Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 3 - 15, doi: 10.31577/ahs-2025-0026.01.0001
Scientific Paper, English

Ladislav MARKOVIČ, Pavel FAŠKO: Extreme precipitation events in Slovakia: A 50-year retrospective of the October 1974 hydro-meteorological event

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• This study investigates extreme precipitation events in Slovakia, focusing on spatial precipitation totals and the maxima of monthly, daily, and multi-day precipitation recorded during October 1974. As 2024 marks the 50th anniversary of this significant hydrometeorological event, revisiting historical extremes provides valuable insights into regional climate and the hydrological cycle. Our analysis uses monthly spatial isohyetal data from 1881 to 2023 and in situ data from over 400 precipitation stations between 1951 and 2023 to assess the extremity of selected precipitation characteristics, identifying record values and evaluating their statistical significance based on standard deviation (sigma) values. Statistical analysis was performed on stations with at least 50 years of data between 1951 and 2023. The results indicate that, based on spatial analysis, October 1974 had the second-highest monthly precipitation overall. Record monthly totals for October 1974 were observed at more than 64% of stations, while maximum daily totals were recorded at over 17% of stations. The extremity of precipitation was most pronounced in monthly totals, which exceeded 400% of the October normal, with 100 stations reporting values at or above the 4-sigma level. Frequency analysis showed that precipitation in October 1974 surpassed the 100-year and 200-year return levels for the analyzed precipitation characteristics. This study highlights the influence of atmospheric circulation patterns on extreme precipitation and underscores the importance of considering both seasonal and spatial dimensions in future analyses of extreme weather events.
  
  KEY WORDS: extreme precipitation, isohyetal analysis, monthly precipitation totals, historical analysis
  
  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

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 16 - 26, doi: 10.31577/ahs-2025-0026.01.0002
Scientific Paper, English

Ali HACHEMI, Mohammed Amin HAFNAOUI, Mohammed MADI, Mosbah Ben SAID, Mohamed Tahar HANAFI, Benkhaled ABDELKADER: Flood typology of arid climates: A case study of Abiod wadi in Biskra region, Algeria

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• This paper serves as an introduction to the characterization and the classification of floods in the Algerian arid to semiarid areas. Instantaneous flood discharge data recorded between 1950 and 2010 at Foum El Gherza dam station are used to describe and interpret the prevailing flood regime in Abiod wadi watershed. The resulted flood hydrographs are assessed using the instantaneous peak discharge (Qp), mean discharge (Qm), characteristic duration (D), rising time and the total flood duration, velocity of flow during floods and the flood hydrograph shape. The findings showed that Abiod wadi watershed floods are generally flash, violent and of short duration with single or multi-peaks. However, some hydrographs are more voluminous with very long rising and falling times. Moreover, the flood that occurred in October, 2011 at Foum El Gherza dam confirms the presence of hydrological risk that must be given great attention and caution.
  
  KEY WORDS: Flood hydrograph; Typology; Arid area; Abiod wadi watershed; Biskra Region; Algeria
  
  Address:
  - Ali HACHEMI, Scientific and Technical Research Center on Arid Regions, Ecology of Arid Ecosystems and Climate Risks Division, Biskra, Algeria; Research Laboratory in Subterranean and Surface Hydraulics –LARHYSS, Université Mohamed Khider, Biskra, Algeria (Corresponding author. Tel.: Fax.: Email: alihachemi.hyd@gmail.com)
  - Mohammed Amin HAFNAOUI, Scientific and Technical Research Center on Arid Regions, Ecology of Arid Ecosystems and Climate Risks Division, Biskra, Algeria; Research Laboratory of Civil Engineering, Hydraulics, Environment and Sustainable Development, LARGHYDE Université Mohamed Khider, Biskra, Algeria
  - Mohammed MADI, Scientific and Technical Research Center on Arid Regions, Ecology of Arid Ecosystems and Climate Risks Division, Biskra, Algeria
  - Mosbah Ben SAID, Scientific and Technical Research Center on Arid Regions, Ecology of Arid Ecosystems and Climate Risks Division, Biskra, Algeria
  - Mohamed Tahar HANAFI, Scientific and Technical Research Center on Arid Regions, Ecology of Arid Ecosystems and Climate Risks Division, Biskra, Algeria
  - Benkhaled ABDELKADER, Research Laboratory in Subterranean and Surface Hydraulics –LARHYSS, Université Mohamed Khider, Biskra, Algeria

