J. Hydrol. Hydromech., Vol. 71, No. 4, 2023, p. 341 - 344, doi: 10.2478/johh-2023-0031
Information, English

Yvetta Velísková: Special issue dedicated to 70th anniversary of foundation of Institute of Hydrology, Slovak Academy of Sciences, Bratislava, Slovakia

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• Data not available
  
  KEY WORDS: Data not available
  
  Address:
  - Yvetta Velísková, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 84104 Bratislava, Slovakia; E-mail: Yvetta.Veliskova@savba.sk

J. Hydrol. Hydromech., Vol. 71, No. 4, 2023, p. 345 - 355, doi: 10.2478/johh-2023-0030
Scientific Paper, English

Natália Botková, Justína Vitková, Peter Šurda, Ioannis Massas, Ioannis Zafeiriou, Ján Gaduš, Francisco Cota Rodrigues, Paulo Filipe Silva Borges: Impact of biochar particle size and feedstock type on hydro-physical properties of sandy soil

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• Biochar, as an organic amendment, could positively change soil properties, especially soil with low organic matter and/or poor structure. Biochar application in sandy soil with low organic matter could be an effective tool for improving hydro-physical parameters of the soil economically and ecologically as well. The effect on bulk density, particle density, porosity, saturated hydraulic conductivity and available water content for plants of two biochar types applied at three different particle sizes in a sandy soil was examined. The results confirmed previous studies, showing decreased bulk density, particle density and saturated hydraulic conductivity and partially increased available water content for plants and porosity. Both biochar type and particle size affected the studied soil hydro-physical parameters. After analysis and comparison of two different types of biochar and three particle sizes, the most effective treatment for sandy soil was proved by the biochar produced from willow with the smallest particle size (<125 μm).
  
  KEY WORDS: Feedstock biochar; Sandy soil; Soil hydro-physical parameters.
  
  Address:
  - Natália Botková, Institute of Hydrology, Slovak Academy of Sciences, Bratislava, Slovakia. Institute of Landscape Engineering, Faculty of Horticulture and Landscape Engineering, Slovak University of Agriculture, Nitra, Slovakia. (Corresponding author. Tel.: Fax.: Email: botkova@uh.savba.sk)
  - Justína Vitková, Institute of Hydrology, Slovak Academy of Sciences, Bratislava, Slovakia.
  - Peter Šurda, Institute of Hydrology, Slovak Academy of Sciences, Bratislava, Slovakia.
  - Ioannis Massas, Department of Natural Resources Management and Agricultural Engineering, Agricultural University of Athens, Greece.
  - Ioannis Zafeiriou, Department of Natural Resources Management and Agricultural Engineering, Agricultural University of Athens, Greece.
  - Ján Gaduš, Institute of Environmental Management, Faculty of European Studies and Regional Development, Slovak University of Agriculture, Nitra, Slovakia.
  - Francisco Cota Rodrigues, Research Center in Biodiversity and Genetic Resources, Azores, Portugal.
  - Paulo Filipe Silva Borges, Research Institute for Agrarian Technology and Environment, University of the Azores, Azores, Portugal.

J. Hydrol. Hydromech., Vol. 71, No. 4, 2023, p. 356 - 368, doi: 10.2478/johh-2023-0026
Scientific Paper, English

Peter Rončák, Zuzana Németová, Justína Vitková, Michaela Danáčová, Lucia Toková, Elena Aydin, Peter Valent, David Honek, Dušan Igaz: Effects of the application of biochar on the soil erosion of plots of sloping agricultural and with silt loam soil

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• The application of biochar is considered to be a beneficial strategy for improving soil ecosystem services. The objectives of this study are to evaluate the differences in the soil erosion of silt loam soil with or without the application of biochar and to compare the impact of the application of biochar on soil erosion for different agricultural practices, namely, bare soil, silage corn, and sown peas. Specifically, the physically-based EROSION 3D model was used to estimate the soil erosion of small plots of sloping agricultural land. In considering various combinations of agricultural practices and rainfalls with different durations and intensities, several scenarios were used to assess the impact of the application of biochar on soil erosion. The results of this study demonstrate that the highest mean values of mean soil erosion in the case study area were simulated without using any biochar on bare soil. The values of the mean soil erosion were reduced with the use of biochar. The effect of the application of biochar was shown for all types of agricultural practices; above all, it reduced soil erosion that occurred above high values (over 30 t ha–1). Although the application and reapplication of biochar showed promise in reducing soil erosion, further research is needed to gain a deeper understanding of its total effects.
  
