Hervey Bay: a salt fountain in subtropical East Australia

Abstract

[Abstract]: Australia’s climate is one of the driest in the world with high year-to-year rainfall variability and many estuaries in the region are characterised by an inverse circulation. This flow is driven by high evaporation, low river runoff and the production of high salinity water in shallow coastal regions. Dense water moves as a gravity current along the seafloor toward the open ocean. To compensate for the outflow of high salinity water, oceanic water of lower salinity is entering the region at the surface. The Mediterranean Sea, the Gulf of California, the Persian Gulf, and Spencer Gulf in South Australia are examples of large ocean basins and coastal embayment which are characterised by inverse circulations. Similar conditions were found for Hervey Bay during a hydrographic survey conducted in early spring 2004. I discuss the observed salinity distribution and introduce a simple model that informs about water residence time scales. Analysis of the historical rainfall and river runoff data supports the hypothesis that the inverse circulation is a climatological feature of this estuary which is not limited to the dry season of the year. It is likely that due to declining rainfall in coastal northeast Australia, these conditions are to persist into the near future and need to be considered for coastal management.