Andrej Šoltész

Reservoir storage capacity is a fundamental parameter for sustainable water infrastructure. Over time, progressive sedimentation reduces usable storage, intensified by climate-driven flow variations and limited flushing. This study evaluates sediment dynamics and management strategies for the shallow lowland Sĺňava Reservoir on the Váh River, Slovakia. The methodology integrates: (i) field sampling and optical granulometry to determine bed material grain-size distribution; (ii) 1D analytical formulations to establish threshold discharge for incipient sediment motion; and (iii) 2D morphodynamic modeling in HEC-RAS 2D to simulate spatial erosion and deposition patterns. Investigated scenarios included baseline natural evolution, maintenance dredging, proposed engineered sedimentation pits, and bank groins under operational flow series and extreme floods (Q₁₀₀). Results demonstrate that backwater delta aggradation is concentrated in the narrow upstream inlet reach between critical bridge profiles. Implementing targeted sedimentation pits combined with localized maintenance dredging proved to be the most effective strategy, trapping coarse bedload while mitigating scour near bridge piers. Conversely, groins provide localized flow redirection but complicate mechanical sediment removal. These findings highlight the necessity of shifting from reactive dredging to proactive morphodynamic management in regulated lowland reservoirs.

Reservoir storage capacity is a fundamental parameter for design and operation. Over time, sedimentation—driven by factors such as geology, hydrology, and flow velocities—reduces usable volume, often significantly. In the context of climate change, opportunities for natural sediment flushing have become increasingly rare, while extensive dredging is often economically unsustainable. Moreover, sedimentation is closely linked to erosion processes that may endanger bank stability or compromise bridge piers. This study presents a case analysis of the Sĺňava Reservoir on the Váh River in Slovakia, a typical shallow, lowland reservoir within the Váh Cascade hydropower system. In recent years, sediment-related issues have intensified due to declining flow rates and limited options for reusing excavated material. To address these challenges, several mitigation measures were proposed, including riverbed dredging, groins, and sedimentation pits. These measures were evaluated using a two-dimensional numerical model developed in HEC-RAS (Hydrologic Engineering Center's River Analysis System) to simulate sediment transport and morphological changes. The results indicate that the most effective approach combines targeted dredging with the implementation of sedimentation pits. Additionally, the findings highlight the importance of monitoring erosion processes near bridge piers to ensure long-term structural stability.

High-resolution topographic data are crucial for accurately modeling hydraulic structures, particularly fish passes, where subtle geomorphic features govern flow heterogeneity and fish navigation. Conventional remote sensing approaches often lack the spatial resolution to resolve such microrelief. This study demonstrates the application of unmanned aerial vehicle (UAV) photogrammetry using Structure-from-Motion (SfM), which generates dense point clouds and digital elevation models (DEMs) with sub-centimeter accuracy. The UAV-SfM workflow enables rapid, non-invasive acquisition under controlled field conditions, followed by point-cloud processing in CloudCompare and rasterization into hydraulically suitable elevation models. These datasets support high-fidelity numerical modeling in 1D, 2D, and 3D, as well as the creation of physical models via 3D printing for laboratory hydraulic experiments. The study highlights the advantages of UAV-SfM in capturing complex terrain, estimating grain characteristics, and improving hydraulic model reliability, while also noting limitations such as restricted visibility areas and computational demands of large point-cloud datasets. By integrating high-resolution UAV-based topographic data, new opportunities for routine, high-detail hydraulic modeling and environmental engineering practice are opened.

During heavy rainfalls, overflowing sewage water flows from the Combined Sewer Overflow (CSO) chambers and pollutes the Trnávka River in Trnava, Slovakia. This paper aims to propose water retention measures for the Trnávka River as a remediation technique for CSO-affected watercourses, which can contribute to the ‘flushing’ of the riverbed. During heavy rainfalls, the Trnávka River is polluted by solid, non-soluble materials, which produce unpleasant odors and are the subject of numerous complaints by citizens, particularly during low water levels. Three inflatable rubber weirs were designed, and their design was verified using a 1D numerical model of the Trnávka River. The simulations of the proposed measures performed in the HEC-RAS 5.0 software excluded the adverse effect of the backwater on the functioning of the CSO chambers in the city of Trnava during normal flow rates and confirmed that, even after installation of the weirs, the transition of the flood wave will pass in the riverbed, not causing the flooding of the adjacent area. The chemical–physical study of the Trnávka River confirmed our assumption that higher flow rates, which can be secured by the regulation of the proposed weirs, can contribute to the purity of the watercourse in the city of Trnava.

