Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 167 - 176, doi: 10.31577/ahs-2021-0022.02.0020
Scientific Paper, English

Zuzana Sabová, Silvia Kohnová, Kamila Hlavčová: Analysis of changes in monthly and m-daily maximum discharges using the MPI and KNMI climate scenarios in the Myjava and Hron river basins in Slovakia

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• The paper is focused on an evaluation of changes in average monthly discharges and selected characteristics of maximum discharges (m-daily maximum discharges and the occurrence of maximum discharges) in the selected gauging station of Myjava in the Jablonica profile (5022) and the Hron gauging station in the Banská Bystrica profile (7160). The Indicators of Hydrological Alteration (IHA) software analyzed the data modelled using the MPI and the KNMI climate scenarios. The researched time period from 1981 to 2100 was divided into 4 thirty-year periods, i.e., 1981–2010, 2011–2040, 2041–2070, and 2071–2100. The paper aims to evaluate the changes in monthly discharges and m-daily maximum discharges in the future as well as to determine the suitability of the simulated scenario, which describes the results from the observed data. The results showed that droughts will continue to occur in the summer months and that the winter months will be accompanied by higher total precipitation in the future.
  
  KEY WORDS: Myjava River, Hron River, IHA program, hydrological regime
  
  Address:
  - Zuzana Sabová, Department of Land and Water Resources Management , Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 811 07 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: zuzana.sabova@stuba.sk)
  - Silvia Kohnová, Department of Land and Water Resources Management , Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 811 07 Bratislava, Slovak Republic
  - Kamila Hlavčová, Department of Land and Water Resources Management , Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 811 07 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 177 - 186, doi: 10.31577/ahs-2021-0022.02.0021
Scientific Paper, English

Stanislav Moskalenko, Liudmyla Malytska: Peak maxima on the rivers of the Prut and Siret basins (within Ukraine)

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• The study performed in the article revealed how the daily mean maximum discharge of water runoff and peak discharge of water runoff corresponding to this day on the rivers in the Prut and Siret basins are correlated. There are only the upper reaches of these rivers with a total catchment area of 11300 km2 within Ukraine. Climatic (significant precipitation) and orographic (35% of the territory of these basins is mountain Carpathians) conditions of the Prut and Siret basins contribute to the formation of significant maxima on rivers during rain floods, which often become dangerous with devastating effects and provide the highest peaks in the year. The analysis of maxima is based on the use of historical series of observations at 12 hydrometric gauges. As a result, we found that for small rivers in the mountains, maximum peaks exceed the daily mean maximum discharges on average by 1.8–2.0 times. In the foothills with an increase in the area of the studied catchments and with a decrease in slopes and heights they exceed by 1.4–1.7 times, and with access to the plain – by 1.0–1.3 times. Such research is influential in assessing and forecasting the hazard of the hydrological situation on rivers.
  
  KEY WORDS: Prut and Siret rivers basins, Ukraine, maximum river runoff, daily mean maximum discharge of water runoff, peak discharge of water runoff
  
  Address:
  - Stanislav Moskalenko, Taras Shevchenko National University of Kyiv, Volodymyrska Street 60, 01033 Kyiv, Ukraine
  - Liudmyla Malytska, Ukrainian Hydrometeorological Institute, Prospekt Nauky 37, 03028 Kyiv, Ukraine (Corresponding author. Tel.: Fax.: Email: malitska30@gmail.com)

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 187 - 199, doi: 10.31577/ahs-2021-0022.02.0022
Scientific Paper, English

Pavel Coufal: Evaluation of flow frequency on streams in the South Moravian Region for the last 40 years

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• The aim of the mentioned article is to evaluate the flow frequency in selected water gauging stations in the South Moravian Region from the CHMI network over the last 40 years. Use derived series of M-day discharges for evaluation, which are based on the flow duration curves of the time series of mean daily discharges and the corresponding probabilities of exceeding. The series of M-day discharges in the observed profiles will be evaluated for the current reference period 1981–2010 and the newly proposed period 1991–2020. To orientate the trend analysis in the time series, use a mass curve of mean daily discharges. The result will therefore be to describe the changes in flow frequencies between these reference periods. The above-mentioned results and conclusions will serve for practical use in applied hydrology, e.g. as a basis for determining the minimum discharges in water management and other purposes within the provision of standard hydrological data of surface waters according to ČSN 75 1400.
  
