Rates of Dissipation of Turbulent Kinetic Energy in a High Reynolds Number Tidal Channel

Geophysics/Hydrodynamics: Justine M. McMillan* and Alex E. Hay Department of Oceanography, Dalhousie University, Halifax, NS Canada. Rolf G. Lueck and Fabian Wolk Rockland Scientific Inc., Victoria, British Columbia, Canada (2016/02/19)

DOI: http://dx.doi.org/10.1175/JTECH-D-15-0167.1

Link: http://journals.ametsoc.org/doi/abs/10.1175/JTECH-D-15-0167.1

The ability to estimate the rate of dissipation (ε) of turbulent kinetic energy at mid-depth in a high speed tidal channel using broadband acoustic Doppler current profilers (ADCPs) is assessed by making comparisons to direct measurements of ε obtained using shear probes mounted on an underwater, streamlined buoy. The investigation was carried out in Grand Passage, Nova Scotia where the depth-averaged flow speed reached 2 m s−1 and the Reynolds number was 4 × 107. The speed-bin averaged dissipation rates estimated from the ADCP data agree with the shear probe data to within a factor of 2. Both the ADCP and the shear probe measurements indicate a linear dependence of ε on the cube of the flow speed during flood, and much lower dissipation rates during ebb. The ebb/flood asymmetry and the small-scale intermittency in ε are also apparent in the lognormal distributions of the shear probe data. Possible sources of bias and error in the ε estimates are investigated, and the most likely cause of the discrepancy between the ADCP and shear probe estimates is the cross channel separation of the instruments and the high degree of spatial variability that exists in the channel.