Fishes are in risk of injury during their downstream migration via hydro-power plants. The knowledge on fish behavior in the near field of fish guidance structures is of importance for both the evaluation of their effectiveness and their optimization. However, up to now, fish-observations have been only qualitatively realized. In the first part of this project an automated image-based 2D Fish-Tracking Module had been developed. It is able to detect either the path of a single fish or the midpoint of a fish schooling from video recordings obtained during etho-hydraulic laboratory flume experiments (Fig. 1). The module is mainly based on the Computer Vision System Toolbox™ of the commercial software MATLAB. However, an unambiguous separation of the full path of each fish in a schooling still remains challenging. In the second part of the project, the 2D Fish-Tracking Module has now successfully been automatized, further developed, and applied to a large data set of different fish species (Fig. 1). The newly developed tool is now ready to be applied for analyzing extensive data sets.
The installation of Hydro Power Plants (HPPs) and dams may cause a number of problems for fish fauna. These include: blocking or delaying up- and downstream fish migrations, damage or mortality of fish when passing turbines or spillways, and mortality due to predation by fish or birds. As a result species population can decline. The revised Swiss Water Protection Act and Water Protection Ordinance introduced in 2011 aim at restoring water bodies and eliminating negative impacts of HPPs as to fish migration within the next 20 years. Similarly, the European water framework directive effective from 2000 demands undisturbed fish migration. For hydropower installations, new fish passages and connections to adjoining waterbodies must be erected, and existing structures must be reviewed and may have to be adapted if they do not function properly. As to downstream fish protection technologies this poses particular challenges to HPP operators and local authorities due to the current lack of design standards. Therefore, the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) conducted an interdisciplinary research project to develop innovative structural means to provide a working and safe downstream fish migration at large Central-European rivers in cooperation with the Swiss Federal Institute of Aquatic Science and Technology (Eawag). The project was commissioned by the Association of Aare-Rhine Power Plants (Verband Aare-Rheinwerke, VAR) and supported by swisselectric research, the Swiss Federal Office of Energy (SFOE, BFE) and the Swiss Federal Office for the Environment (FOEN, BAFU). The research project contributes to the sustainable and efficient usage of water power in Switzerland and Europe.
This study focused on mechanical behavioural fish guidance structures such as Louvers and angled bar racks. The former is characterized by bars which are set orthogonally to the main flow direction, β = 90° independent of the rack angle, a = 15° to 30° while the latter features slats that are always perpendicular to the rack axis, β = 90°−a (Fig. 1a). Both guidance structures create high turbulent flow zones, flow separations around the bars, and changes in flow velocities and directions, so that fish can sense them and react with behavioural avoidance. Successful applications of such structures exist at HPPs in the Northeast U.S. However, there is a lack of knowledge on the energy production losses caused by them, upstream and downstream flow fields and their guidance efficiency for the local fish species in Switzerland. To fill the research gap and further improve the geometry of angled bar racks (modified angled bar racks, β = 45° Fig. 1a), three physical model tests with the scales of 1:35, 1:2 and 1:1 were conducted in the laboratory.
In a first step the local hydraulic losses and the flow field near guidance structures were determined in a model scaled 1:2. Subsequently, ethohydraulic tests scaled 1:1 with live fish were conducted to quantify the guidance efficiency for typical European fish species (Fig. 1b, c). Finally, a general HPP model with a scale of 1:35 was employed to investigate the impacts of guidance structures on power production and plant operation.
The complete final report including design example is published as VAW report no. 230 (PDF, 48.8 MB).
A project overview is shown in this movie.