Flood hazard connected with the failure of hydraulic structures and flood risk associated with areas subject to flooding need to be estimated using flood hydrographs. Multivariate statistics of flood wave parameters enable quantitative conclusions about such flood hazards and risks. This study focuses on uncertainties in their estimates using unbounded and bounded marginal distributions of flood durations in the joint modelling of flood peaks, volumes, and durations with vine copulas. We have respected the seasonality of floods by distinguishing between the durations of summer and winter floods. We propose to use the bounded Johnson's SB distribution to represent the hydrological constraints associated with flood durations. The practical consequences of selecting various unbounded and bounded distributions for modelling flood durations for the joint overall and conditional probabilities of the exceedance of flood peaks, volumes, and durations were demonstrated on data from the Parná River in Slovakia. Differences in modelling joint probabilities due to the tail behaviours of the marginal distributions tested were found. Although these are not critical for practical applications, accepting upper and lower bounds as hydrological constraints improves the quality of the statistical models.

The influence of land use change on transport of water and energy in ecosystem and climate change Increasing population led to the increasing demand to food, raw materials, water and energy, followed by the increasing intensification of land use, and increasing industrial and agricultural production. This led to fossil fuels combustion and related carbon dioxide emissions, to building of structures impermeable to water as industrial infrastructure, transport facilities and dwelling structures, which basically change land properties, structure of water and energy fluxes of biosphere, and to climate change of the Earth. The aim of this paper is to quantify the influence of modified evaporating surfaces by land use changes on water and energy fluxes in modified ecosystems. The influence of land use changes on energy fluxes in the boundary layer of atmosphere is compared to the influence of carbon dioxide concentration increase. It was demonstrated that the contribution of land use changes can be more significant than the influence of carbon dioxide emissions on atmosphere boundary layer temperature.

During last twenty years, a number of extremely dry years have occurred in a number of European river basins.In Slovakia, the lowland streams of southern Slovakia have been particularly affected by drought.One of these streams is the Ipeľ River.In this basin we have three continuous observations of daily flows since 1931: from Krupinica at Plášťovce, Litava at Plášťovce, and from Ipeľ at Holiša station.The first part of the paper is devoted to the statistical analysis of the Litava flow series.In the second part, the hydrological balance in the Litava basin for the three subperiods (1931-1960, 1961-1990, and 1991-2020) in annual time step has been elaborated.The first thirty years 1931-1960 were the wateriest (runoff was 205 mm).In the last thirty years, the runoff coefficient was only 0.2 (runoff 131 mm) in Litava basin.In the final part of the study, the BILAN balance model (in a monthly step) was used to compute the contribution of several runoff components in the Litava basin during period 1930/31-2019/20.The long-term average baseflow accounts for 40.7% of the total modelled runoff, interflow accounts for 46.8% and direct runoff accounts for 12.5% of the total modelled runoff.

One of the main sources of water supply in the Ukrainian part of the Danube delta is the Danube lakes, one of which is Katlabukh. The main revenue part in the water balance of the adjacent delta Lake Katlabukh is the inflow of Danube water through canals with offtakes. The water levels in the lake are determined with the rules of the use of the reservoir, as well as with the hydrological regime of the Danube. Water exchange is carried out by off takes Hromadsky and Zhelyavsky. The reduction of water exchange processes with the Danube in combination with anthropogenic impact on the catchment area of small rivers flowing into Lake Katlabukh, as well as the negative phenomena associated with climate change; create many environmental, water, and social problems for the lake. One of the main problems is the unsatisfactory state of water quality in terms of hydrochemical parameters, in particular high mineralization, which limits the use of the lake water for water supply. The permanents monitoring and analysis of the hydrochemical state of the lake waters will allow to development of scientifically based recommendations for improving water quality and rational use.

The effect of different

Sediment reservoirs (SR) are an important part of the irrigation systems, and their construction and operation are resource intensive. At present, such facilities are constructed on water structures mainly to deposit sediments in water by slowing down the flow rate. The design form of the SR is frequently rectangular which makes it difficult to control the sedimentation process by sediment fractions along the length of the flow. Based on the results of the theoretical analyses and field experiments, the design parameters of the SR were improved, and a computational method of sediment distribution developed. A new design of the SR, which allows separating the sediments by fractions has been proposed. In the developed SR, muddy water flows into a special reservoir that reduces the flow velocity, and the sediments are separated by fractions along the length of the cross-section, the width of which increases onwards. Large fractions are deposited by the SR itself and are removed from the facility through the sedimentation gallery. Water flowing through the regulated water-releasing gate equals 5% of the water inflowing to the SR.

ACTA HYDROLOGICA

The presented paper deals with the numerical modeling of groundwater response to the extreme hydrological situations in the Danube River.A 3-D numerical groundwater modeling is carried out using MODFLOW (McDonald and Harbaugh, 1998) and Groundwater Modeling System (AQUAVEO, 2021) simulation packages for available hydrological, geological, and hydro-geological parameters to study how the groundwater responded to the flood event in the Danube River that occurred in June 2013.

The course of soil moisture in the organic horizon of the forest soil depends mainly on the distribution of atmospheric precipitation and the air temperature during the year.The hydrological significance of the organic horizon of forest soil lies in the rainfall water retention and transfer of water to the lower (mineral) part of forest soil profile.Forest soil with a well developed organic horizon has a higher ability to retain soil moisture than the mineral component of forest soil.The effect of the forest type on the interception capacity is related to the leaf shape.The primary aim of this paper was to analyse and statistically evaluate the changes of soil moisture in the organic horizons under the different tree species (oak, sycamore maple and beech).The evaluation of soil water storage (SWS) in examined organic horizons during the selected dry and wet period was another aim of paper.The soil moisture was measured with frequency domain reflectometry sensors every 10 days in the period from 29.6.2018 to 15.1.2020.The mean value of soil moisture measured in organic horizon under the oak was 13.44%, under sycamore maple 16.08% and under the beech 19.64%.The SWS in the examined organic horizons was determined for the selected dry (29.6.2018-30.8.2018) and wet period (14.3.2019-31.5.2019).The statistically significant difference was found between SWS in the organic horizon under the beech and other two examined organic horizons only during wet period.

Nitrates belong to the major nutrient required for plant growth and they are generally very well soluble in water often used as fertilizers in agriculture. The higher values of nitrates concentration will occur in the case of large amounts use of fertilizer in intensive agriculture, pipe damage or damaged drainage near wells. The fertilization reduction could be one of this problem solution for health protection, environmental and economic reasons. In our study, the spectrophotometric determination of nitrates concentration in 5 times over-fertilized soil in lysimeters localized in the Eastern Slovakia Lowland showed nitrates leaching in the 40 cm layer of sandy soil, while in the silty-loam soil profile nitrates were not detected. The main goal of the experimental work was to show different nitrates leaching through two types of soil profile differing in hydraulic soil properties. Low retention capacity and high hydraulic conductivity of sandy soil (locality Poany) were favourable for nitrate leaching in comparison with higher retention and conductivity of silty-loam soil (locality Vysok nad Uhom) under relatively low precipitation events in the studied period from April 29 th to May 28 th 2019.