Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 157 - 162, doi: 10.31577/ahs-2022-0023.02.0017
Scientific Paper, English

Justína VITKOVÁ, Lucia TOKOVÁ, Natália BOTKOVÁ: Modeling of soil water retention curves based on two programs

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• We compared two methods of modeling soil water retention curves used by scientists in Slovakia. The first modeling was done using the GENRET program and the second using the RETC program. Samples of pure sandy soil and sandy soil with applied biochar in three different particle sizes were used for the simulation. Sandy soil has a very low retention capacity therefore the modeling of soil water retention curves is not easy. Our results showed that the GENRET program can model the curve even at high pressures, which the RETC program modeled only in one variant, but the RETC program had better agreement with measured data. The most significant differences between the programs were at the lowest and highest pressures.
  
  KEY WORDS: soil water retention curve, modeling, RETC, GENRET
  
  Address:
  - Justína VITKOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: vitkova@uh.savba.sk)
  - Lucia TOKOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Natália BOTKOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic., Institute of Landscape Engineering, Faculty of Horticulture and Landscape Engineering, SUA , Hospodárska 7, 949 76 Nitra, Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 163 - 171, doi: 10.31577/ahs-2022-0023.02.0018
Scientific Paper, English

Etienne UMUKIZA, James M. RAUDE, Andrea PETROSELLI, Simon M. WANDERA, John M. GATHENYA, Ciro APOLLONIO: Drainage systems design in urbanized areas under land use changes scenarios: case study of Narok Town (Kenya)

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• Land use/land cover (LULC) changes due to urbanization have a strong influence on runoff process. In the case of Narok town, in Kenya, several flash floods have caused human losses and economic damages. Design hydrograph and its peak flow are the key elements to determine hydraulic geometrical properties in designing an adequate drainage system. In consideration of LULC changes and consequent hydrograph variability, in this study existing channel geometric properties were verified, using field measurements through a ground survey employing Real-Time Kinematic equipment at Kakia and Esamburmbur channels of Narok town. To improve the drainage system, the evaluated peak flows under assumed future LULC scenarios were used to design hydraulic properties for a sustainable urban drainage system. Three hydrological/hydraulic models (EBA4SUB, Manning's equation, and Civil 3D) were used under different LULC scenarios for computing channel geometry and correspondent water level. The change in channel geometry was found to obstruct free flow for different scenarios of peak discharge and flow volume. The presented results could be used to support the design of storm water drainage systems by local authorities, in order to mitigate flood hazards and consequently to reduce the hydraulic risk.
  
  KEY WORDS: Peak flow estimation, Rainfall-runoff modeling, LULC changes, Kenya case study, EBA4SUB model, Drainage systems
  
  Address:
  - Etienne UMUKIZA, Pan African University, Institute of Science, Technology and Innovation, Civil Engineering and Environmental, Jomo Kenyatta University of Agriculture and Technology, P. O. Box 62000 – 00200 Nairobi, Kenya
  - James M. RAUDE, Soil, water, and Environmental Engineering Department, Jomo Kenyatta University of Agriculture and Technology, P. O. Box 62000 – 00200 Nairobi, Kenya
  - Andrea PETROSELLI, Department of Economics, Engineering, Society and Business, Tuscia University, 01100 Viterbo, Italy
  - Simon M. WANDERA, Department of Civil, Construction and Environmental Engineering, Jomo Kenyatta University of Agriculture and Technology, 00200 Nairobi, Kenya
  - John M. GATHENYA, Soil, water, and Environmental Engineering Department, Jomo Kenyatta University of Agriculture and Technology, P. O. Box 62000 – 00200 Nairobi, Kenya
  - Ciro APOLLONIO, Department of Agriculture and Forest Sciences, Tuscia University, 01100 Viterbo, Italy (Corresponding author. Tel.: Fax.: Email: ciro.apollonio@unitus.it)

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 172 - 179, doi: 10.31577/ahs-2022-0023.02.0019
Scientific Paper, English

Aybek ARIFJANOV, Luqmon N. SAMIEV, Zokhidjon ABDULKHAEV, Dilbar ABDURAIMOVA, Shodiyor YUSUPOV, Tatiana KALETOVÁ: Model of urban groundwater level management in drainage systems

