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Roman Výleta  - - - 
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Peter Valent

10 shared publications

Department of Land and Water Resources Management, Faculty of Civil Engineering, Slovak University of Technology, Radlinského 11, 810 05 Bratislava, Slovakia

Michaela Danáčová

3 shared publications

Formerly at The Centre for Water Resource Systems, Vienna Universtity of Technology, Vienna, Austria

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Publication Record
Distribution of Articles published per year 
(2014 - 2019)
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9
 
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Article 0 Reads 0 Citations A Joint Sedimentation-Flood Retention Assessment of a Small Water Reservoir in Slovakia: A New Hope for Old Reservoirs? Peter Valent, Roman Výleta, Michaela Danáčová Published: 03 April 2019
Geosciences, doi: 10.3390/geosciences9040158
DOI See at publisher website ABS Show/hide abstract
The intensification of agricultural production brings problems related to water erosion, even to the upper parts of river basins. Soil particles that have eroded from unprotected agricultural land are often deposited in small water reservoirs, the efficiency or function of which might be compromised. This study presents an analysis of changes in the retention capacity of a small water reservoir over a period of 8 years. Within the study, a detailed bathymetry of the reservoir was conducted using an acoustic Doppler current profiler. The results, when compared to a 2008 geodetic survey, showed that the retention volume of the reservoir was reduced by only 2%, which was also confirmed by mathematical modeling. The possibility of strengthening the reservoir’s role in flood protection was also investigated. A flood wave with a return period of 100 years was estimated using a design storm approach. A simple numerical model was proposed to transform the flood wave through the reservoir by considering four different scenarios of the elevation of the initial water level. The model, which is based on a water balance equation, uses simple hydraulic relationships to control the discharge through the reservoir’s outflow objects. The results demonstrate that by reducing the initial water level, significant improvements in terms of the flood peak’s attenuation and a longer time to peak values could be achieved.
Article 0 Reads 0 Citations ADCP Discharge Measurements on the River Danube: Post-Processing and Correction of Data Roman Výleta, Peter Valent Published: 01 March 2019
Slovak Journal of Civil Engineering, doi: 10.2478/sjce-2019-0002
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Accurate measurements and analyses of river discharges are one of the key tasks of hydrology. Nowadays, the traditional methods of discharge measurements are being supplemented or even replaced by novel approaches that utilize state-of-the-art technologies. One approach, which has recently become very popular in the hydrological practice both in Slovakia and abroad, is a method utilizing the Doppler effect of sound waves. In this study, a dataset of 185 discharge measurements on the River Danube was created using a RiverRay portable Acoustic Doppler Current Profiler (ADCP). All the measurements were taken on the River Danube at four different cross-sections in Slovakia. The measurements were processed using the manufacturer’s WinRiver II software and further adjusted in Agila, which is a specialised third-party post-processing software aimed at correcting measurement errors from ADCP discharge measurements. Currently, some but not all countries lying in the Danube basin have included Agila post-processing in their methodologies. This causes problems and disputes between national water authorities when exchanging information about discharge measurements in the border regions. In order to respond to this problem, the main objective of this study was to compare the results of both original and corrected discharges, which were measured under a number of different circumstances, and to propose recommendations about the suitability of using Agila post-processing for discharge measurements of the River Danube.
Article 1 Read 0 Citations Evaluation of Surface Runoff Generation Processes Using a Rainfall Simulator: A Small Scale Laboratory Experiment Michaela Danáčová, Peter Valent, Roman Výleta Published: 21 December 2017
IOP Conference Series: Earth and Environmental Science, doi: 10.1088/1755-1315/95/2/022016
DOI See at publisher website ABS Show/hide abstract
