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Environmental Restoration and Changes of Sediment and Hydrodynamic Parameters in a Section of a Renaturalised Lowland Watercourse
In Europe, the routes of most watercourses were straightened and shortened, leading to the destruction and degradation of many natural environments. Currently, in places where it is possible, as part of the implementation of the Water Framework Directive, efforts are made to improve environmental sustainability, including improving the ecological condition of rivers. This paper presents the impact of three in-stream deflectors on changes in the section of a small lowland river—the Flinta (Poland)—where (from 2018 to 2023) detailed, systematic geodetic, and hydrometric research and an assessment of the ecological conditions were carried out. The presented results show the influence of deflectors on the initiation of fluvial processes in the transverse and longitudinal layouts of the channel. The river channel was narrowed from 6 to 5 m, and the current line shifted by almost 3 m. Changes were observed in the distribution of velocities and shear stresses, varying along the surveyed section of the river. In the first year after their application, an increase in velocity at the deflectors can be observed (from 0.2 m∙s−1 to 0.6 m∙s−1 in the deflector cross-section). In the following years, on the other hand, a clear decrease in velocity was observed in the sections between the deflectors (to 0.3 m∙s−1). The introduction of deflectors resulted in a significant increase in the values of shear stresses (from an average value of 0.0241 N∙m−2 in 2018 to 0.2761 N∙m−2 in 2023) and local roughness coefficients (from 0.045 s∙m−1/3 before the introduction of the deflectors to 0.070 s∙m−1/3 in 2023). Based on analyses of sediment samples, erosion and accumulation of bottom material were initially observed, followed by a subsequent stabilisation of particle size. Differences in grain size were observed, especially in the cross-section of the deflectors (increase in granularity d50% downstream of the deflector from 0.31 mm to 3.9 mm already 2 years after the introduction of deflectors). This study confirmed the positive impact of using deflectors on hydromorphological processes as deflectors facilitate the achievement of a good ecological status, as required by the WFD. The innovation of this paper lies in demonstrating the possibility of using small, simple structures to initiate and intensify fluvial processes, which may contribute to improving the ecological conditions of watercourses.
Application of Multi-Criteria Analytic Methods in the Assessment of the Technical Conditions of Small Hydraulic Structures
Increasing water demand, combined with unfavourable climate change, creates a need for well-thought-out water management. Such goals are realised thanks to appropriate hydrotechnical infrastructure, the efficiency and functionality of which depend on its technical condition. In the literature, there is no method for the assessment of the technical condition of small damming structures, including sluice gates. The aim of this article was to present the possibility of using the multi-criteria AHP decision support method to assess the technical condition of small damming structures. The assessment included both concrete elements (spillways, abutments, and apron) and steel elements (gates and hoisting equipment). The analyses considered the effects of growing vegetation, the condition of concrete surfaces (e.g., cracks, cavities, exposed rebar) and steel elements (corrosion, deterioration). A hybrid method was used to study the assessment of the technical condition of water structures. It consisted of a modified Zawadzki’s method and weights which were determined by different groups of respondents with industry backgrounds (university students and experts) using the AHP method. The obtained results show that the factors related to the holes and corrosion of the gate elements had the highest value of the matrix solution vector. The last level of the tree structure indicated that the condition of the spillway and gate is the most important factor in the technical condition assessment. As the assessment considers commonly available parameters, the proposed method is universal and can be used in the assessment of other structures of this type in different regions of the world, which is important in terms of their functioning, planned repairs, and optimal use in water resource management.
The concept for innovative Comprehensive Assessment of Lowland Rivers
Current river assessment methods focus on evaluating a single aspect (e.g. the physical and chemical quality of the water or its hydromorphological state) and usually do not integrate various factors. The lack of an interdisciplinary method makes it difficult to correctly assess the condition of a river as a complex ecosystem significantly influenced by humans. This study aimed to develop a novel Comprehensive Assessment of Lowland Rivers (CALR) method. It is designed to integrate and evaluate all-natural and anthropopressure-related elements that influence a river. The CALR method was developed using the Analytic Hierarchy Process (AHP). The application of the AHP allowed the assessment factors to be determined and given weights to define the importance of each assessment element. As a result of AHP analyses, the following ranks were determined for the six main parts of the CALR method: hydrodynamic assessment (0.212), hydromorphological assessment (0.194), macrophyte assessment (0.192), water quality assessment (0.171), hydrological assessment (0.152) hydrotechnical structures assessment (0.081). In the comprehensive assessment of lowland rivers, each of the six elements listed above is rated on a scale of 1–5 (where 5 means very good and 1 bad) and multiplied by an appropriate weighting. After summing up the obtained results, a final value is obtained, classifying the river. CALR can be successfully applied to all lowland rivers thanks to its relatively simple methodology. The widespread use of the CALR method may facilitate the assessment process and enable the comparison of the condition of lowland rivers worldwide. The research conducted in this article is one of the first attempts to develop a comprehensive method for evaluating rivers that considers all aspects.