  KEY WORDS: South Moravia, flow frequency, minimum discharges, flow duration curve, Morava River
  
  Address:
  - Pavel Coufal, Czech Hydrometeorological Institute, Hydrology Department, Kroftova 2578/43, 616 00 Brno, Czech Republic (Corresponding author. Tel.: Fax.: Email: pavel.coufal@chmi.cz)

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 200 - 206, doi: 10.31577/ahs-2021-0022.02.0023
Scientific Paper, English

Liudmyla Gorbachova, Borys Khrystiuk: Extreme low flow change analysis on the Tysa River within Ukraine

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• In the current conditions of a changing climate, which directly affects the variability of river runoff, it is very important to have the knowledge about the trends of its extreme flow. Extreme low flows, just like floods are causing a significant material damage. The Tysa River has the two periods with the low flow during year. In addition, some years are dry and such years can be observed for several years in a row. This research used the Indicators of Hydrologic Alteration method (IHA) for investigation of extreme low flow characteristics and their changes along the Tysa River within Ukraine. The research was carried out based on the observations of 4 gauging stations that are located along the Tysa River within Ukraine. The mean daily discharges were used from the beginning of observations until 2018 inclusive. It turned out that at the Tysa River – Vylok Village gauging station the low flow trends differ from the trends at other gauging stations that are located in the upper part of the Tysa River.
  
  KEY WORDS: extreme low flow, IHA, Tysa River, statistical analysis
  
  Address:
  - Liudmyla Gorbachova, Ukrainian Hydrometeorological Institute, 37, Prospekt Nauky, 03028 Kyiv, Ukraine (Corresponding author. Tel.: Fax.: Email: gorbachova@uhmi.org.ua)
  - Borys Khrystiuk, Ukrainian Hydrometeorological Institute, 37, Prospekt Nauky, 03028 Kyiv, Ukraine

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 207 - 219, doi: 10.31577/ahs-2021-0022.02.0024
Scientific Paper, English

Viliam Šimor, Ľudovít Ľupták: Trend changes analysis of the minimum and average annual discharges in selected Slovak rivers during the two periods 1961–2000 and 1961–2015

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• This paper deals with the development of trends of minimum and average annual discharges for the period 1961–2015 and their comparison with the trends for the period 1961–2000, which have been used by the Slovak Hydrometeorological Institute (SHMI) since 2006 as a reference period. In assessing both periods, we have dealt with their comparison with each other and subsequent analysis of any change. In general, time series trends can become an important indicator of whether there is a change in selected hydrological characteristics. In this paper, discharge series were processed and statistically analysed using a simple linear trend and the non-parametric Mann-Kendall test.
  
  KEY WORDS: Mann-Kendall test, Sen’s slope, Average annual discharge, Minimum annual discharge
  
  Address:
  - Viliam Šimor, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: viliam.simor@shmu.sk)
  - Ľudovít Ľupták, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 220 - 229, doi: 10.31577/ahs-2021-0022.02.0025
Scientific Paper, English

Marija Šperac, Ivan Djedović: Hydrological analysis of the Danube regime on the section through the Republic of Croatia and the Republic of Serbia

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• The flow regime of the Danube in the area of the middle part of the basin, on the section of the Danube through Croatia and Serbia, was analyzed. This paper contains a hydrological analysis of the Danube regime using measured flow data at four regression stations; Batina in the Republic of Croatia, and the regression stations Bezdan, Bogojevo and Smederevo in the Republic of Serbia for the period 1992–2018. On this section, two large rivers, the Drava and the Sava, flow into the Danube, which significantly affect the Danube regime. Parde's method of modular coefficients was used to classify the flow regime. Comparing the curves of mean monthly flows expressed through modular coefficients for the Danube, Drava and Sava, it can be concluded that the Danube has an alpine snow regime at the top of the analyzed section, just like the Drava that flows into the Danube. At the regression station Smederevo, the curve of mean monthly flows expressed in modular coefficients is similar to the curve for the Sava, which flows into the Danube upstream from Smederevo, and the Danube has a combined flow regime like the Sava.
  
