Hervey Bay: an inverse subtropical estuary

Abstract

[Abstract]: Declining rainfall, persistent drought conditions along Queensland coasts and increasing temperatures are impacting upon hydrological and coastal marine conditions. During a four day hydrographic survey into Hervey Bay, near-coast salinity values were found to be higher than those of oceanic water. This distribution of salinity is indicative of an inverse circulation within the Bay. The evaporation-precipitation-runoff balance which is dominated by a net loss of freshwater leading to the production of high salinity water during the period of the survey yields further evidence of a possible inverse circulation within the Bay. To compensate for the export of this high salinity water, oceanic water with lower salinity is entering the Bay at the surface. Analysis of the historical water balance indicates that the inverse circulation is likely to be a climatological feature of this estuary which is not limited to the dry season of the year. Simple physical modelling of the oceanic circulation led to some insight into Bay flushing and water exchange time scales between Bay and oceanic water. Due to declining rainfall in coastal northeast Australia, inverse circulation conditions are likely to persist into the near future and should to be considered for coastal management.