Search

An assessment of the landslide risk (Rls) for the territory of Bulgaria by administrative districts has been made by combining the vulnerability (V) and landslide hazard (Hls) maps. Landslides are a significant part of geological hazards and are widespread throughout the country. In order to assess the landslide risk for the territory of Bulgaria, it is necessary to take into account not only all landslides for a given region, but also its vulnerability, and thus to assess the level of landslide risk for this region, Rls = f (V, Hls). Landslide risk is determined by a risk matrix, using selected indicators and weighting coefficient of vulnerability and landslide hazard. Assessing the vulnerability of a region subjected to geological hazards is a key component of risk assessment. These include the exposure of infrastructure, industrial facilities and production capacity, residential buildings, regional GDP per capita and potential for human disability (defined by population density in the district). The data used is combined to create a map showing the vulnerability of each administrative district. Indicators of population density, GDP, length of road and railway networks and number of residential buildings were used to assess the vulnerability. The landslide hazard in each administrative district is determined by the intensity of landslide processes in the district, depending on the level of their activity and the affected area. The normalized (distributed) hazard of landslides for an administrative region is given depending on the area of the given administrative region. Landslides are categorized as active, potential and stabilized. The results express the weighted average hazard. Landslide hazard is rated from 1 to 5, where 1 means no landslide hazard and 5 means that landslide hazard has a very high intensity (very high hazard). The high degree of landslide hazard in turn leads to possible economic losses, social and environmental consequences (landslide risk). The intensity (level) of landslide vulnerability, hazard and risk is assessed as very low, low, medium, high and very high, and is shown on the relevant maps.

The article presents the results of the landslide mapping in the area of the town of Polski Trambesh, central Northern Bulgaria. A total of 37 new landslides have been described, which have not been included in the landslide register so far. Landslides are classified by area, type and activity. Their location is mapped in a GIS environment.

A specific sample area was selected, where an assessment model was made for the stability of aslope subjected to anthropogenic impacts. A hillside slope zone from the foot of the Vitosha and Lozen mountainsin the southern periphery of the Sofia Kettle was chosen as an exemplary area for a part of the hazardsarising in the Trans-Balkan valleys. The anthropogenic impact on their slope stability was studied on threeparticular slopes. The study area is about 1.25 km2 and has a maximum distance of up to 3.80 km betweenthe slopes. Landslide processes resulting from anthropogenic impact often occur on the territory of the SofiaValley. The rise of construction, the development of hard-to-reach terrains with steep slopes, their undercutting,the seismic impact and the low values of the strength-deformation parameters of the geological varietiesbuilding up the respective terrains contribute to their occurrence. The deforestation, the loads with heavy embankments, the hydration and the inhomogeneity of the layers of the earth base have a strong destabilizing effect. The paper presents the results of field and laboratory tests and analyses of slope stability by the methodof Fellenius. The severity of the impact of the various destabilizing factors was assessed.

The liquid limit is one of the most commonly used index properties of soils. The paper comparesliquid limit values determined by the Vasiliev cone penetrometer method and by the Casagrande cup method,based on 45 natural clay samples collected from the Kozloduy Town area (North Bulgaria). An empirical correlationbased on these liquid limit results has been derived.

This research is focused on registering the movements along the slope of the several slopes located on south-west of the mountain Stara Planina and establishing their average annual values. Currently at national level there are a low number of studies targeted at operational monitoring of the investigated slopes. These objects are quite specific for research since those kind of natural phenomena are inaccessible by other means or are quite dangerous to be investigated. On the other hand, the moving slopes are causing damages to infrastructural objects such as roads, bridges or power lines. Their behavior is difficult to forecast and for this reason they can be considered as natural hazards. Obtaining precise data for the single slope movements is done by in-situ investigations such as geodetic acquisitions, terrestrial laser scanning, and geological observations, which all require financial resources and human effort. For this reason, we used remotely sensed data from satellite based SAR instruments processed using the DInSAR method in order to analyze the motions of single slope and to establish a technique for the investigation of mountain slopes. An advantage of the selected method is the possibility to register the vertical movements of the whole slope with centimeter accuracy. This approach is based on the free access to the SAR data and tools for their thematic processing provided by ESA. In this study an emphasis is put on the manner how the obstacles encountered during the interferometric processing (e.g. presence of vegetation or topography) have been overcome. From the downloaded set of SAR images covering the region created were two multitemporal InSAR data series from ascending and descending orbits of the satellite. The results from the autumn-winter pairs exhibited good correlation with the expected displacements along the studied slope having a magnitude of 0.8 m.

