Understand why part of Brazil’s largest beach is closed due to mud

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A two-kilometre stretch of Cassino Beach, in the Rio Grande (RS), has been closed due to mud build-up caused by the natural transport of sediment from the regional river basin, exacerbated by deforestation and poor land use.

About two kilometers of Cassino Beach in Rio Grande (RS) was closed after mud swept the area. This is considered the largest in Brazil, with a continuous length of 256 km. This measure was taken for security reasons. the land Consult an oceanographer to explain why this happened.

According to the casino secretariat, the mud cleansing process took place on the 20th. Teams went to the site to place marachas – small berms – to limit and restrict access from the Rua Rio de Janeiro area to the area adjacent to the Farrupilha drainage canal.

Furthermore, according to a memorandum from Secretary Miguel Saat, the administration continues to monitor the site and, if necessary, further intervention will be carried out. But, after all, why does this happen?

According to Osmar Olinto Mueller Jr., professor of oceanography at the Federal University of Rio Grande (FURG), this phenomenon is linked to the natural transport of sediments, which originate in the river basin, whose waters flow into the ocean by Lagoa dos Patos Lake, which is the largest in South America.

He also points out that studies indicate that this material, made up of silt and clay, is discharged into the ocean at a rate of tons per day, and when there are big storms, it ends up being transported to the beach.

“During periods of heavy and frequent rainfall at the end of winter and spring, several tons per day are released directly into the ocean,” he asserts.

It has nothing to do with dredging

The professor confirms that the burial site of these sediments is stable, meaning that it is not subject to erosion after dredging in the area. He describes: “There is a clay deposit that is more liquid, easier to resuspend, and is more or less concentrated at a depth of 6 metres. Typically, this material is deposited in the hole, the deepest part between the two sand banks. Its thickness, area and volume were constantly monitored. This is the material available to be released during the storm.”

Since 2018, an agreement between Furg, Portos RS and researchers from the Brazilian Coastal Monitoring System (Simcosta) has been monitoring different aspects of the port area and the coastal zone, where bathymetric surveys of the landfill site and the thickness of the mud pocket are being carried out.

Mueller Jr. explains that the problem of this mud on the beach is related to the conditions of the river basin, which is poorly treated with deforestation, poor soil use, riparian deforestation, and the growth of urban areas.

“Deforestation, in addition to exposing the soil to erosion, also reduces evaporation, which increases runoff. This also increases with the growth of urban areas, as the rate of impermeability decreases and more water flows into the rivers. What should we do? To take better care of the river basins! This is difficult, it depends on public policies, the movements of basin committees where different interests mix, among other things. Therefore, blaming dredging is easier.”