Biodiversity preservation is a primary challenge of the 21st century, focusing on restoring unobstructed river flows and mitigating the effects of barriers, supported by European biodiversity strategies up to 2030. Maintaining ecological continuity, such as unblocking fishways clogged by floating debris disrupting natural fish migration paths, remains a challenge despite conventional protective methods. This study, taking a vertical slot fish pass in Wrocław on the Odra River as a case study and based on research on bridge piers, suggests modifying pier shapes from rectangular to rounded in order to reduce debris accumulation. Field studies, utilizing an OTT MF Pro flow meter, were conducted to validate the numerical model. The measured flow rate in the field was 3.15 [m³·s⁻¹], while the numerical modeling yielded a flow of 3.19 [m³·s⁻¹]. Focusing on optimizing the shape of cross-wall piers to enhance fish migration conditions, the study examined six different pier configurations, analyzing flow speed in the main slot, crucial for migration. Using 2D hydraulic modeling with Iber, it assessed the migratory potential of different pier designs by analyzing hydraulic conditions and comparing them with the swimming capabilities of fish species native to the Odra River. Results indicate that rounding the pier edges positively affects flow speeds in the main slot, enhancing fish migration possibilities, contributing to fish pass functionality improvement and supporting broader biodiversity and ecosystem health goals.

The application of UAV to acquire data on the morphometry of frazil ice floe in motion is demonstrated in the measurements conducted in the area of the Wrocław Water Junction at the Opatowice weir on the Odra River (Poland). Image processing was performed using open-source software dedicated to image analysis. The methodology presented in the publication offers a cost-effective and low-overhead technique for describing ice phenomena in lowland rivers. The focus of the methodology was on measuring the area, average size, perimeter, and circularity of frazil ice floe. The measurements were carried out for individual frames captured by a UAV, and the results were analyzed using statistical techniques. In prior research, the team effectively assessed ice velocity on an identical test sample. Deriving the average velocity, surface area, and fundamental morphological traits of frazil ice facilitates the automated segmentation, classification, and prediction of potential risks related to ice blockages on water routes. These risks encompass potential waterway obstructions, as well as infrastructure impairments, and may pose a danger to human safety.

Floating debris (FD), encompassing both woody and anthropogenic materials, disrupts fishway hydraulics and ecological efficiency. Despite frequent usage in scientific literature, the term remains ambiguous. Motivated by the need to enhance fishway performance, this study examines the concept of FD. A substantial review of environmental, economic, and safety impacts was conducted, focusing on marine debris, microplastics, and woody debris. Additionally, a systematic analysis of 560 articles published from 2018 to 2023 assessed how FD is described across diverse contexts. Through an elimination process, 55 papers underwent detailed manual analysis. FD was categorized into natural floating debris (NFD) and anthropogenic floating debris (AFD), a distinction crucial for engineering and scientific applications. This classification supports fishway management by facilitating the identification and monitoring of debris accumulation, thus enabling strategies to mitigate hydraulic and ecological consequences. While FD poses risks such as habitat disruption and pollutant bioaccumulation, natural FD also provides potential ecological benefits, including habitat creation. To address these challenges, the study advocates innovative waste management strategies informed by concepts like the doughnut economy and ecological economics. These approaches aim to reconcile ecological sustainability with economic activities, reducing anthropogenic FD while leveraging the advantages of NFD.

The transport and accumulation of woody debris in watercourses play a significant role in shaping river morphology and supporting ecosystem functioning. However, these processes can also pose a threat to hydraulic infrastructure. Accumulation is particularly problematic in fish passes, where it reduces hydraulic capacity and impedes the migration of aquatic organisms. This study experimentally investigated how the shape of fish pass baffles influences debris retention and how log length affects blockage susceptibility. Two configurations were tested: one with rectangular baffles and another with rounded ones. The results showed that log length had a statistically significant effect on the accumulation rate (Effective Accumulation, EA), with larger logs more likely to be retained in both configurations. The highest EA was observed for large logs in the rectangular variant (EA = 0.51), followed by the rounded variant (EA = 0.33). Small logs exhibited minimal accumulation (EA ≈ 0.04–0.05), and no significant differences between shapes were found in this class. Although the total EA was higher for the rectangular configuration (EA = 0.24) than for the rounded one (EA = 0.16), this difference was not statistically significant, highlighting the need for more detailed spatial and size-based analyses. The jamming effect was also observed, where newly introduced logs accumulated on previously retained ones, reinforcing the blockage over time. These findings suggest that both baffle geometry and log size are critical factors influencing debris retention in fish passes and should be carefully considered in their design to balance ecological and hydraulic functions.