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 27 - 39, doi: 10.31577/ahs-2025-0026.01.0003
Scientific Paper, English

Ladislav HOLKO, Michal DANKO, Martin JANČO, Patrik SLEZIAK, Svetlana VARŠOVÁ: Precipitation characteristics estimated from the data given by recording raingauges and automatic weather stations

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• Recording raingauges coupled with other automatic weather station sensors can provide interesting information for climatological or hydrological studies, e.g. regarding the share of potentially solid and liquid precipitation, wind-induced errors of precipitation measurements or the number of significant snowfall events during winters. We compared precipitation amounts measured manually by the standard raingauge and automatically by the weighing gauge and disdrometer in Liptovský Mikuláš (570 m a. s. l.) during hydrological years 2013–2023 for several time scales. Annual precipitation measured by the three instruments on the whole did not differ by more than 5%. The differences in monthly precipitation were within ± 20%. Precipitation amounts from the weighing gauge were better comparable to those from the standard raingauge than the amounts obtained from the disdrometer. Hourly data from the weighing gauges located at 570 m a. s. l. and 1500 m a. s. l. showed that heavy precipitation (intensity 10–50 mm hour-1 ) was rare at both altitudes. Disdrometers in Liptovský Mikuláš and at Skalnaté Pleso (1778 m a. s. l.) documented the differences in the occurrence of snowfalls in a large mountain valley where snow represented on average 18% of registered annual precipitation, and in the Tatra Mountains (52%). Disdrometric and air temperature data suggested that the air temperature of +1°C was the threshold below which most precipitation fell as snow. Based on this threshold, the amount of potentially solid precipitation in the Liptovská kotlina valley and in the Western Tatra Mountains was estimated and compared for winters 2013–2023. A significant snowfall event, i.e. an event capable of creating a thicker, continuous snow cover, was defined on the basis of the threshold air temperature and cumulative precipitation amount over an uninterrupted sequence of days with precipitation. The number of such significant snowfall events was relatively small even in the mountains (4–8 events in winters 2013–2023). Most of the potentially solid precipitation at 570 m a. s. l. and at 1500 m a. s. l. fell at a wind speed of up to 1.5 m s -1 . The wind speed during the liquid precipitation was more often greater (up to 2.5 m s -1 ), especially at 1500 m a. s. l. The time series of the obtained data did not indicate substantial changes in the period 2013–2023.
  
  KEY WORDS: precipitation measurement, rain-snow temperature threshold, significant snowfalls, wind – induced errors
  
  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
  - Svetlana VARŠOVÁ, Earth Science Institute SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 40 - 51, doi: 10.31577/ahs-2025-0026.01.0004
Scientific Paper, English

Bence BOLLA, Ján SZOLGAY, Zoltán GRIBOVSZKI, Péter KALICZ, Márton DOBÓ, András SZABÓ: Analysis of the fluctuations of main water balance components at six forest stands in the Great Hungarian Plain

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• The hydro-meteorological measurement network of the Forest Research Institute of the University of Sopron monitored the water balance of six aged lowland forest stands (Bócsa: Grey poplar Gyula: Pedunculate oak, Jászberény: Pedunculate oak, Kecskemét: Scots pine, Püspökladány: Pedunculate oak, Pusztaszer: Black locust). Meteorological, soil moisture, and groundwater level data were used to estimate the differences between reactions of the water use of forest stands and changes in water balance in a predominantly dry period of 2019 to 2024. The available groundwater resources for the forest decreased significantly during this period, and the annual recharge cycle dampened or even diminished after the 2022 extreme compound warming and drought event, while the moisture stored in different soil layers, crucial for the survival of lowland forests, continued its recharging. The results contribute to understanding the variability and decrease of the access of the lowland forests to groundwater and soil moisture under conditions of warming climate, prolonged droughts and compound extremes.
  
