Assessing water renewal time scales for marine environments from three-dimensional modelling: A case study for Hervey Bay, Australia

We apply the three-dimensional COupled Hydrodynamical Ecological model for REgioNal Shelf Seas (COHERENS) to compute water renewal time scales for Hervey Bay, a large coastal embayment situated off the central eastern coast of Australia. Water renewal time scales are not directly observable but are derived indirectly from computational studies. Improved knowledge of these time scales assists in evaluating the water quality of coastal environments and can be utilised in sustainable marine resource management. Results from simulations with climatological September forcing are presented and compared to cruise data reported by Ribbe (2006). A series of simulations using idealised forcing provides detailed insight into water renewal pathways and regional differences in renewal timescales. We find that more than 85 % of the coastal embayment’s water is fully renewed within about 50-80 days. The eastern and western shallow coastal regions are ventilated more rapidly than the central, deeper part of the domain. The climatological simulation yields temperature and salinity patterns that are consistent with the observed situation and water renewal times scales in the range of those derived from idealised model studies. While the reported simulations involve many simplifications, the global assessment of the renewal time scale is in the range of a previous estimate derived for this coastal embayment from a simpler model and observational data.