  KEY WORDS: Application of biochar; Soil erosion; EROSION 3D model; Rainfall.
  
  Address:
  - Peter Rončák, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia. (Corresponding author. Tel.: Fax.: Email: roncak@uh.savba.sk)
  - Zuzana Németová, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology, Radlinského 11, 81005 Bratislava, Slovakia.
  - Justína Vitková, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Michaela Danáčová, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology, Radlinského 11, 81005 Bratislava, Slovakia.
  - Lucia Toková, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Elena Aydin, Institute of Landscape Engineering, Faculty of Horticulture and Landscape Engineering, Slovak University of Agriculture, 949 76 Nitra, Slovakia.
  - Peter Valent, Institute of Hydraulic Engineering and Water Resources Management, TU Wien, Vienna, 1040, Austria.
  - David Honek, T.G. Masaryk Water Research Institute, Podbabská 2582/30, 16000 Prague, Czech Republic.
  - Dušan Igaz, Institute of Landscape Engineering, Faculty of Horticulture and Landscape Engineering, Slovak University of Agriculture, 949 76 Nitra, Slovakia.

J. Hydrol. Hydromech., Vol. 71, No. 4, 2023, p. 369 - 381, doi: 10.2478/johh-2023-0034
Scientific Paper, English

Milan Gomboš, Andrej Tall, Branislav Kandra, Anca Constantin, Dana Pavelkova: Changes in crack width on the surface of heavy soils during drought, determined by precise measurement and calculation

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• In heavy soils, changes in humidity incur soil volume changes. In the horizontal plane, these are manifested by cracks formation and in the vertical plane by the movement of the soil surface. Cracks have a significant impact on hydrodynamics of the soil profile. The work is based on the hypothesis that soil volume changes depend on both the content of clay particles in soil and soil volumetric moisture. The aim of the work is to measure and analyze the changes in the width of the cracks and their reaction to the changes in volumetric soil moisture. One of the objectives of the work was to design a simple tool for accurate measurement and calculation of the crack width on the soil surface. For the study of crack width, a soil profile in an area on the East Slovakia Lowland was selected. The profile was examined under conditions of extreme drought, at the turn of July and August 2022. Crack width varied between 1.0 cm and 3.3 cm. The calculation procedure was evaluated as satisfactory for estimating the change in crack width on the soil surface.
  
  KEY WORDS: Heavy soil; Crack width; Volume changes; Volumetric soil moisture.
  
  Address:
  - Milan Gomboš, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Andrej Tall, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Branislav Kandra, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Anca Constantin, Ovidius University from Constanta, Faculty of Civil Engineering, 22b Unirii str, Constanta, Romania.
  - Dana Pavelkova, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia. (Corresponding author. Tel.: Fax.: Email: pavelkova@uh.savba.sk)

J. Hydrol. Hydromech., Vol. 71, No. 4, 2023, p. 382 - 398, doi: 10.2478/johh-2023-0028
Scientific Paper, English

Pavla Pekárová, Zbyněk Bajtek, Ján Pekár, Roman Výleta, Ognjen Bonacci, Pavol Miklánek, Jörg Uwe Belz, Liudmyla Gorbachova: Monthly stream temperatures along the Danube River: Statistical analysis and predictive modelling with incremental climate change scenarios

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• The aim of the study is to analyse changes and predict the course of mean monthly water temperatures of the Danube River at various locations for the future. The first part of the study involves conducting a statistical analysis of the annual and monthly average air temperatures, water temperatures, and discharges along the Danube River. The study examines long-term trends, changes in the trends, and multiannual variability in the time series. The second part of the study focuses on simulating the average monthly water temperatures using Seasonal Autoregressive Integrated Moving Average (SARIMA) models and nonlinear regression models (NonL), based on two RCP based incremental mean monthly air temperature scenarios. To assess the impact of future climate on stream temperatures, the historical long-term average of the monthly water temperature (1990–2020) was compared with scenarios S1 (2041–2070) and S2 (2071–2100). The simulation results from the two stochastic models, the SARIMA and NonL, showed that in scenario S1, the Danube River's average monthly water temperature is projected to increase by 0.81/0.82°C (Passau), 0.55/0.71°C (Bratislava), and 0.68/0.56°C (Reni). In scenario S2, the models predict higher increases: 2.83/2.50°C (Passau), 2.06/2.46°C (Bratislava), and 2.52/1.90°C (Reni). Overall, the SARIMA model proved to be more stable and effective in simulating the increase in monthly water temperatures in the Danube River.
  
