LONG-TERM DYNAMICS OF THE HARMANI-SOZOPOL BEACH-DUNE SYSTEM, BULGARIAN BLACK SEA COAST.

The Bulgarian Black Sea Coast is a well-formed mosaic of pockets, small, gravellysandy beaches, and erosion-prone or erosion-resistant cliffs. A significant portion of the depositional cost along the Strandzha sector includes sand beaches with frontal and stabilized dunes, whose high-resolution mapping is a major task in this work. Currently, unmanned aerial systems (UAS) are the main method for topographic reconstruction. The world's experience in UAS surveys and the rapid capture of hard-to-reach large shore areas are the reasons why we emphasize using drones to map coastal landforms. Based on high-resolution UAS-derived data, a map of depositional landforms was created for the Harmani-Sozopol beach-dune system for the first time. Raster RGB orthophoto mosaics have been used to digitalize and classify different types of dunes. Elevation data from DSM with 15 cm resolution were used to identify beach and dune morphological features: shoreline position, dune foot line, dune crest line, and stable vegetation line. The spatial analysis in the Digital Shoreline Analysis System (DSAS) of the obtained elements allows an accurate assessment of the shoreline changes (erosion/accretion) and dynamics of the dune field. For the time period of 1918-2022, using the Linear Regression Rate (LRR) indicator, an average accretion rate of +0.02 m/yr was reported for Harmani beach-dune system. For the last 100 years, the area has registered a decrease in area by over 55% from 14.5 ha to 6.5 ha. The paper aims to present a multidisciplinary approach to the study of highly dynamic coastal landforms, the results of which would benefit local authorities in drawing up management plans for the Bulgarian Black Sea coast. [ABSTRACT FROM AUTHOR]