The aim of this study is to analyze the toxicity of the sediments accumulated in the vicinity of hydropower plants (HPs) on the Ślęza and Bystrzyca rivers in Poland and the possibility of using these sediments for soil enrichment purposes. Thus far, there has been little comprehensive research related to the analysis of the impact of HPs on the properties of sediments. The analysis of the granulometric composition, physicochemical properties, heavy metals (HMs) content in sediments, and the growth of three plant species was carried out, including toxicity (HMs) and germination indices (plants). Most parameters were significant between the points upstream and downstream of the analyzed HPs. It has been shown that the most dangerous toxic factor is the high concentrations of Cu, Ni, and Zn in the sediments upstream of the HP on the Ślęza. In most cases, the HMs content was observed to decrease downstream of the HPs (e.g., Cu in Ślęza River: average of 13.44‐times), a result of changes in the particle size composition and accumulation of sediments at the site of the dam wall. Typically, the sediments tested stimulated growth in the plant species studied in comparison with the control groups (e.g., germination index for Sorghum saccharatum, Bystrzyca: 273.5% downstream of HPs). The C:N ratio increased downstream of the HPs by an average of 37.11% for the Ślęza River and 10.88% for the Bystrzyca River. The requirements for composting material were not met; however, the sediment could be used to enrich soils with an excessively wide C:N ratio.

Hydropower plants affect the distribution and composition of sediments. The main aim of this study was to analyze the spatial distribution of sediment pollution in the vicinity of a small hydropower plant. The grain composition of the sediments, the content of heavy metals (Cu, Ni, Cr, Zn, Pb, and Cd) and select physicochemical properties (pH, electrolytic conductivity) were tested at 14 points upstream and downstream of the hydropower plant on the Ślęza River in Poland, as well as at reference point. The interactions between the tested parameters were also verified. The results of the conducted analysis show that hydropower plants significantly affect the composition and properties of sediments. Large amounts of sediment are deposited on damming weirs, accumulating heavy metals and other substances. The differences in the concentrations of elements were significant, and Cu, Ni, Cr, Zn and Pb were 8.74, 9.53, 3.63, 8.26 and 6.33 times higher, respectively, than the median value at points upstream of the hydropower plant than downstream. It was shown that the tested parameters of the sediments interact with each other and are correlated; heavy metals showed a synergistic effect, while other parameters configurations showed an antagonistic effect. The higher content of heavy metals upstream of the hydropower plant resulted from the presence of finer sediment—classified as silt—in this section. Downstream of the hydropower plant, there were mainly sands, which showed a lower ability to absorb substances. This work contributes to improving the rational management of the worldwide issue of sediments within dams located in river valleys. Moreover, it is in line with the 2030 Sustainable Development Goals adopted by the United Nations, particularly in the fields of clean water and sanitation, clean and available energy, and responsible consumption and production.

Assessing the changing parameters of water quality at different points in the river–reservoir system can help prevent river pollution and implement remedial policies. It is also crucial in modeling water resources. Multivariate statistical analysis is useful for the analysis of changes in surface water quality. It helps to identify indicators that may be responsible for the eutrophication process of a reservoir. Additionally, the analysis of the water quality profile and the water quality index (WQI) is useful in assessing water pollution. These tools can support and verify the results of a multivariate statistical analysis. In this study, changes in water quality parameters of the Turawa reservoir (TR), and the Mała Panew river at the point below the Turawa reservoir (bTR) and above the Turawa reservoir (aTR), were analyzed. The analyzed period was from 2019 to 2020 (360 samples were analyzed). It was found that TN, NO₂-N, and NO₃-N decreased after passing through the Turawa reservoir. Nevertheless, principal component analysis (PCA) and redundancy analysis (RDA) showed that NO₂-N and NO₃-N contribute to the observed variability of the water quality in the river-reservoir system. PCA showed that pH and PO₄-P had a lower impact on the water quality in the reservoir than nitrogen compounds. Additionally, RDA proved that the values of the NO₃-N and NO₂-N indicators obtained the highest values at the aTR point, PO₄-P at the bTR, and pH at the TR. This allows the conclusion that the Turawa reservoir reduced the concentration of NO₂-N and NO₃-N in comparison with the concentration of these compounds flowing into the reservoir. PCA and RDA showed that both parameters (NO₂-N and NO₃-N) may be responsible for the eutrophication process of the Turawa reservoir. The analysis of short-term changes in water quality data may reveal additional sources of water pollution. High temperatures and alkaline reaction may cause the release of nitrogen and phosphorus compounds from sediments, which indicates an increased concentration of TP, PO4-P, and N_org in the waters at the TR point, and TP, PO₄-P, and NH₄-N concentrations at the bTR point. The water quality profile combined with PCA and RDA allows more effective monitoring for the needs of water management in the reservoir catchment area. The analyzed WQI for water below the reservoir (bTR) was lower than that of the reservoir water (TR), which indicates an improvement in water after passing through the reservoir.