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• Currently, it is proposed to design horizontal drains for the city of Fergana to reduce the negative impact of the rise in the level of groundwater on the environment, agricultural crops, buildings, and structures, as well as on underground communications. Groundwater depth measurements were carried out in observation wells in the city area and the results were analysed. The depth of groundwater level drop within the horizontal drainage effect is physically and mathematically modelled. For this, long-term data from observation wells were analysed and the hydraulic parameters of horizontal drainage were selected considering the hydrogeology of the area. Taking into account the terrain and characteristics of the soil layers, the possibility of diverting the collected water outside the city through the "Margilan Say" waterwork passing through the city centre has been developed. The differential equation of groundwater movement is solved by numerical calculation and the results are analysed graphically. According to the analysis of the results of numerical calculation, it is proved that it is possible to control the groundwater level with horizontal drainage. The adequacy of the results was assessed by comparing data collected in natural field conditions.
  
  KEY WORDS: horizontal drainage, groundwater, depth of groundwater, coefficient of hydraulic conductivity, mathematical model
  
  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
  - Zokhidjon ABDULKHAEV, Department of Construction of Engineering Communications, Fergana Polytechnic Institute, 86 Fergana, Fergana 150107, Uzbekistan
  - Dilbar ABDURAIMOVA, Department of Hydraulics and Hydroinformatics, Tashkent Institute of Irrigation and Agricultural Mechanization Engineers, 39 Kari Niyazov, Tashkent 100000, Uzbekistan
  - Shodiyor YUSUPOV, 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, Tulipánová 7, 94976 Nitra, Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 180 - 189, doi: 10.31577/ahs-2022-0023.02.0020
Scientific Paper, English

Renáta DULOVIČOVÁ, Radoslav SCHŰGERL, Yvetta VELÍSKOVÁ: Hydraulic conductivity of saturated bed silts in Chotárny channel, ŽO area, Slovakia

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• This paper deals with the comparison of two different ways used for determination of saturated hydraulic conductivity values of bed silts located along the Chotárny channel, obtained from field measurements in 2018. The Chotárny channel is one of three selected monitored channels at the ŽO area – the flat lowland with channel network. The permeability of bed silts impacts water flow between surface water in the channel and surrounding groundwater in the scope of their interaction at this area. It is expressed by its value of saturated hydraulic conductivity. The bed silts along Chotárny channel were extracted and obtained by two ways, as disturbed samples and as undisturbed samples. The selection of sampling place was made by thickness of bed silt in the measured profiles. The samples were extracted in three different vertical parts of bed silt – from top, middle and bottom part of bed silt layer. In case of the disturbed samples the empirical formulas based on the grain size analysis were used for determination of saturated hydraulic conductivity value. In case of undisturbed samples was used the falling head method for determination of saturated hydraulic conductivity value. The values of saturated hydraulic conductivity obtained from disturbed samples of bed silts Kd were calculated by using of several empirical formulas: 1. Bayer – Schweiger; 2. Špaček I.; 3. Špaček II.; 4. Hazen I.; 5. Bayer; 6. USBR and 7. Orechova. The results in Table 1 show that the valid values Kd for Chotárny channel in 2018 were from 1.00x10-10 to 1.19x10-04 m s-1. The recommended formula for calculation of Kd of bed silts by empirical formulas in Chotárny channel, based on criterium of the largest number of valid obtained results, is Hazen I. formula. The values of saturated hydraulic conductivity obtained from undisturbed samples of bed silts Ku were determined according the relation for calculation of average value of saturated hydraulic conductivity (by falling head method in laboratory). These values are illustrated in Table 2. The values Ku for Chotárny channel in 2018 reached values from 7.68x10-08 – 4.53x10-05 m s-1. All the results from both methods of determination of saturated hydraulic conductivity were compared.
  
  KEY WORDS: bed silts, permeability of bed silts, saturated hydraulic conductivity, disturbed and undisturbed samples, grain size analysis, falling head method
  
  Address:
  - Renáta DULOVIČOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: dulovicova@uh.savba.sk)
  - Radoslav SCHŰGERL, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Yvetta VELÍSKOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 190 - 196, doi: 10.31577/ahs-2022-0023.02.0021
Scientific Paper, English

Zoltan Arpad LIPTAY: Neurohydrological prediction of water temperature and runoff time series

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• In this paper we give an overview of experiments with artificial neural networks on the Hungarian reach of the Danube River carried out by the Hungarian Hydrological Forecasting Service. Two areas were selected: rainfall-runoff modelling and water temperature simulation. The statistical machine learning method is a universal interpolation and classification tool, but showed poor performance when applied for correlation in complex hydrological situations. Despite very strong learning skills of neural networks even a conceptual model gave more consistent and superior results through validation, and the statistic method is more sensitive to overlearning than deterministic methods. Despite deterministic models being superior artificial neural networks still provide satisfactory results that confirms their application.
  
