Investigation of Danube river plume formation and propagation based on numerical modeling

The relevance of the studied circulation caused by the water river runoff deals with the anthropological impact on the ecological state of the shelf. River waters, entering into the sea, form mesoscale structures in the delta’s area, characterized by low salinity with a high level of suspended matter and dissolved organic matter. Such structures are called “plume” in modern literature. In this case, the inertial motion of the plume is free to form a rounded area or “bulge” like anticyclonic circulation type of flow. The purpose of this work is to investigate the propagation of freshened waters, formed by the river inflow, the formation of the waters hydrological structure regularities, dynamics of the buoyancy current, and thermohaline front formation on the base of numerical modeling. Numerical modeling is used to study the formation of a river plume and downward propagation of buoyancy current on the shelf without taking into account the tides forcing. A three-dimensional σ-coordinate numerical model was used, adapted for the shelf and estuaries. The calculations were carried out for a rectangular box area. The influence of changes in the main parameters of the runoff, the mouth geometry and wind forcing are considered to development of the plume and the alongshore propagation of buoyancy current. The obtained modeling results for the conditions of the Northwestern Black Sea shelf and the Danube discharge are consistent with the estimates of plume characteristics based on the archival hydrological observations data of water temperature and salinity. The results of this work can be used for further study of hydrological processes in the region of river mouths, the peculiarities of the plumes formation and evolution, assessment of the suspended matter, biogenic elements and microplastics transport in the sea and ocean coastal zones.