Physical Oceanography, Vol. 18, No. 6, 2008
MODELING OF HYDRODYNAMICS AND TRANSPORT PROCESSES
IN THE DNIEPER–BUG ESTUARY
A. A. Nesterov
and V. S. Maderich
A numerical model of baroclinic circulation based on the use of a double sigma coordinate sys-
tem is presented and its application to the simulation of flows and temperature and salinity fields
in the Dnieper-Bug Estuary is described. The model reproduces the salinity and temperature
fields surveyed in 1998. The results of simulations reveal the existence of a global influence of
the relatively narrow and deep ship channel (through which Black-Sea waters can penetrate deep
into the estuary) on the transport processes.
The Dnieper–Bug Estuary (DBE) (Fig.
1) is a unique ecosystem in which the flows of seawater and river
water with absolutely different physical and chemical properties are mixed under the influence of hydrological
and meteorological factors . The main rivers flowing into the estuary are the Dnieper (93.8% of the fresh-wa-
ter inflow) and the South Bug (5.7% of the fresh-water inflow). In its west part, the DBE is connected with the
Black Sea through the Kinburnskii Strait. The major part of the estuary is shallow
the only exception
is an artificial ship channel about
in width and
in depth. Salty waters can penetrate through this
channel into the Dnieper, even upstream from Kherson, and into the South Bug, upstream from Nikolaev, both
located more than
away from the estuary mouth. The isolation of the water layer at the bottom by halo-
cline leads to anoxia and significantly affects entire ecosystem . Due to the large area
relatively small depth of the estuary, wind and variations of the water level caused by the wind-induced surges,
changes in the water level of the Black Sea, and the inflow of fresh waters from the Dnieper and South Bug play
the role of important factors affecting the processes of mixing in the DBE. The phenomenon of wind-driven
upwelling in the coastal area of the northwest part of the Black Sea  leads to significant changes in the salinity
and temperature of waters penetrating into the DBE through the Kinburnskii Strait.
Hence, only 3D models capable of the adequate description of bathymetric features in the DBE and the pro-
cesses running inside the estuary and on its boundaries can be used to simulate the thermohydrodynamics of the
estuary and its ecology. The presence of the relatively narrow and deep channel causes some difficulties for
numerical simulation. The
σ-coordinate systems (in the vertical direction) extensively used in
the models of coastal hydrodynamics have several disadvantages. In the first system, the vertical resolution of
shallow water becomes too coarse and, moreover, the stepwise approximation of the bottom topography intro-
duces numerical perturbations in the simulated flows. In the second system connected with the
tem by the relation zH−= +ησ η( ), where H is the depth of still water and η is the deviation of the water
level, high bottom gradients “traced” by the
2) introduce errors in the horizontal pressure gradients
and result in the formation of fictitious numerical diffusion in the vertical direction.
National University, Singapore.
Institute of Mathematical Machines and Systems Problems, Ukrainian National Academy of Sciences, Kiev, Ukraine.
Translated from Morskoi Gidrofizicheskii Zhurnal, No.
66–77, November–December, 2008. Original article submitted April 23,
2007; revision submitted September 5, 2007.
0928-5105/08/1806–0345 © 2008 Springer Science+Business Media, Inc. 345