  KEY WORDS: hydrology, artificial neural networks, modelling, forecast
  
  Address:
  - Zoltan Arpad LIPTAY, Hungarian Hydrological Forecasting Service, General Directorate of Water Management, Márvány u. 1/d., 1012 Budapest, Hungary (Corresponding author. Tel.: Fax.: Email: liptay.zoltan@ovf.hu)

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 197 - 206, doi: 10.31577/ahs-2022-0023.02.0022
Scientific Paper, English

Veronika BAČOVÁ MITKOVÁ: Trend changes and frequency analysis of the annual maximum volumes for various runoff duration on the Morava River at Moravský Svätý Ján

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• In the present paper we analyzed, the occurrence of annual maximum runoff volumes with t-day durations for a 99-year series (1920–2020) of mean daily discharge of the Morava River at Moravský Svätý Ján gauge (Slovakia). The runoff volume is, apart from the peak runoff, another very important hydrological characteristic of a river for flood hazard assessment. The maximum runoff volumes with t-day duration were determined. Subsequently, trends of the annual maximum runoff volumes with t-day durations were identified. We analyzed how the annual maximum runoff volumes of the Morava River have changed over the period 1922–2020 and how they have changed over dry and wet periods. The results indicate that the trends of the annual maximum runoff volumes with t-day durations decrease, especially in wet periods. On the Morava River usually the maximum annual discharges occur simultaneously with the annual maximum runoff volume of waves with a given duration t. However, the corresponding values in terms of significance are not equivalent. Based on the exceeding probability curves of the annual maximum runoff volumes, it is possible to determine to the selected volume Vtmax for different t-days the probability of its exceeding and return period. The Log-Pearson distribution type III was used to determine the T-year values of the maximum runoff volumes with t-day duration.
  
  KEY WORDS: The Danube River, wave volume, Log-Pearson III probability distribution, T-year volume
  
  Address:
  - Veronika BAČOVÁ MITKOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: mitkova@uh.savba.sk)

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 207 - 216, doi: 10.31577/ahs-2022-0023.02.0023
Scientific Paper, English

Viktor VYSHNEVSKYI, Serhii SHEVCHUK: Impact of climate change and human factors on the water regime of the Danube Delta

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• Climate changes in the Danube Delta, as well as changes in water temperature, water runoff and sediment yield, have been identified on the basis of available observational data. It has been shown that the intra-annual distribution of water runoff has become more uniform in recent decades. It decreased in April-May and increased in February-March. At the same time, there has been a significant decrease in sediment transport. Changes due to anthropogenic impact were detected in water runoff in the largest river branches, in particular, the reduction of the share of the Kiliyskyi branch. Over the past 60 years, the water temperature in the Danube Delta has increased significantly, by more than 2°C. In general, the water temperature is higher than the air temperature, especially in autumn. Some features of the delta formation have been identified.
  
  KEY WORDS: the Danube River; delta, water discharge, sediment yield, air and water temperature
  
  Address:
  - Viktor VYSHNEVSKYI, National Aviation University, Liubomyra Huzara Ave 1, Kyiv, 03058, Ukraine (Corresponding author. Tel.: Fax.: Email: vishnev.v@gmail.com)
  - Serhii SHEVCHUK, Central Geophysical Observatory, Nauky Ave, 39/2, Kyiv, 03028, Ukraine

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 217 - 225, doi: 10.31577/ahs-2022-0023.02.0024
Scientific Paper, English

Pavla PEKÁROVÁ, Zbyněk BAJTEK, Pavol MIKLÁNEK, Ján PEKÁR, Katarína JENEIOVÁ, Jakub RIDZOŇ: Changes in the hydrological balance in the Litava river basin during the 90-years period 1931–2020

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• 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.
  
