River regulation often leads to uniform conditions within the river channel, alters sediment dynamics, and contributes to the degradation of aquatic habitats. Deflectors are increasingly used as habitat-forming elements in river restoration projects. However, the interaction between hydraulic conditions, sediment inflow, deflector location, and surface roughness and their effects on the spatial extent of sediment removal remain insufficiently studied. Laboratory experiments were conducted in a flow channel using three geometrically identical deflectors arranged according to the configuration observed in the Flinta River in western Poland. The studies were conducted for the following combinations: three discharges (Q = 0.40, 0.64, and 1.70 dm3 s−1), three water depths (h = 0.03, 0.06, and 0.09 m), three cumulative surrogate-sediment masses (Rum = 0.5, 1.0, and 1.5 kg), three dimensionless longitudinal positions (ξ = 0.21, 0.61, and 1.00), and two deflector roughness specifications—smooth or rough. The two-dimensional extent of the sediment-free zone was quantified based on aerial photographs using the normalized surface index A∗. Dimensionless water depth and dimensionless discharge were the dominant factors χ > Q∗ > R∗ ≫ ξ, and their interaction Q∗×χ constituted the strongest two-way effect, whereas sediment mass had a significant but secondary influence. Surface roughness did not independently affect the mean A∗ value but altered the spatial characteristics: longitudinal position was non-significant for smooth deflectors but became significant for rough deflectors, particularly through interactions between depth and location and between depth, location, and surface. These findings indicate that deflector roughness should not be specified as an isolated design parameter but should be selected jointly with the expected flow-depth regime and the longitudinal placement of successive structures. In practical terms, the results can support the preliminary design and positioning of habitat-forming deflectors intended to create or maintain spatially differentiated sediment-cleared zones in regulated channels, thereby contributing to more evidence-based and sustainable river restoration.

Beaver dams can substantially modify flow conditions and increase local water retention, particularly in small urban and peri-urban streams exposed to hydrological alterations and increasing water deficits. This study evaluates the influence of beaver dams on hydraulic conditions, retention capacity, and water resources in the Junikowski Stream in Poznań, Poland. Field surveys, geodetic measurements, and spatial data were used to develop a one-dimensional hydraulic model in HEC-RAS. Three management scenarios were analysed: a channel without impoundment structures, the 2022 configuration including beaver dams and two artificial weirs, and the 2025 configuration representing a more developed beaver-dam cascade together with the functioning weirs. Simulations were conducted for a range of characteristic and probability flows to assess changes in water levels, inundation extent, and retained water volume. The results show that beaver dams exert the strongest effect under low-flow conditions, when they significantly increase water levels and improve local retention. Their hydraulic influence decreases with increasing discharge, although they continue to affect the spatial distribution of water in the valley. The proposed artificial structure may partly maintain retention benefits in the event of beaver dam degradation or removal. The findings demonstrate that beaver dams may function as effective nature-based solutions supporting water retention and potentially contributing to drought resilience and sustainable management of urban stream valleys.

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.

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.

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.

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.