  KEY WORDS: flow regime, modular coefficients, „central Danube region”
  
  Address:
  - Marija Šperac, J. J. Strossmayer University of Osijek, Faculty of Civil Engineering and Architecture Osijek, Vladimira Preloga 3, 31000 Osijek, Croatia (Corresponding author. Tel.: Fax.: Email: msperac@gfos.hr)
  - Ivan Djedović, Institut IGH d.d. Regional Centar Osijek, Drinska 18, 31000 Osijek, Croatia

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 230 - 236, doi: 10.31577/ahs-2021-0022.02.0026
Scientific Paper, English

Zuzana Danáčová, Katarína Jeneiová, Lotta Blaškovičová: Hydrological situation on Slovak rivers from the point of view of hydrological drought assessment in the period 2011–2020

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• In this paper, the occurrence of the area-wide droughts during the years 2011 to 2020 in Slovakia is assessed on the data from 164 water gauging station displayed online on the drought monitoring webpage of Slovak Hydrometeorological Institute and further analysed on 43 selected water-gauging stations. The mean monthly discharges are compared with the long-term mean monthly discharges for the reference period 1961–2000. Trend detection analysis of the mean monthly discharges in period 1961–2020 was concluded by Mann-Kendall trend test. The months of April, June, July, August and October were detected as the months with the highest occurrence of mean monthly discharges below 40% long – term mean monthly discharges for the reference period. The trend analysis of the mean monthly discharges confirmed significant decreasing trend in April, May, June, July and August. These results reinforce the need of continuous monitoring of the mean monthly discharges. Results of the monitoring available online in form of simple graphical output can present a tool for the timely detection of the incoming long-term drought periods with possibility of implementation of appropriate measures.
  
  KEY WORDS: hydrological drought, mean monthly discharge, online monitoring, Mann-Kendal trend test
  
  Address:
  - Zuzana Danáčová, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic
  - Katarína Jeneiová, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: katarina.jeneiova@shmu.sk)
  - Lotta Blaškovičová, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 237 - 247, doi: 10.31577/ahs-2021-0022.02.0027
Scientific Paper, English

Dana Halmová, Pavla Pekárová, Ján Pekár, Pavol Miklánek, Veronika Bačová Mitková: Identification of the historical drought occurrence on the Danube River and its tributaries

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• In the presented paper, the changes in the minimum flows at five stations along the length of the Danube River and at its 5 selected significant tributaries were analyzed. Average daily flows with the longest possible series of observations (since 1901 or since 1921) were used as input data. In the first part, low water content, hydrological drought were statistically analyzed and long-term trends of 1- to 90-day minimum flows were identified. The second part presents changes in T- year minimum daily flows in selected stations. The most extreme drought at Hofkirchen occurred in 1921. Drought at Orsova occurred around 1862/63, 1882/83, 1900, 1920/21, 1946/47, 1961/62, 1971, 1991/92 and 2017 / 19. The analyzes show that there is a more or less regular alternation of water and low-water periods along the entire length of the Danube. Multi-annual dry periods along the length of the Danube occur in the same periods. In contrast, on the Danube tributaries, the dry seasons are time-shifted.
  
