Sediment plume evolution in the Black Sea after the Kakhovka Dam breach.

The sediment plume resulting from the breach of the Kakhovka Dam on 06 June 2023 could lead to severe, long-term environmental pollution in the northwestern Black Sea (NWBS), as the floodwater transported contaminated sediments, chemicals, and polluted water from the reservoir and upstream sections of the Dnieper River. Although this event has raised significant concern among scientists and coastal managers, studies examining the plume's evolution and its environmental impact remain limited, posing a substantial challenge. In the present study, we apply a Lagrangian approach using SedimentDrift, a module of the open-source framework OpenDrift, to track suspended sediment particles after the breach. The model incorporates key driving forces, including high-resolution 10-m wind fields, ocean currents, and Stokes drift velocities. The model successfully reproduced the sediment plume, which was in good agreement with Sentinel-3 satellite observations, resulting in high skill scores, particularly in June and early July. Wind forcing plays a critical role in controlling the evolution of the sediment plume in both the vertical and horizontal dimensions. In particular, Ekman transport driven by southwesterly wind contributes significantly to the eastward sediment movement and thereby affects its deposition area. Furthermore, the propagation of the sediment plume was shown to be sensitive to the sediment grain size: coarse particles deposited near the coast, whereas finer particles remained suspended in the water column and dispersed widely across the region. The Dnieper-Bug coastal zone was identified as the most environmentally impacted region. This study provides a basis for further investigations of the environmental impacts of the large-scale Kakhovka Dam failure in the NWBS.