The turbulent structure of the bottom boundary layer in a tidal current

Measurements of turbulence in the neutrally stratified bottom boundary layer of a tidal current are described. It is shown that whereas the bottom boundary layer is similar to its atmospheric counterpart, in terms of appropriately scaled spectra of the turbulent velocity fluctuations and the Reynolds stress, there is less evidence to suggest that it is structurally similar when measured in terms of the Reynolds stress tensor components. These differences appear to be more pronounced in deep flows where there is some evidence to suggest that the indices of structural similarity may vary over the tidal cycle; this behaviour may be due in part to the presence of inactive motions in the boundary layer.