Nowadays, rainfall simulators are being used by many researchers in field or laboratory experiments. The main objective of most of these experiments is to better understand the underlying runoff generation processes, and to use the results in the process of calibration and validation of hydrological models. Many research groups have assembled their own rainfall simulators, which comply with their understanding of rainfall processes, and the requirements of their experiments. Most often, the existing rainfall simulators differ mainly in the size of the irrigated area, and the way they generate rain drops. They can be characterized by the accuracy, with which they produce a rainfall of a given intensity, the size of the irrigated area, and the rain drop generating mechanism. Rainfall simulation experiments can provide valuable information about the genesis of surface runoff, infiltration of water into soil and rainfall erodibility. Apart from the impact of physical properties of soil, its moisture and compaction on the generation of surface runoff and the amount of eroded particles, some studies also investigate the impact of vegetation cover of the whole area of interest. In this study, the rainfall simulator was used to simulate the impact of the slope gradient of the irrigated area on the amount of generated runoff and sediment yield. In order to eliminate the impact of external factors and to improve the reproducibility of the initial conditions, the experiments were conducted in laboratory conditions. The laboratory experiments were carried out using a commercial rainfall simulator, which was connected to an external peristaltic pump. The pump maintained a constant and adjustable inflow of water, which enabled to overcome the maximum volume of simulated precipitation of 2.3 l, given by the construction of the rainfall simulator, while maintaining constant characteristics of the simulated precipitation. In this study a 12-minute rainfall with a constant intensity of 5 mm/min was used to irrigate a corrupted soil sample. The experiment was undertaken for several different slopes, under the condition of no vegetation cover. The results of the rainfall simulation experiment complied with the expectations of a strong relationship between the slope gradient, and the amount of surface runoff generated. The experiments with higher slope gradients were characterised by larger volumes of surface runoff generated, and by shorter times after which it occurred. The experiments with rainfall simulators in both laboratory and field conditions play an important role in better understanding of runoff generation processes. The results of such small scale experiments could be used to estimate some of the parameters of complex hydrological models, which are used to model rainfall-runoff and erosion processes at catchment scale.
Article 0 Reads 0 Citations Monitoring and Assessment of Water Retention Measures in Agricultural Land Roman Výleta, Michaela Danáčová, Andrej Škrinár, Róbert Fenc... Published: 21 December 2017
IOP Conference Series: Earth and Environmental Science, doi: 10.1088/1755-1315/95/2/022008
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One of the most interesting events, from the environmental impact point of view, is the huge storm rainfall at which soil degradation processes occur. In Slovakia, agricultural areas with a higher slope have been recently increasingly denudated by water erosion processes. Areas having regular problems with muddy floods and denudation of soil particles have been currently identified. This phenomenon has long-term adverse consequences in the agricultural landscape, especially the decline in soil fertility, the influence on soil type and the reduction of depth of the soil profile. In the case of storm rainfall or long-term precipitation, soil particles are being transported and deposited at the foot of the slope, but in many cases the large amounts of sediment are transported by water in the form of muddy floods, while putting settlements and industrial zones at risk, along with contamination and clogging of watercourses and water reservoirs. These unfavourable phenomena may be prevented by appropriate management and application of technical measures, such as water level ditches, erosion-control weirs, terraces and others. The study deals with determination of the soil loss and denudation of soil particles caused by water erosion, as well as with determination of the volume of the surface runoff created by the regional torrential rains in the area of the village of Sobotište. The research is based on the analysis of flood and erosion-control measures implemented in this area. Monitoring of these level ditches for protection against muddy floods has been carried out since 2015 using UAV technology and terrestrial laser scanning. Monitoring is aimed on determination of the volume of the ditch, changes in its capacity and shape in each year. The study evaluates both the effectiveness of these measures to reduce the surface runoff as well as the amount of eroded soil particles depending on climatological conditions. The results of the research point to the good efficiency of these measures; however, in conjunction with belt crops cultivation they could form a comprehensive flood and erosion-control protection to eliminate the muddy floods and protect the settlements from surrounding slopes.
Article 0 Reads 0 Citations Optimizing Use of Water Management Systems during Changes of Hydrological Conditions Roman Výleta, Andrej Škrinár, Michaela Danáčová, Peter Valen... Published: 01 October 2017
IOP Conference Series: Materials Science and Engineering, doi: 10.1088/1757-899X/245/3/032075