  KEY WORDS: Litava River, hydrological balance, simulation, model BILAN
  
  Address:
  - Pavla PEKÁROVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: pekarova@uh.savba.sk)
  - Zbyněk BAJTEK, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Pavol MIKLÁNEK, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Ján PEKÁR, Faculty of Mathematics, Physics, and Informatics, Department of Applied Mathematics and Statistics, Comenius University in Bratislava, Mlynská dolina, 842 48 Bratislava, Slovak Republic
  - Katarína JENEIOVÁ, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic
  - Jakub RIDZOŇ, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 226 - 233, doi: 10.31577/ahs-2022-0023.02.0025
Scientific Paper, English

Kostiantyn SOKOLCHUK, Marek SOKÁČ: Comparison of spatial interpolation methods of hydrological data on example of the Pripyat river basin (within Ukraine)

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• The article considers four methods of spatial interpolation: method of inverse weighted distances (IDW), triangulation (TIN), Spline interpolation and Kriging. The Pripyat basin was chosen as the study area, and the regularities of the spatial distribution of hydrological characteristics across the territory were assessed. For this territory, maps of spatial distribution of the specific discharge by four chosen methods were created; the accuracy of the obtained results was assessed. Based on the results of the work it was determined that the IDW method with a distance coefficient P=2 gives better results for the generalization of hydrological data over the studied area. The next most reliable methods are Kriging, which shows small errors, and Spline, with smooth transitions. The least suitable among the studied methods is TIN method. To study boundaries and territories that are outside the boundaries defined by GIS based on input data, in this case – Pripyat basin, IDW method is recommended to use, while every other can be used to study the central part of the catchment, with different reliability for the boundary territories.
  
  KEY WORDS: spatial interpolation, geographic information systems, map creation, IDW method, Kriging method, spline, TIN, Pripyat.
  
  Address:
  - Kostiantyn SOKOLCHUK, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 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 (Corresponding author. Tel.: Fax.: Email: sokolcuk@uh.savba.sk)
  - Marek SOKÁČ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 234 - 240, doi: 10.31577/ahs-2022-0023.02.0026
Scientific Paper, English

Borys KHRYSTIUK, Liudmyla GORBACHOVA, Vitalii SHPYG: Verification of the automated flood forecasting system on the Stryi River

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• The physical and geographical location of the Stryi River Basin causes the formation of catastrophic floods, which are regularly forming in this region and cause significant material damage and, sometimes, the death of people. The last catastrophic flood took place on the Stryi River in June 2020. Thus, the creation of a modern system for forecasting the streamflow of the Stryi River is a very important task. This paper describes such an automated flood forecasting system (FFS Stryi) that is developed at the Ukrainian Hydrometeorological Institute of the State Emergency Service of Ukraine and the National Academy of Sciences of Ukraine. The basis of the system is the hydrological module NAM of the Rainfall-Runoff software complex MIKE 11 (Denmark), which uses the forecasted weather parameters from the numerical mesoscale atmospheric model WRF ARW v. 3.6.1 (USA). The objective of this study is to verify this system and identify the factors that affect the accuracy of flood forecasting of the Stryi River. The system of streamflow forecasting of the Stryi River uses the continuous series of calculated (historical) levels and discharges, air temperature, precipitation, evaporation, as well as the forecast of meteorological indicators for 5 days. The system is set to work with a three-hour time step in the automatic regime. Verification of FFS Stryi according to the historical meteorological data showed that the system reproduces the streamflow of the Stryi River with satisfactory quality. The accuracy of discharge forecasting depends on the accuracy of weather parameters forecasting and, above all, the quantity of precipitation and the time of their falling out. Errors of hydrological forecasting are caused by an imperfect hydrometeorological network of observations (number of points and frequency of measurement), a digital model of the relief of the Stryi River basin and errors of weather parameters forecasts.
  
  KEY WORDS: short-term forecasting, weather forecast, NAM RR MIKE 11, WRF ARW v. 3.6.1, Stryi River
  
  Address:
  - Borys KHRYSTIUK, Ukrainian Hydrometeorological Institute, 37, Prospekt Nauky, 03028, Kyiv, Ukraine
  - Liudmyla GORBACHOVA, Ukrainian Hydrometeorological Institute, 37, Prospekt Nauky, 03028, Kyiv, Ukraine (Corresponding author. Tel.: Fax.: Email: gorbachova@uhmi.org.ua)
  - Vitalii SHPYG, Ukrainian Hydrometeorological Institute, 37, Prospekt Nauky, 03028, Kyiv, Ukraine

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 241 - 248, doi: 10.31577/ahs-2022-0023.02.0027
Scientific Paper, English

