Marine Hydrophysical Institute of RAS, Sevastopol

MORPHODYNAMICS OF THE BAKALSKAYA SPIT
OF THE BLACK SEA
Vladimir V. Fomin, v.fomin@ukr.net
Ludmila V. Kharitonova, kharitonova.dntmm@gmail.com
Dmitrii V. Alekseev, dalexeev@rambler.ru
Elena V. Ivancha, ev_ivancha@rambler.ru

The Karkinitsky Bay of the Black Sea and The Bakalskaya Spit
The Karkinitsky Bay of the BlackSea due to its morphologicalfeatures (10 – 35 m depths, sandy
and muddy bottom structure withthe addition of shell limestone, thepresence of islands and spits) is anarea of intense morphodynamic
processes.
The Bakalskaya Spit which juts
out into the Karkinitsky Bay at 8 km
distance is characterized by special
dynamic activity.
The width of the spit westernbranch is 30 – 80 m, of the easternbranch – 1200 – 2000 m. A narrow
underwater sandbank extends at up
to 40 km distance to the North.
The depths above its peak reach
3.5 – 4 m.

Investigation of the dynamics of the Bakalskaya Spit coastal zoneдо 115мдо 95м

до 50м

до 150м

Shoreline position of the Bakalskaya Spitfrom the Landsat satellite dataConfiguration changes of the distal part according
Satellite Landsat (top), GPS-shooting (below)(Yu.N. Goriachkin, L.V. Kharitonova, and V.V. Dolotov, 2009)

The Karkinitsky Bay of the Black Sea and The Bakalskaya Spit
The main morphodynamic
processes in the area of theBakalskaya Spit are- the erosion of the spit
western coast;- the extension of its distal part
into the Karkinitsy Bay waterarea in the north-east
direction;
Island-reduction of the spit width in the areaof the isthmus, which connects themain part of the spit with its distalpart;- separation of distal part from themain part of the spit.
After the storms which took place inautumn, 2010 the isthmus was erodedand has not recovered yet, and thedistal part of the spit became anisland.

THE FIELDS OF INTEREST
The dynamics of sediments in the Bakalskaya Spit region depends on wind waves
and sea level oscillations, which should be reasonably taken into account during thenumerical simulation.
The setting of these parameters based on the field data or numerical calculations
always contain some uncertainty.
So the estimation of the dependences of morphodynamic process simulation
occuring in the Bakalskaya Spit region on the variations of wind wave parameters
and the sea level is of interest.
In this work such estimations are carried out on the basis of XBeach (eXtreme Beachbehavior) numerical hydrodynamic model.

Structure of the XBeach numerical hydrodynamic model(eXtreme Beach behavior)

SWAN model
Boundaryconditions

BLOCK 1.

(XBeach model description and manual, 2010)
BLOCK 2.
BAROTROPIC CURRENTS

SHORT WIND WAVES• The wind waves

parameters• Parameters of the rollers

Waves androllers
intensity• Vertically averaged

current velocities

BLOCK 3.
SEDIMENTDYNAMICS• The flows of bed-load and suspended

sediments• Erosion and accumulation• The bed and the coast deformation

INPUT PARAMETERS: Digital model of the studied region relief
Navigation chart
the Karkinitsky Bay
1:200 000 scale
The expedition
data obtained inJuly, 2007

Bathymetricobservations

Cross sectionof beachprofiles

The height ofisthmus- up to 0.9 m
BOUNDARY PARAMETERS•in cell centers - depth, level, sedimentconcentration, wave and roller energy•the middle of lateral boundaries –current velocity components, sedimentflows

Rectangular staggered grid
Dimensions
Grid steps
2.22.9 km
x=17 m, y=19 m

INPUT

PARAMETERS

WIND WAVEPARAMETERS

SEDIMENT PARAMETERS
The storm wave
running from

Data of Spectral wave model SWAN
(Simulating Waves Near Shore) :• the significant wave height = 4 m,
• the wave peak period = 6 s,
• the spectral peakedness = 3.3,• the index of angularwave dissipation = 10
(V.V. Fomin, D.V. Alekseev, L.V. Kharitonova, 2013)

The spit and the seabed consistof medium sand.
Particle size – D50= 5*10-4Density – 2650 kg/m3
STORM SURGE
PARAMETERS
5 constant in time values of surges:
0.00 ; 0.25; 0.50; 0.75; 1.00 m

After 24 hours of 4 m height wave running from the west
Land and seabed relief (m)Relief changes

Storm surges – 0.0 m

Relief changes

Storm surges - 0.75 m

After 24 hours of 4 m height wave running from the south- west
Land and seabed relief (m)Relief changes

Storm surges – 0.0 m

Relief changes

Storm surges - 0.75 m

After 24 hours of 4 m height wave running from the north-west
Land and seabed relief (m)Relief changes

Storm surges – 0.0 m

Relief changes

Storm surges - 0.75 m

CONCLUSIONS In all considered cases the XBeach model reproduces basic characteristics ofthe Bakalskaya Spit dynamics, obtained from the observational data analysis :- spit head displacement in the north-west direction due to erosion of its
western part and sediment accumulation near its north-eastern part;- spit erosion in the area of the isthmus, which connects the main part of thespit with its distal part up to its separation.

CONCLUSIONS
The most intensive erosion of the isthmus between the Bakalskaya Spit headand main part in the absence of surges occurs at wave running from the west.
The wave running from the south-west and north-west causes erosion
processes of almost equal intensity.
Seabed erosion occurs along the entire coastline of the spit with different
intensity. Sediment accumulation takes place seawards of erosion areas, but
not continuously along the entire coast. The areas of most significant
sediment accumulation are located to the east from spit head and to thesouth-east from the scour.

CONCLUSIONSStorm surge effect on the morphodynamic process characteristics depends
on the direction of wave running.
In case of wave running from the south-west and north-west, seabed
erosion intensity in the isthmus area increase with the surge height rising.
At wave running from the north-west the isthmus erosion is somewhat more
intensive than at wave running from the south-west.
In case of wave running from the west, the increase of surge height resultsin the decrease of isthmus erosion depth.
The presence of surges has no effect on the location of erosion areas.
Sediment accumulation areas at that extend seawards.