Hydroelectric plant and buffalo alter the course of rivers in Amapá – 06/04/2023 – Environment

Jaime Lucian dos Santos Filho grew up on a stilt house on the banks of the Araguari River, in the village of Bom Amigo, in Amapá. His family, as well as dozens of others in the region, used to eat fish from the river, raised buffaloes on its banks and watered the garden with water from the Araguari. To go to the market, all you had to do was take a boat up the river.

At the time of the floods, the Araguari, normally a sheet of water 4 km wide, transforms into a powerful current. However, in the early 2000s, everything started to change.

That’s when Santos noticed the decrease in the speed of the waters. Blocks of sand began to form and gradually grow.

Around 2013, the Araguari —up to its mouth in the Atlantic, 20 km away— was already full of silt and no longer passed through the village of Bom Amigo.

Santos says it was a double-edged sword. “There’s more land for us to plant. But water is scarcer.”

A few kilometers of the old Araguari bed are still flooded during the rainy months, but they soon dry up and become hard as stone. Bom Amigo began to lose its meaning, and residents began to move.

Around the same time, the riverside people of another locality, called Junco, 15 km to the south, were also impacted by the transformation of a river. There, however, the scenario was one of flooding.

In 2012, Domingo Maciel da Costa got a job guarding a buffalo farm east of Junco, on the north bank of the Amazon River. Like a small channel, the Urucurituba River crossed the land and flowed into the Amazon.

Costa says that before the 1990s, the Urucurituba was one block wide and ran only a few kilometers from its source, in the forest, to its mouth.

Then it started to grow. While working on the farm, the river reached ten times the width of the Tietê River, in São Paulo, and reached 15 km in length. In a few days, the river swallowed up more than two meters from its banks, he recalls.

“In a short time, it became this monster you see.” Floating with the boat on top of the old ranch where he lived, almost 1 km from the current bank of the river, he exclaims: “Here was our house, our pasture, our land.” But where did this monster come from?

Scientists who study the Araguari and Urucurituba rivers have concluded that the silting up of the first and the continuous expansion of the second are two sides of the same coin: consequences of a hydroelectric plant built on the Araguari and the introduction of buffalo farming in the region.

James Best, a professor of geology from the United States, says he is surprised at how quickly the two rivers are changing. He warns that more surprises like these should emerge in the future, as human occupation grows on the banks of rivers around the world.

In an article he published in the journal Nature Geoscience, he describes as risks the extensive extraction of sand from rivers, the accelerated construction of hydroelectric dams, the introduction of non-native species and other “anthropogenic stressors”. He predicts that “ecosystem collapse is possible in some large rivers”.

Today in Urucurituba, wide swamps surround the river, where the forest used to be. Buffalo move through the mud.

The movement of the Asian species, brought to Brazil in the 19th century, helped break the small elevation that kept the Araguari and Amazonas basins separate, explains Alan Cunha, professor of civil engineering at the Federal University of Amapá. Cunha says that the animals were one of the two powerful forces that together blocked the lower Araguari and ended up expanding the Urucurituba.

Until the early 2000s, a natural dam of sediments about one meter high separated the rivers, delimiting the two basins. Geologically, though, the floodplains are young, made up of sediments deposited too recently to have solidified, so it’s “extremely fragile and vulnerable,” says Cunha.

Supported by the military government in the 1980s, farmers began to introduce buffalo in the region. Today around 200,000 roam freely there. Compared to common cattle, they swim better and eat more types of grass. They happily wallow in swamps and streams, a particular behavior that has made them a problem for the separation between the Amazon and the Araguari.

Usually they march in single file, like soldiers digging trenches in the ground, says Cunha. The hulls open trenches that fill and drain with each cycle of the tide. This effect was added to the opening of trenches by farmers, either to create navigation paths or to bring water to vegetable gardens. Thus, with the two basins connected, the Araguari began to flow into the Urucurituba.

Cunha emphasizes, however, that farmers and their animals alone did not cause this phenomenon. The Coaracy Nunes hydroelectric plant, the first of three large hydroelectric plants built in Araguari, played an important role in this.

Valdenira Santos, a geologist at the Institute of Scientific and Technological Research in Macapá, says that the engineers “did not consider the downstream effect of the hydroelectric plant”, which went into operation in 1976.

The researcher wrote her dissertation on the Araguari. The river flow above the power plants varies greatly between the wet and dry seasons. Constructed reservoirs smooth out these variations, stabilizing energy production and thereby altering the natural movement of sediments.

Before the Araguari “clogged”, its pororocas were admirable. Waves carried thousands of tons of sediment upstream and dumped it on the riverbed. Cunha says that ebb tides used to flush out these deposits, keeping the river mouth clean.

With the plant, however, during the dry season, when the river is already flowing more slowly, the operators retain water to let it accumulate in the reservoir, which maintains the energy supply.

Cunha also suspects that the mud released by the Urucurituba, which gradually expands, has aggravated the Araguari problem. And so more water was poured into the Urucurituba, in a vicious cycle.

The Urucurituba will continue to grow, say the researchers, flooding forests and advancing along the Junco. Domingo points out that the city also lost 25 acres of açaí groves, almost 14 less football fields in what is an important source of income for the locality.

Riverside dweller José Freitas hopes to build a new house elsewhere before the river floods the current one. But he has not been able to move for the time being. “Everywhere we go, there’s already an owner. And we don’t have the money to buy new land.”

The Araguari, close to where the Urucurituba begins, also continues to widen. In the municipality of Pracuúba, where there is a fork in the road, dozens of people dismantled their homes and rebuilt them further inland.

James Best, a geologist at the University of Illinois at Urbana-Champaign, says that millions of people around the world could soon be forced to leave their homes, as are the residents of Junco, Bom Amigo and Pracuúba.

“This is going to have a big impact on the humans that live in the riverside corridors”, he concludes.

Geologist Valdenira Santos sees a warning here, and not just for those who live in river basins. “Human beings must not have the illusion that we can tame all of nature. She will always be stronger than us.”

_{The report was produced with support from the Pulitzer Center.}