Objectives and methodology
The AU-IOTA prescribes that prior to the start of work on the foundations, the project owner must model the dispersion of suspended matter and assess their impact on the fish resource.
The project owner shall submit a report to the management and monitoring committee for its opinion:
Modelling results and impacts on the fisheries resource.
The conditions and procedures for carrying out the work.
The conditions for carrying out follow-up and monitoring measures.
The alert and critical thresholds that condition the execution of the work.
In order to assess the influence of drilling work for a tailings discharge close to the bottom or surface, a three-dimensional hydrodynamic and sediment modeling system was set up, calibrated and validated by comparison with the measurements acquired by Ailes Marines in the siting area (Actimar, 2019). It can then be used to represent the variation of the various parameters (current, turbidity, deposition) over the entire water column and to estimate the influence of the vertical position of the discharge on the dispersion of sediments at sea, which is necessary to identify the conditions of least impact with regard to environmental preservation.
In line with previous studies carried out by Actimar on the same subject, the assumptions on drilling scenarios have been considerably refined for greater realism. In particular, as the work technique depends on the vertical structure of the nature of the seabed, this has been taken into account based on coring and granulometric analyses in order to reproduce, as realistically as possible, the volumes of material discharged at sea and the phasing of operations within the modelling system.
The study led by Actimar also focused on assessing the natural variability of in situ turbidity and the impact of the work on the local fisheries resource. In fine, these studies led to the proposal of thresholds and a turbidity monitoring programme during the work phase. The thresholds and the monitoring methodology were the subject of a prefectoral decree.
Planning and Status
The modeling was carried out and presented to the Management and Monitoring Committee.