Flood Frequency Analysis (FFA) and the non-stationary FFA approaches are used in flood study, water resource planning, and the design of hydraulic structures. However, there is still a need to develop these methods and to find new procedures that can be used in estimating simple distributions in controlled catchments. The aim of the study is a comparison of three-parameter distributions in controlled catchments for stationary and non-stationary data series and further to develop the procedure of the estimation the simple distributions. Ten rivers from the Czech Republic and Poland were selected because of their existing or planned reservoirs as well as for flood protection reasons. The annual maximum method and the three-parameter Weibull, Log-Normal, Generalized extreme value, and Pearson Type III distributions were used in this study. The analyzed time series are stationary and non-stationary. The methodology used in this study, which makes use of the Maximum Likelihood Estimation, allows one to simplify the analysis whenever there is a series of data that is both stationary and non-stationary. The novelty in our research is the standardization and development of a new procedure for a stationary and non-stationary data series, taking into account to read a specific value of the maximum flow with a given exceedance probability from the lower or upper tail. It determines the optimal choice of the theoretical distribution that can be used, for example in the design of weirs in rural areas (lower quantiles) or in the design of hydrotechnical structures in areas at risk of flooding (upper quantiles).

Climate change and extreme weather events have the potential to increase the occurrences of flooding and hydrological droughts. Dam reservoir operation can mitigate or aggravate this impact. This study aims to evaluate the influence of the planned Kamieniec Ząbkowicki dam reservoir on the flow patterns of the Nysa Kłodzka river in the context of changing hydrological conditions and climate change. In the study, a 40-year observational series of hydrological data was used to simulate changes in water flow through the river valley in a numerical model. This simulation was conducted both for the natural river valley and for the same river valley but with the added reservoir dam. Flow simulations revealed that dam operation increased downstream flow values, reducing variability in extreme high-flow events. Addition, the mixture log-normal distribution shows that the operation of the dam resulted in a reduction in the variability of both low flows and extreme high-flow events. Furthermore, the model illustrates that moderate-flow conditions remain relatively stable and similar before and after dam construction. The Mann–Kendall trend test, Sen slope trend test and Innovative Trend Analysis indicated that the dam had a significant impact on flow trends, reducing the negative trend. This hydrotechnical structure stabilizes and regulates flows, especially in response to climate-induced changes. These findings highlight the effectiveness of the dam in mitigating flood risk and supporting water resource management. It is essential to consider the role of the dam in adapting to changing hydrological conditions influenced by climate change. For practical application, efficient flow regulation by reservoir administration is crucial.

The key goal of the Water Framework Directive is to achieve a good ecological status in water bodies. The ecological status is mainly determined by the biological elements, which are a very good indicator of the changes taking place in water environments. Thus, this article focuses on the analysis of different methods of assessment of the ecological status of water bodies based on macrophytes used in selected countries in the European Union (the Macrophyte Index for Rivers (MMOR)—Poland; the Mean Trophic Rank (MTR)—Ireland; the Trophic Index of Macrophytes (TIM)—Bavaria, Germany; the Bulgarian Reference Index of Macrophytes (RI-BG)—Bulgaria). Three research sections have been selected for research on the river Ślęza: The reference section, the section above the barrage and the section below the barrage. The analysis carried out revealed considerable similarity between the results obtained by all these methods—the differences were at most by one class of ecological status (and the analysis of sums of Wilcoxon’s ranks revealed that there were no differences between the results obtained using different methods, i.e., p = 0.860). With respect to surface waters, investigation of biological elements is important because it allows one to retrace the past and foresee the future based on the past and present trends in the changes occurring in the species diversity and structure of not only macrophytes, but also other groups of organisms. Further action is required that would determine the scope of influence of barrages with hydroelectric buildings on the environment (in the case of the investigated barrage this influence is negative).