  KEY WORDS: the Danube River basin, low flow and failure characteristics, hydrological drought, IHA model
  
  Address:
  - Dana Halmová, Slovak Academy of Sciences, Institute of Hydrology, Dúbravská cesta 9, 841 04 Bratislava (Corresponding author. Tel.: Fax.: Email: halmova@uh.savba.sk)
  - Pavla Pekárová, Slovak Academy of Sciences, Institute of Hydrology, Dúbravská cesta 9, 841 04 Bratislava
  - Ján Pekár, Comenius University in Bratislava, Faculty of Mathematics, Physics, and Informatics, Department of Applied Mathematics and Statistics, Mlynská dolina, 842 48 Bratislava
  - Pavol Miklánek, Slovak Academy of Sciences, Institute of Hydrology, Dúbravská cesta 9, 841 04 Bratislava
  - Veronika Bačová Mitková, Slovak Academy of Sciences, Institute of Hydrology, Dúbravská cesta 9, 841 04 Bratislava

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 248 - 255, doi: 10.31577/ahs-2021-0022.02.0028
Scientific Paper, English

Zinaw D. Shenga, Andrej Šoltész, Danica Lešková: Groundwater response to extreme flows in the Danube River

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• 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.
  
  KEY WORDS: Danube River, groundwater head, groundwater-surface water interaction, GMS MODFLOW package
  
  Address:
  - Zinaw D. Shenga, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: zinaw.shenga@shmu.sk)
  - Andrej Šoltész, Slovak University of Technology in Bratislava, Vazovova 5, 812 43 Bratislava, Slovak Republic
  - Danica Lešková, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 256 - 263, doi: 10.31577/ahs-2021-0022.02.0029
Scientific Paper, English

Tetiana Zabolotnia, Borbala Szeles, Liudmyla Gorbachova, Juraj Parajka, Rui Tong: Comparison of winter design floods between Austrian and Ukrainian Danube River tributaries

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• The consequences of large-scale floods in several regions have drawn attention to prevention and protection of territories from such natural phenomena. Therefore, it is important to determine the expected magnitudes of floods, their differences, as well as to understand the factors controlling the magnitude of snowmelt design floods. This paper compares snowmelt design floods in 24 catchments situated in two regions in Austria (the upper Steyr River Basin) and Ukraine (the upper Rika River Basin). The two regions are similar in terms of catchment sizes and elevation but differ in climate characteristics, because the Ukrainian catchments are influenced by increased continentality. The aim of this paper is thus to compare the magnitude of design floods with 2-, 5-, 10-, 50-, and 100-year return periods occurring during the cold periods of the year (November–April). The objective is to estimate design values of winter floods and to explore factors controlling their differences. The results show that the design floods scaled with catchment area are larger in the upper Rika River Basin (Ukraine) than in upper Steyr River Basin (Austria) for all examined periods. The winters in Ukrainian catchments tend to be warmer and occur earlier. The magnitude of scaled floods in Ukrainian catchments is larger, even the mean annual maximum snow depth (Dmam) is approximately 40% lower than in the Austrian catchments. The results of this initial analysis can improve the understanding and hence management of water resources in catchments with similar hydrological characteristics, but slightly different climate characteristics.
  
  KEY WORDS: frequency analysis, design floods, winter floods, climate zones
  
  Address:
  - Tetiana Zabolotnia, Ukrainian Hydrometeorological Institute, Nauky Prospekt 37, 03028 Kyiv, Ukraine (Corresponding author. Tel.: Fax.: Email: tzabolotnia@gmail.com)
  - Borbala Szeles, Institute of Hydraulic Engineering and Water Resources Management, Faculty of Civil Engineering, Vienna University of Technology, Karlsplatz 13, A-1040 Vienna, Austria
  - Liudmyla Gorbachova, Ukrainian Hydrometeorological Institute, Nauky Prospekt 37, 03028 Kyiv, Ukraine
  - Juraj Parajka, Institute of Hydraulic Engineering and Water Resources Management, Faculty of Civil Engineering, Vienna University of Technology, Karlsplatz 13, A-1040 Vienna, Austria
  - Rui Tong, Institute of Hydraulic Engineering and Water Resources Management, Faculty of Civil Engineering, Vienna University of Technology, Karlsplatz 13, A-1040 Vienna, Austria

