Temporal, Spatial, Statistical Distribution of the Rate of Dissipation of TKE in Islay Sound

Turbulence measurements were conducted with a vertical turbulence microstructure profiler (VMP) in the Sound of Islay, a tidal channel that is slated for of tidal energy extraction. The work is part of the Turbulence in the Marine Environment (TiME) project. The magnitude and variability of the measured rate of dissipation of turbulent kinetic energy (ε) in this environment are remarkable, and this data set provides new information for site assessments, numerical flow models, and engineering designs of tidal energy extraction devices.

The data were collected during spring tides and during maximum current speeds, which exceeded 4 m s⁻¹ in both directions. The turbulence is very intense with ε reaching up to 2×10^-3 W kg⁻¹, placing these data among the highest rates of dissipation measured in open natural water. A total of 108 profiles were collected along two north-south transect lines. The lines were separated in the east-west by 1600 m and straddle the location of a moored turbulence float and a bottom-mounted ADCP. There are no significant statistical variations in neither the meridional nor the zonal directions. However, the rate of dissipation is two times larger during current flow to the west compared to flow to the east, even though current to the west is slightly weaker than to the east.

Turbulence data from the vertical profiles agree well with those from the moored platform. The average and median rate of dissipation increases with increasing depth. The mean rate is projected to reach 1 and 2×10^-3 W kg⁻¹ at the bottom. The rate of dissipation is distributed lognormally with the standard deviation of 0.6, which means that there is a high probability of dissipation rates that are 10 times larger than the mean rate.