Fish migration past a hydro power plant (HPP) requires not only flow in the actual fish passage (e.g. fish ladder) but also sufficient water to attract the fish to the entrance. Such attraction water is typically created by spilling water of the order of 10 m3/s, and there are potential savings if the amount of water can be reduced without loss of functionality.
The possibility to use ejectors (jet pumps) to pump water from the area downstream of the HPP into the fish passage has been investigated with physical model tests and numerical modelling (CFD). The ambition has been to make use of fairly simple geometries without changing the layout of the suggested fish ladder, and a solution in which the ejectors are located in a separate channel parallel to the fish ladder has been evaluated. The results show that the required spill can be reduced to 1/3 despite the low head (7 m) of the considered HPP, and the savings will be even larger in HPPs with higher head.
More energy efficient ways to attract fish can be obtained if the jets are positioned within the actual fish way, but a prerequisite for such solution is that the fish is not intimidated by the jets. Another interesting option to evaluate is the possibility to guide the fish to the fish ladder entrance by an array of individual jets positioned in the river. To investigate these ideas tests with live fish are scheduled during second half of 2018.