Ladislav HOLKO, Michal DANKO, Martin JANČO, Patrik SLEZIAK: Empirical models to calculate the snow water equivalent in the high mountain catchments of the Western Carpathians

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• Empirical models based on the relationship between snow depth (SH) and density (ρ) are used to estimate the snow water equivalent (SWE) from SH. However, ρ is poorly correlated with SH while the correlation between SH and SWE which can be directly obtained from snow measurements, is much better. We derived models based on the SH-SWE correlations for two datasets obtained in the high mountain catchments in Slovakia (The Low and Western Tatra Mountains). The models consider time (months from January to April) and elevation zones. Evaluation of the models against independent data showed that they are transferrable to other climatic conditions. About a half of estimated point SWE values was well comparable to measured values, i.e. the differences were approximately within ±15%. Substantial overestimation of measured SWE by more than 35% was obtained for about 10% of the values in January when the same equation was used for all elevation zones. Our final validation employed independent data from the High Tatra Mountains. It showed that about 60% of SWE values calculated for the entire snow courses as an average of 20 values calculated by the derived models from SH compared well (±15%) to values obtained by the traditional approach, i. e. as a product of the snow course mean SH (20 measurements) and ρ (3 measurements). Although the results of our models can be comparable to those provided by models based on snow density, due to recurrent use of SH and almost no correlation between SH and ρ, the models based on the SH-SWE relationship represent in our opinion a more correct approach.
  
  KEY WORDS: regression models, snow cover, hydrology, headwater catchments
  
  Address:
  - Ladislav HOLKO, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: holko@uh.savba.sk)
  - Michal DANKO, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Martin JANČO, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Patrik SLEZIAK, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 249 - 256, doi: 10.31577/ahs-2022-0023.02.0028
Scientific Paper, English

Michaela DANÁČOVÁ, Michal DANKO, Roman VÝLETA, Kamila HLAVČOVÁ: The generation of surface runoff in laboratory conditions using two portable rainfall simulators – an experimental study

 Full Text in PDF     22 DOWNLOADS

• The use of laboratory methods in soil water erosion studies and rainfall simulation experiments has recently been considered more important because of the many advantages in controlling rainfall-runoff processes and sediment transport. In a laboratory study, rainfall simulation experiments (one alone and two identical rainfall simulators connected in a series) were focused on an analysis of the impact of the size of the irrigated area on the temporal distribution and volume of the surface runoff and the amount of eroded soil material. The experiments were conducted on a disturbed soil sample exposed to quasi-continuous 60-minute simulated rainfall events with an intensity of 2.7 mm min-1. The two experiments were carried out on slopes of different lengths of 0.25 m (irrigated area: 0.0625 m2) and 0.5 m (irrigated area: 0.125 m2). The results showed the effects of the size of the irrigated area on surface runoff generation and changes in the soil structure, sediment concentration, and amount of soil loss. Knowledge of the rate of changes in the volume of the surface runoff and soil loss with respect to the size of the irrigated area in the laboratory conditions and subsequent generalization of the results provides essential information, which is irreplaceable for the preparation of field measurements and obtaining essential calibration and validation data for erosion and rainfall-runoff modelling.
  
  KEY WORDS: laboratory experiment, rainfall simulator, surface runoff, eroded sediments
  
  Address:
  - Michaela DANÁČOVÁ, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava Radlinského 11, 810 05 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: michaela.danacova@stuba.sk)
  - Michal DANKO, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Roman VÝLETA, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava Radlinského 11, 810 05 Bratislava, Slovak Republic
  - Kamila HLAVČOVÁ, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava Radlinského 11, 810 05 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 257 - 266, doi: 10.31577/ahs-2022-0023.02.0029
Scientific Paper, English

Martin KUBÁŇ, Juraj PARAJKA, Ján SZOLGAY, Silvia KOHNOVÁ, Kamila HLAVČOVÁ, Patrik SLEZIAK, Adam BRZIAK: Improvement of runoff simulation efficiency using satellite soil moisture data for typical monthly runoff regimes in Austria

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• The availability of remote sensing data opened possibilities for assimilating these into rainfall-runoff models. We examined the quality of the simulated monthly runoff regime in catchments in which the inclusion of a new satellite soil moisture dataset (ASCAT SW1) into the calibration of the TUW rainfall-runoff model outperformed in the model verification the conventional runoff-only calibration in 198 Austrian basins. Using k-means clustering, catchments with similar mean monthly runoff regimes were grouped. Three variants of the multi-objective approach were analysed for each month of the year in Carinthia, Styria and Upper and Lower Austria regions. Improvement in the simulated monthly runoff using the ASCAT data was mainly noticeable in the winter and spring months. The runoff simulation efficiency decreased in the driest summer and autumn months. It has also been confirmed that improvements in the simulations can be expected in the flat river basins compared to the hilly types and in river basins with lower average slopes. The findings refine previous recommendations regarding when hydrological models could benefit from considering information beyond the runoff signatures in their calibration.
  
