DOI: 10.3897/jbgs.e168786

Authors: Davis Dinkov, Lyubka Pashova

Abstract: High-resolution Digital Elevation Models (DEMs) are critical for accurate coastal flood risk assessment, particularly in low-lying areas vulnerable to sea-level rise, storm surges, and other natural hazards. This study presents a comparative evaluation of five DEMs with varying spatial resolutions and data sources for a test area along the northeastern Bulgarian Black Sea Coast around the Durankulak Lake—an area identified as at risk of coastal flooding. A high-resolution Uncrewed Aerial Vehicle (UAV) derived DEM was generated using Structure-from-Motion and Multi-View Stereo (SfM-MVS) photogram-metry and compared against three other DEMs: BG DSM (4 m), MGS DEM (10 m), and re-sampled TanDEM-X (10 m). The vertical accuracy of DEMs was assessed using control points (CPs), including GNSS-measured and geodetic reference points, and parametric and non-parametric statistical methods, along with statistical tests to assess the error distribution. Results indicate that the UAV and BG DSM models exhibited normal error distributions with high vertical accuracy (root mean square error: 0.098 m and 0.776 m, respectively), while the MGS and TanDEM-X models display significant deviations from normality and lower precision. The UAV-derived DEM has offered the highest accuracy and reliability, though it requires significant field and processing resources. The findings highlight the importance of selecting DEMs based on the required precision, available resources, and application-specific context, particularly for hydrologic and hydrodynamic modeling and flood risk mapping under the EU Floods Directive. This study provides a robust methodological framework for evaluating DEM quality and suitability in coastal hazard assessments and contributes to improved geospatial data practices in flood-prone regions.

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DOI: 10.3897/jbgs.e153003

Authors: Tsvetan Parov

Abstract: During the 33rd Bulgarian Antarctic Expedition, field studies were conducted to examine the internal microclimate of crevasse-drainage systems of the three glaciers: Balkan Ice Field, Johnsons and Contell Glaciers. The research is focusing on the relationship between fluctuations of surface meteorology parameters, internal air glacier temperatures in the crevasses and possible connection with solar activity. The total duration of the study exceeds 60 days, making it the longest temperature monitoring of glacier crevasses in Antarctica. Measurements of air temperature, humidity, and atmospheric pressure were carried out using autonomous sensors, while ultrasonic anemometers recorded airflow direction and speed inside the crevasses. Sensors were placed at depths of up to 25 m in central zones and 10 m near the glacier edges. The study identified a distinct temperature gradient at 3-meter intervals and mapped the depth of zones with persistently negative temperatures. Increased solar activity was associated with lower internal glacier temperatures and stronger air circulation. A negative correlation was found between solar activity and both temperature and downward airflow within crevasses. A glacial cave under the Balkan Ice Field allowed access to subglacial waters and sediment sampling. For the period of one year, the ablation zone of the Balkan Ice Field had expanded, and the constant negative temperature zone had deepened by 6–7 m since the previous expedition. Contell Glacier showed greater thermal stability and resistance to change compared to the larger ice fields. The extended daylight in January (approximately 20 hours) facilitated reliable correlation with solar activity patterns.

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DOI: 10.3897/jbgs.e149029

Authors: Nikolai Dobrev, Plamen Ivanov, Konstantin Kostov, Emil Oynakov, Nina Nikolova, Boyko Berov, Orlin Dimitrov, Elena Koleva-Rekalova, Miroslav Krastanov, Rosen Nankin

Abstract: This article aims to present the results of an 11-year monitoring of micro-tectonic movements along dangerous cracks opening in caves at Cape Kaliakra, Northeast Bulgaria. Two 3D monitoring devices TM71, were installed in two caves, the purpose of which is to monitor the movements of the rock blocks along dangerous cracks. The obtained results of microdisplacement measurements from 2013 to 2023 show active movement along the observed cracks. This is expressed not only in linear trends but also in sudden shifts and short-term shifts followed by recovery (oscillations). The comparison with the local and regional seismicity shows a correlation between the abrupt movements and seismic events along the Batovo fault. Data from the automatic weather station in the town of Kavarna point to a possible link between some oscillation type movements and heavy rainfall in the research area. The results of the analyzes show the importance of long-term monitoring in clarifying the recent geodynamics in the research area. The results obtained provide valuable information about the dynamics of this region, and hence about the geomorphological evolution and the physical-geological hazardous phenomena. The registered movements show the connection between gravitational movements and tectonic ones. For the first time, data obtained through instrumental observations are published, proving the activity of fault structures in this part of Bulgaria. The results can also be used to predict dangerous slope destabilizations, as well as to reduce the risk of their occurrence.

