Measurements of turbulence near the sea bed in a tidal current

The turbulent fluctuations of velocity have been measured, using an electromagnetic flowmeter, at heights up to 1.75 meters above the sea bed. The area of observations was off Anglesey, North Wales, in depths of 12 to 22 meters, on a firm, sandy bottom and during neutrally stable conditions. A number of records of the longitudinal (u) and vertical (w) components of velocity were obtained, and a few records included the lateral (v) component. From these the intensities, autocorrelations, and cross correlations for various time lags were computed and the corresponding u, v, w, and uw spectra were determined. Sufficient numbers of records have been obtained to enable mean values to be derived for a given set of physical conditions.