It is estimated that two thirds of these inhabitants reside in Brazil and that more than half are concentrated in urban centers. The result is that there are wide stretches where the Amazon snakes through sparsely populated areas, which in turn poses a double handicap: uneven distribution and few high-capacity roads that can be connected by a bridge.

The populations scattered around the Amazon have adapted to this scenario to a certain extent and whenever they need to move they resort to ferries, outboards, boats and canoes, among other boats. Consequence: “There is not a sufficiently pressing need for a bridge across the Amazon”, they comment from the ETH in Zurich to livescience.

The river and its surroundings do not make it easy for us. That’s right, regardless of how much demand an infrastructure of this type may be in the Amazon, the reality is that the environment and the river itself do not make it easy for us either. Whoever wants to link both shores will have to face significant challenges. The main one, perhaps, is that the Amazon is not the same in the dry season as in the rainy season. Its width can multiply from one season to another: if the average is 3.2-9.7 km in the first case, in the second it reaches 48 km with a notable increase in the water level.

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Such variations make it difficult to use pontoons and other floating structures, a handicap to which other not minor ones are added: the complexity of working on the land of its swampy areas, the changes in the course of the river and its depth as the year progresses. … factors that would not make it easy for the builders and would also affect the cost of the project. The complexity of the terrain alone would require the use of deeper foundations.

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Do we want there to be bridges in the Amazon? That is the question. Perhaps the most important question of all is that: Are we interested in having bridges crossing the Amazon? Given the technical and logistical challenges and in view of the fact that it does not seem like a social emergency either, is it worth starting to build viaducts? What impact would it have at an environmental level?

For years, experts have warned of the negative effect of the roads that already cross the Amazon and point out that they are contributing to deforestation and the deterioration of waterways. A study published in 2018 by researcher Cecilia Gontijo Leal indicates that the roads that cross the Brazilian Amazon are negatively affecting fish. “The data confirmed that the dirt roads are devastating the Amazonian streams”, she ditches.

The impact is explained by the erosion of the coast, the accumulation of sediments, a deterioration in the quality of the water and the barrier effect of “badly designed” roads, which can make it difficult for fish to reach places where they can feed, reproduce or take refuge. Gontijo encountered numerous stream crossings, makeshift “bridges”—sometimes to link illegal highways—that “have deeply fragmented the freshwater ecosystem.”

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A project that has already been put on the table. Technical complications, demand and environmental impact apart, the truth is that the construction of viaducts in the Amazon has already been considered. In 2019, the president of Brazil, Jair Bolsonaro, expressed his desire to build a bridge within the framework of his Rio Branco Project. So far, no progress has been reported.

What we do already have is Ponte Río Negro, a similar infrastructure that was completed in 2021 and connects one of the main tributaries of the Amazon. When it was finished, a similar project was proposed for the Upper Amazon that would connect the city of Manaus with the BR3-19 highway. “It would give deforesters access to about half of what remains of the country’s Amazon rainforest,” biologist Philip Fearnside warned in an article published in 2020. mongabay.

Images | Ivars Utināns (Unsplash), NASA and The Voyages of the Crab (Flickr)

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