  KEY WORDS: SARIMA models; Nonlinear regression models; Water temperature changes; Climate change; Incremental scenarios.
  
  Address:
  - Pavla Pekárová, Slovak Academy of Sciences, Institute of Hydrology, Dúbravská cesta 9, 841 04 Bratislava, Slovakia. (Corresponding author. Tel.:+421 2 3229 3505 Fax.: Email: pekarova@uh.savba.sk)
  - Zbyněk Bajtek, Slovak Academy of Sciences, Institute of Hydrology, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Ján Pekár, Comenius University in Bratislava, Faculty of Mathematics, Physics, and Informatics, Department of Applied Mathematics and Statistics, Mlynská dolina, 842 48 Bratislava, Slovakia.
  - Roman Výleta, Slovak University of Technology in Bratislava, Faculty of Civil Engineering, Department of Land and Water Resources Management, Radlinského 11, 810 05 Bratislava, Slovakia.
  - Ognjen Bonacci, Faculty of Civil Engineering, Architecture and Geodesy, University of Split, Matice hrvatske 15, 21000 Split, Croatia.
  - Pavol Miklánek, Slovak Academy of Sciences, Institute of Hydrology, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Jörg Uwe Belz, Federal Institute of Hydrology, Am Mainzer Tor 1, 56068 Koblenz, Germany.
  - Liudmyla Gorbachova, Ukrainian Hydrometeorological Institute, 37 Nauki Prospect, 03028 Kyiv-28, Ukraine.

J. Hydrol. Hydromech., Vol. 71, No. 4, 2023, p. 399 - 412, doi: 10.2478/johh-2023-0033
Scientific Paper, English

Pavla Pekárová, Dana Halmová, Zuzana Sabová, Ján Pekár, Pavol Miklánek, Veronika Bačová Mitková, Stevan Prohaska, Silvia Kohnová, Marcel Garaj: Sensitivity of runoff due to changes in the characteristics of the water balance in the Danube River region

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• Climate change is presently a widely discussed subject in relation to alterations in water storage capacity and the components of the hydrological balance within catchment areas. This research study was directed at two main objectives: 1. The indirect estimation of long-term mean annual runoff using an empirical model; 2. The determination of changes in the annual runoff regime of fifty Danube sub-basins. Monthly areal precipitation, discharges, and air temperature data from 1961 to 1990 were collected for selected headwater sub-basins of the Danube River. In the first part, Turc-type empirical equations for the estimation of the long-term average annual runoff R in the Danube basin were employed. The parameters of the empirical equations were determined through nonlinear regression. Given the underestimation of the actual (territorial, balance) evapotranspiration ET values determined from the balance equation, the precipitation totals were corrected by +10%. With a 10% increase in precipitation, the values of balance ET reached the values ET determined by the Budyko–Zubenok–Konstantinov method. In the second part, fifty equations for the estimation of changes in the average annual runoff, depending on increases in the air temperature and changes in the annual precipitation separately for each of the 50 sub-basins, were established. In conclusion, the results suggest that, on average, a 100 mm increase in the average annual rainfall in the Danube River headwater sub-basins, will cause a 50 mm increase in outflow, and a 1 °C increase in the average annual air temperature will lead to a 12 mm decrease in runoff.
  
  KEY WORDS: Danube River basin; Hydrological balance; Runoff; Climate change; Precipitation correction.
  
  Address:
  - Pavla Pekárová, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic. (Corresponding author. Tel.: Fax.: Email: Pavla.Pekarova@savba.sk)
  - Dana Halmová, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic.
  - Zuzana Sabová, Slovak University of Technology, Faculty of Civil Engineering, Department of Land and Water Resources Management, Radlinského 11, 810 05 Bratislava, Slovak Republic.
  - Ján Pekár, Comenius University in Bratislava, Faculty of Mathematics, Physics, and Informatics, Mlynská dolina, 842 48 Bratislava, Slovak Republic.
  - Pavol Miklánek, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic.
  - Veronika Bačová Mitková, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic.
  - Stevan Prohaska, Jaroslav Černi Institute for the Development of Water Resources, Belgrade, 1000, Serbia.
  - Silvia Kohnová, Slovak University of Technology, Faculty of Civil Engineering, Department of Land and Water Resources Management, Radlinského 11, 810 05 Bratislava, Slovak Republic.
  - Marcel Garaj, Institute of Hydrology SAS, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic. Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovak Republic.

