Tatiana Orehova

• Doctor of Philosophy
• Professor (Associate) at Climate Atmosphere and Water Research Instiute of Bulgarian Academy of Sciences

Eftimi, R., Andreychouk, V., Malík, P., Orehova, T., Nita, M., Qiriazi, P. 2024. Factors influencing the groundwater and its circulation in Mali me Gropa karst massif, Central Albania. Abstract There are 23 carbonate karst areas in Albania with a total area of 6440 km 2 , distributed in all tectonic zones of the country. Mali me Gropa karst massif...

Water balance calculation is an important stage of the groundwater research. Surface runoff in open karst conditions is usually absent, and the outflow of karst system occurs through springs. The aim of the study is to analyze the water regime and balance of two karst springs near the town of Kyustendil in West Bulgaria. WaterbalANce software is us...

This is a book of proceedings of the 6th International Conference of the Climate, Atmosphere and Water Research Institute of the Bulgarian Academy of Sciences. The collection of papers is devoted to the detection and attribution of contemporary changes in the elements of the climate system, including the interrelationships between the atmosphere, h...

Groundwater is an important component of river runoff, the quantification of which provides valuable information for water management. This study aims to evaluate the spatial and temporal variations in the contribution of groundwater to the river flow in the Mesta River Basin. Two tasks were performed with corresponding research methods and study p...

The conference's purpose is to present and discuss scientific research on the "Climate System: Climate, Atmosphere, and Waters," interdisciplinary achievements and problems of the environment, surface and underground leads, and projections for their change in climatic conditions, as well as the influence of natural and anthropogenic factors on thei...

Groundwater is one of the most important natural resources. The groundwater regime shows seasonal variations and long-term variations, induced by rainfalls and climatic droughts. The seasonal, interannual and decadal cycles of the groundwater level fluctuations are analyzed for two wells in England for the period 1891–2015 provided by the British G...

An analysis is made of the formation factors and regime of floating river sediments on the territory of Bulgaria, considering the influence of the relief (land surface), climatic conditions such as rainfall intensity, snowmelt, wind effects, water erosion, afforestation (forest vegetation), the amount of river runoff, and anthropogenic activity. A...

Materials from FOURTH SCIENTIFIC CONFERENCE, SOFIA, 13-14 OCTOBER 2022

Simulation of the groundwater regime for an aquifer is useful for a variety of purposes: understanding the main factors influencing variations in groundwater levels, recovering missing data, as well as forecasting future time series. The aim of the paper is to simulate the time series of groundwater levels of two observation wells in Bulgaria. The...

The regime of karst springs in Bulgaria is rather variable on different time scales. The most important limitation for water management are seasonal low flows. Modeling the regime of large karst springs is challenging due to variety of factors that act both in time and space. Determining the minimum input data required is important to clarify the k...

FIRST SCIENTIFIC CONFERENCE, DEDICATED TO THE 150-th ANNIVERSARY OF THE BULGARIAN ACADEMY OF SCIENCES, and THE 1-th ANNIVERSARY OF THE CLIMATE, ATMOSPHERE AND WATER RESEARCH INSTITUTE// CLIMATE, ATMOSPHERE AND WATER RESOURCES IN THE FACE OF CLIMATE CHANGE// BOOK OF PROCEEDINGS// БЪЛГАРСКА АКАДЕМИЯ НА НАУКИТЕ// ИНСТИТУТ ЗА ИЗСЛЕДВАНЕ НА КЛИМАТА, АТМ...

The main reason of landslide activation is rising of groundwater, saturation by rain, water infiltration and snow melting. One part of landslides in Northeast Bulgaria starts after heavy rainfalls, as was evident during the last 20-year wet period. The interconnection between the landslides in Northeast Bulgaria, rainfalls and groundwater maxima is...

Study region: Lom depression, Bulgaria. Study focus: A multi-tracer investigation was applied to identify the recharge conditions and isotope hydrological character of four aquifers in the Lom depression (Northwest Bulgaria) using environmental isotopes (δ18O, δ2H, δ13C, 3H, 14C) and noble gases. The radiocarbon age model of Ingerson and Pearson w...