Analysis of the Influence of Hydraulic and Hydrological Factors on the Operating Conditions of a Small Hydropower Station on the Example of the Stary Młyn Barrage on the Głomia River in Poland
The operation of water structures causes various problems. They are related, for example, to the material carried by the water, hydrological conditions, range of operation of hydroelectric turbines, or water elevations at the lower position of the hydroelectric power plant. Among the various operational problems, this article focuses mainly on the impact of the backwater of Gwda river on the water level elevations at the lower station of the Stary Młyn hydropower plant in Dobrzyca. The power plant is located on Głomia river. The analysis was carried out for different flow variants in both the Gwda and Głomia rivers. The effect of characteristic flows on the water surface level at the lower station of the hydropower plant was examined. It was found that the water surface level at the lower station of the hydropower plant is strongly influenced by flows higher than the average high flow on Gwda river. Due to the extent of the backwater in current operating conditions, the hydroelectric power plant is shut down from flows on Gwda river of 30–28 m3/s (flows that are not much higher than the multi-year average SSQ). The modeling results were confirmed by an analysis of power plant shutdowns of normal operation especially in wet years, when the plant did not operate for almost half of the year (188 days), with losses of 203 MWh. It was also shown that even a small additional damming of water, e.g., of the order of 0.2 m, can extend the operating time of a power plant up to 249 days even under unfavorable hydrological conditions. Factors related to climate change are beginning to play an increasingly important role in the current operating conditions of small lowland hydroelectric power plants. They can contribute to a reduction in electricity production. The proposed solution related to the possibility of greater water retention on dammed-up water barrages allows one to partially offset these problems as well.
Hydrological Effects of the Planned Power Project and Protection of the Natura 2000 Areas: A Case Study of the Adamów Power Plant.
The planned construction of a steam–gas unit at the Adamów Power Plant raises questions about the potential hydrological impact on the neighboring Natura 2000 protected areas, particularly the Middle Warta Valley (PLB300002) and the Jeziorsko Reservoir (PLB100002). These ecosystems play a key role in protecting bird habitats and biodiversity, and any changes in water management can affect their condition. This paper presents a detailed hydrological analysis of the Warta River and Jeziorsko Reservoir for 2018–2022, with a focus on low-flow periods. The Peak Over Threshold (POT) method and Q70% threshold were used to identify the frequency, length, and seasonality of low-flow periods in three water gauge profiles: Uniejów, Koło, and Sławsk. The longest recorded low-flow episode lasted 167 days. The permissible water intake for the investment (up to 0.8 m3∙s–1) is in accordance with the applicable permits and is used mainly for cooling purposes. Calculations indicate that under maximum intake conditions, the water level reduction in the Jeziorsko Reservoir would be between 1.7 and 2.0 mm∙day–1, depending on the current level of filling. Such changes do not disrupt the natural functions of the reservoir under typical conditions, although during prolonged droughts, they can pose a threat to protected areas. An analysis of the impact of periodic water overflow into the Kiełbaska Duża River indicates its negligible effect on water levels in the reservoir and flows in the Warta River. The results underscore the need for the integrated management of water and power resources, considering the increasing variability in hydrological conditions. Ensuring a balance between industrial needs and environmental protection is key to minimizing the potential impact of investments and implementing sustainable development principles.
Beaver Dams as a Significant Factor in Shaping the Hydromorphological and Hydrological Conditions of Small Lowland Streams
Beavers play a key role in creating temporary water reservoirs that significantly impact the natural environment and local river hydrology. The primary aim of this study was to assess the potential of increasing the number of beaver dams (Castor spp.), as an alternative method of water retention in the environment. Research conducted on three small lowland streams in central Poland revealed that beaver dams, even in modified riverbeds, enable the formation of shallow floodplains and ponds. Innovative analyses considered the structural materials of the dams and their impact on river hydromorphology and sediment transport. The findings emphasise the importance of beavers in water retention processes, the stabilisation of water levels during low flows and the protection of biodiversity. The study also demonstrated that beaver dams play a critical role in storing surface- and groundwater, mitigating drought impacts, reducing surface runoff, and stabilising river flows. These constructions influence local hydrology by increasing soil moisture, extending water retention times, and creating habitats for numerous species. The collected data highlight the potential of beaver dams as a tool in water resource management in the context of climate change. Further research could provide guidance for the sustainable utilisation of beavers in environmental conservation strategies and landscape planning.
