Estuaries

Unusual features of southeastern Australian estuaries

Generally there is a freshwater input at the head of the estuary. As the water flows through the estuary, it is mixed with seawater carried into the mouth with the incoming tide. The tidal outflow exceeds the tidal inflow so that there is a net movement of water through the estuary. Most southeastern Australian estuaries do not fit this model. Many have sand barriers across their mouths, which cut off or restrict the inflow of seawater for periods of months to several years. Also, under conditions of hot weather and low rainfall, in southeastern Australia evaporation of water from the estuary may be similar to the freshwater input. Under these conditions, salt concentrations in parts of the estuary will be similar to that of seawater, or even slightly higher. Evaporation rates of Southeastern Australian estuaries never greatly exceed the freshwater input which produces the hypersaline estuaries of northwestern Australia.

Importance of estuaries

Estuaries are used by the Australian population for transport, commercial and recreational pursuits. They are also important for fisheries and wildlife. They are highly productive coastal environments, providing habitat for a wide variety of fish and invertebrates (crabs, prawns and oysters) of commercial and recreational importance. Also estuaries provide food for many resident and migrant birds.