J. Hydrol. Hydromech., Vol. 71, No. 4, 2023, p. 413 - 424, doi: 10.2478/johh-2023-0024
Scientific Paper, English

Andrej Tall, Branislav Kandra, Dana Pavelková, Sascha Reth, Milan Gomboš: Evaluation of precipitation measurements using a standard rain gauge in relation to data from a precision lysimeter

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• The construction of modern lysimeters with a precise weighing system made it possible to achieve an unprecedented accuracy of precipitation measurement. This study compares two methods of measuring precipitation in the conditions of the humid continental climate of the Eastern Slovakian Lowland (Slovakia): measurement using a standard tipping-bucket rain gauge vs. precision weighable lysimeter. Data from the lysimeter were used as a reference measurement. The comparison period lasted four years (2019–2022). Only liquid rainfall was compared. The rain gauge was found to underestimate precipitation compared to the lysimeter. Cumulative precipitation for the entire monitored period captured by the rain gauge was 2.8% lower compared to lysimeter measurements. When comparing hourly and daily totals of precipitation and precipitation events, a very high degree of agreement was detected (r2 > 0.99; RMSE from 0.22 to 0.51 mm h–1). A comparison based on precipitation intensity showed a decreasing trend in measurement accuracy with increasing precipitation intensity. This tendency has an exponential course. With increasing intensity of precipitation, increasing intensity of wind was also recorded. In order to correct measurement errors, simple correction method was proposed, which helped to partially eliminate the inaccuracies of the rain gauge measurement.
  
  KEY WORDS: Tipping-bucket rain gauge; Precision weighable lysimeter; Precipitation measurement; Rainfall intensity.
  
  Address:
  - Andrej Tall, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia. (Corresponding author. Tel.: Fax.: Email: tall@uh.savba.sk)
  - Branislav Kandra, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Dana Pavelková, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Sascha Reth, Umwelt-Geräte-Technik GmbH, Eberswalder Str. 58, 15374 Müncheberg, Germany.
  - Milan Gomboš, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.

J. Hydrol. Hydromech., Vol. 71, No. 4, 2023, p. 425 - 438, doi: 10.2478/johh-2023-0032
Scientific Paper, English

Barbora Považanová, Milan Čistý, Zbyněk Bajtek: Using feature engineering and machine learning in FAO reference evapotranspiration estimation

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• The authors of this study investigated the use of machine learning (ML) and feature engineering (FE) techniques to accurately determine FAO reference evapotranspiration (ETo) with a minimal number of climate variables being measured. The recommended techniques for areas with insufficient measurements are based solely on daily temperature readings. Various ML methods were tested to evaluate how sophisticated an ML algorithm is for this task necessary. The main emphasis was on feature engineering, which involves converting raw variables into inputs better suited for ML algorithms, resulting in improved results. FE methods for estimating evapotranspiration include approximations of clearsky solar radiation based on altitude and Julian day, approximate relative humidity and wind velocity, a categorical month variable, and variables interactions. The authors confirmed that the ability of ML in such tasks is not solely dependent on choosing the suitable algorithm but also on this frequently ignored step. The results of computational experiments are presented, accompanied by a comparison of the proposed method against standard ETo empiric equations. Machine learning methods, mainly due to the transformation of raw variables using FE, provided better results than traditional empirical methods and sophisticated ML algorithms without FE. In addition, the authors tested the applicability of the developed models in the broader area to evaluate the possibility of their generalizability. The potential of this approach to deliver improved predictions, reduced input requirements, and increased efficiency holds interesting promise for optimizing water management strategies, irrigation planning, and decision-making within the agricultural sector.
  
  KEY WORDS: Reference evapotranspiration; Input data reduction; Machine learning; Feature engineering.
  
  Address:
  - Barbora Považanová, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovakia.
  - Milan Čistý, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovakia. (Corresponding author. Tel.:+421 904 002 302 Fax.: Email: milan.cisty@stuba.sk)
  - Zbyněk Bajtek, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovak Republic.