Rock collapses phenomena are one of the main processes constituting the geological hazard. Most commonly, the concept of "collapses" covers several different types of rock deformations: rockfall (linear and wedge-shaped), rock toppling, etc. It is difficult to predict the exact moment of the occurrence of a rock collapse. For this reason, it is necessary to know the potentially dangerous regions and areas in which this phenomenon may occur or to plot the sites by susceptibility to rock collapses. This will give an idea of location of hazardous areas with preconditions for collapses, and on this basis the necessary preventive measures can be identified. The main types of rock collapses and slope conditions - engineering geological, geomorphological, tectonic, are discussed. The methodological approach is given for the mapping of the terrains by susceptibility to rock collapses. Issues related to the scale of the maps compiled are clarified.

The territory of Bulgaria is at risk of a number of unfavorable and destructive geological processes and phenomena constituting the geological hazard. The generally high hazard degree necessitates analyzing, evaluation and mapping of the geological hazard and risk processes. Evaluation and mapping of geological risk is the final stage of a long-lasting gathering of information for each destructive geological process. The purpose of the present study is to analyze the principles and order in assessing and mapping the overall geological hazard. Typical hazardous geological processes for the territory of our country are taken into account (active faults, abrasion/sea erosion, erosion, landslides, rockfalls, collapse, swelling, liquefaction of dispersed soils, etc.). A methodological approach is presented to combine all hazardous geological processes into an integrated hazard map. The study presents the results obtained during the implementation of the project “Elaboration of analysis, evaluation and mapping of geological risk” realized in 2016 by a large research team and supported by the Ministry of Regional Development and Public Works in Bulgaria.

International audience; Debris flows are natural hazard triggered by intensive rainfall or snowmelt and represent rapid movement of water-saturated colluvial and proluvial earth masses. The propagation of this hazardous event could change ecosystems, increase the solid discharge in the rivers and dam siltation, and affect infrastructure and people. The compound character of debris flows requires collection and analysis of various information and for this purpose, the computer technology and geographic information systems provide great opportunity. The aim of the paper is to present a conceptual model of debris flow information system, which to be used for risk assessment and to support decision making. The study emphasizes to factors and prerequisites, debris flow data, analyses and visualization. A fuzzy logic model for integrated risk assessment of the debris flow due to the multiple natural factors (as rainfall duration, rainfall amount, slope, erosion etc.) is proposed. An example of geoinformation portal is presented.

Mapping the landslides is one of the main activities in the overall spectrum of geological hazards and geological risk. Landslides form the most serious part of the geological hazard in Bulgaria after the earthquakes. They are widespread in the all country’s territory. All known landslide types of internationally accepted classification of Varnes (Landslides, analysis and control, 1978) are represented there. The main attention is paid to the level of activity and the territorial scope of landslides according to the criteria involved in the National Programme for Landslide Prevention of Bulgaria (2014) aimed at prioritizing landslides depending on the level of activity and the risk they carry. Thus 5 degrees of landslide hazard are accepted. Hazards and vulnerabilities are considered to be weighed, i.e. they can be assessed in advance in terms of what will be the weight of the probability of landslide hazard of the research area and what will be the results (vulnerability) due to its occurrence. The vulnerability is represented by indicators of GDP per capita and density of population. The intensity of the hazard can be very low, low, medium, high and very high, which correspond respectively to classes from I to V. The third stage is the determining factor of landslide hazard. This stage is determined by the intensity of the landslide hazard for the study area. It is obtained according to the district class of intensity for landslide hazard. The results express the weighted average hazard. They are obtained through a combination of the weight of the landslide hazard and its intensity that is accepted for the zone concerned. The weights for landslide hazard and its ratios derived from the potential intensity are multiplied to obtain individually weighted hazard score.