  KEY WORDS: ASCAT, TUW dual-layer model, soil moisture assimilation, multi-objective calibration, runoff regime
  
  Address:
  - Martin KUBÁŇ, Slovak University of Technology, Faculty of Civil Engineering, Department of Land and Water Resources Management, Radlinského 11, 810 05 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: martin.kuban@stuba.sk)
  - Juraj PARAJKA, Centre for Water Resource Systems, TU Wien, Vienna, 1040, Austria
  - Ján SZOLGAY, Slovak University of Technology, Faculty of Civil Engineering, Department of Land and Water Resources Management, Radlinského 11, 810 05 Bratislava, Slovak Republic
  - Silvia KOHNOVÁ, Slovak University of Technology, Faculty of Civil Engineering, Department of Land and Water Resources Management, Radlinského 11, 810 05 Bratislava, Slovak Republic
  - Kamila HLAVČOVÁ, Slovak University of Technology, Faculty of Civil Engineering, Department of Land and Water Resources Management, Radlinského 11, 810 05 Bratislava, Slovak Republic
  - Patrik SLEZIAK, Institute of Hydrology SAS, Dúbravská cesta 9, 84104 Bratislava, Slovak Republic
  - Adam BRZIAK, Slovak University of Technology, Faculty of Civil Engineering, Department of Land and Water Resources Management, Radlinského 11, 810 05 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 267 - 272, doi: 10.31577/ahs-2022-0023.02.0030
Scientific Paper, English

Tatiana SOĽÁKOVÁ, Martina ZELEŇÁKOVÁ, Viktoria MIKITA, Helena HLAVATÁ, Dorota SIMONOVÁ, Hany ABD ELHAMID: Assessment of meteorological and hydrological drought using drought indices: SPI and SSI in eastern Slovakia

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• The current article presents a one-dimensional frequency analysis of historical drought events in the years 1972 to 2014 in the eastern part of Slovakia. Two physical drought types: meteorological and hydrological are classified by SPI – standardized precipitation index and SSI – standardized streamflow index. These indexes have the same mathematical calculation, the difference is only in the input initial monitored data collected from seven rain gauge stations and seven river stations. The most appropriate theoretical probability distribution of selected data is performed using the Kolmogorov-Smirnov test, which is done in EasyFitt program. The basic parameters of meteorological and hydrological drought are determined by the application of the RUN method. One – dimensional frequency analysis of two physical droughts is created for a purpose of estimating the probability of their occurrence in time and identifying the spatial vulnerability of this area. The main benefit of this work is the identification of the average return time of drought events. On average we can expect a moderate meteorological drought in 18.14 to 36.8 months and a hydrological drought in 26 to 60 months.
  
  KEY WORDS: frequency analysis, SPI, SSI
  
  Address:
  - Tatiana SOĽÁKOVÁ, Department of Environmental Engineering, Faculty of Civil Engineering, Technical University of Košice, Vysokoškolská 4, 040 01 Košice, Slovak Republic
  - Martina ZELEŇÁKOVÁ, Department of Environmental Engineering, Faculty of Civil Engineering, Technical University of Košice, Vysokoškolská 4, 040 01 Košice, Slovak Republic (Corresponding author. Tel.: Fax.: Email: martina.zelenakova@tuke.sk)
  - Viktoria MIKITA, Faculty of Earth Science, University of Miskolc, 3515 Miskolc-Egyetemváros, Hungary
  - Helena HLAVATÁ, Slovak Hydrological Institute, branch office Košice, Ďumbierska 26, 041 17 Košice, Slovak Republic
  - Dorota SIMONOVÁ, Slovak Hydrological Institute, branch office Košice, Ďumbierska 26, 041 17 Košice, Slovak Republic
  - Hany ABD ELHAMID, Department of Water and Water Structures Engineering, Faculty of Engineering, Zagazig University, Zagazig, 44519, Egypt., Department of Environmental Engineering, Faculty of Civil Engineering, Technical University of Košice, 040 01 Košice, Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 273 - 281, doi: 10.31577/ahs-2022-0023.02.0031
Scientific Paper, English