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 264 - 275, doi: 10.31577/ahs-2021-0022.02.0030
Scientific Paper, English

Mirza Sarač, Maja Koprivšek, Oliver Rajković, Azra Babić, Merima Trako, Saša Marić, Adnan Topalović, Srđan Marjanović, Dejan Petković, Marija Ivković, Ervin Kalač, Danijela Bubanja: Improvement of the operational HEC-HMS hydrological model embedded in the Flood Forecasting and Warning System of the Sava River Basin

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• In 2017 the HEC-HMS model for the Sava River Basin was embedded under the Flood Forecasting and Warning System in the Sava River Basin (Sava FFWS) and coupled with many hydraulic models. Since the model was initially calibrated as the event-based model, a lack of accuracy has been recognized during the continuous simulations within the Sava FFWS operational use. Therefore, the Sava FFWS users organizations: ten forecasting organizations from five Sava countries, agreed to upgrade and improve this hydrological model. The activities of the model improvement were performed in period January 2019 till June 2020. It was implemented by the national experts from the Sava FFWS users’ organizations as a true joint action and coordinated by the Secretariat of the International Sava River Basin Commission. This paper presents the results of the Sava HEC-HMS model improvements and updated parameters, including a comparison of results of initial and improved models within the operational forecasting system. The paper also discusses the potentials of the remote sensing and radar- and satellite-based data that will be used for the future model improvements.
  
  KEY WORDS: forecasting, modelling, calibration, Sava River Basin
  
  Address:
  - Mirza Sarač, International Sava River Basin Commission (Corresponding author. Tel.: Fax.: Email: msarac@savacommission.org)
  - Maja Koprivšek, Slovenian Environment Agency, Slovenia
  - Oliver Rajković, Croatian Meteorological and Hydrological Service, Croatia
  - Azra Babić, Federal Hydrometeorological Service, Bosnia and Herzegovina
  - Merima Trako, Federal Hydrometeorological Service, Bosnia and Herzegovina
  - Saša Marić, Republika Srpska Hydro-Meteorological Service, Bosnia and Herzegovina
  - Adnan Topalović, Sava River Watershed Agency, Bosnia and Herzegovina
  - Srđan Marjanović, Republic Hydrometeorological Service of Serbia, Serbia
  - Dejan Petković, Republic Hydrometeorological Service of Serbia, Serbia
  - Marija Ivković, Public Water Management Company “Srbijavode”, Serbia
  - Ervin Kalač, Institute of Hydrometeorology and Seismology, Montenegro
  - Danijela Bubanja, Institute of Hydrometeorology and Seismology, Montenegro

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 276 - 283, doi: 10.31577/ahs-2021-0022.02.0031
Scientific Paper, English

Tomáš Vlasák, Jakub Krejčí: Statistical post-processing of short-term hydrological ensemble forecasts using the application of the dressing method

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• Probabilistic hydrological forecasts used in forecasting offices are often based only on different variants of precipitation forecast, which are the dominant source of forecast uncertainty during flood periods. The proposed method called dressing extends the uncertainty of meteorological forecast input by estimating the uncertainty of hydrological modeling using statistical analysis of deviations derived from simulated and observed flows. Adjustment of probabilistic flow forecasts is applied by post-processing without interfering with the hydrological model itself. The method is focused primarily on runoff phases, where heavy precipitation is not expected and the dispersion of the original ensemble is insufficient. A comparison of the success of short-term operative ensemble predictions of river discharge in the upper Vltava basin before and after adjusting by the dressing method showed a clear improvement in statistics.
  