River channel deflectors are environmentally friendly low head hydraulic structures constructed from wood, stones and coarse gravel Their aim is to protect river banks against erosion, to change the direction of river flow making the river course naturally meandrous instead of artificially straight, to provide natural refugia for fish and invertebrates and finally to improve hydraulic discharge conditions. However, from the designing point of view they are difficult to represent in hydrodynamic models since they are constructed and fixed in the river bed differently. For this reason, in hydraulic models’ deflectors may be treated as modifications to the value of the watercourse bed roughness or reduction in the active part of the cross-section. Thus, to test the suitability of one-dimensional models for river restoration involving river deflectors, a 1-D numerical model of the lower section of the Flinta river (Wielkopolska Province, Poland) was prepared. To do that, firstly three channel flow deflectors were constructed and installed in the lower section of the Flinta river. Secondly, hydrometric measurements were continued systematically over three years. Next, based on field studies and field data, calculations were made using the HEC-RAS 1-D software. Several variants of the shape and the effect of deflectors were tested. On this basis, the variability of the roughness coefficient value for the Flinta riverbed after the implementation of deflectors was analyzed. The novelty of the research is that the obtained results show that river channel deflectors have a significant influence on the processes of morphological changes (such as: velocity distribution, grain size changes, tendency towards channel meandering, channel slope) of the riverbed and thus also on changes in hydromorphological parameters of river flow. The presented case study confirmed the potential for effective deflector operation for the velocity range of 0.10 – 0.30 m·s−1. The maximum changes of the river bed elevation after the deflectors had been introduced reached 0.10 m. It was also found that the effect of deflectors on roughness at high water levels was non-significant and did not increase the risk of flooding. For Q1% flow, the implementation of flow deflectors had no significant effect on the capacity of the studied river section. Only slight subduction of 0.02 – 0.03 m of the water surface in the vicinity of the deflectors could be observed compared to the model from before the restoration activities. The greatest impact of the channel deflectors is seen at low water levels and low flows that do not exceed average flow values. Finally, it was shown that the best solution to implement deflectors into a one-dimensional model is to consider their influence as a change in the value of Manning's coefficient. The obtained results can be considered universal in relation to typical transformed small lowland watercourses that have been straightened and regulated and are to be subjectedto the process of river restoration.

Highly modified riverbeds are not able to spontaneously reproduce natural processes. The restoration of natural river systems is an important challenge to modern river engineering. Various procedures and solutions, both technical and non-technical, are applied in this process. This involves looking for simple solutions that are close to nature and that interfere with river ecosystems to a minimal extent. One of these solutions is deflectors, which constitute a type of simplified spur. This study presents the results of the research on the transformations of hydromorphology and macrophytes on selected sections of the Flinta River, which represents the most common type of river in the Central European Lowlands (a small river with a sandy substrate). Two neighbouring sections of the watercourse were selected. The first one has not been subject to any regulatory measures for over 30 years and is undergoing spontaneous restoration, while the second one was significantly altered (straightened, cleared of hydrophytes, and desilted) ten years ago. Three deflectors were introduced in this section in the years 2017–2018. Research conducted on both sections enabled the determination of the possibility of initiating renaturalisation processes by way of implementing simple solutions in the form of low-cost wooden deflectors. It also provided the basis for the assessment of the impact the measures taken had on the hydromorphological status of the watercourse and on macrophytes. Based on the studies conducted, it was possible to determine the size, dynamic, and scope of the changes taking place in the river under various conditions of its transformation, including those resulting from anthropopressure.

The main problem presented in this paper is the safety inlet navigation of the waterway below the bridge in the city of Kaunas in Lithuania. The analyzed reach is located in the Nemunas river downstream of the Kaunas dam. It is a part of the waterway E–41 leading to the Klaipeda harbor on the southern coast of the Baltic Sea. The work was initiated by the Lithuanian company UAB “Inžinerinis projektavimas” with funds from the project called European Union Trans-European Transport Network (EU TEN-T). The main requirement imposed along this reach is to keep sufficient depth even in the range of the lowest flows. The depth is sufficient if it is not lower than 1.15 m for minimum flows such as Q95% and Q95% with ice. The hydraulic conditions for maximum flow Q50%, Q5%, and Q1% are also taken into account for control because the threat of hydraulic jump generation was also noticed. The research is based on georeferenced data from public and non-public sources. The hydrologic data were received from the Lithuanian Hydrometeorological Service. The physical model was created in the Water Laboratory of the Department of Hydraulic and Sanitary Engineering at Poznan University of Life Sciences, Poland. The preprocessing of spatial data in ArcGIS 10.8.2 and rules of hydraulic similarity were implemented in the process of physical model preparation. Three experiments were conducted in the laboratory with scaled values of Q95%, Q5%, and Q1%. The measurements of the water surface and evaluations of the average velocity were used to validate the 2D numerical model prepared in HEC-RAS 6.3.1. The basic layers of the HEC-RAS model were preprocessed in ArcGIS 10.8.2 by ESRI company. The numerical model was implemented to test different values of unknown roughness of the channel bottom. The simulations were conducted for the real values of Q95% and Q95% with ice and Q50%. The results of the simulations were depth and Froude number maps. These maps were classified into zones of no risk, middle risk, and high risk. ArcGIS in the post-processing phase was applied to identify the locations of the hazards. The magnitude of risk was expressed in terms of minimum depth achieved, maximum Froude number, as well as the length of the reaches with high risk related to these two factors. The threat of hydraulic jump formation below the bridge was also noticed. Conducted results confirmed that the combination of hydrodynamic simulations and geoprocessing in the pre- and post-processing stages could be a powerful tool in hydraulic engineering analyses. Additionally, it is worth noting that numerical modeling enables a wider analysis of potential conditions than could be possible with a physical model only.