J. Hydrol. Hydromech., Vol. 71, No. 4, 2023, p. 439 - 448, doi: 10.2478/johh-2023-0025
Scientific Paper, English

Patrik Sleziak, Michal Danko, Martin Jančo, Juraj Parajka, Ladislav Holko: Spatial and temporal variability of saturated areas during rainfall-runoff events

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• Spatially distributed hydrological model Mike SHE was used as a diagnostic tool to provide information on possible overland flow source areas in the mountain catchment of Jalovecký Creek (area 22.2 km2, elevation range 820–2178 m a.s.l.) during different rainfall-runoff events. Selected events represented a sequence of several smaller, consecutive events, a flash flood event and two large events caused by frontal precipitation. Simulation of hourly runoff was better for runoff events caused by heavy rainfalls of longer duration than for the flash flood or consecutive smaller runoff events. Higher soil moisture was simulated near the streamflow network and larger possibly saturated areas were located mainly in the upper parts of mountain valleys. The most pronounced increase in the areal extent of possibly saturated areas (from 6.5% to 68.6% of the catchment area) was simulated for the event with high peak discharge divided by a short rainfall interruption. Rainfall depth exceeding 100 mm caused a large increase in the potentially saturated areas that covered subsequently half of the catchment area or more. A maximum integral connectivity scale representing the average distance over which individual pixels were connected varied for the selected events between 45 and 6327 m.
  
  KEY WORDS: Mountain catchment; Hourly runoff simulation; Saturated area; Integrated connectivity scale.
  
  Address:
  - Patrik Sleziak, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia. (Corresponding author. Tel.: Fax.: Email: sleziak@uh.savba.sk)
  - Michal Danko, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Martin Jančo, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Juraj Parajka, Institute of Hydraulic Engineering and Water Resources Management, TU Wien, 1040 Vienna, Austria. Centre for Water Resource Systems, TU Wien, 1040 Vienna, Austria.
  - Ladislav Holko, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.

J. Hydrol. Hydromech., Vol. 71, No. 4, 2023, p. 449 - 463, doi: 10.2478/johh-2023-0027
Scientific Paper, English

Roman Výleta, Peter Rončák, Anna Liová, Peter Valent, Tomáš Bacigál, Zoltán Gribovszki, Zuzana Danáčová, Peter Šurda, Justína Vitková, Kamila Hlavčová: The testing of a multivariate probabilistic framework for reservoir safety evaluation and flood risks assessment in Slovakia: A study on the Parná and Belá Rivers

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• Intense floods represent a challenge to risk management. While they are multivariate in their nature, they are often studied in practice from univariate perspectives. Classical frequency analyses, which establish a relation between the peak flow or volume and the frequency of exceedance, may lead to improper risk estimations and mitigations. Therefore, it is necessary to study floods as multivariate stochastic events having mutually correlated characteristics, such as peak flood flow, corresponding volume and duration. The joint distribution properties of these characteristics play an important role in the assessment of flood risk and reservoir safety evaluation. In addition, the study of flood hydrographs is useful because of the inherent dependencies among their practice-relevant characteristics present on-site and in the regional records. This study aims to provide risk analysts with a consistent multivariate probabilistic framework using a copulabased approach. The framework respects and describes the dependence structures among the flood peaks, volumes, and durations of observed and synthetic control flood hydrographs. The seasonality of flood generation is respected by separate analyses of floods in the summer and winter seasons. A control flood hydrograph is understood as a theoretical/synthetic discharge hydrograph, which is determined by the flood peak with the chosen probability of exceedance, the corresponding volume, and the time duration with the corresponding probability. The framework comprises five steps: 1. Separation of the observed hydrographs, 2. Analysis of the flood characteristics and their dependence, 3. Modelling the marginal distributions, 4. A copula-based approach for modelling joint distributions of the flood peaks, volumes and durations, 5. Construction of synthetic flood hydrographs. The flood risk assessment and reservoir safety evaluation are described by hydrograph analyses and the conditional joint probabilities of the exceedance of the flood volume and duration conditioned on flood peak. The proposed multivariate probabilistic framework was tested and demonstrated based on data from two contrasting catchments in Slovakia. Based on the findings, the study affirms that the trivariate copula-based approach is a practical option for assessing flood risks and for reservoir safety.
  
  KEY WORDS: Copula-based approach; Flood risk; Flood seasonality; Trivariate analysis; Synthetic hydrographs.
  
  Address:
  - Roman Výleta, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovakia. (Corresponding author. Tel.:+ 421 232 888 727 Fax.: Email: roman.vyleta@stuba.sk)
  - Peter Rončák, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Anna Liová, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovakia.
  - Peter Valent, Institute of Hydraulic Engineering and Water Resources Management, Technische Universität Wien, Vienna, 1040, Austria.
  - Tomáš Bacigál, Department of Mathematics and Constructive Geometry, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovakia.
  - Zoltán Gribovszki, Institute of Geomatics and Civil Engineering, Faculty of Forestry, University of Sopron, Bajcsy-Zsilinszky u. 4., 9400 Sopron, Hungary.
  - Zuzana Danáčová, Slovak Hydrometeorological Institute, Jeséniova 17, 833 15 Bratislava, Slovakia.
  - Peter Šurda, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Justína Vitková, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 04 Bratislava, Slovakia.
  - Kamila Hlavčová, Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology in Bratislava, Radlinského 11, 810 05 Bratislava, Slovakia.