Ocena jakościowych i ilościowych zmian mikrobiomu bakteryjnego w procesie beztlenowego rozkładu materii organicznej
Wpływ zbiornika retencyjnego Jeziorsko na układ dna i transport rumowiska na odcinku od zapory czołowej do Uniejowa
Opportunities for the Transformation and Development of Power Plants Under Water Stress Conditions: Example of Adamów Power Plant
In the vicinity of the Adamów power plant, which operates in the catchment area of the Kiełbaska river, there is a significant shortage of water resources caused by the intensive use of water by the energy industry and agriculture. The development of the plant by replacing the outdated coal-fired (lignite-fired) units with modern gas and steam units may contribute significantly to reducing the negative impact on the environment and reduce the demand for water resources relative to coal technology. Gas and steam units are a much more energy-efficient technology. This implies a lower demand for water, a reduction in pollutant emissions, and greater operational flexibility, which enables the units to adapt to changing hydrological and environmental conditions. The high efficiency of these units limits the need for frequent water-refilling, while allowing for a more sustainable and stable production of energy. Based on an analysis of hydrological data for the years 2019–2023, it was estimated that water stress is observed in this catchment area on 198 days per year, which accounts for c.a. 54% of the hydrological year. Therefore, it is assumed that inter-catchment pumping stations with a flow of 0.347 m3∙s−1 will be required. This sets the demand for water at 5.95 million m3 per year. The planned water transfer will be carried out from Jeziorsko reservoir on the Warta river through the catchment area of Teleszyna river. Moreover, there are plans for the reconstruction of the layout of Kiełbaska Duża and Teleszyna rivers, which would involve the restoration of natural run-offs, following the discontinuation of open-pit lignite mining. This will additionally be supported by the reduced demand for water in the water use system when using the modernised power plant. The analysed data made it possible to develop hydrological scenarios that take the future reduction in water stress into account by implementing plans to restore the former hydrographic system in the region. These investments would also foresee the creation of new retention reservoirs (in former mining pits) with a capacity of nearly 900 million m3, which will significantly increase the region’s water resources and retention potential, supporting hydrological and energy security for the years to come.
The Impact of Plant Debris on Hydraulic Conditions in a Semi-Natural Fish Pass
Fish passes are essential hydraulic structures that maintain longitudinal connectivity in regulated rivers, but their hydraulic performance may be affected by debris accumulation at chamber openings. This study investigates the influence of partial and total inlet blockage by plant debris on flow conditions within a semi-natural fish pass under field conditions. Hydraulic measurements were conducted at multiple locations along the fish pass, and the effects of debris covering were evaluated using statistical and mixed-effects modeling approaches. Field measurements demonstrated that the Froude number decreases systematically with increasing distance from the inlet, indicating progressive longitudinal dissipation of flow energy along the chamber sequence. Partial debris accumulation caused only marginal changes in the Froude number, remaining close to the threshold of statistical significance. In contrast, mean flow velocity decreased markedly with increasing inlet blockage, by approximately 17% at 50% covering and by about 36% under full blockage, indicating that debris primarily acts as a hydraulic damper rather than inducing a change in flow regime. The highest variability in hydraulic conditions was observed in chambers associated with changes in flow direction and local geometry. These results highlight the dominant role of longitudinal layout and chamber geometry in shaping hydraulic conditions in semi-natural fish passes, while moderate debris accumulation affects local velocities without fundamentally compromising hydraulic functionality. From an ecological perspective, transition zones with elevated hydraulic variability may represent critical locations influencing the swimming effort and passage efficiency of migrating fish.