  KEY WORDS: lowland forests, precipitation, temperature, groundwater, soil moisture, drought
  
  Address:
  - Bence BOLLA, Forest Research Institute, University of Sopron, Frankel L. str. 1, H-1027 Budapest, Hungary (Corresponding author. Tel.: Fax.: Email: bolla.bence@uni-sopron.hu)
  - Ján SZOLGAY, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovak Republic
  - Zoltán GRIBOVSZKI, Institute of Geomatics and Civil Engineering, Faculty of Forestry, University of Sopron, Bajcsy-Zsilinszky str. 4, H-9400 Sopron, Hungary
  - Péter KALICZ, Institute of Geomatics and Civil Engineering, Faculty of Forestry, University of Sopron, Bajcsy-Zsilinszky str. 4, H-9400 Sopron, Hungary
  - Márton DOBÓ, Forest Research Institute, University of Sopron, Frankel L. str. 1, H-1027 Budapest, Hungary
  - András SZABÓ, Forest Research Institute, University of Sopron, Frankel L. str. 1, H-1027 Budapest, Hungary

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 52 - 60, doi: 10.31577/ahs-2025-0026.01.0005
Discussion, English

Andrej ŠOLTÉSZ, Lea ČUBANOVÁ, Martin ORFÁNUS, Wael ALMIKAEEL, Dana BAROKOVÁ: Revitalization measures – Case study on the Vlára River

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• This study investigates bank erosion processes along the Vlára River in central Považie, Slovakia, focusing on a modified section near the D1 highway. The river’s steep gradient (6‰) and mountainous terrain result in high sediment transport capacity, particularly during floods. Despite previous stabilization efforts using gabion structures, localized failures at the base of banks have caused deep scours, threatening embankments and bridge foundations. 1D and 2D HEC-RAS numerical models were applied to evaluate hydrodynamic conditions. Results reveal flow velocities exceeding 5 m·s⁻¹ in critical areas, such as concave bends and the confluence with the Váh River. These velocities render conventional vegetative stabilization ineffective under extreme hydraulic stresses. A hybrid stabilization approach is proposed, combining stone riprap fortification in high-stress zones, transverse sills to mitigate scour and regulate sediment transport, and localized bioengineering solutions where feasible. The study underscores the importance of integrating geotechnical and hydrodynamic assessments to design effective, sustainable stabilization strategies. The proposed measures aim to enhance river resilience by balancing flood protection with ecological functionality.
  
  KEY WORDS: bank fortification, water level regime, vertical velocities, simulation
  
  Address:
  - Andrej ŠOLTÉSZ, Department of Hydraulic Engineering, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: andrej.soltesz@stuba.sk)
  - Lea ČUBANOVÁ, Department of Hydraulic Engineering, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovak Republic
  - Martin ORFÁNUS, Department of Hydraulic Engineering, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovak Republic
  - Wael ALMIKAEEL, Department of Hydraulic Engineering, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovak Republic
  - Dana BAROKOVÁ, Department of Hydraulic Engineering, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 61 - 69, doi: 10.31577/ahs-2025-0026.01.0006
Scientific Paper, English

Adel KHENTOUCHE, Nassim BELLA: The impact of climatic and water drought on the dams siltation (north east of Algeria)

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• The aim of the present study was to know the impact of climate on siltation in some dams located in the north east of Algeria (Chafia, Zerdaza). According to a semi-quantitative approach which takes into account the comparison of bathymetric surveys and the calculations carried out by empirical formulas widely used in Algeria (SPI. SSFI. FMI). The siltation is clearly varied according to the following phases: - From the impoundment of the dams until 1994: this phase was characterized by a high sedimentation between 10 and 14 Mm3 , FMI >70, Flow > 0.43 m3 s -1 and specific solid transport is >1000 T km-2 Y-1 . then the frequency of wet and dry years leaned to humid effects. - Frome 1995 to 2020: the siltation is low between 2.7 and 2.86 Mm3 and corresponds with the decreasing values of the hydroclimatic parameters (rainfall <672mm; FMI <72.93; liquid flow < 0.50 m3 s -1 and erosion less than 1000T Km-2 y -1 ) while the climate leaned to dried effects.
  
