05/26/2024 – 11:46
Erosion on the coast of Rio de Janeiro is an old problem, which worsens in times of large storm surges, as occurred last weekend in Macaé, in the north of Rio de Janeiro. The waves that reached almost 3 meters (m) caused damage to Praia Barra de Macaé, in the Fronteira neighborhood, north of the city, and resulted in the closure of 74 properties, with seven having partial or total collapses. Five poles were also recorded falling and the coast road was lost. In addition, four people were left homeless and 180 displaced.
Marine geographer from Universidade Federal Fluminense (UFF) Eduardo Bulhões explained that the beach is very close to the mouth of the Macaé River and has this instability caused, among other factors, by the occupation of land close to the water line.
Related news:
“A relevant issue for public authorities to understand is that there are no definitive measures to end the problem of erosion, since we basically work on the symptoms, the consequences and not necessarily the causes of it. For example, we can’t avoid a very strong hangover. We can prepare the coast to better deal with these impacts. The first step is to understand that we need measures to control the problem and not definitive solutions, as many managers want to sell the idea”, he defended in an interview with Brazil Agency.
Bulhões is one of the members of the working group that will carry out the technical and environmental study agreed by the city hall of Macaé, in the north of Rio de Janeiro, with the Federal University of Rio de Janeiro (UFRJ). “They [da prefeitura] They want to train themselves to better understand how these events and processes occur. They know there is a risk, but they don’t know why”, he added.
The study will be carried out by the Polytechnic Institute and the Institute of Biodiversity and Sustainability (Nupem) at UFRJ, under the coordination of the dean of the Multidisciplinary Center of the educational entity in the municipality, professor Irnak Barbosa. The intention is to analyze the process of coastal erosion that has been affecting the municipality for some time. The work will also be monitored by the Public Ministry of the State of Rio de Janeiro (MPRJ).
Atafona
In Atafona, a district in the city of São João da Barra, also in the north of Rio de Janeiro, the loss of buildings and the expansion of the sand strip have evolved over the years. The problem doesn’t stop there. “In Atafona, more than 500 buildings have already been destroyed. It also has an impact on Rio das Ostras, in Campos dos Goytacazes. Close to the capital, it has significant impacts on Maricá. Praia da Macumba, in the city of Rio de Janeiro, is one of the most vulnerable places and every now and then the coastline has to be reconstructed. Coastal erosion in Brazil occurs in several municipalities. I have been working on this topic for many years”, highlighted Bulhões, citing affected locations.
Study
The geographer estimated that, by this week, the group that will carry out the study will have their names published in the Official Gazette of the Municipality, which is a procedure to start the work. “Once established, we will work on erosion control solutions”, she pointed out.
Based on this, said the expert, structural measures such as restoration of the beach and restinga vegetation must be analyzed. “I think this is a more modern way to deal with the problem. We assume that the beaches, the restinga vegetation and the small frontal dunes act as a de facto defense of the coast. This is the understanding of the international literature on this, recomposing the ecosystem and using it as a barrier to the attack of waves and storms. Structural measures can be works and also composition of coastal ecosystems.”
Bulhões also highlighted some non-structural measures. One of them is the so-called planned retraction, when a group of buildings installed in an inappropriate location is removed and, therefore, cannot remain in that location.
“For example, in these houses that collapsed, we cannot allow the reconstruction of residences in the same location. So, the retraction brings the idea that in some cases we need to retreat our structures so that we can restore the ecosystem and for it to function as a natural barrier”, explained the geographer.
Bulhões added that these types of measures also include the forecast and warning system and what he called climate literacy, which would be convincing society that some areas of the coast need to be vacated.
In 2018, the geographer was part of a group that produced the book Panorama of Coastal Evasion in Brazil, composed of 17 chapters, one for each state that experiences this type of problem. He participated in what concerns Rio de Janeiro, which covers the strip from São Francisco de Itabapoana, in the north of the state, on the border with Espírito Santo, to Paraty, on the border with São Paulo. “We have many areas in erosion, the most serious being Atafona, but we have them in Rio das Ostras, Cabo Frio, Campos, Macaé, the city of Rio de Janeiro, Angra dos Reis,” he said.