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DOI: 10.3897/jbgs.e99206

Authors: Zvezdelina Marcheva, Tsvetan Kotsev, Assen Tchorbadjieff, Velimira Stoyanova

Abstract: This study aims to reveal the arsenic dynamics in groundwater of а river floodplain contaminated with mine tailings under temperate climate conditions and natural river hydrodynamics. Arsenic concentrations were monitored in the primary morphological units of the floodplain in the upper stretch of the Ogosta River in NW Bulgaria. Iron, lead-silver, and gold mining heavily affected the river valley in the second half of the 20th century. We used groundwater monitoring data from 21 piezometers for the period 2016-2020. Based on the geochemical and geomorphological conditions in the valley, the piezometers were grouped into three clusters. Regression models were developed for each cluster and representative piezometers to predict arsenic concentrations. In the active floodplain, seasonal fluctuations in arsenic concentrations followed the river and groundwater regime. In this part of the valley floor, we determined two periods of elevated arsenic concentrations during the spring and autumn/winter seasons that coincide with high river water stages. Arsenic content in the groundwater of the higher floodplain was less dependent on the water level fluctuations but followed changes in redox potential, electrical conductivity, and water temperature. The obtained results showed the elaborated models as valuable tools for studying arsenic dynamics in alluvial aquifers of contaminated river floodplains. The suggested models could be coupled with groundwater monitoring systems to monitor arsenic concentrations and identify periods of the year with levels below and above threshold values.

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DOI: 10.3897/jbgs.2020.43.10

Authors: Alexander Yanakiev

Abstract: Rapid development of remote sensing technologies, including the introduction of new sensors and platforms opened up a whole new field of their application such as monitoring of vulnerable habitats without direct contact, bearing potential harm of the ecosystems within them. The paper explores such opportunities and looks at the conditions of riverine forests along Kamchia river in 2019, using Sentinel-2a, b imagery.

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DOI: 10.3897/jbgs.2020.42.12

Authors: Svetla Stankova, Tzanko Tzankov, Raina Hristova, Milena Stoyanova, Milen Penerliev

Abstract: The article is dedicate to the life and the creation of one notable Bulgrian investigator, scientist and pedagogue – Prof. Todor Ivanov Krastev DSc (Geography). The principal features of his personality are the big creative energy, impressive capacity for work and restless research spirit. It worldly and creative way is a splendid example for a dedicated work for the science. The results of Prof. Krastev investigations belong to the most Bulgarian Natural Geography achievements for the second part of the twenty century.

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DOI: 10.3897/jbgs.2020.42.6

Authors: Valentin Nikolov

Abstract: The article is dedicated to the creative path and the scientific heritage of Vladimir Popov – one of the remarkable scientists for the Bulgarian geography of the last century. The experience during the professional development from a research precision and focused interest in geomorphology, karstology and physical geography. In this respect, original are the researches on the contemporary relief genesis and evolution, karst region and caves in Bulgaria. The karst in Bulgaria occupies an area of 26 170 km2 or 22.7 % of the territory of the country (Popov 1970). It is distributed in carbonate bodies with a different structure, dynamics and spatial relationships. New zoning of karst is being carried out for the Bulgarian territory. It is divided into: plain; marine and transformed marine karst into plain and plain-marine karst; plateau-like karst; mountain and intermountain karst; karst wetlands and gravitation karst, provoked by catastrophic earthquakes. Karst in Bulgaria is characterized by great diversity due to the complex combination of the factors and conditions of its formation (geological, tectonic, geomorphologic, hydrological and hydrogeological, climatic, etc.) and to the geodynamic development. Regardless of the fact that karst is well studied, there are still fundamental problems in karstology that have not been solved as a whole. In 1970 and 1976yy Popov made the first zoning of surface and underground karst in Bulgaria according to the geological base.

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