  KEY WORDS: Drought, Rainfall erosivity, Siltation, Bathymetric surveys
  
  Address:
  - Adel KHENTOUCHE, University Batna2, Institute of Earth Sciences and Universe, Natural hazards and Territorial Development, Laboratory, Batna, 05000, Algeria (Corresponding author. Tel.: Fax.: Email: : a.khentouche@univ-batna2.dz)
  - Nassim BELLA, University Batna2, Institute of Earth and Universe Sciences, Batna, 05000, Algeria

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 70 - 81, doi: 10.31577/ahs-2025-0026.01.0007
Scientific Paper, English

Khaled KOUIDER, Messaoud MAZARI, Izabela CHMIELEWSKA, Aissa BENSELHOUB, Stefano BELLUCCI: Enhancing prediction quality for groundwater pollution parameters of the Mitidja aquifer, by applying a new cross-validation strategy

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• The availability of reliable data in sufficient length is vital for optimal water resources management. Water resource managers are often faced with the problem of missing or unsubstantial data, in particular the monitoring of groundwater pollution parameters, which must be carried out strictly and regularly. Geostatistical modeling is a widely used technique for studying the spatial and temporal distribution of data shortfalls. In the framework of this study, we consider the problem of constructing an accurate prediction strategy on the basis of a relatively small number of samples. This work proposes a validation strategy, estimated on the association of the classic Leave-One-Out procedure with a preliminary prediction operation. The targeted selection of prediction models by performance level allows optimal and maximum use of the available data. This studied choice, by identifying the central models, effectively contributes to reducing predictive losses. The implementation of proposed approach to groundwater pollution data of the Mitidja aquifer, has allowed assessing its performance. Obtained results showed an improvement in the estimation quality of the interest variable, through identification of the predictors having better spatial representativeness.
  
  KEY WORDS: Data shortfalls, Geostatistics, Kriging, Predictive losses
  
  Address:
  - Khaled KOUIDER, Faculty of Civil Engineering, University of Sciences and Technology Houari Boumediene, Algiers, Algeria (Corresponding author. Tel.: Fax.: Email: kouider.usthb@gmail.com)
  - Messaoud MAZARI, Abderrahmene Mira University, Department of Mining and Geology, Faculty of Technology, Bejaia, Algeria
  - Izabela CHMIELEWSKA, Silesian Centre for Environmental Radioactivity, Central Mining Institute National Research Institute, 40-166 Katowice, Pl. Gwarków 1, Poland
  - Aissa BENSELHOUB, Environmental Research Center (C.R.E), Annaba, Algeria; University of Vienna, Vienna, Austria (Corresponding author. Tel.: Fax.: Email: aissabenselhoub@cre.dz)
  - Stefano BELLUCCI, INFN-Frascti National Laboratories, Frascati, Via E. Fermi 54, 00044, Rome, Italy; National Institute of Materials Physics, Bucharest, Romania

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 82 - 91, doi: 10.31577/ahs-2025-0026.01.0008
Scientific Paper, English

Lili MURAKÖZY, Gábor KOVÁCS, Ján SZOLGAY, Péter KALICZ, Roman VÝLETA, Zoltán GRIBOVSZKI: Reconstruction and regime change analysis of manually recorded meteorological data from the Botanical Garden in Sopron, Hungary

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• Meteorological observations in Sopron began in the early 18th century and have been carried out daily without interruption since 1870. From 1924 to 1974, the Botanical Garden's meteorological station served as the official station, which was then moved to the Kuruc Hill. The paper focuses on reconstructing and unifying the data of the Botanical Garden station, which continued to be operated by the University of Sopron on a voluntary basis. The data was examined, corrected and gaps reconstructed and crosschecked with the homogenized series of Kuruc Hill. This paper aims to demonstrate how abandoned local historical data and simple exploratory analysis with new simple metrics and comparative reasoning can be used to look for changes in data series. The reconstructed Botanical Garden series was used to detect local changes due to climate and landuse change and the impact of urbanization between the 1930–60 and 1989–2019 periods. The distribution and quantity of air temperature and precipitation were examined on annual, monthly and daily time scales. Differences in the water balance elements between the two periods were detected by the Thornthwaite monthly water balance model.
  
