A series of numerical experiments was carried out to study the mechanism of storm deformations of the coastal zone relief and the redistribution of different sediment fractions after the parameters of the wind waves directed almost normally to the coastline, are changed. Data and methods. The lithodynamic processes taking place at the Western Crimea coastal zone in the region of the Lake Bogaily bay-bar were investigated using the XBeach mathematical model. The in-situ data on the bottom relief and the sediments granulometric composition obtained during monitoring observations in the Western Crimea coastal zone performed by the Marine Hydrophysical Institute of RAS was used as the model input parameters. The granulometric composition was preset as a mixture of three components distributed along the profile of the underwater coastal slope; at that the ratios of volume concentrations were different. Results. It is shown that influence of the storm waves results in intensive beach erosion, strong alteration of the profile of the underwater coastal slope upper part and formation of an accumulative body. Main changes of the initial profile and redistribution of the sediment fractions are observed during the first 3-6 hours and depend on the wave period. The rate of the water edge retreat and the values of the coastal zone relief deformation were quantitatively assessed for various time periods of the wave action. Position of the marine boundary of the site within which significant motion of sediments and their accumulation during a storm took place was calculated. Discussion and conclusion. Possibility of the bay-bar crest erosion is analyzed for the wind wave' different periods. It is shown that the volume concentrations of different components of the mixture change mainly after the fine fractions are rapidly removed to the seaward part of the bottom profile and the coarser fractions are redistributed in the upper part of the underwater coastal slope. The obtained results provide a possibility of indirect determining the conditions for blocking the alongshore sediments transport in case of building a hydraulic structure.

Purpose. Based on the mathematical modeling methods, influence of the wind waves on redistribution of the sand fractions in the semi-closed estuary-type water area is estimated using the Balaklava Bay as an example. Methods and Results. A two-dimensional version of the XBeach model with a constant grid spacing 10 m was used. The characteristics of wind waves were preset using the JONSWAP spectrum. The calculations were carried out for a storm event lasting about 12 hours once a year. The in-situ data on the particle size distribution in the bottom sediments resulted from the monitoring observations in the Balaklava Bay region was used in the numerical experiments. Conclusions. The results of modeling showed that the basic determining factors regulating the sediments movement were the depth and the bottom slope. It is noted that changing of the bottom inclination angle between the isobaths 6–7 and 7–8 m leads to deposition of the large and medium fractions, and in the area between the isobaths 9–10 and 10–12 m – to accumulation of fine sand. It was revealed that in the Balaklava Bay water area, the main redistribution of sand material caused by the storm waves took place within the southern basin, as well as at the bay exit in the coastal zone of the Megalo-Yalo Gulf. This is primarily determined by the features of the Balaklava Bay coast orography, namely, the knee-shaped narrowness separating the northern and southern basins. Nevertheless, in the isolated northern part of the Balaklava Bay being affected by the storm waves, insignificant dynamics of sand material was observed. The fractions of bottom sediments are redistributed from the western coast to the central part of the basin and to the eastern coast of the bay.