On the impact of sediment plumes generated by offshore platform removal in the Adriatic Sea

The Adriatic Sea is rich in offshore platforms that have reached the end of their life. Their complete removal, however, can result in significant impact on the surrounding environment, as these are often located near the coast or in proximity to protected areas. We here provide a simple and physics-based methodology to estimate the length scale of the potential impact of sediment plumes (“impact distance”) generated by the excavation and suspension of sediments during the operations of total platform removal. A thorough parametric analysis was performed using numerical simulations with the mixing-diffusion model CORMIX, testing varying sediment discharges and environmental conditions (water depth, ambient velocity, and distance from the coast). Input data largely come from in-situ observations, while unavailable data has been integrated using acknowledged databases (e.g. EU Copernicus Marine Service). Using a precautionary approach, predictive relationships were established for the impact distances in the Adriatic Sea, leading to a simple and representative index suitable for the implementation in a decision support system for the removal of offshore platforms. Further, simulations revealed rapid near-field dilution (53.8–67.1% within minutes) transitioning to far-field dispersion (99.96–100% dilution within 2.5–25 km), driven by ambient currents. For the Adriatic area, impact distances are transient and range between 0.1 and 14.6 km in direction sub-parallel to the coastline, with negligible hazards beyond 10 km. The implementation of the results in a decision system will support regulators in prioritizing mitigation, balancing ecological, economic and social constraints during decommissioning.