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 key challenge for sustainable water management is to carry out a proper assessment of the technical condition of hydrotechnical constructions. Maintaining them in a good state is a prerequisite for ensuring the safety of objects, as well as adjacent areas. This paper compares the results of field research obtained by three methods to assess the technical condition of structures located on the Wełna River. The main objective is to determine the differences between the methods and to indicate the most important assessment elements and criteria. Moreover, it was checked if the Analytic Hierarchy Process (AHP) can be used to carry out the correct assessment of hydrotechnical construction. An assessment that will be based on the hierarchy of factors, which is not often used in other methods. The AHP was applied for the first time to assess the technical condition of hydrotechnical constructions. Based on AHP, three variants of different weights for factors, including exploitation problems and damage to construction elements, were selected. The new variants developed by the authors allow for a more accurate, multifactor assessment. The use of scales to determine the importance of individual elements contributes to the actual representation of the technical condition of the object, which is often over- or underestimated by other assessment methods. The analysis shows that the AHP method is a useful tool to support the assessment of the technical condition of hydrotechnical construction. The use of AHP as a universal assessment method will compare the technical condition of hydrotechnical constructions located all over the world.

The ecological water quality in rivers and streams is influenced both by the morphological factors (within the watercourse channel and by the dynamic factors associated with flow), as well as biological factors (connected with the flora and fauna characteristic of its specific area). This paper presents an analysis of the effect of river channel shading by trees and shrubs on hydromorphological changes in a selected reach of the Wełna River, Poland. The analysis was conducted on two adjacent cross-sections (one in a reach lined with trees, the other in an open area with no tree or shrub vegetation). Data were collected during field surveys in the years 2014 and 2019. According to the Water Framework Directive, the Wełna River represents a watercourse with small and average-sized watershed areas, with sand being the dominant substrate of the river bottom. Flow volume, distributions of velocity in the sections, as well as substrate grain-size characteristics and river bottom morphology, were determined based on field measurements. In the study, the leaf area index (LAI) of vegetation was measured in the reach lined with trees, while the number and species composition of macrophytes were determined in the investigated river reaches. Moreover, a digital surface model (DSM) and Geoinformation Information System GIS tools were used to illustrate variability in shading within the tree-lined reach. The DSM model was based on Light Detection and Ranging (LIDAR) data. The results of this study enable us to establish the relationship between river shading by vegetation covering the bank zone, and changes in hydromorphological parameters of the river channel.