Loess and loess-like sediments cover approximately 11% of the Bulgarian territory mostly in northern part of the country. From the Danube River to the ForeBalkan, the loess soils together with paleosoils constitute a loess complex where its depth varies from 50– 60 meters in north to few meters in south, respectively. Generally, the unsaturated zon...

The widespread loess deposits with a typically deep unsaturated zone are a specific feature of Northern Bulgaria. The vadose zone thickness varies from 1–2 up to 40–50 m. The downward water flux occurs as a diffuse infiltration in depth. It is controlled and in the same time characterized by so-called “soil-water retention curve”, representing the...

The studied karst spring Palilula from Northwest Bulgaria is characterized by fast reaction to rainfall events and water temperature about 14°C. Based on field explorations of the area, most possible location of inflow of surface waters from the Lipenska River is identified. Obviously, the spring receives water from the neighbor rivers-most possibl...

Groundwater and aquifers in mountainous regions are important sources for public water supply. Quantification of groundwater resources in such regions with predominantly fissured environment and scarce hy-drogeological information requires application of specific methodological approaches. In this study, an approach for approximate evaluation of th...

The ground surface relief, geological settings, river network and hydrogeological conditions along the Bulgarian-Greek border are analysed. As a result three transboundary aquifers are identified: the alluvial aquifer in Maritsa River valley and the Neogene porous aquifer Svilengrad-Orestiada in the eastern part of the border, and the karst aquifer...

A major issue in groundwater and surface water management and monitoring is transboundary groundwater flow between neighbouring countries. The subject of our study is the assessment of the groundwater flow across the state border between Bulgaria and Greece, which is characterized by complex natural features. We present a study on the factors that...

The study area in the upper part of the Osam River basin (central North Bulgaria) is characterized by highly variable mountain relief and diversified geological and hydrogeological conditions. Mesozoic clayey-terrigenous sediments are widespread in the area. Triassic and Jurassic carbonate rocks are developed locally, mainly in the upper part of th...

The study area is located in Dobrudzha (Northeastern Bulgaria) and is characterized by widespread karstified limestone of Sarmatian age covered by the loess formation. The main rivers draining the study area are the Suha River flowing to North and the Batova River flowing eastward to the Black Sea. Total precipitation sums in the region are low (41...

The Arda River is the main river course in the mountain range Rhodopes located in Southern Bulgaria. Its river basin is characterized by highly variable relief and diversified geological and hydrogeological conditions. The groundwater is recharged mostly from precipitation and forms baseflow of the Arda River and its tributaries. The aim of the stu...

This work is an environmental isotope investigation of groundwater samples from a multi-layered aquifer system in the Lom depression of Danubian Plain in Bulgaria. Our previous studies in the Carpathian-Pannonian Region had been convinced through groundwater researches using noble gas temperatures that the recharge temperature difference between th...

This paper is devoted to the objective and progress of the activities undertaken in the frames of the project DFNI -E02/4. The aim of the project is to quantify water flow within the unsaturated zone of the loess complex, which is widespread in North Bulgaria. With respect to substantial variability of precipitation and evaporation, water fluxes ch...

The object of the study is evaluation of the groundwater recharge to the river runoff in the Vitosha Nature Park. This mountain area with widespread rock aquifers is poorly studied in terms of hydrogeology. An updated Hydrogeological map is prepared based on the map produced in 1975 on scale 1: 200 000. Delineation of the aquifers, aquifer complexe...

Long-term groundwater recharge is a valuable characteristic for the groundwater management. It is subject to changes under pressure of the substantial climate variability, common for South-Eastern Europe. The aim of the study is to evaluate the groundwater recharge for the Danubian Plain (Northern Bulgaria) based on climatic data. The method used i...

Groundwater is a renewable resource. Quantification of the groundwater recharge is important for the management of water resources. The choice of methods depends on local conditions and the available data. Water balance methods with a daily time step are commonly used for this purpose. The aim of the study is to develop a spreadsheet to estimate th...

