Hydraulic and biological aspects of fish passes for Atlantic salmon

This paper describes a series of novel experiments testing the relative efficiencies in passing juvenile salmon parr) through a range of model fish passes incorporating devices such as vertical slots, orifices, weirs, and combinations of all three. The hydraulic parameters-head loss, velocity patterns, and turbulence structure-were measured under each set of test conditions. A significantly higher proportion of fish moved through submerged orifices and vertical slots than through overflow weirs for any given flow rate, velocity, and head loss. The orifice and vertical slot efficiencies were directly correlated to the velocities at their entrances. To reach the tested devices, salmon parr tended to remain near the bottom of the flume and followed paths providing them with low velocities and cover along the sides of the test arena. The movements of salmon approaching entrances were consistent with energy-conserving strategies. The paper presents a tentative approach for computing energy expenditure for a range of fish pass devices.