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P U B L I C I D A D E

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Environmentally correct

Using appropriate equipment, environmental dredging uses studies and monitoring to reduce environmental impacts of the conventional operation

Currently, the access between Góes Beach and Santa Cruz dos Navegantes Beach, in the city of Guarujá (SP), at the region of Baixada Santista, may be carried out only by the sea. At that place, the historic route built more than 300 years ago to connect both communities collapsed due to the increase of the hydrodynamic force of the waves at the entrance of Santos Harbor. Although many people thought that the destruction was merely due to the rising of sea level, a research showed that it was actually caused by the dredging process carried out to deepen the port channel.

In addition to the destruction of the route, other social and environmental impacts are being reported in the nearby communities, such as silting in beaches from Santos and Guarujá, destruction of the vessel mooring dock and increase of erosion, in addition to a stronger advancement of the sea during hangover periods, invading streets and buildings located at the borders of the port channel in the district of Ponta da Praia.

The research was carried out by the expert on port logistics Rafael Alves Pedrosa. According to him, dredging works in the canal of Santos Harbor are essential and bring a relevant economic bias. But it is still not possible to equalize the structural and environmental questions that change spaces used daily by the nearby community. This demands mitigating measures from public organs.

Pedrosa took part in a public hearing carried out in the 3rd Court of Federal Police two years ago. Currently, he sees a clear difference between the interests of the Public Prosecution (MP) and the São Paulo State Dock Company (Codesp). “The MP proved—with resulting images and data that came from bathymetry (depth check) of the estuary—the impacts that occurred in the beaches, mainly the erosions observed at Ponta da Praia, in Santos, and the silting of Góes Beach, in Guarujá, and at the region of the submarine emissary from Santos”, says him. “On the other hand, Codesp reported that invested more than 40 million reais in studies about the possible impacts of the project, denying this way that dredging works were responsible by what occurred in the beaches. Above all, it highlighted the importance of continuing the dredging process for the local and national economic development. The company also pointed out that the end of the dredging works will not result in the end of erosion”, tells Pedrosa.

The audience ended with Codesp being pressed by the MP to carry out new studies about the impacts. The University of São Paulo (USP) will be involved to develop a study about the width reduction of the canal in the most external section of the estuary. And the Port Authority will make available reports about bathymetry, speed of currents and energy of local waves each two months.

DEMANDS

A high-tech process carried out in several parts of the world is the environmental dredging, which starts to get space in Brazil. It can reduce the impact of the works, minimizing environmental damages by matching equipment such as suction and discharge dredges, barges and dragline excavators to impact studies and monitoring the dispersion of contaminated sediments.

Pumps used in the works have filtering sensors that remove sediments with high content of solids and low content of water. “During the process, they remove the sediments in surface layers to prevent the new suspension of contaminating compounds, reducing considerably the impact generated in the dredging process”, explains Pedrosa. “Since they do not move the bottom of the canal, the equipment prevents the liberation of heavy metals that reach the sea eco-system.”

In environmental dredging, the deepening of the canal keel is preceded by a study that defines its limit of depth, to prevent the collapse of its side walls. According to Leonardo Cavalcanti, director of communication from Luschi Soluções em Engenharia, Saneamento e Meio Ambiente, pulp pumps work with up to 70 percent of solids, removing a higher fraction of contaminated material using less water. Suction and discharge dredges may be operated by remote control and reach a dredging depth up to 28 m below the waterline. “The equipment efficiency allows a low-impact dredging which results in harbor development without environmental damages”, observes him.

Solutions may reach a maximum discharging distance up to 1 km from the dredging point, depending on the power of the pump. “Modular floating units have dimensions that allow their transport on trucks. They are also appropriate for work in shallow water”, explains Cavalcanti.

These dredges are coupled to electric submersible pumps with diameter of 4 to 12 inches with dredging pumping flow of 80 to 900 cu.mt. per hour, that also may be integrated to dredging systems built with existing equipment. “The high pumping capacity of solids allows a dredging production of approximately 1000 cu.mt. per hour”, estimates Cavalcanti.

In addition to equipment, the expert considers that the best way to carry out a dredging work is to have efficient technical assistance and a trained team that may find solutions and develop studies and methodologies to deal with unforeseen events, in a way to prevent any possibility of environmental impact. “Equipment helps to control contamination, but the expertise to deal with adversities of the environment is fundamental”, says also him.