The study area is located in Southeast Bulgaria. The main factors affecting climate in Burgas lowland are the proximity to the Black Sea and to mountains. The aim of the study is to quantify the long-term value of the baseflow and other water balance elements. The methods include Turc-Radiation equation, equation relating baseflow coefficient with...

Увод. Подхранването на подземните води е един от елементите на водния баланс, които силно зависят от климата. Дунавската равнина, заемаща равнинната част на Северна България, е покрита с льосови отложения. Климатът тук е умереноконтинентален, като валежната сума закономерно намалява от юг на север. Целта на настоящето изследване е оценка на многого...

Groundwater is a valuable resource yet vulnerable to long-lasting droughts. One of the drought indices is the Standardized Precipitation Index (SPI) that allows monitoring of droughts at different time scales. For the study area from the Northeast Bulgaria (Do-brich region) the impact of drought on the groundwater system is investigated based on th...

Vitosha is the first natural park in Bulgaria and on the Balkan Peninsula. The “Development of Water and Water Resource System Balance for the Territory of the Vitosha Natural Park” is the first comprehensive study of its kind on the water resources of the Vitosha Mountain and the possibilities of their use for the purposes of the integrated manage...

Estimation of the long-term groundwater recharge based on the chloride mass balance (CMB) method is easy for practical applications. This method is reliable only if the atmospheric chloride deposition is known. The direct measuring of this deposition is difficult and is time-consuming. In this study, the chloride deposition at the catchment scale i...

Long-term observations of the spring flows in Southwestern Bulgaria showed their considerable variability during decades. On the other hand, previous research has identified the North Atlantic Oscillation (NAO) as one of the dominant atmospheric factor responsible for the temporal evolution of precipitation and temperature in the Southern Europe. D...

Groundwater recharge in Bulgaria is characterized by well-expressed seasonal and interannual variability. The long-term drought period (1982-1994) had harmful influence on the groundwater replenishment. As a result, substantial reduction in spring discharges and declining groundwater levels has been observed. During the last decades, great interest...

Groundwater recharge in Bulgaria is characterized by well-expressed seasonal and interannual variability. The long-term drought period (1982-1994) had harmful influence on the groundwater replenishment. As a result, substantial reduction in spring discharges and declining groundwater levels has been observed. During the last decades, great interest...

The aim of the study is to evaluate the potential recharge to the ground- water for the chosen study area – the Ogosta River basin in Northwestern (NW) Bulgaria. Various techniques are used for quantifying groundwater recharge. Some of them are based on water budget methods. The Budyko-type curves al- low partitioning of the long-term precipitation...

The present paper deals with evaluation and mapping of the intrinsic vulnerability for the Ogosta River Basin in northwestern Bulgaria. The protective cover and infiltration conditions (PI) method is used developed within the scope of COST 620 Project. According to this method, PI factors are evaluated and groundwater vulnerability map is prepared....

Groundwater regime in Bulgaria is influenced by climate variability. The impact is evident especially for karst water. A time series analysis of spring discharge for selected karst basins was performed. The impact of the 1982-1994 drought period on groundwater regime was detected. For springs that drain open and mountainous karst, the impact of cli...

Human activities may have serious impact on groundwater. Shallow aquifers suffer mostly from pollutants. The most widespread non-point source pollutant of groundwater in Bulgaria are nitrates The study refers to the Ogosta River basin in NW Bulgaria. Different kinds of human pressure are presented and assessed. The results show that human pressure...

Karstic water is an important source of water in the rural areas of Bulgaria. In this study, we estimate the impact of climate variability on the regime of karstic springs of two mountainous regions of the country. Since 1981 Bulgaria has experienced a continuous decrease in rainfall combined with an increase in air temperature. As a result, ground...

Effective management of water resources requires adequate knowledge of groundwater system including the influence of climate variability and climate change. The drought of 1982-1994 in Bulgaria has led to important decrease of springflow and lowering of water levels. Therefore, groundwater demonstrated its vulnerability to drought. The purpose of t...