  KEY WORDS: hydrological forecast, ensemble forecast, dressing, post-processing
  
  Address:
  - Tomáš Vlasák, Czech Hydrometeorological Institute, Na Šabatce 17, 140 00 Praha 4, Czech Republic (Corresponding author. Tel.: Fax.: Email: tomas.vlasak@chmi.cz)
  - Jakub Krejčí, Czech Hydrometeorological Institute, Na Šabatce 17, 140 00 Praha 4, Czech Republic

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 284 - 293, doi: 10.31577/ahs-2021-0022.02.0032
Scientific Paper, English

Viktor I. Vyshnevskyi, Olena A. Donich: Snow cover in the Ukrainian Carpathians

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• Based on the results of regular monitoring during 1961–2020, the main features of snow cover in the Ukrainian Carpathians were determined. The observation data at the meteorological stations, mainly located at high altitude, show an increasing trend in snow cover depth in winter and in the first half of spring. At the same time, there is a decrease in snow cover duration at low altitudes and an increase at high altitudes. General trends for the mountain area are higher air temperature and lower wind speed. Simultaneously precipitation changes are small or absent. It has been shown that decrease of wind speed over the last decades should be taken into account to determine the actual changes in snow cover. As a result of this decrease, the snow cover depth in the mountains became more uniform than at the beginning of the observations: larger on mountain tops and smaller in ravines and mountain forests. This means that in general, the snow cover depth and snow water equivalent in the mountains are stable. This was confirmed by the fact that during spring flood the water runoff of local rivers remained without essential changes.
  
  KEY WORDS: snow cover, air temperature, precipitation, wind speed, river runoff, the Ukrainian Carpathians
  
  Address:
  - Viktor I. Vyshnevskyi, National Aviation University, Liubomyra Huzara Ave, 1, 03058, Kyiv, Ukraine (Corresponding author. Tel.: Fax.: Email: vishnev.v@gmail.com)
  - Olena A. Donich, Central Geophysical Observatory, Nauka Ave, 39, 03028, Kyiv, Ukraine

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 294 - 303, doi: 10.31577/ahs-2021-0022.02.0033
Scientific Paper, English

Ladislav Markovič, Pavel Faško, Jozef Pecho: Climatology of the extreme heavy precipitation events in Slovakia in the 1951–2020 period

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• In this study, we investigate extreme heavy precipitation events in the Slovak Republic in the period 1951–2020 in terms of their spatial and temporal distribution with goal to create dynamic-climatological analysis of those patterns of the atmospheric circulation that can eventually lead to the occurrence of the extreme multi-day precipitation events. Heavy precipitation is defined as maximum precipitation total over five consecutive days (Rx5D) where a non-zero daily precipitation total must be recorded every day of selected 5-day period. Spatial and temporal distribution of multiday precipitation totals is affected by many factors, mainly by the processes taking place in the troposphere eventually represented by the synoptic scale atmospheric circulation and by the orographic diversity of the area, which together significantly affects distribution of precipitation in the selected area. Our study is therefore constructed as an analysis of relationships between localized tropospheric circulation defined by the Czechoslovak catalogue of the typified synoptic situations (Brádka, 1968), the predominant wind patterns and the spatiotemporal distribution of Rx5D.
  
  KEY WORDS: extreme precipitation, precipitation events, dynamic climatology
  
  Address:
  - Ladislav Markovič, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: ladislav.markovic@shmu.sk)
  - Pavel Faško, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic
  - Jozef Pecho, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 304 - 312, doi: 10.31577/ahs-2021-0022.02.0034
Scientific Paper, English

Adrián Varga, Yvetta Velísková: Assessment of time course of water and air temperature in the locality of the Turček reservoir during its operation in the period 2005–2019

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• In the future, during the ongoing climate change, water reservoirs will play an important role in the provision of raw water for the subsequent production of drinking water for the inhabitants of Slovakia. The Turček water reservoir is the fifth largest water reservoir in Slovakia with a total volume of 9.9 mil. m3, which is used for the production of drinking water for the towns Prievidza, Žiar nad Hronom, Handlová and a connection to the water mains of the Žarnovica district is also planned. The paper deals with the trend analysis of water and air temperatures data for a selected period of time (2005–2019). We used the non-parametric Mann-Kendall test, which is one of the most widely used nonparametric tests to detect significant trends over time. The results of this test answer the question if there existed a significant trend for mentioned temperatures in this locality or not. Analysis confirmed that it is not possible to determine a significant trend at the significance level of 5%. Anyway, value of annual air temperature increased by 0.57°C during the study period 2005–2019.
  
