Injury and Mortality to Fish Passing Through Pumping Stations

An unwanted side effect of pumping stations is that fish suffer from injury and mortality when passing through the pumps and that fish migration is hampered. In recent years, the development of so-called “fish-friendly pumping stations” is becoming a hot topic among European governmental institutions and pump manufacturers. In the Netherlands, many field studies have been conducted over the last decade, to assess the chances of survival for fish passing through pumps. However, a clear correlation between observed injury or mortality and (for example) flow rate, shaft speed or pump type could not be established. This paper presents a new analysis of the above mentioned field studies. It makes use of American studies on the biological criteria for fish injury, the most important of which are pressure changes, shear forces, and mechanical injury. A blade strike model was adapted to fish passing through centrifugal pumps of radial, mixed-flow, and axial type. It reveals the relation between fish injury and the type of pump, its size, shaft speed, and pressure head. The results correlate well with experiments. The flow through a typical mixed-flow pump is calculated using CFD. The results show that pressure fluctuations and shear forces are not likely to add to fish mortality. The paper concludes with guidelines for the design and selection of “fish-friendly pumps” in pumping stations.