Posted on October 2, 2024
- Brazil has committed to dredge major Amazon rivers in response to record drought that has lowered water levels and made ship passage, a key transportation lifeline, difficult or impossible.
- The dredging is aimed at supporting local communities, who rely on river navigation to get supplies in from outside, and producers, who need to ship their commodities out.
- But experts question whether dredging is a sustainable solution, raising concerns about long-term ecological impacts and advocating for community involvement and innovative technology for better outcomes.
- The environmental risks of dredging include ecosystem disruption, increased erosion, water contamination, and harm to aquatic species such as manatees and river dolphins.
For the second year in a row, record-breaking drought in the Amazon has caused environmental havoc and left entire communities stranded. Water levels in the major Amazonian rivers have dropped to historical lows. And because they serve as the main transport conduit in the region, the consequences of critically low water levels that prevent boat traffic are far-reaching for all segments of the population.
This year’s calamity had long been foretold. The Brazilian government announced in mid-June an investment of 505 million reais ($90 million) in licenses for dredging stretches of the Amazon River and two of its main tributaries, the Solimões and Madeira, over the next five years. That amount is almost four times what was spent in emergency response to 2023’s drought.
The move came as a result of months of negotiations between the federal government and the state of Amazonas, where industries’ economic output dropped by 16.6% because they couldn’t get supplies in or commodities out by boat during the last drought.
Brazil’s Ministry of Ports and Airports has called the proposed dredging operation “the largest volume of dredging in the history of the Amazon.” The National Department of Transport Infrastructure, DNIT, told Mongabay in an email that it would collect sediment from the riverbed using a suction mechanism, and then pump it to a different location to increase water levels in a particular channel.
A dredger at work in the Madeira River. The Brazilian government announced an investment of 505 million reais ($90 million) for dredging stretches of the Amazon, Solimões and Madeira rivers.
The plan “takes into account the vessels navigating the river, the characteristics of the riverbed, the river levels throughout the year, and the amount of silt accumulated,” DNIT wrote. “In addition to dredging, the installation of nautical signs is being planned for the sections included in the contract, to guide navigators and mark the navigation channel.”
In addition to helping producers move their goods, dredging rivers also helps vulnerable populations that are disproportionately affected by the drought, Robert Muggah, chief innovation officer at the Igarapé Institute, a think tank, told Mongabay by email. These populations “depend on rivers for everything from subsistence fishing to trading goods,” he said.
“Riverine families often struggle to access basic essentials, including food and supplies, as the cost of goods starts to rise,” Muggah said, noting that challenges to navigation and extended travel time result in higher costs for shipping of goods and services — and higher prices for end consumers. “What’s more, the shrinking of rivers also restricts access to key fishing areas.”
Reshaping the largest basin in the world
However, dredging operations bring environmental risks, according to experts.
Dredging and the subsequent sediment redeposition may reduce access to fishing areas, increase erosion in high-risk residential zones, and deteriorate water quality.
Risks to nature also include silting and changes to the water’s pH, conductivity, salinity, turbidity and temperature, all of which pose drastic consequences for riverine ecosystems.
In the state of Pará, dredging started in mid-August, and manatees and river dolphins, species already threatened by droughts, have been found dead along the Amazon River, as well as countless smaller fish.
In 2023, more than 220 freshwater dolphins have died in lakes connected to rivers, possibly killed by excess heat in the historic Amazon drought.
One of the main points of concern associated with dredging, however, is the disturbance of sediment layers on the riverbed, which can release and expose any contaminants buried there, including heavy metals such as mercury, whose presence in the Madeira River is a growing problem.
All threats are higher in a complex ecosystem like the Amazon. “We need to talk about the superlatives of the Amazon Basin,” Rogério Ribeiro Marinho, a professor of physical geography at the Federal University of Amazonas, told Mongabay. “It is the largest river basin in the world, with over 6 million square kilometers [2.3 million square miles], more than half the area of the South American continent.”
