The Piaçaguera Channel, located in the Santos Estuary, is an important navigation route linking the TIPLAM and USIMINAS terminals to the navigation channel of the Santos Port, considered the most important port of South America.
For years the Piaçaguera Channel could not be fully dredged due to the existence of environmental restrictions on direct oceanic disposal, related to the presence of inappropriate sediments in the channel.
During 2015 and 2016 the environmental restoration process initiated with the dredging of approximately 300,000.00 cubic meters of sediment not suitable for oceanic disposal, while TIPLAM new berth implementation dredging occurred. The initial solution for this issue was the use of geobags for sediment confinement at a CDF (Confined Disposal Facility), built at a site contiguous to the TIPLAM area.
Due to the significantly larger volume of material that needed to be dredged for maintenance and deepening of the Piaçaguera Channel, in the order of 2.3 million cubic meters, it was necessary to find an alternative solution from the one used in the TIPLAM berths implementation. In this way, several engineering and environmental studies were carried out in the search for a technical, economic and environmental solution that would allow the safe handling and disposal of the sediments not suitable for oceanic disposal from the Piaçaguera Channel. The decision matrix indicated the better alternative as an underwater Confined Aquatic Disposal - CAD cell in the interior of the Santos estuary, near the Piaçaguera Channel, in an area duly licensed and authorized by the Brazilian authorities based on rigorous and complex environmental studies carried out to obtain the permitting.
The CAD’s main purpose is isolate the dredging material of lower quality inside the subaquatic cell which will be capped with better quality material. The disposal can be in natural depressions in the seafloor, in borrow pits in the seafloor from mining operations (e.g., beach nourishment), or in specifically designed and constructed cells to contain the contaminated dredged material, what is exactly the case at Piaçaguera Channel.
Thus, during the years 2016 and 2017, an underwater CAD cell was built to accomodate aproximadely 2.3 millions cubic meters using different dredging methodologies and following strict control and monitoring standards, with the opening of the cell being completed in June 2017.
Once the CAD was opened, it began to be filled with the dredged material of the Piaçaguera Channel. The first step of filling was finalized on December 2017, since then the deposited material is consolidating by its own weight for a few months until optimum density is reached so the second step of filling can be carried out and, subsequently, the CAD will be capped with suitable material to isolate the lower quality material disposed inside the CAD.
The objective of this article is to present the history, criteria and premises that support decision making for the use of an underwater CAD cell as an alternative for the dredging of the Piaçaguera Channel, as well as the constructive methodology, technical management, environmental controls and learned lessons in the distinct phases of the CAD implementation.