Bulhões recalled that, in Praia da Macumba, in the west of the capital, in 2005 a project was carried out on the waterfront with a promenade and the installation of kiosks and a cycle path. “Since then, that place has suffered from hangovers more than six times. We, as a society, built in the wrong place. The main problem on urban beaches in large cities is the advance of urbanization towards the sea. This is a serious problem, because in fact these structures were not created to contain the advance of the sea, but to give a more urbanized look to the coast and end up being subject to these impacts”, he stated.
Another mistake, in the geographer’s opinion, was the Rio city hall project that intended to install concrete blankets under the strip of sand that extends from stations 3 to 8, at Praia da Barra da Tijuca, in the west zone. After criticism from experts, the MPRJ ordered the work to be halted, and the municipality interrupted the work. “We thought that was very wrong, because the main way to combat erosion is to give space to the beach, to reestablish the strip of sand and restinga vegetation. These ecosystems naturally have this function of defending the coast.”
Hangover strength
Oceanographer Marcelo Sperle Dias, professor at the Faculty of Oceanography at the State University of Rio de Janeiro (Uerj), warned that not only the height of the waves determines the strength of the undertow. According to him, the wave period, which is the time it takes to hit the beach, can cause great damage. This was the case of Macaé.
“Specifically this hangover had a very long period of waves. The average wave period in the state of Rio de Janeiro is in the range of eight to ten seconds. In this hangover, like others that have already occurred, the period was 16 to 18 seconds. In terms of water fluid, this works almost like a tsunami. The longer the wave period, the more it invades the coast”, explained Dias in an interview with Brazil Agency.
Alerts
The professor said that the Navy’s warnings about the occurrence of hangovers usually include forecasts of wave heights and the periods it will take for them to break. And this is important for planning care. According to the oceanographer, alerts normally have four main pieces of information: the stretch of coastline that will be most affected, the direction of the waves (whether they are coming from the south, southeast), the height of the wave and the period. In view of this, he suggested that city halls have teams capable of making these observations to propose measures to avoid further damage. “We need the Civil Defense of city halls to have trained professionals accustomed to working with this type of problem.”
Dias has participated since 1997 in the group of specialists of the Erocosta project, which deals with coastal erosion and monitors several points called hotspots of the Rio de Janeiro coast, including this stretch of Macaé and Atafona which, according to him, is increasingly critical. “O hot spot It is an area of the coast where several conditions, not just the undertow and wave energy, several other forces, which we call, condition that that point eventually has impacts associated with the issue of coastal erosion”, he explained.
The professor highlighted that the impact of hangovers in these locations will also depend on the orientation of the coast, defined by the direction in which the waves depart. “Depending on where the waves are coming from, one or the other of these will have a greater impact. It doesn’t happen all at the same time, because each of them is likely to be more in front of where the big waves associated with the undertow are coming from,” he revealed.
The expert reinforced the understanding that urban occupation contributes to the occurrence of damage to the coast, caused by hangovers. “Everyone was a child and built a castle in the sand on the beach. A wave comes and knocks down the castle. Today there are people who build their houses almost on the sand of the beach, they want to leave the house and step on the sand. In addition, a cycle path or a kiosk is installed, which extends over the beach. In other words, any type of building, solid work, will receive the impact of waves. Our grandparents already said ‘soft water hits hard rocks until it pierces’. There’s no way. Over time, these structures suffer these impacts and eventually end up collapsing,” he noted.
The oceanographer also highlighted that, according to the federal government’s Integrated Seashore Management Project, of which Erocosta is a member, the recommendation is that the buffer area in urban regions should be 50 m beyond the beach. And, in non-urban areas at least 200 m behind the beach line.
“We know that this is ideal, it is to have a buffer zone for the dissipation of wave energy to happen naturally. Our beaches and restingas, the entire coastal region, are like a natural filter for wave energy. If there were no buildings there, naturally, whatever the undertow was, it would be dissipated by the passage of the wave itself. It would flood the entire beach, reach the vegetation area and the energy would be lost. If the buildings were behind the buffer area, many things would be avoided”, he indicated, suggesting that in the affected area of Macaé the rubble should be removed and the restinga vegetation should be recovered instead.
“We are going to have more and more storms, hangovers and heavier rains, floods and greater droughts. It is a period of climate change, there is no doubt, but we human beings have to use our knowledge to adapt to it,” she said.
#Improper #constructions #worsen #problem #coastal #erosion #Brazil