Viera RATTAYOVÁ, Marcel GARAJ, Kamila HLAVČOVÁ: Spatial and temporal variability of Aridity Index in lowland areas of Slovakia

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• Changes in precipitation and temperature caused by global warming are reasons for the increasing occurrence of hydrological extremes such as floods or droughts. The aridity index is a significant indicator of local climate changes and is often used for quantifying the long-term climate conditions of a given location. In addition, the values of the aridity index are indicators of the water conditions of the area and their potential tendency to change in humidity. Therefore, understanding the spatio-temporal patterns of the aridity index is a crucial goal for agricultural and water management of watersheds. This research investigates the spatial and temporal variations of the aridity indices at 27 climatological stations situated in the lowland areas of Slovakia. The stations were divided into three main lowland areas according to their spatial location. The United Nations Environmental Program (UNEP) method was used, and 40 years climatological measurements data from the Slovak Hydrometeorological Institute (SHMI) was considered for calculating the monthly and yearly mean values of the aridity index and assessing its spatial and temporal patterns. Trends in the monthly and yearly spatial mean values of the aridity index showed significant variability between selected areas. The annual mean of the aridity index of stations situated in the Juhoslovenská kotlina lowland indicates increasing trends in the aridity index in winter months and in July. In the case of other lowlands, there were no trends in the monthly and yearly values. Other significant differences were observed in the seasonal variability of the mean monthly values of the aridity index in selected areas.
  
  KEY WORDS: Aridity Index, Drought Assessment, Reference Evapotranspiration
  
  Address:
  - Viera RATTAYOVÁ, Department of Land and Water Resource Management, Faculty of Civil Engineering, Slovak University of Technology, Vazovova 5, 812 43 Bratislava 1, Slovak Republic (Corresponding author. Tel.: Fax.: Email: viera.rattayova@stuba.sk)
  - Marcel GARAJ, Department of the Climatological Service, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic
  - Kamila HLAVČOVÁ, Department of Land and Water Resource Management, Faculty of Civil Engineering, Slovak University of Technology, Vazovova 5, 812 43 Bratislava 1, Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 282 - 287, doi: 10.31577/ahs-2022-0023.02.0032
Scientific Paper, English

Andrej ŠOLTÉSZ, Martin ORFÁNUS, Jakub MYDLA: Design of detention spaces in the Ulička and Ublianka River catchment

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• Based on morphological and hydrological data, a hydrodynamic model of surface water flow was created in the HEC-RAS program. The model simulated a 100-year flood wave propagation in the basins of the Ulička and Ublianka streams as a part of the upper Uzh River catchment. After calibration, protection measures were added to the model whose task was to transform the flood discharge. For the transformation of the flood wave, detention and multi-purpose reservoirs were proposed, which could improve the flow rates in the riverbeds in times of drought. The proposed measures were selected on base of the terrain recognition of the research team in September and October 2021 in several profiles of mentioned rivers as well as on their tributaries.
  
  KEY WORDS: hydrodynamic modelling, flood transformation, HEC-RAS software, flood protection measures, detention reservoirs
  
  Address:
  - Andrej ŠOLTÉSZ, Slovak University of Technology in Bratislava, Faculty of Civil Engineering, Radlinského 11, 810 05 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: andrej.soltesz@stuba.sk)
  - Martin ORFÁNUS, Slovak University of Technology in Bratislava, Faculty of Civil Engineering, Radlinského 11, 810 05 Bratislava, Slovak Republic
  - Jakub MYDLA, Slovak University of Technology in Bratislava, Faculty of Civil Engineering, Radlinského 11, 810 05 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 288 - 295, doi: 10.31577/ahs-2022-0023.02.0033
Scientific Paper, English

Marek SOKÁČ, Yvetta VELÍSKOVÁ: Dispersion process in conditions of real sewer systems – in situ experiments