The necessity of contemporary assessment of the natural hazardous processes on the territory of Bulgaria leading to disastrous and catastrophic situations in a number of regions is motivated by their high activity resulting in destruction of building fund, infrastructure, historicalmonuments, land use disturbance and annihilation of areas, interrupting of communications, aggravation of ecological conditions, human health threats, social stress enhancement. The landslide manifestations displayed recently along the Black Sea coast and the Danubian riparian area, the Rhodopes and other parts of the country and their serious consequences confirm the long ago ascertained truth that the Bulgarian territory is characterized by a high degree of landslide hazard. The geological-tectonic conditions and the relief of the country determine the development of a large number of landslides on its territory. The many years of research and applied activities on landslides have led to the establishment of important relationships for their distribution, factors for origin and activation, mechanism and dynamics, etc. The origin and activation of landslides is a consequence of the influence of many factors — tectonic, seismic, geomorphologic, climatic and technogenic ones. A part of them act permanently, while others have short-term impact. Both separately and in combination they reduce slope stability and provoke the manifestation of big and destructive landslides. The impact of the destabilizing factors and the distribution of 403 landslides are analyzed in this work. Regions with different degree of landslide hazard have been distinguished. Diagrams are shown for the regional distribution and time of landslide display. The weighted effect of the destabilizing factors for slope stability formation is different. A part of them as the contemporary vertical movements and earthquakes are of regional importance, others act locally — erosion, abrasion, precipitation. The origin of the active landslides may be closely related to contemporary tectonic activity. The regional distribution of the landslides according to their volume shows that landslides with a volume up to 10 million m3 are the prevailing type in the country. The most numerous landslides in this group — about 50% of the total number — are observed along high Danubean Bank and Northern Black Sea coast, in the tectonically active grabens as Sofia, Pernik or Simitli and the landslides along some of the faults in the Strouma zone. The largest landslides with a volume of more than 100 million m3 are encountered along the Danubean Bank, the Northern Black Sea coast and in Rhodope Region.

The Oryahovo town is located at high Danube coast, and has been affected by landslide. Many houses and streets in the town are heavily deformed by continually ongoing landslide movements. The slope is affected by deep-seated landslide from translational type, which is in stabilized or in condition of slow creep. In the landslide body are created shallow landslides of rotation and flow type occur, which create the major problems of the town. In this regard, the conditions and factors of landslide activity have been analyzed. For this purpose, are composed three profiles for slope stability, located about 850 m apart. Current level of sustainability of the land is determined by applying the Janbu in “effective stress”. For the zoning of the landslide in Oriahovo were used the lowest values of the factor of safety along the three profiles. The calculations of slope stability in critical sectors of the town showed that the main factors of shallow landslides are groundwater fluctuation that is both of natural and/or man- made origin and the vibrations from heavy transport machines. An additional factor is seismic tremors that occurred from Vrancea seismic zone. The coefficient of stability decreases with 3 % from intensive traffic of heavy trucks through the town. On this basis, a Susceptibility hazard map of Oryahovo town has been compiled that represents the real situation of landslide hazard of the researched area. The map shows that the most endangered parts are the eastern ones and these above the ferry harbor of the town.

The Northern Bulgarian Black Sea coast is about 100 km strip that almost along its entire length is affected by landslides. Тhese landslides are irregularly distributed in four landslide areas. Most of the landslides are complex and deep-seated. The present article analyses the old and recent sliding phenomena along the coastal zone in this part of Bulgaria. The analysis of the structures of the landslides along the Northern Bulgarian Black Sea coast gives the reason to considerate the earthquakes as one of the main factors that activate their creation and their periodical reactivation. The other factors are the slow tectonic movements, the fluctuation of groundwater level during rainfalls or snow melting, the abrasion and different types of man-made impacts that contribute to decreasing of slope stability along the coast line.

The present paper aims to analyse and to discuss the state of landslide problems in Bulgaria. It separates the main factors of instability of slopes Bulgarian landslides: tectonic movements, earthquakes, erosion, abrasion, surface water and groundwater, precipitation and human impact. Landslides are concentrated in certain regions: Black Sea Coast, Danube bank, the Fore-Balkan, Rhodope Mts, active tectonic grabens in South Bulgaria and Maritsa-Iztok coal basin. 917 landslides affecting urban areas are presented on Map of landslides in Bulgaria, in scale 1:500,000. They are divided into three groups: (1) shallow landslides, (2) deep-seated landslides, conditionally stable, and (3) deep-seated landslides with periodic (re)activation of some parts of them. National Program for Landslide Mitigation has been made. The program envisages countermeasures on selected 170 most dangerous landslides in the country.