  KEY WORDS: climate change, air temperature, water temperature, Turček water reservoir, trend analysis
  
  Address:
  - Adrián Varga, Institute of Hydrology SAS, Dúbravská cesta 9, 84104 Bratislava, Slovak Republic; Slovak University of Agriculture, Tulipánová 1117/7, 949 76 Nitra, Slovak Republic (Corresponding author. Tel.: Fax.: Email: varga@uh.savba.sk, xvargaa2@uniag.sk)
  - Yvetta Velísková, Institute of Hydrology SAS, Dúbravská cesta 9, 84104 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 313 - 319, doi: 10.31577/ahs-2021-0022.02.0035
Scientific Paper, English

Aybek Arifjanov, Luqmon N. Samiev, Tatiana Kaletová: Improvement of design parameters of the sediment reservoirs

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• 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.
  
  KEY WORDS: sediment reservoir, sediment trap model, rate of sediment removal, irrigation
  
  Address:
  - Aybek Arifjanov, Department of Hydraulics and Hydroinformatics, Tashkent Institute of Irrigation and Agricultural Mechanization Engineers, 39 Kari Niyazov, Tashkent 100000, Uzbekistan (Corresponding author. Tel.: Fax.: Email: obi-life@mail.ru)
  - Luqmon N. Samiev, Department of Hydraulics and Hydroinformatics, Tashkent Institute of Irrigation and Agricultural Mechanization Engineers, 39 Kari Niyazov, Tashkent 100000, Uzbekistan
  - Tatiana Kaletová, Department of Hydraulics and Hydroinformatics, Tashkent Institute of Irrigation and Agricultural Mechanization Engineers, 39 Kari Niyazov, Tashkent 100000, Uzbekistan; Faculty of Horticulture and Landscape Engineering, Slovak University of Agriculture in Nitra, Tulipanova 7, 94976 Nitra, Slovakia

Acta Hydrologica Slovaca, Vol. 22, No. 2, 2021, p. 320 - 325, doi: 10.31577/ahs-2021-0022.02.0036
Scientific Paper, English

Justína Vitková, Peter Šurda, Peter Rončák, Natália Botková, Anton Zvala: Statistical analysis of soil water content differences after biochar application and its repeated application during 2020 growing season

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• Soil water content is an important factor influencing crop yield quantity and quality. Extreme meteorological events are more frequent in our geographical conditions in last years and they affect soil water storage. Biochar is an organic material and one of its properties is soil water holding for a longer time. This is one of great benefits during non-precipitation days. Our study is focused on soil water content changes with biochar amendment in comparison to soil without biochar. In addition, we analyzed biochar repeated application as well. It means addition another biochar dose into the soil where the biochar had been applied previously. Our results confirmed positive effect of biochar application and repeated application on soil water content. The soil water regime with biochar repeated application was the most stable in 2020 in comparison to other variants of experiment.
  
  KEY WORDS: biochar, repeated application, soil moisture, statistical analysis
  
  Address:
  - Justína Vitková, Institute of Hydrology SAS, Dúbravská cesta 9, 84104 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: vitkova@uh.savba.sk)
  - Peter Šurda, Institute of Hydrology SAS, Dúbravská cesta 9, 84104 Bratislava, Slovak Republic
  - Peter Rončák, Institute of Hydrology SAS, Dúbravská cesta 9, 84104 Bratislava, Slovak Republic
  - Natália Botková, Institute of Hydrology SAS, Dúbravská cesta 9, 84104 Bratislava, Slovak Republic; Institute of Landscape Engineering, Faculty of Horticulture and Landscape Engineering, Slovak University of Agriculture in Nitra, Tulipánová 7, 949 76 Nitra, Slovak Republic
  - Anton Zvala, Institute of Hydrology SAS, Dúbravská cesta 9, 84104 Bratislava, Slovak Republic