Modeling of River Plume Propagation in the Coastal Zone of Non-Tidal Sea

M. V. Tsyganova✉, Е. M. Lemeshko, V. V. Fomin, Yu. N. Ryabtsev

Marine Hydrophysical Institute of RAS, Sevastopol, Russian Federation

✉ e-mail: m.tsyganova@mhi-ras.ru

Abstract

Purpose. The purpose of the work is to investigate the propagation of river waters as they flow into the sea, the formation of plume and coastal buoyancy currents as well as to assess the plume characteristics and their evolution parameters depending on river discharge and hydrological conditions of the Black Sea northwestern shelf in the absence of wind forcing.

Methods and Results. The plume formation and propagation were studied by numerical simulation based on the POM three-dimensional σ-coordinate numerical model applied to calculate circulation in the coastal zone with due regard for river runoff. The performed series of numerical experiments took into account the impact of both river seasonal changes in discharge and salinity and the seawater stratification on plume dynamics within the range of Froude numbers up to 1. The calculations were performed for a rectangular area. The average climatic data on river discharge, sea- and fresh-water temperature and salinity were used as the model input parameters. The quantitative estimates of plume characteristics and evolution parameters as well as its depth, radius and center position depending on the balance of buoyancy forces (Burger number) and inertia (Froude and Rossby numbers) were obtained. They are consistent with the data of hydrological observations carried out under conditions of weak winds, with their speed less than 5 m/s. Application of the TVD schemes in the model has provided monotonicity of numerical solutions for areas with high spatial gradients in hydrophysical parameters and also reduced computational viscosity significantly. It has been established that the discharges of freshwater transported by the coastal current are proportional to the square of its available potential energy; the dependence is described by a linear regression equation with high determination (~ 0.95) and correlation (~ 0.97) coefficients.

Conclusions. The obtained relationships for plume depth and width and coastal current discharge can be used for assessing these parameters based on hydrological information or satellite data at a wind speed of less than 5 m/s. On average, after ~ 10 days, a quasi-stationary regime is formed, in which the coastal current discharge stabilizes at ~ 40% of the river discharge, while the remaining ~ 60% continue to circulate within the plume. The obtained results can be used in planning marine expeditions and assessing the impact of catastrophic water discharges in rivers on the hydrochemical regime and environmental state of the coastal zone.

Keywords

coastal zone, river plume, marine shelf, continental runoff, hydrofront, numerical modeling, Danube, Black Sea, water circulation

Acknowledgements

The study was carried out within the framework of state assignment of FSBSI FRC MHI on theme FNNN-2024-0016.

Original russian text

Original Russian Text © The Authors, 2025, published in MORSKOY GIDROFIZICHESKIY ZHURNAL, Vol. 41, Iss. 5, pp. 658-680 (2025)

For citation

Tsyganova, M.V, Lemeshko, E.M, Fomin, V.V. and Ryabtsev, Yu.N., 2025. Modeling of River Plume Propagation in the Coastal Zone of Non-Tidal Sea. Physical Oceanography, 32(5), pp. 668-689.

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