Effects of wind and tide on upper-layer currents at Davies Reef, Great Barrier Reef, during MECOR (July-August 1984)

Abstract

At Davies Reef, flow over the east reef flat was unidirectional downwind at 10-20 cm s^-1 with strong winds and smaller tides but was semi-diurnal tidal reversing at 5-15 cm s^-1 with lighter winds and higher tides. The flood direction was to the south-east out of the lagoon and the ebb into the lagoon. Wave overtopping was estimated to contribute at least 40% of the flow over the reef flat-the first estimate of this component of flow over reef flats. Transit times over the reef flat were 30-170 min and flushing times for the east lagoon were estimated as ½ -1 day for strong winds to the north-west but 2-4 days for lighter winds.

In the east lagoon, the upper-layer currents were semi-diurnal tidal reversing all the time at speeds up to 20 cm s^-1, with longer-term net flow downwind at about 2 cm s^-1 with strong winds but upwind at 0.2 cm s^-1 with light winds. In the east passage, the strongly tidal currents (up to 60 cm s^-1.) had a long-term net flow to the south at about 2 cm s^-1 without any clear correlation with the wind.