This study aims to develop an advanced deep learning model, Hydro-Informer, for accurate water level and flood predictions, emphasizing extreme event forecasting. Utilizing a comprehensive dataset from the Slovak Hydrometeorological Institute SHMI (2008–2020), which includes precipitation, water level, and discharge data, the model was trained using a ladder technique with a custom loss function to enhance focus on extreme values. The architecture integrates Recurrent and Convolutional Neural Networks (RNN, CNN), and Multi-Head Attention layers. Hydro-Informer achieved significant performance, with a Coefficient of Determination (R²) of 0.88, effectively predicting extreme water levels 12 h in advance in a river environment free from human regulation and structures. The model’s strong performance in identifying extreme events highlights its potential for enhancing flood management and disaster preparedness. By integrating with diverse data sources, the model can be used to develop a well-functioning warning system to mitigate flood impacts. This work proposes a novel architecture suitable for locations without water regulation structures.

The Bratislava region in Slovakia aims to improve its transport infrastructure by connecting the airport with the railway network. As part of the Trans-European Network for Transport project (TEN-T), an underground railway line is proposed to be constructed on both sides of the Danube River, connecting the airport in Bratislava to the Petržalka region on the river’s right side. However, underground construction is likely to have an impact on the groundwater flow regime. This construction, which will be built below the ground surface, should be built by excavating from above under the protection of sealing walls to prevent significant changes to the groundwater level regime (GWL). Therefore, a numerical model based on the finite element method (FEM) was established to evaluate the effect of the planned underground construction on the GWL, and technical measures were introduced to mitigate any potential impacts. The results of the model revealed possibilities for controlling the groundwater level in the aquifer affected by the railway structure during and after the construction.

The paper deals with results of continuing research activities of the Department of Hydraulic Engineering, Faculty of Civil Engineering, STU in Bratislava in the field of revitalisation of water bodies (old river branches) in the Medzibodrožie region which belongs to the southern part of the East Slovak Lowland. This problem was solved in the past in frame of INTERREG IIIA Initiative between the Hungary and Slovak Republic. The problem remained, just new aspects for solving the water supply were analysed in the presented paper. The first aspect is to supply old river branches due to gravity using outlet structures on pumping stations Boľ and Pavlovo on the Bodrog and Latorica Rivers. This solution is closely connected with high surface water levels in rivers, especially during floods. The second possibility – to our opinion more appropriate – is the revitalisation of river branch system by realisation of the rubber weir on the Latorica River and flooding of existing drainage channel system through outlet structures in the left-hand protection dyke of the Latorica River. The fundamental difference between mentioned methods of revitalisation of water bodies is that the second possibility can be utilized almost all over the year not depending on the flow rate in the Latorica River. Numerical modelling analysis of such a solution has quantified the amount of water supply into the river branch system, its water level regime at different discharges in the Latorica River during the year with respect to interaction with groundwater flow in the surrounding region. The analysis was connected with detailed hydrological, morphological and hydropedological survey.

The paper deals with an analysis of a drought in the small basin of the Gidra River in Slovakia due to problems with the abstraction of water from small reservoirs and ponds. A detailed hydrological assessment of the M-daily discharges for a long-term period was based on a dataset from the only gauging station on the upper part of the river. Because of the existing water structures with prescribed operations during the year, hydrometric and geodetic measurements were taken by the authors. The solution to this problem represents the conditions for the minimum required Q₃₅₅ discharge in the river anytime and anywhere. This can only be solved with a master operational manual for the whole river to be able to flexibly react to the current hydrological situation.