Australian estuaries can be classified into five groups on the basis of the
ir hydrology: Mediterranean, Temperate, Transitional, Arid Tropical and Sub
tropical, and Wet and Dry Tropical and Subtropical. Most Australian estuari
es (68%) are wet and dry tropical and subtropical systems. The five groups
of estuaries found in Australia are similar to those found in other parts o
f the world, but within each individual category the estuaries are more var
iable. This variability reflects a combination of the extreme hydrology of
Australian rivers and the geomorphology of Australian estuaries, which are
shallow due to tectonic stability and low coastal relief. Episodic freshwat
er flows control the transport, retention, and transformation of material i
n most Australian estuaries, and for only a small part of the year during h
igh flow events do most Australian rivers and estuaries contribute a signif
icant amount of material to the continental shelf. Research and monitoring
efforts need to be directed toward evaluating the role episodic freshwater
discharges play in the functioning of Australia's estuaries.