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This thesis deals with the evaluation of surface and groundwater quality changes in the periods of water scarcity in river catchment areas. The work can be divided into six parts. Existing methods of drought assessment are discussed in the first part, followed by the brief description of the software package HydroOffice, designed by the author. The software is dedicated to analysis of hydrological data (separation of baseflow, parameters of hydrological drought estimation, recession curves analysis, time series analysis). The capabilities of the software are currently used by scientist from more than 30 countries around the world. The third section is devoted to a comprehensive regional assessment of hydrological drought on Slovak rivers, followed by evaluation of the occurrence, course and character of drought in precipitation, discharges, base flow, groundwater head and spring yields in the pilot area of the Nitra River basin. The fifth part is focused on the assessment of changes in surface and groundwater quality during the drought periods within the pilot area. Finally, the results are summarized and interpreted, and rounded off with an outlook to future research.



Chapter 1. Introduction

The goal of the thesis was to evaluate changes in the surface- and groundwater quality during periods of hydrological drought. The Upper Nitra river catchment was selected as a study area. Before the evaluation of the drought in this catchment, the occurrence and character of hydrological drought in 75 profiles of Slovak rivers was processed. This regional evaluation was used for comparison of the relationship between the local and regional drought occurrences. Subsequently, the occurrence and nature of meteorological and hydrological droughts in the surface water and groundwater were analysed in the evaluated area. Partial results were compared afterwards. The study of hydrological drought was followed by the assessment of the surface water and groundwater quality at various quantitative conditions. The water quality within periods of water scarcity was assessed at the two levels. As the threshold levels, value of median and 90th percentile estimated from the flow duration curve were used. Individual results were summarized. The last chapter deals with a general assessment of the dependence between quantitative and qualitative conditions of the surface- and groundwater within the drought periods. In addition to the described work, a new software tools for the hydrology and hydrogeochemistry were developed and used for the data processing and results assessment.
Miloš Gregor

Chapter 2. Methodology

The term “drought” has nowadays a large number of definitions and it is seen from different perspectives. Drought generally starts with a lack of rainfall. Its symptoms significantly affect the intensity of evapotranspiration. It affects the air and soil moisture, runoff characteristics of the surface- and groundwater. Definitions of drought we know relatively numerous, due to its temporal and spatial variability, as well as due to different ways of perception with regard to the purposes for which it is defined. The definitions of drought, which are used in practice, determine the start, end and eventually the intensity of the impacts on various assessed fields.
Miloš Gregor

Chapter 3. Software Tools Used at Work

At the processing of the presented thesis we used larger number of software tools. The essential tool was table calculator—MS Excel. From the additional tools there was used for spatial analysis the open-source tool MapWindow 6, allowing using number of spatial functions as well as framework for spatial analysis. As often happens, software tools are not sufficient, especially for specific purposes and goals. Therefore, author of this thesis designed and programmed several new programs
Miloš Gregor

Chapter 4. Area of Interest and its Natural Conditions

Area of interest, where we have processed the majority of analyses in present work is located in the western part of Slovakia in the territory of upper part of the Nitra river catchment (Fig. 4.1).
Miloš Gregor

Chapter 5. Analysis of Hydrological Drought

This chapter, entitled Analysis of hydrological drought is the first part of a self author’s work. It deals with a comprehensive analysis of hydrological drought. This chapter is divided into several subchapters. The first deals with the analysis of hydrological drought in the rivers profiles in Slovakia. This chapter includes profiles that are distributed through the entire Slovakia and these profiles were assessed for determining the basic characteristics and regularities of the drought occurrences and their time course in the regional scale, especially as a reference source for local assessment of drought in the upper part of the Nitra river catchment.
Miloš Gregor

Chapter 6. Water Quality Assessments in Dry Seasons

This chapter focuses on the water quality assessment in dry seasons, and it is divided into several subchapters. The first subchapter is devoted to the input data and evaluation methods for surface and groundwater quality assessment. The following three subchapters deal with general, spatial and temporal assessment of surface and groundwater quality in the upper part of the Nitra river catchment. The next part concerns water quality evaluation in the assessed area in the differing surface and groundwater quantitative states. The last subchapter briefly summarizes the knowledge acquired from this water quality evaluation.
Miloš Gregor

Chapter 7. Summary of Thesis Results

The first result of this author’s contribution is marked by development of new hydrological and hydro-geochemical software tools. Their ongoing gradual development has exceeded their initial focus on hydrological drought assessment and the evaluation of water quality. They currently present a comprehensive, multi-purpose package which begins with the processing of various time series of measurement and ends with modelling infiltration processes in catchments, and solute transport modelling in dynamic rives systems.
Miloš Gregor

Chapter 8. Recommendation for Further Research

Many new questions have arisen from this thesis and its results, and answers will require further work and a lot of effort. In assessing the meteorological drought, the regionalization of results obtained from observed points in individual meteorological stations was quite interesting. The results from all the individual stations were averaged for this entire evaluated area which involved considerable simplification. Spatial distribution of the meteorological stations and errors measurement can significantly distort overall results. Therefore, it is appropriate to study the regionalization methods, which can bring new knowledge.
Miloš Gregor

Chapter 9. Conclusions

The aim of this thesis is to evaluate the quality of surface- and groundwater during low flows in the catchment. The chosen area was the upper part of the Nitra river catchment area in Slovakia. This dissertation summarizes the results of research in described problematic areas, and my results can be divided into three separate groups.
Miloš Gregor


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