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• A general assumption of most current models used to simulate flow in sewer systems (pipes) is that the sewers are considered as prismatic channels. However, in real conditions there are many factors, which affect the real flow. One of them is the occurrence of the sediments and deposits in sewer pipes, which significantly changes the flow conditions, as well as the dispersion process in sewer systems by creation of “dead zones”. Paper describes the effects of these zones on hydrodynamic dispersion process, which are particularly noticeable in hydraulic conditions of low flow rates in sewer system (sanitary, flow rates during dry period without rain …). In the study, there were applied two types of tracers and both used substances give identical results. Experimental results show that even though sewer pipes are considered as prismatic hydraulic channels, in the real conditions some irregularities resulted with dead zones creation are presented. Their influence on the mass concentration time-course shape is depending on the sediment layer thickness. Gaussian approximation of the one-dimensional advection dispersion equation for instantaneous pollution entry is not suitable for the sewer pipes with sediments occurrence. In case of sediments presence, the GEV and Gumbel’s approximation function looks to be more accurate.
  
  KEY WORDS: sewer systems, sediments, hydrodynamic dispersion, dispersion coefficient, in situ-experiments
  
  Address:
  - Marek SOKÁČ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: sokac@uh.savba.sk)
  - Yvetta VELÍSKOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 296 - 304, doi: 10.31577/ahs-2022-0023.02.0034
Scientific Paper, English

Zbyněk BAJTEK, Pavla PEKÁROVÁ, Katarína JENEIOVÁ, Jakub RIDZOŇ: Analysis of the water temperature in the Litava River

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• River water temperature is important in many environmental applications, hydrology, and ecology research. It mainly depends on several parameters of water bodies such as streamflow, groundwater interactions, and their surrounding atmosphere. It has been correlated with air temperature as a substitute due to the ease of applicability for rivers with some limitations over detailed meteorological data. An evaluation of integrated river water temperature and streamflow fluctuations is proposed to evidence biological activity, chemical specimen, oxygen solubility, self-purification capacity of a river system, and variation of flows due to hydro-climatic changes. The possibility of predicting the river water temperature at various locations over a river basin is vital for water quality management. Modelling of river water temperature is usually based on a suitable mathematical model and field measurements of various atmospheric factors. The aim of the study is the analysis and subsequent simulation of monthly and daily water temperatures in the Litava River at the Plášťovce station. First of all, the statistical analysis of a series of daily values of Litava water temperature and air temperature (Bzovík meteorological station) was done. In the second part of the study, the several multi-regression models of the daily water temperatures are analyzed.
  
  KEY WORDS: Litava River, water temperature, simulation, multi-regression models
  
  Address:
  - Zbyněk BAJTEK, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: bajtek@uh.savba.sk)
  - Pavla PEKÁROVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Katarína JENEIOVÁ, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava , Slovak Republic
  - Jakub RIDZOŇ, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava , Slovak Republic

Acta Hydrologica Slovaca, Vol. 23, No. 2, 2022, p. 305 - 316, doi: 10.31577/ahs-2022-0023.02.0035
Scientific Paper, English

Saeid OKHRAVI, Marek SOKÁČ, Yvetta VELÍSKOVÁ: Three-dimensional numerical modeling of water temperature distribution in the Rozgrund Reservoir, Slovakia

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• The Rozgrund water reservoir is one of the oldest reservoirs of the water supply system in the vicinity of Banská Štiavnica. In the past, it was one of the important reservoirs supplying the population with drinking water. Knowing the spatial and temporal variations of water temperature in the reservoir is the primary step to investigate and model water quality. Therefore, the present study was planned to simulate water temperature distribution in the Rozgrund Reservoir by incorporating atmospheric and bathymetric conditions using MIKE 3 FM model and took a step forward to model extreme hydrological and meteorological events impacts. The simulations were performed for July 2022 and the model provided 3D visualization of water temperature variations and corresponding temporal differences during the entire simulated period. The results revealed that the Rozgrund Reservoir experienced temperature stratification (i.e. non-isothermal layers) in the period of simulation when the initial temperature was given to the model, while the constant initial temperature condition needs a long time to reproduce water temperature stratification. In addition, this study assessed the impacts of high inflows on patterns of current flows and water temperature throughout the Rozgrund Reservoir. The present work has implications for improving the understanding of changes in water temperature distribution in the Rozgrund Reservoir and similar reservoirs and supports further works, as well.
  
  KEY WORDS: 3D hydrodynamic model, Rozgrund Reservoir, spatial and temporal variability, water temperature distribution and stratification
  
  Address:
  - Saeid OKHRAVI, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: saeid.okhravi@savba.sk)
  - Marek SOKÁČ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Yvetta VELÍSKOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic