Many pumping stations in drainage & irrigation applications are currently equipped with conventional (not fish friendly designed) pumps. Field tests have been performed [1] for several pump types of a certain size at certain pumping conditions to assess survival rates of fish passing through pumps. In order to compare different pump types of different sizes at different pumping conditions, a general criterion is required.

Testing of fish friendliness of pumps is expensive and involves animal tests with living fish for which permits are required. Therefore, pump manufacturers prefer to perform fish friendliness tests for a single pump size. In order to convert such results to other pump sizes, a scaling law is desired. Van Esch [2, 3] made a first attempt to address scaling principles for fish friendliness of pumps.

In the current study a general criterion is described to predict fish friendliness of pumps by means of models of mortality rates of fish passing through pumps. The criterion is validated with literature data [1–3] and experimental full-scale test data from the newly developed fish-friendly axial flow concrete volute pump by Flowserve with an impeller diameter of 850 mm. The full-scale tests involved a total of 1800 roach, perch and eel deployed over 7 pumping conditions, including 3 different heads and 5 different rotational speeds.

The fish-friendliness criterion includes different aspects that together predict the survival rate of fish passing through pumps. The first and most important contributor is the impeller, which can have an axial, mixed or radial flow design. The criterion involves the leading edge shape of the blades. Secondly, the diffuser or volute is considered, which provides a strike probability with diffuser vanes or volute tongue(s). In case the gap between the trailing edge of the impeller vanes and the leading edge of the diffuser vanes or volute tongue(s) is small relative to the fish size, there is the possibility of a “scissor” effect. Research in the USA for fish friendliness of hydropower turbines [4–7] showed that shear velocity and pressure drops can be of importance. Also cavitation (involves pressure drop & vapor bubble implosions), recirculation and turbulence can influence survival rates. At this stage these flow effects are roughly captured using the pump performance curve. This way, extensive CFD calculations to evaluate detailed flow effects can be avoided. For open impellers, the gap between the impeller vanes and wear ring is included in the criterion. In addition, fish species-dependent effects are taken into account, since fish vary widely in their internal and external building plan. For instance salmonid, percid and cyprinid fish respond differently to the same pump design than for example eel. Sharp edges and rough surfaces (for example caused by cavitation, erosion or corrosion) can also be harmful to fish but are not included at this stage.

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