HF radar: A tool for coral reef planning and management

Abstract

This paper builds on previous research on turbulent kinetic energy concepts in the coral reef domain, and develops it as a management tool. HF ocean radar data from the southern Great Barrier Reef are used to identify times and locations when a critical value of the Simpson-Hunter parameter is exceeded and the water column becomes vertically mixed. When this happens, any stratification is removed and with it the potential for a warm surface layer to form under insolation is diminished. Further, it is the destruction of stratification that is a primary condition for mitigation of coral bleaching conditions. Therefore, the Simpson-Hunter parameter evaluated by HF ocean radar becomes an indicator of one of the drivers of a fully mixed water column; if this driver is present then irrespective of wind, waves or cloud cover, coral bleaching will be inhibited. This paper reviews the contribution that currents make to mixing in the water column and takes a further step to evaluate the use of surface current data to provide an index of vertical mixing. The phased array HF Ocean Radar deployed in the southern part of the Great Barrier Reef maps surface currents on a 4 km grid covering an area of over 150 km × 150 km. This instrument provides a map of surface currents with high spatial resolution every 10 minutes over the grid. Variation in maximum surface current is a strong indicator of variation in turbulent mixing, and over a meso-scale area one would expect to find some reefs that enjoy a more turbulent current regime, and hence exhibit more resilience against coral bleaching. The end-point of this research is to produce a map of the Capricorn/Bunker groups of islands and reefs in the southern Great Barrier Reef which shows relative susceptibility to coral bleaching.