Fluid shear arises when two bodies of water, travelling at different velocities, intersect. Fish entrained at the interface of these two water masses will experience shear stress; which can be harmful. The stress magnitude is dependent on waterbody mass and velocity; with the fish impact largely related to body size. Elevated shear stress occurs where rapidly flowing water passes near spillways, across screens, within turbine draft tubes or other passage routes. A flume was used to determine critical tolerances of silver shark (Balantiocheilos melanopterus) to different shear stress rates generated by a high velocity jet. Fish experienced higher levels of injury and mortality as shear stress was increased. Excessive shear forces had damaging impacts on fish. Mortality occurred at shear levels higher that 600/s. It is important that developers should attempt to model potential shear profiles expected during turbine passage in selected designs. These data will be critical to determine potential impacts on fish. If the likelihood of adverse impact is high, then alternative designs which have lower shear stress could be explored.
Revised: June 2, 2017 |
Published: February 9, 2017
Baumgartner L.J., G. Thorncraft, O. Phonekhampeng, C.A. Boys, A. Navarro, W. Robinson, and R.S. Brown, et al. 2017.High fluid shear strain causes injury in Silver shark: Preliminary implications for Mekong hydropower turbine design.Fisheries Management and Ecology 24, no. 3:193-198.PNNL-SA-115761.doi:10.1111/fme.12213