Verification of Methods for Determining Flow Resistance Coefficients for Floodplains with Flexible Vegetation
In terms of the hydraulic effect of plant flexibility, of particular note is the calculation formula that was proposed by Kouwen, which combines the roughness of the riverbed with the plant community parameter MEJ (including the modulus of elasticity). Kouwen’s method was developed on the basis of laboratory experiments with low vegetation (grasses). According to the authors of this work, the method can also be used to evaluate the resistance of medium vegetation (shrubs) deforming under the influence of water flow. The main objective of the presented research was to verify the application of Kouwen’s method in order to calculate the flow resistance coefficient λ for quasi-regular formed plant obstructions (e.g., basket willow plantations). In a water laboratory, a comprehensive study of the biomechanical and hydraulic properties was carried out for flexible shrubs in floodplains. The results of the hydraulic measurements were compared with the results of the calculations that were made by four various methods using the Chezy-Manning, Garbrecht/Pasche, Lindner/Kaiser, and Kouwen formulas. For all of the flows through the vegetated zone that was tested, the best results were obtained when using the Kouwen calculation procedure and the worst were found for the Lindner formula, which did not include information on the plant flexibility.
Hydraulic Calculations of a Slotted Separator Using the SSIIM Program
Analysis of the results of the hydraulic calculations of a slotted separator, allowed for changes in the separator design taking into account the reduction of flow turbulence, ensuring the continuity of water flow and sediments as well as optimal location of the slots. The separator is an important element of the installation for hydromechanical removal of sediments from the bottom of a water reservoir. Tests were carried out on the physical and mathematical model. Hydraulic calculations and numerical simulations were carried out using the SSIIM (Simulation of sediment movements in water intakes with multiblock option) program. The program enables three-dimensional analysis of flows and transport of sediments in rivers and canals by solving the Navier-Stokes equation and the turbulent model k-. A number of numerical experiments of the separator work were carried out for various design solutions regarding the geometry of the inlet and outlet channels and their connection with the chambers as well as slots system. The numerical simulations and conducted research on a physical model, allowed to develop an optimal solution.
The Role of Hydropower in Climate-Resilient Energy Systems: Case Study of the Jeziorsko Reservoir (Poland).
Impact of Channel Confluence Geometry on Water Velocity Distributions in Channel Junctions with Inflows at Angles α = 45° and α = 60°
Understanding flow dynamics in open-channel node systems is crucial for designing effective hydraulic engineering solutions and minimizing energy losses. This study investigates how junction geometry—specifically the lateral inflow angle (α = 45° and 60°) and the longitudinal bed slope (I = 0.0011 to 0.0051)—influences the water velocity distribution and hydraulic losses in a rigid-bed Y-shaped open-channel junction. Experiments were performed in a 0.3 m wide and 0.5 m deep rectangular flume, with controlled inflow conditions simulating steady-state discharge scenarios. Flow velocity measurements were obtained using a PEMS 30 electromagnetic velocity probe, which is capable of recording three-dimensional velocity components at a high spatial resolution, and electromagnetic flow meters for discharge control. The results show that a lateral inflow angle of 45° induces stronger flow disturbances and higher local loss coefficients, especially under steeper slope conditions. In contrast, an angle of 60° generates more symmetric velocity fields and reduces energy dissipation at the junction. These findings align with the existing literature and highlight the significance of junction design in hydraulic structures, particularly under high-flow conditions. The experimental data may be used for calibrating one-dimensional hydrodynamic models and optimizing the hydraulic performance of engineered channel outlets, such as those found in hydropower discharge systems or irrigation networks.
The Use of a Multi-Criteria Decision Analysis Method to Select the Most Favourable Type of Fish Pass in Mountainous Areas
Fish passes are a key element enabling the migration of aquatic organisms in the context of restrictions resulting from the presence of weirs. Multi-criteria decision analysis, AHP, and Rembrandt methods were used to assess the effectiveness of fish passes on mountain rivers. Three common types of fish passes were considered: slotted fish pass, block ramps, and a circulation channel with boulders. The results of the study indicated that block ramps proved to be the most favourable solution, achieving the highest preference values in both methods (Rembrandt: 0.77, AHP: 0.63). The key factors influencing the effectiveness of the fish passes are the availability of space and the water requirements, which reached values of 0.38 and 0.27 in the Rembrandt method and 0.33 and 0.28 in the AHP method, respectively. The differences between the results of both methods were minimal and did not have a significant impact on the final choice. The discussion emphasised the advantage of nature-like fish passes, such as block ramps, which better preserve the ecological continuity of rivers and can be more easily adapted to local hydrological conditions. The study also indicated the need for continuous monitoring of the fish passes and their optimisation to reduce problems related to sedimentation and flow blocking. The obtained results can provide a valuable basis for decision making in the planning and construction of fish passes, especially in demanding mountainous conditions, contributing to improving the effectiveness of fish migration and minimising negative impacts on the natural environment.