  KEY WORDS: data reconstruction, climate change, water balance modelling
  
  Address:
  - Lili MURAKÖZY, 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: lili.murakozy@stuba.sk)
  - Gábor KOVÁCS, Institute of Environmental Protection and Nature Conservation, Faculty of Forestry, University of Sopron, Bajcsy-Zsilinszky utca 4, H-9400 Sopron, Hungary
  - Ján SZOLGAY, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovak Republic
  - Péter KALICZ, Institute of Geomatics and Civil Engineering, Faculty of Forestry, University of Sopron, Bajcsy-Zsilinszky utca 4, H-9400 Sopron, Hungary
  - 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
  - Zoltán GRIBOVSZKI, Institute of Geomatics and Civil Engineering, Faculty of Forestry, University of Sopron, Bajcsy-Zsilinszky utca 4, H-9400 Sopron, Hungary

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 92 - 100, doi: 10.31577/ahs-2025-0026.01.0009
Scientific Paper, English

Andrej TALL, Branislav KANDRA, Dana PAVELKOVÁ, Milan GOMBOŠ: Development of water-balance components in lysimeter with a controlled groundwater level

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• The introduction of precise weighable lysimeters has enabled the monitoring of the water balance components of the soil profile with unprecedented precision. Lysimeters, which are equipped with a system for controlling and maintaining the groundwater level, also allow for direct quantification of water flows at the lower boundary of the soil aeration zone, i.e. capillary rise from the groundwater level and gravitational percolation towards the groundwater level. This study analysed the water balance components of a silty-loam soil profile with a maintained groundwater level at a depth of -1 m during the year 2023. To maintain a constant groundwater level during dry seasons, it was necessary to pump water into the lysimeter or pump it out during periods of excess water. Monitoring the flows at the lower boundary of the lysimeter showed that 162 mm of water reached the aeration zone through the capillary rise and 327 mm of water drained through the percolation process. Water flows at the upper boundary of the lysimeter were also quantified. The flow from the lysimeter to the atmosphere is represented by actual evapotranspiration. In the opposite direction, it is mainly precipitation and so-called “non-rain water” such as dew, fog, hoarfrost, soil water vapour adsorption, etc.
  
  KEY WORDS: weighable lysimeter, capillary rise, percolation, evapotranspiration
  
  Address:
  - Andrej TALL, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: tall@uh.savba.sk)
  - Branislav KANDRA, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Dana PAVELKOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Milan GOMBOŠ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 101 - 112, doi: 10.31577/ahs-2025-0026.01.0010
Scientific Paper, English

Veronika BAČOVÁ MITKOVÁ, Dana HALMOVÁ, Igor KOKAVEC, Ivan BARTÍK: Long-term trends and modelling of physicochemical indicators of surface water quality: Alkalinization in unregulated rivers of Slovakia

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• Climate change may negatively impact the quality and quantity of various parameters in inland water ecosystems. These changes may disrupt stream functions and lead to the degradation of ecological quality. This paper presents an evaluation of long-term data spanning 45 to 51 years on dissolved oxygen, surface water temperature, acidity, and conductivity in four streams in Slovakia: Nitra, Varínka, Biely Váh, and Bystrica. All streams are considered unregulated, with a seminatural character and no transverse barriers or reservoirs. The aim of the study is to identify significant changes in the time series of selected physicochemical surface water indicators, assess the strength of relationships between these quality indicators, and model them using appropriate autoregressive models. The study revealed significant long-term increasing trends in acidity for all streams, both monthly and annually. Alkalinization of running surface waters is observed globally and may pose a new threat to freshwater biodiversity. Conductivity values showed significant increasing trends for Nitra and Varínka, while Biely Váh exhibited a significant decreasing trend. Significant intercorrelations were found between acidity and conductivity, as well as oxygen and surface water temperature. A selected autoregressive model effectively simulates changes in the monthly concentrations of physicochemical indicators, and subsequently may be used to predict the development of given surface water quality indicators. Modeling and prediction of the hydrosphere components is crucial for surface water resource management, especially in the context of ongoing climate changes.
  
