A research team at the Technical University of Munich (TUM) investigated various types of hydropower plants and compared their effects on fish and fish habitats. They determined that while all hydropower plants and technologies can cause fish damage, but that alterations can be made to lower the probability of fish damage.
Hydropower is an important energy source for reducing CO2 emissions, but often draws criticism because of negative ecological impacts on aquatic ecosystems.
Jürgen Geist, professor for aquatic systems biology at TUM, and his team have been investigating the impacts of hydroelectric power plants on fish migrating downstream and on aquatic ecosystems since 2014. The team analyzed plants in southern Germany operated with various technologies and turbine types. The plants included modern hydroelectric plants such as those with VLH (very low head) turbines and low fall height, screw turbines and moveable power plants with Kaplan turbines. They also looked at conventional systems with Kaplan turbines.
Geist’s team analyzed fish mortality and specific injuries after the fish had passed a hydroelectric plant. They examined both natural downstream fish migration and fish they put into the water and later caught in standardized procedures. They also used a sonar system to analyze fish behavior in downstream migration.
“Sonar technology is especially well suited for capturing the movements of fish in front of hydroelectric power plants, because it functions independent of turbidity, light conditions and water depth,” Geist said.
In addition, the team looked at the composition of the aquatic ecosystems, including fish, invertebrate animals, water plants and algae. They also examined environmental factors such as temperature, dissolved oxygen and pH values of the upstream and downstream water.
One finding was that new hydroelectric power plants are not always better for fish. It has been assumed that modern power plants protect fish better, as they were designed to keep fish from swimming through the turbines or featured turbines that let fish pass through with the least possible damage.
“The mortality rates for the plants with newer technologies weren’t always lower than those of conventional plants,” said Geist.
The study shows that all, conventional and innovative, plants can cause fish damage. “Even with one and the same technology, significant differences in the effects on fish were observed, depending on the respective locational circumstances,” Geist said. Protection depends to a large extent on how the technologies are operated and implemented and what fish species are present in the water.
The investigations show a wide range in mortality rates and the patterns of injury to fish. This results from various factors, such as the anatomical and behavioral differences among the fish species. The location-specific circumstances of the plant — for example design, type of turbine, fall height and operational modes — play an important role as well.
Small fish in particular were found to follow the main flow and were not kept from passing through the turbines by strainer screens. At several power plants, most fish failed to use bypasses that would permit migrating fish to swim downstream around the plant. The decisive factors here are the directional effect of the strainer screens, water volumes in the drop tubes and position of the drop tubes.
In addition, running VLH and Kaplan turbines slower and reducing the number of blades lowers the probability of injuring fish. Other positive factors are maintaining the greatest possible distance between turbine blades and using the thickest or widest possible rounded blade edge. Injuries in screw turbines are primarily the result of collisions, which are particularly frequent at the entry edges of the turbine and at the turbine outlet.
Regarding aquatic ecology surrounding the plant, Geist said: “The negative impacts of the interruption of water and matter fluxes by transverse structures should be compensated for to the greatest extent possible. We recommend to keep the interruption of the river continuum to a minimum and to create alternative habitats for fish and other animals in the water and ecological restoration whenever possible.”
TUM is a European research university focused on the engineering sciences, natural sciences, life sciences and medicine, combined with economic and social sciences.
