Measurement of net flow through a channel

The flow through the North Channel of the Irish Sea has been measured from summer 1993 to autumn 1994 by a surface current HF radar system, which covered the width of the channel, and a broadband 150 kHz ADCP. The ADCP was deployed in a low profile sea bed frame. Its transducers pointed at 20° to the vertical; currents were recorded in 5 m cells from 12.5 m above the sea bed to 15 m below the surface in 142 m of water. The ADCP´s backscattered signal exhibited daily and seasonal cycles consistent with the scatterers being zooplankton. Preliminary results showed that one surge was twice as large as the rest; near surface shear was confined at most to the top 15 m; the mean current at the ADCP site was directed out of the Irish Sea near the bed and into it near the surface; there was a strong surface flow out of the Irish Sea near the Scottish coast