J. Hydrol. Hydromech., Vol. 71, No. 4, 2023, p. 464 - 474, doi: 10.2478/johh-2023-0023
Scientific Paper, English

Saeid Okhravi, Mahdi Alemi, Hossein Afzalimehr, Radoslav Schügerl, Yvetta Velísková: Flow resistance at lowland and mountainous rivers

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• This study initially examines the various sources of flow resistance in sand-bed (lowland) and gravel-bed (mountainous) rivers along with the limitations of traditional estimation methods. The nondimensional hydraulic geometry approach, relating dimensionless flow discharge (q*) to the Darcy-Weisbach friction factor (f), has demonstrated good performance for both river types, covering shallow to moderately deep flows. However, accuracy in estimating f is affected by simplifications like assuming uniform and deep flow, neglecting bed load transport and vegetation effects, which require further evaluation. To address these issues, the proposed method is evaluated using data from four sand-bed rivers in Slovakia (with vegetation), and three gravel-bed rivers in Iran (dominated by cobbles and boulders). Bedforms prove to be significant resistance sources in all studied rivers. The approach yields separate predictors for each river type, showing a satisfactory agreement between observed and calculated values within a maximum deviation of ±20% error bands. These predictors are further validated using field data and established equations from rivers with similar physiographic characteristics. Results indicate the method performs well in predicting flow resistance in sand-bed rivers, slightly overestimating overall (+40%). It effectively captures riverbed features and vegetation influence under small-scale roughness conditions. However, the predictor's validity for gravel-bed rivers is somewhat limited due to high variability in water-surface profiles, making it challenging to accurately capture flow dynamics under large-scale roughness conditions. Addressing complex characteristics of gravel-bed riverbeds, including boulders and local energy extraction, is crucial for improving the estimation of water-surface profile variations and flow resistance using the hydraulic geometry approach.
  
  KEY WORDS: Flow resistance; Hydraulic geometry; Gravel-bed river; Sand-bed river; Field data; River engineering.
  
  Address:
  - Saeid Okhravi, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 84104, Bratislava, Slovak Republic. (Corresponding author. Tel.:+421-944624921 Fax.: Email: saeid.okhravi@savba.sk)
  - Mahdi Alemi, Departamento de Engenharia Civil, Faculdadede Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, Porto 4200-465, Portugal.
  - Hossein Afzalimehr, Department of Civil Engineering, Iran University of Science and Technology, Tehran 1311416846, Iran.
  - Radoslav Schügerl, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 84104, Bratislava, Slovak Republic.
  - Yvetta Velísková, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 84104, Bratislava, Slovak Republic.

J. Hydrol. Hydromech., Vol. 71, No. 4, 2023, p. 475 - 485, doi: 10.2478/johh-2023-0029
Scientific Paper, English

Yvetta Velísková, Marek Sokáč, Maryam Barati Moghaddam: Inverse task of pollution spreading – Localization of source in extensive open channel network structure

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• This paper is focused on the problem of the pollutant source localisation in streams in other words the solution of the inverse problem of pollution spreading with in an extensive open channel network structure, i.e. in a complex system of rivers, channels and creeks in natural catchments or sewer systems in urban catchments. The design of the overall localisation procedure is based on the requirement that the entire localization system be operative and fast enough to enable quick operative interventions and help prevent the spread of pollution. The proposed model, as well as, the overall localisation procedure was calibrated and tested on a real sewer system, which represents in this case an extensive open channel network structure with free surface flow. The test results are successful and confirmed applicability of proposed localization tool in simple real conditions. However, the localisation procedure has pros and cons, which are discussed in the paper.
  
  KEY WORDS: Pollution; Sources; Localisation; Open channel; Network; Inverse task.
  
  Address:
  - Yvetta Velísková, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 01, Bratislava, Slovak Republic.
  - Marek Sokáč, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 01, Bratislava, Slovak Republic. (Corresponding author. Tel.: Fax.: Email: sokac@uh.savba.sk)
  - Maryam Barati Moghaddam, Institute of Hydrology, Slovak Academy of Sciences, Dúbravská cesta 9, 841 01, Bratislava, Slovak Republic.