Estimation of the extent of marine pollution as a consequence of the Kakhovka reservoir dam destruction based on simulation results

Abstract

Problems Statement and Purpose. In June 2023, as a result of the Kakhovka reservoir dam destruction, pollutants from the Dnipro River entered the Black Sea. This paper discusses the problem of determining the possible accumulation zones of these pollutants in the bottom sediments of the north-western Black Sea water area. The urgency of the problem is determined by the fact that these accumulation zones are potential long-term sources of secondary pollution of the marine environment. Preliminary identification of these zones is necessary for assessing damage done to the natural resources of the sea, as well as for the preparation of marine environment monitoring after the end of military operations. Numerical modelling is used to determine zones of marine pollution, since contact studies in the open sea and in the coastal areas are currently impossible. The hypothesis is accepted that the zones of pollutant accumulation in bottom sediments correspond to those sea areas where the concentration of conservative spill of neutral buoyancy was high in the bottom water layer.

Data and Methods. The numerical hydro- and thermodynamic model Delft3D Flow Flexible Mesh (D-Flow FM), developed by an independent institute for applied research Deltares (Delft, the Netherlands), was used to solve the above problem. The distribution of conservative spill of neutral buoyancy and mineral suspended matter coming with polluted transitional waters from the Dnipro-Bug estuary during June 2023 was modelled. Near the mouth of the Dnipro River an open lateral boundary was set in the model. Based on the data from the hydro-meteorological station “Port Kherson”, boundary conditions in the form of water level time-series were imposed. During the simulation, the concentration of the conservative spill of neutral buoyancy was assumed to be equal to 1 conditional unit at the open boundary. The mineral suspended matter concentration was set equal to 100 conventional units. The gravitational settling velocity of suspended particles was assumed to be 5 ×⋅10^-5 m s^-1. The variability of meteorological parameters (zonal and meridional components of wind speed, atmospheric pressure reduced to mean sea level, air temperature, relative air humidity, percentage of total cloudiness) was set at the upper boundary of the computational domain based on data from the forecast archive of the global weather model GFS (Global Forecast System).

Results and Discussion. The simulation results allowed us to estimate the spatial extent and relative level of pollution of the sea water in the north-western Black Sea area both in the surface and near the seabed. This estimation would not be possible using remote sensing methods only. Areas with possible significant level of sediment contamination and potential sources of secondary marine pollution (due to resuspension) were highlighted. It is recommended to conduct a verificatory monitoring of water and sediment contamination levels for these areas after the end of military operations.