  KEY WORDS: physicochemical quality surface water indicators, long-term trends, interrelationships, autoregressive model
  
  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)
  - Dana HALMOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Igor KOKAVEC, Institute of Zoology SAS, Dúbravská cesta 9, 845 06 Bratislava, Slovak Republic
  - Ivan BARTÍK, Slovak Hydrometeorological Institute, Department Quality of Surface Water, Jeséniova 17, 833 15 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 113 - 122, doi: 10.31577/ahs-2025-0026.01.0011
Review, English

Viera KOVÁČOVÁ: Seasonal evaluation of surface water quality and vegetation growth

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• This paper reviews degradation of surface water; the role of nutrients enrichment to response of biota and monitoring due to the seasonal changes. The major influencing factors on water contamination, such as temperature, pH, dissolved oxygen, conductivity, nutrients inputs (nitrogen, phosphorus), element balance, microbiological conditions, hydrodynamics and turbidity. The international and national legislative determines the chemical status, biological status, supporting physicalchemical and hydro-morphological quality elements have been investigated. Most researchers have concluded that no single factor is responsible, but rather interactions between two or more factors control the rates vegetation growth. Flow velocity in vegetation growth channel is reduced. Vegetation is strongly dependent on the season, the roughness coefficient can be fairly different for summer and winter conditions. River aquatic systems that have been heavily loaded with nutrients (nitrogen and phosporus) can display change both seasonally and spatial. Climate change in recent years has also greatly affected surface water quality. Total parameters status index (TPSI) is an expression of the state of surface water contamination between 1 – 10, values were determined. In Danube Lowland channel network reaches average value 7.2.
  
  KEY WORDS: surface water, quality parameters, flow characteristics
  
  Address:
  - Viera KOVÁČOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: kovacova@uh.savba.sk)

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 123 - 131, doi: 10.31577/ahs-2025-0026.01.0012
Scientific Paper, English

Zbyněk BAJTEK, Igor LEŠČEŠEN, Katarína JENEIOVÁ: Analysis of trends of low flow in river stations in Ipeľ with respect to Málinec reservoir

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• The Málinec reservoir plays a key role in the region's drinking water supply and energy stability. However, like any reservoir, Málinec faces a number of challenges that can affect its efficiency and sustainability. One of the critical issues that may affect it is the minimum flows, i.e. the lowest flows that need to be maintained in order to maintain the ecological balance and ensure a reliable water supply. Minimum flows play a crucial role in the protection of aquatic ecosystems by ensuring sufficient oxygen and nutrients for life in rivers and streams, thus contributing to the maintenance of biodiversity. In addition to the ecological aspects, minimum flows are also important from an economic point of view, as they have an impact on water quality and its availability to the population. The Málinec Reservoir on the Ipeľ River was completed in the early 1990s as part of the Slovak Republic's comprehensive water management system. With increasing climatic changes and changes in hydrological cycles, maintaining optimal flows is becoming an increasingly difficult task. This paper focuses on the analysis of minimum flows in the tributaries of the Málinec reservoir. Specifically, we will discuss the use of the lfstat package in the R programming language, which allows a comprehensive analysis of hydrological data. The aim of the paper is to provide an overview of the current state of minimum flows in the Málinec reservoir. Based on the analysis of minimum flows, it will be possible to better understand the dynamics of flows and their implications for management and monitoring.
  
  KEY WORDS: low flow, Ipeľ, water reservoir, lfstat package
  
  Address:
  - Zbyněk BAJTEK, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: bajtek@uh.savba.sk)
  - Igor LEŠČEŠEN, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic
  - Katarína JENEIOVÁ, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 132 - 143, doi: 10.31577/ahs-2025-0026.01.0013
Scientific Paper, English

Marek SOKÁČ, Márta KOCZKA BARA, Yvetta VELÍSKOVÁ, Valentín SOČUVKA: Rainfall data in urban drainage: What do we need?