The paper presents the methodology and results of research conducted on the physical model in the stretch of the Neman [Polish: Niemen] River at Kaunas. The study comprised an assessment of hydraulic conditions in the river bed in the bridge profile at 214+200 km. Additionally analyses were conducted for two river bed reconstruction variants. The aim of the planned reconstruction is to adapt the Neman river bed to the parameters required for the E41 International Waterway. These studies were commissioned by a Lithuanian design office in view of the planned reconstruction and modernisation of the river fragment in accordance with the provisions of the AGN agreement concerning the network of international waterways. The river stretch in Kaunas is of key importance, as it holds a large river port, while bridge profiles are the bottlenecks due to the insufficient minimum waterway depth for safe navigation. The experimental part of the study consisted in the construction of a physical model for a 1100m river stretch including two bridge profiles (a road bridge and a railway bridge) at 214+200 km (fig. 1). The model in the 1:50/200 scale was constructed at the water laboratory of the Department of Hydraulic and Sanitary Engineering, the Poznan University of Life Sciences. The initial step was to construct a box, in which the model was made. Model geometry was recreated using the profiles/cross-sections made based on a numerical model of the area. The distance between the profiles was 50 cm. The model was supplemented with bridge piers and the existing river regulation structures (groynes and longitudinal training dams). The total dimensions of the model were 10 x 3.5 m, of which the modelled river stretch accounted for 5.5 m. Fig. 1. Physical model with the bridges and elements of the river regulation Measurements were taken for 3 variants including the current status and two reconstruction variants (dredging and development of regulation structures). Each variant was scanned in the 3D technology. The aim was to facilitate further verification of model representation accuracy with results obtained from numerical models. Hydraulic analyses were performed for four selected discharge values Q95%=1.01 dm3/s, Q50%=15.03 dm3/s, Q5%=30.31 dm3/s and Q1%=43.54 dm3/s, corresponding to actual discharges of Q95%=71.6 m3/s, Q50%=1212 m3/s, Q5%=2143 m3/s and Q1%=3079 m3/s, respectively. In order to determine conditions in the river bed for each variant in selected constant measurement profiles the distributions of water flow velocity was measured using an ADV probe. Water table gradients were measured using hydrometric gauge pins, while discharge was recorded with the use of an electromagnetic flow meter. The results were analysed with the application of e.g. the Surfer software, which was used to determine velocity distribution in the profiles above and below the bridge piers. These distributions show a considerable effect of bridge piers on velocity values and the concentration of discharges between the bridge piers (fig. 2). A similar effect on river conditions was found for the hydraulic structures strongly concentrating and directing the current within the established waterway(fig. 3). In order to provide spatial visualisation of velocity distributions tests were also conducted using a pigment. The recorded image of the pigment distribution constituted additional material facilitating qualitative evaluation of the tested variants. Fig. 2. Spatial distribution of velocities Fig. 3. Magnitudes of the flow velocities in bridge cross section The aim of the measurements was to investigate distributions of velocity and filling for all the analysed reconstruction and discharge variants. On this basis the accuracy of planned investments was verified and a slightly different location and parameters of the river regulation structures were proposed. These included two elements, i.e. the construction of groynes and training dams, and dredging of the river bed in locations identified as the shallowest. Analyses confirmed the applicability of physical modelling techniques for complex hydraulic systems and their results, next to the results of hydrodynamic modelling, may constitute a source of data for the verification of adopted design assumptions.

An analysis of the possibility of reconstruction and modernization of the Welna river water way system in Nowy Mlyn is presented in the paper. The system includes two weirs, channels of the river Welna and mlynowka and planned small hydroelectric power. Based on modeling results received from the HEC-RAS program, the most important factors affecting the work of the water way system for its current operating conditions and the planned redevelopment have been identified. In the assumptions of the planned reconstruction important role is played by the aspect of active tourism on the discussed section of the Welna river. The conditions for the operating of the water way system were also determined taking into account the need to preserve the integrity of the river ecosystem including fish migration. The possibilities and limitations of the planned investment are outlined.

W pracy przedstawiono analizę możliwości przebudowy oraz modernizacji węzła wodnego Nowy Młyn na rzece Wełnie. W skład w/w budowli wchodzą dwa jazy oraz układ koryt rzeki Wełny i młynówki wraz z planowaną małą elektrownią wodną. W oparciu o wyniki modelowania w programie HEC-RAS ustalono najważniejsze czynniki wpływające na pracę węzła dla aktualnych warunków jego funkcjonowania oraz w perspektywie planowanej przebudowy. W założeniach planowanej przebudowy istotną rolę odgrywa aspekt aktywnego ruchu turystycznego na badanym odcinku rzeki. Warunki funkcjonowania węzła wodnego zostały ustalane również z uwzględnieniem konieczności zachowania ciągłości ekosystemu rzeki w tym migracji ryb. Przedstawiono możliwości oraz ograniczenia związane z planowaną inwestycją.