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When designing the water management systems and their components, there is a need of more detail research on hydrological conditions of the river basin, runoff of which creates the main source of water in the reservoir. Over the lifetime of the water management systems the hydrological time series are never repeated in the same form which served as the input for the design of the system components. The design assumes the observed time series to be representative at the time of the system use. However, it is rather unrealistic assumption, because the hydrological past will not be exactly repeated over the design lifetime. When designing the water management systems, the specialists may occasionally face the insufficient or oversized capacity design, possibly wrong specification of the management rules which may lead to their non-optimal use. It is therefore necessary to establish a comprehensive approach to simulate the fluctuations in the interannual runoff (taking into account the current dry and wet periods) in the form of stochastic modelling techniques in water management practice. The paper deals with the methodological procedure of modelling the mean monthly flows using the stochastic Thomas-Fiering model, while modification of this model by Wilson-Hilferty transformation of independent random number has been applied. This transformation usually applies in the event of significant asymmetry in the observed time series. The methodological procedure was applied on the data acquired at the gauging station of Horné Orešany in the Parná Stream. Observed mean monthly flows for the period of 1.11.1980 - 31.10.2012 served as the model input information. After extrapolation the model parameters and Wilson-Hilferty transformation parameters the synthetic time series of mean monthly flows were simulated. Those have been compared with the observed hydrological time series using basic statistical characteristics (e. g. mean, standard deviation and skewness) for testing the quality of the model simulation. The synthetic hydrological series of monthly flows were created having the same statistical properties as the time series observed in the past. The compiled model was able to take into account the diversity of extreme hydrological situations in a form of synthetic series of mean monthly flows, while the occurrence of a set of flows was confirmed, which could and may occur in the future. The results of stochastic modelling in the form of synthetic time series of mean monthly flows, which takes into account the seasonal fluctuations of runoff within the year, could be applicable in engineering hydrology (e. g. for optimum use of the existing water management system that is related to reassessment of economic risks of the system).
Article 2 Reads 7 Citations A regional comparative analysis of empirical and theoretical flood peak-volume relationships Ján Szolgay, Ladislav Gaál, Tomáš Bacigál, Silvia Kohnová, K... Published: 01 December 2016
Journal of Hydrology and Hydromechanics, doi: 10.1515/johh-2016-0042
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This paper analyses the bivariate relationship between flood peaks and corresponding flood event volumes modelled by empirical and theoretical copulas in a regional context, with a focus on flood generation processes in general, the regional differentiation of these and the effect of the sample size on reliable discrimination among models. A total of 72 catchments in North-West of Austria are analysed for the period 1976–2007. From the hourly runoff data set, 25 697 flood events were isolated and assigned to one of three flood process types: synoptic floods (including long- and short-rain floods), flash floods or snowmelt floods (both rain-on-snow and snowmelt floods). The first step of the analysis examines whether the empirical peak-volume copulas of different flood process types are regionally statistically distinguishable, separately for each catchment and the role of the sample size on the strength of the statements. The results indicate that the empirical copulas of flash floods tend to be different from those of the synoptic and snowmelt floods. The second step examines how similar are the empirical flood peak-volume copulas between catchments for a given flood type across the region. Empirical copulas of synoptic floods are the least similar between the catchments, however with the decrease of the sample size the difference between the performances of the process types becomes small. The third step examines the goodness-of-fit of different commonly used copula types to the data samples that represent the annual maxima of flood peaks and the respective volumes both regardless of flood generating processes (the traditional engineering approach) and also considering the three process-based classes. Extreme value copulas (Galambos, Gumbel and Hüsler-Reiss) show the best performance both for synoptic and flash floods, while the Frank copula shows the best performance for snowmelt floods. It is concluded that there is merit in treating flood types separately when analysing and estimating flood peak-volume dependence copulas; however, even the enlarged dataset gained by the process-based analysis in this study does not give sufficient information for a reliable model choice for multivariate statistical analysis of flood peaks and volumes.
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