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• The paper presents the use of precipitation data in the field of urban drainage and analyses the need for precipitation data in this area with a specific focus on Slovakia. In the introduction, the different types of precipitation data needed to solve urban drainage tasks are analysed, as well as the requirements for these data. The study further compares historical precipitation data, which formed the foundation for the design and dimensioning of existing urban drainage systems in Slovakia, with more recent data. The analysis of these data in selected locations did not show a clear trend of increasing intensities of short-term rainfall for higher periodicity values (e.g. p=0.5). However, for lower periodicity values (p=0.2–0.01) the comparison shows an increase in the intensities of these short-term rainfalls. Subsequently, the paper analyses the possible impacts of these increased short-term rainfall intensities on urban drainage systems, as well as the need for specific precipitation data to evaluate the effectiveness of the design (reconstruction) of urban drainage systems in response to anticipated climate change, or in connection with new requirements resulting from the updated EU Waste Water Directive.
  
  KEY WORDS: rainfall data, urban drainage, climate change, adaptation measures, combined sewer overflows
  
  Address:
  - Marek SOKÁČ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: sokac@uh.savba.sk)
  - Márta KOCZKA BARA, 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
  - Valentín SOČUVKA, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 144 - 149, doi: 10.31577/ahs-2025-0026.01.0014
Scientific Paper, English

Lucia TOKOVÁ, Justína VITKOVÁ: Influence of biochar addition on water repellent sandy soils

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• This study presents results on changes in infiltration characteristics and water repellent parameters following the application of biochar to water repellent sandy soils. Water repellency is a common phenomenon that negatively affects water flow into the soil and, consequently, the entire hydrological process within the soil. The potential of biochar to eliminate soil water repellency and enhance the water retention capacity of sandy soils has not been widely studied; therefore, we aim to achieve this objective within a biochar field study in Sekule village (Borská nížina Lowland, Slovakia). Our experimental sites S1 and S2 consist of water repellent sandy soils located in a birch forest, while biochar was applied on site S2. Experimental sites S3 and S4 also comprise water repellent sandy soils found in a pine forest, with biochar applied at site S4. Our results demonstrate that both examined water repellency parameters significantly decreased (p<0.05) following the application of biochar in birch and pine forests. Water drop penetration time significantly decreased (p<0.05) by 36% in the pine forest, and the repellency index significantly decreased (p<0.05) in the birch and pine forests by 68% and 65%, respectively.
  
  KEY WORDS: biochar, sandy soil, repellency index
  
  Address:
  - Lucia TOKOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: tokova@uh.savba.sk)
  - Justína VITKOVÁ, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 150 - 155, doi: 10.31577/ahs-2025-0026.01.0015
Scientific Paper, English

Anton ZVALA: Comparison of saturated hydraulic conductivity with depth in coniferous and deciduous forest soils

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• The surface of the forest soil contains organic matter. The high content of organic matter on the surface of forest soil formed by dead plant litter and has a significant impact on the hydrophysical properties of forest soil. Organic matter on the surface of the forest soils has high porosity, very low bulk density, peculiar texture and structure determined by the level of mechanical and biochemical decomposition. Organic matter forms the organic horizon of forest soil on the surface. The scientific paper measured and analyzed the impact of litter from coniferous and deciduous forests on saturated hydraulic conductivity. For comparison, we measured the saturated hydraulic conductivity of the mineral horizon of the forest soil. The research sites with forest soil sampling points were Kokavske luky and Zelezna studnicka. We used a variable hydraulic head to measure the saturated hydraulic conductivity of forest soil. We found differences in the saturated hydraulic conductivity of forest soil caused by the forest, the decomposition of organic matter and the specific properties of the organic matter of forest soil.
  
