Piping fish over dams

Hydraulic structures disrupt fish migration thereby contributing to declines in fish populations around the world. Methods for piping fish upstream over dams can offer much steeper lift than conventional fishways. We describe the lifting mechanism of a tube fishway, demonstrated using numerical modelling, verified by a physical model. Efficacy is demonstrated by safely lifting two species of Australian native fish over 8 m up an embankment. Significant volumes of water can be transported from a chamber at the foot of a dam over its crest using simple conduits and two valves. Unsteady flow contributes entirely or significantly to the volume of water lifted. We explore how this piped system could be scaled up, while controlling turbulence impacts on fish. We propose new methods of characterising hydraulic efficiency for fishways that recognise the energy used and the value of the water discharged.