Relationship between Upstream Swimming Behaviors of Juvenile Grass Carp and Characteristic Hydraulic Conditions of a Vertical Slot Fishway

Enhancing migratory potential in fish passes: The role of pier shape in minimizing debris accumulation

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.

Identifying three-dimensional swimming corridors for fish to match their swimming characteristics under different hydropower plant operations: Optimization of entrance location for fish-passing facilities

Fish that require migration are often diverse in the dam-built river, and some of them are benthic. For fish to pass efficiently across the dams, it is necessary to identify the swimming corridors and possible cluster areas of the target fish. However, previous studies have only predicted the two-dimensional swimming corridors of a single species. In this study, the relationships between the swimming behaviours of different species of fish and the three-dimensional (3D) hydrodynamic field were determined, and a model of the 3D swimming corridors corresponding to the fish swimming characteristics was constructed. The model was verified by a fish acoustic telemetry experiment. By simulating the river 3D hydrodynamic field in different scenarios, the possible swimming corridors and clustering areas of the target fish were further evaluated. We showed that the swimming corridors of the target fish were different among different scenarios, and the swimming corridors were mainly concentrated on both sides of the mainstream. With increased flow due to power station operation, the proportion of potential swimming corridors of target fish throughout the basin gradually decreased, and the proportion of velocity barrier zones of target fish gradually increased. By analyzing the possible swimming corridors of the target fish, the slow-flowing areas near the suddenly narrowed swimming corridors were considered to be the areas of target fish clustering. The cluster areas of the target fish weres also the optimal choice of the fish passing facility entrances, so as to ensure the best fish-crossing effect. The reliable and quantitative 3D fish swimming corridors model proposed in this study can provide a scientific basis for the layout of fish-crossing facilities and facilitate the scientific operation and management of the reservoir in the fish spawning season.