  KEY WORDS: saturated hydraulic conductivity, forest soil, organic matter, mineral soil
  
  Address:
  - Anton ZVALA, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: zvala@uh.savba.sk)

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 156 - 161, doi: 10.31577/ahs-2025-0026.01.0016
Scientific Paper, English

Anton ZVALA: Saturated hydraulic conductivity of the forest soil and natural conditions

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• Knowledge of hydraulic properties is essential to understanding the movement of water in the soil. Saturated hydraulic conductivity is defined as the ability of a water saturated soil to conduct water. Differences in saturated hydraulic conductivity are caused by relief, spatial variability of soil, texture and structure of soil, fluvial and erosional activity. Most infiltration methods measure the saturated hydraulic conductivity only one depth at or near the surface. Measurement results extend the theory of hydraulic conductivity of the soil at various depths. An organic horizon is created on the forest floor surface, which causes an increase in saturated hydraulic conductivity. Hydraulic conductivity with soil depth decreases, this claim applies to research sites 3, 4, 5 and 6. Research sites 1 and 2 differ in hydraulic conductivity. The impact of relief on saturated hydraulic conductivity at soil sampling point 1 in the dead arm of river, where saturated hydraulic conductivity increases at a soil depth 0.5 m. The increase in saturated hydraulic conductivity may be caused by soil erosion from the dead arm of river slope, which covered the organic horizon of the forest soil.
  
  KEY WORDS: saturated hydraulic conductivity, texture a structure of soil, relief, fluvisol, soil erosion, hydrogeology, groundwater recharge
  
  Address:
  - Anton ZVALA, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic (Corresponding author. Tel.: Fax.: Email: zvala@uh.savba.sk)

Acta Hydrologica Slovaca, Vol. 26, No. 1, 2025, p. 162 - 171, doi: 10.31577/ahs-2025-0026.01.0017
Scientific Paper, English

Márton DOBÓ, Péter KALICZ, Zoltán GRIBOVSZKI, Bence BOLLA, András SZABÓ: Long term analysis of groundwater uptake strategies based on groundwater level fluctuations in pedunculate oak and hybrid poplar forests in the Great Hungarian Plain

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• This study examines the groundwater uptake characteristics of two tree species – hybrid poplar (Populus × euramericana cv. Agathe F) and pedunculate oak (Quercus robur L.) – in the Great Hungarian Plain using high-resolution groundwater level (GWL) measurements recorded over a 10-year period (2015–2024). Through analysis of diurnal GWL fluctuations, the relative groundwater consumption of each species and their responses to changing hydrological conditions were assessed. Results indicate that hybrid poplar exhibits higher water demand and larger seasonal GWL fluctuations compared to pedunculate oak. However, trends in daily GWL fluctuation suggest that groundwater uptake by hybrid poplar has decreased, while pedunculate oak has shown increasing reliance on groundwater in recent years. Precipitation events temporarily reduced groundwater dependency of the forest stands, with oak displaying a slower return to pre-rainfall groundwater uptake levels than poplar. Overall, the decline in groundwater levels hinders access to groundwater for both species, highlighting the need for sustainable forest management strategies to mitigate climate-induced water stress. These findings provide valuable insights for adaptive forestry planning in water-limited environments.
  
  KEY WORDS: groundwater fluctuation, forest groundwater uptake, groundwater uptake strategies, hybrid poplar, pedunculate oak
  
  Address:
  - Márton DOBÓ, Forest Research Institute, University of Sopron, Frankel L. str. 1, H-1027 Budapest, Hungary (Corresponding author. Tel.: Fax.: Email: dobo.marton@uni-sopron.hu)
  - Péter KALICZ, Institute of Geomatics and Civil Engineering, Faculty of Forestry, University of Sopron, Bajcsy-Zsilinszky str. 4, H-9400 Sopron, Hungary
  - Zoltán GRIBOVSZKI, Institute of Geomatics and Civil Engineering, Faculty of Forestry, University of Sopron, Bajcsy-Zsilinszky str. 4, H-9400 Sopron, Hungary
  - Bence BOLLA, Forest Research Institute, University of Sopron, Frankel L. str. 1, H-1027 Budapest, Hungary
  - András SZABÓ, Forest Research Institute, University of Sopron, Frankel L. str. 1, H-1027 Budapest, Hungary