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The Paleogene sedimentary rocks in the north-easternmost part of the territory of Bulgaria have been penetrated by numerous boreholes. In terms of regional tectonic zonation, the study area is a part of the onshore sector of the Moesian Platform, which partly includes the South Dobrogea Unit and the easternmost part of the North Bulgarian Dome with its eastern slope. The lithostratigraphy of the Paleogene successions consists of six formal units (the Komarevo, Beloslav, Dikilitash, Aladan, Avren, and Ruslar formations) and one informal unit (glauconitic marker). For compiling an overall conception of the regional aspects (lithology, thickness, spatial distribution, and relationships) of the individual lithostratigraphic units and for illustration of their spatial distribution, a 3D lithostratigraphic model based on reinterpretation of individual borehole sections has been created. The model database was compiled by integration of the original lithological data from 338 borehole sections.

This study is based on primary lithological data from 96 boreholes and lithostratigraphic interpretation of 17 seismic profiles from the onshore part of the Dolna Kamchiya Basin, which belongs to the onshore sector of the Moesian Platform and comprises the south-easternmost part of the Southern platform zone. Nine formal Paleogene lithostratigraphic units were recognized (the Byala, Komarevo, Dvoynitsa, Beloslav, Dikilitash, Aladan, Avren formations, the Dolni Chiflik Member of the Avren Formation, and the Ruslar Formation). For visualization of their spatial relationships and revealing the deep structure of the basin, a 3D lithological model was created. In addition, new data on the lithology, thicknesses and ages of the units were provided.

Morphometric features of the topographic surface are one of the main prerequisites (conditioning factors) for the occurrence of erosion and debris flows. The following morphometric parameters of the river Byuyukdere watershed were calculated in the current study: basin area, basin relief, basin length, relief ratio, Melton’s index, slope and stream power index. The analysis shows higher susceptibility to erosion and debris flows of the 1st and 2nd order basins (Strahler’s method). The elevated values of the stream power index indicate an intensive erosion in the lower part of the river Byuyukdere watershed, which is related to the volcanogenic-sedimentary rocks and the faulted nature of the river valley. The morphometric analysis was performed in ArcGIS Pro on the base of a 12.5 m resolution digital elevation model.