Increasing frequency of extreme weather events demands new engineering solutions, experts say

05/17/2024

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Marcia Musskopf and Sandra Barzotto, who own two stores in Roca Sales, Rio Grande do Sul — Foto: Arquivo pessoal

It remains unclear when reconstruction efforts will begin in Rio Grande do Sul. However, engineers, urban planners, and the state government agree on one thing: simply rebuilding houses, schools, streets, bridges, and water treatment plants as they existed before this year’s historic floods will not suffice.

Given the new reality of more frequent extreme weather events, the unanimous view is that many cities in Rio Grande do Sul will need to take on new forms.

Among the ideas being suggested are transforming neighborhoods into parks, building houses on stilts, and constructing new barriers and dikes in urban areas. In extreme cases, where cities have been almost entirely submerged, a drastic measure is being considered as a possible solution.

“We face a series of challenges, and we cannot rule out the possibility of having to relocate entire cities from where they currently are, or even rebuild them in other locations,” Vice-Governor Gabriel Souza told Valor.

“This has happened in some places around the world and even in Brazil. Of course, it requires dignified living conditions, public resources, and compensation. But where it is unfeasible to keep people living, it is better to provide them with another place.”

The number of cities affected by the historic floods has reached 452, and 77,000 people are living in shelters. The heavy rains began to hit the state on April 29.

The state government has yet to detail how and where to rebuild the affected structures. However, experts have outlined some priorities.

One of them is critical infrastructure. Roads and water supply systems should be designed to be quickly repairable, said Professor Vanderley John from the University of São Paulo’s engineering school. In the case of water, it would be better to place some facilities in more distant and higher locations, out of the reach of floods, even if this is less cost-efficient. But it would be more efficient in terms of risk, he said.

The same could apply to electrical substations and sewage treatment plants.

There is currently no precise assessment of the damage. However, the government reports that more than 700 schools, hospitals, military barracks, fire stations, police stations, roads, bridges, viaducts, sewage treatment plants, water treatment plants, and power substations have been affected. Half of Rio Grande do Sul’s infrastructure has been destroyed or impacted, said the vice-governor.

William Mog, an architect and urban planner and a member of the Prosecution Service of Rio Grande do Sul, does not believe in a single, large solution but rather in several strategies to address likely future floods.

One of the most important, according to Mr. Mog, is relocating populations from neighborhoods in flood-prone plains and those living on hillsides. “In these cases, it would not be enough to relocate and leave these areas vacant. One option to be considered would be the construction of linear parks in these areas,” he said.

A second change would come in the form of land use in a strip of land behind these parks. “In this second strip, some developments could be allowed but with restrictions, such as requiring buildings to be elevated on stilts so that the ground floor is left open and with permeable soil to act as a sponge.”

Projects involving mass relocations—whether entire cities or neighborhoods—tend to be complex, controversial, and costly.

However, the risk of new losses and more deaths seems to be pushing some residents of cities in Rio Grande do Sul to seek exactly that: to leave their homes permanently.

“In September last year, during the first flood, we said, ‘This happens once in a lifetime; it won’t happen again,’” recalls Sandra Panis Barzotto, 51, a businesswoman in the city of Roca Sales, a town of 10,400 inhabitants in the Taquari Valley, one of the regions heavily affected by the floods. In September, the waters invaded everything, reaching a height of 2 meters. In November, there was another flood, though less destructive. “We told people it wouldn’t happen again. But then came this May flood, and now people in the city are saying they will leave, they will look for another town. There are people who no longer have a house. And we no longer dare to encourage them to stay; we can’t say it won’t happen again.”

Ms. Barzotto and her sister, Márcia Regina Musskopf, 56, are business owners in Roca Sales, with stores selling clothes and shoes. The losses they suffered from last year’s two floods may have reached R$800,000, and this year’s losses are about R$300,000. With streets impassable due to mud, part of Roca Sales’ commerce remains closed.

The sisters repeat the questions many residents have been asking: What can be done? Deepen the riverbed, build barriers? “It will be expensive and laborious, but if nothing is done and another flood like this comes, no one will want to stay in the city,” said Ms. Barzotto.

After the September 2023 floods in the Taquari Valley, the government decreed that rebuilding homes in areas that had been engulfed by the flood would not be allowed.

River dredging, drainage systems such as retention basins, raising bridges, and building and rebuilding dikes to protect urban areas from future floods are other measures being mentioned by the state government and experts as options that should be on the state’s agenda when reconstruction begins.

However, opinions on barriers are divided. Some believe these structures could increase the speed of water in downstream cities.

“The fact is that we cannot do things the same way. All calculations were based on the rainfall of the last hundred years, but all of this is outdated,” said Nilson Sarti, vice president of Environment and Sustainability at the Brazilian Chamber of Construction Industry (CBIC).

A few days ago, Governor Eduardo Leite presented a preliminary estimate of reconstruction costs: R$19 billion. But shortly thereafter, a bridge collapsed, raising the total.

“The estimated cost is only for rebuilding. We are not including the construction of anything new in that amount. Just reconstruction,” said Mr. Souza.

“It seems that the United States needed $50 billion to rebuild the area affected by Katrina [the hurricane that devastated parts of the southern country in 2005]. I cannot give an exact number, but it will certainly be much more than R$20 billion, which means that the state will not be able to make all this reconstruction effort on its own.”

*Por Marcos de Moura e Souza — São Paulo

Source: Valor International

https://valorinternational.globo.com/