The project set out to reconcile two demanding objectives for modern river weirs: the protection of fish and other aquatic life and the efficient extraction of hydropower through a vertical‑axis turbine. Because these goals impose conflicting hydrodynamic constraints, the research required a comprehensive optimisation that combined large‑scale computational fluid dynamics (CFD) with experimental validation. The first phase focused on a single weir stage, while the second phase extended the analysis to a full cascade, ensuring that both fish‑friendly passage and energy yield were simultaneously maximised.

Using validated CFD models, the team characterised the flow field inside the weir, including the formation of vortices and the influence of a movable “shifter” (Schieber) that can alter the velocity profile. Simulations revealed that the vortex core depth depends strongly on the shifter length, and that optimal positioning of the shifter reduces peak velocities at the weir lip, thereby widening the velocity window that is safe for fish passage. The CFD results were compared with measurements taken with autonomous probes that mimic fish behaviour. The probes, equipped with real‑time sensors, were deployed in a pilot fish‑friendly weir in Bühlau and in a 1:1 model at TU Dresden. The experimental data confirmed the simulated velocity distributions and showed that the critical velocities for fish downstream migration were maintained below the thresholds identified in ecological studies.

Further simulations investigated the probability of collision between fish and the turbine blades. By varying the head difference between upstream and downstream channels, the researchers identified a range of operating conditions that minimise collision risk while preserving hydraulic performance. The cascade optimisation incorporated these findings, ensuring that each stage of the weir met the German DWA‑M 509 standard for fish passage. The final design achieved a balance between a channel diameter of less than five metres—required for ecological compliance—and sufficient head to drive the turbine. The cascade model also demonstrated that the overall energy extraction could be increased by up to 15 % compared with conventional weirs, without compromising fish passage.

The project’s collaborative framework was essential to its success. The core partners included the Institute of Water Engineering (IWD) at TU Dresden, the Institute of Fish Biology (IGF) in Jena, and Hydropower4U, which supplied the detailed geometry for the CFD studies. The Hochschule Zittau/Görlitz contributed ecological expertise, particularly in validating fish‑friendly criteria. After the departure of the industrial partner Käppler & Pausch GmbH, the consortium reorganised and maintained a productive schedule, extending the project duration cost‑neutrally to accommodate the full hydrodynamic investigations. The research was funded by German national research agencies, ensuring compliance with the EU Water Framework Directive and the German Water Resources Act.

In summary, the project delivered a scientifically robust, fish‑friendly weir design that integrates efficient energy extraction. Through iterative CFD modelling, experimental validation with autonomous probes, and a multidisciplinary partnership, the team produced a cascade configuration that satisfies both ecological and energetic requirements. The findings provide a set of best‑practice guidelines for future river‑bank power installations, supporting the broader goal of sustainable water‑resource management.