It also covers an incredibly complex and dynamic hydrological system. The Madeira, for instance, home to the most diverse fish life in the Amazon River Basin, varies from very low flows during the dry season to becoming larger than the Congo, the world’s second-largest river, during the rainy season, said Naziano Filizola, a professor of hydrology at the Federal University of Amazonas.
“A river whose flow rates vary so much carries a huge volume of sediments,” Filizola told Mongabay.
Greenpeace Brazil activist holds a protest sign on the dried riverbed of the Solimões River in the city of Manacapuru, Amazonas.
The Solimões also transports large amounts of sediment. Even far upstream, at the point where it enters Brazil from Peru, in the municipality of Tabatinga, the annual sediment load amounts to 541 million metric tons, according to Marinho. That’s equivalent to 94 times the weight of the Great Pyramid of Giza.
During a drought, this sediment, once moved uninterrupted by the river’s powerful flow, tends to accumulate along its course, causing siltation, making sections of the river shallower and changing the watercourse. That’s when dredging is proposed.
According to the DNIT, the operation to be carried out will “rearrange the riverbed by removing sediments from an identified natural channel and redepositing it within the same river, at a point that does not obstruct or pose risks to navigation.” While the department didn’t say where the redepositing will take place, it said that “this measure aims to not reduce the water level, which means that maintenance dredging does not interfere with the river’s overflow cycle.”
However, dredging by its nature involves changes to the geometry of the river and to its currents. “For most of the Amazon Basin, we know very little about how the velocity of the current is distributed, meaning that we can’t predict the impact that a seemingly small change to the shape of a channel can have, especially on flow intensity during a flood,” Marinho said. That is particularly concerning given that the Brazilian Amazon has witnessed some of its worst floods in history over the past decade alone.
Previous studies of other rivers have found that channels that have undergone dredging tend to silt up more frequently, making this an unsustainable solution in the long term. “If you redeposit the sediment close to the dredged area, the tendency is that the river will go back to its original state,” Filizola said.
That’s why both he and Marinho referred to the endeavor as “drying ice,” a Brazilian expression for a useless effort — one that, in this case, is also highly costly, both financially and environmentally.
Mongabay sought comment from both the Amazonas state environmental agency and the Ministry of the Environment and Climate Change, but neither had responded by the time of publication.
The Paraná do Manaquiri River, a tributary of the Amazonas, has dried out in 2024’s extreme drought.
Finding balance
Filizola said that amid the emergency nature of the drought and its impact on communities in the Brazilian Amazon, the dredging plan may seem like a necessity.
“States like Amazonas depend heavily on fluvial channels, so the drought is indeed a situation of emergency, and we can’t just leave the entire region isolated from the rest of the world. We need to ensure the population a minimum standard of quality of life,” Filizola said. “The question is: Are we doing it the right way?”
One of the challenges, he said, is how long it takes to complete such an operation. Add in the time lost to bureaucracy, and the emergency might have passed once the heavy machinery is in place. “By the time it is ready to operate, the drought event may already be over,” Filizola said.
According to Muggah, emerging dredging technology could represent a less damaging alternative. “There are remote-operated unmanned vehicles equipped with sonar and other sensors that can undertake extremely selective and precise dredging to minimize turbidity and optimize sediment transportation,” he said in his email. “These technologies are particularly well suited to areas where standard dredging is challenging and restricted.”
Muggah added that, in times of emergency, such technologies need to be “supplemented with short-term assistance and social programs for vulnerable communities, such as water, food and medicines.”
For Marinho and Filizola, however, any sustainable long-term solution must necessarily include talks with locals. “It is essential to learn how to better interact with the public. Rather than arriving with the intent of lecturing the communities on what to do, we must learn from their experiences and from the solutions they have created themselves,” Filizola said.
Banner Image: Drought-stricken river in the Capoto-Jarina Indigenous Territory in the Upper Xingu region of Mato Grosso on September 12th, 2024.