Groundwater resources in Bulgaria are important sources for rural and industrial water supply. Some of the existing scenarios for future climatic development of the country predict more frequent droughts. The last drought period 1982-1994 observed in Bulgaria had negative impact on groundwater resources in the country. This paper presents the first...

Общата теза на студията е в областта на много сложна, недостатъчно изследвана и безкрайно дискусионна, но изключително актуална проблематика – сравнително бързото изменение на климата в резултат на икономическото развитие на човешкото общество и породените засушавания със сложните природни, икономически и социални измерения с отрицателни последстви...

The main idea of the research is to investigate water resources in Bulgaria during the drought period 1982-1994. The aim is to take in consideration climate variability, economical and social development and their influence to the natural processes. The research is in direction to evaluate sustainable development in conditions of limited water reso...

The main idea of the research is to investigate water resources in Bulgaria during the drought period 1982-1994. The aim is to take in consideration climate variability, economical and social development and their influence to the natural processes. The research is in direction to evaluate sustainable development in conditions of limited water reso...

The purpose of the paper is to analyse the seasonal variability of the groundwater regime for several aquifers in Bulgaria. Stations from the National Hydrogeological Network were used. Observations of discharge for karstic springs and water level for wells were analysed. Time series for the 40-year period were processed. The behaviour of the ratio...

The purpose of the present contribution is to clarify the influence of the recent drought period (1982—1994) on groundwater in Bulgaria. Taking into account the global climate change conception, this period may be considered as a model of future behavior of water resources. The groundwater regime in Bulgaria is described over the three main territo...

Transboundary aquifer along the Maritsa River is shared between Bulgaria, Greece and Turkey. Specific features of the multiannual water balance for the lower reach of the Maritsa River within Bulgarian territory are described. This is water balance in situ on entry into the groundwater system. Seasonality is well expressed, and the water budget ele...

The paper gives a general view on groundwater for the watershed of the Tundja that is transboundary river. Several known cases of surface water - groundwater interaction are presented. Some specific aspects of groundwater regime are concerned. For the purpose of implementation of the EU Water Framework Directive, groundwater bodies in Bulgaria have...

The purpose of the present contribution is to clarify the impact of the temperature and precipitation anomalies during the Water Year 2002 on the groundwater regime in Bulgaria. The analysis is based on data from National Hydrogeological Network: spring discharges and water levels for observational wells. Mean monthly tempera- tures and monthly pre...

Two 3-cellular models giving 3-item equation for recession curve are described and compared on the base of solutions of differential equations for instantaneous recharge to the aquifer. The first model infers that under recharge there is initially distribution of water between porous blocks, fissures and conduits, but no water exchange between them...

In the upper Struma river basin several karstic springs drain elevated massifs of Triassic limestones and dolomites. Low variability of flow during year is the characteristic feature of these springs. The flow regime of spring N 86 at the village of Polska Skakavitza was simulated using a linear response model. The spring is part of the National Hy...

The Upper Jurassic - Lower Cretaceous aquifer is the most productive in Bulgaria. It has national importance as a huge groundwater reservoir and is a transboundary aquifer shared between Bulgaria and Romania. Modelling is a powerful method for the purposes of groundwater management. Part of this aquifer was modelled. Due to large modelled area, ava...

Based on the multi-annual variations of the river runoff in Bulgaria different scenarios for natural development of the river runoff with consideration of anthropogeneo us impact were created. On the basis of scientific studies for influence of solar activity into climate and the reports of the Intergovernmental Panel on Climate Change, two main gr...

Temporal variability of the groundwater recharge was evaluated for a study area situated in the Central North part of Bulgaria. For the purposes of the study, a simple model was developed in Excel that produces the partitioning of the rainfall amount (on monthly basis) between evapotranspiration and groundwater recharge. Both multi-annual value of...

National Hydrogeological Network (NHGN) in Bulgaria was found in 1958-1961. The structure of NHGN is presented. The frequency of measurements is mainly once per month. For some karstic springs the daily data are obtained using rating curves. Water level in observational wells is measured usually once in a month. Water level recorders are available...