Often the upriver routes taken by fish are obstructed. „They can be made passable by the use of fish lift systems,“ explains Boris Lehmann, Professor of Hydraulic Engineering at the TU Darmstadt. Fish lifts are widely used including on the Ruhr, which contains many dams. The starting situation at Lake Baldeney is a little tricky, though. The system consists of three weir fields, a lock, a disused pumping station and a power station with two turbines. The difference in height between the upper and lower water is 8.75 metres, and there is no room along the shores for a conventional fish lift. „Finally, an interdisciplinary group of experts brought in a fish lift to be installed in the former pumping station,“ said Lehmann. The problem: there are no standard solutions for these kinds of systems. Furthermore, the licensing authority has issued special rules for constructions that need to be built in a special way. For instance, it has to be proved in advance that the fish will be able to access and use the lift.
In order to provide this evidence, Boris Lehmann‘s team – initially still working at the Karlsruhe Institute for Technology (KIT) – designed an ethohydraulic investigation concept. Ecological and biological issues are linked with engineering calculations in order to achieve the optimum results. But how is it possible to know in advance which route the fish really will take? „The river flow is the most important criterion for the orientation of the fish,“ explains Lehmann.
Flow conditions can easily be simulated on a computer using hydrodynamic-numerical models. In particular, the team looked at all the relevant outflow and operating conditions of the barrage, especially when the power station‘s turbines were in operation. The simulations were calibrated using a wide range of data, measurements and observations made on site. The calculated flow conditions were then used to estimate the migratory corridors of the fish.
The findings of all the preliminary investigations culminated in a large-scale model of the fish lift that was constructed in the test channel of the hydraulic engineering laboratory at the KIT. Two lifts were positioned beside each other in order to ensure that the barrage could be swum through at all times, as required by the authority. While one lift is in operation, the fish can be guided into and collected in the other.
Their swimming in and out is initiated by the calculated guiding current that can be halted by means of regulating elements. Trials with fish resulted in extremely good functionality of the system – and the evidence of function was provided. „When the lift goes into operation,“ says Lehmann, „then during the spawning season thousands of fish can be transported into the upper water of the Ruhr.“
Project and partners
An ethohydraulic investigation concept was carried out for the Ruhr weir on Lake Baldeney by the Department of Hydraulic Engineering at the TU Darmstadt in order to provide proof of functionality of a fish lift system. The project partners are the Institute for Water and Water Body Development at the KIT, the company Hydroenergie Roth, the Office for Environmental Planning, Water Body Management and Fishing, and LFV Hydroakustik GmbH.