Short-term dispersion and turbulence in a complex-shaped estuarine embayment

Initial dispersion of material in complex-shaped embayments is examined using observations and scaling based in Crail Bay, Pelorus Sound, New Zealand in autumn of 2005. These observations show the highly variable nature of dispersive transport in an embayment with multiple headlands. Acoustic current profiler-derived typical flow speeds were around 0.05 m s−1 which resulted in drifter-derived short-term (<6 h) horizontal eddy diffusivities of the order of 1 m2 s−1 which is somewhat larger than the empirical paradigm. Microstructure estimates of the turbulent kinetic energy dissipation rate were in the range 10−9–10−7 m2 s−3, with some evidence that sidewalls influence the variability and that headlands increase the dissipation rate by at least and order of magnitude. A new parameter relating horizontal diffusivity to circulation and the tide is proposed. This and other scaling comparisons indicate that the headlands in Crail Bay create similar effects to those studied in other systems. However, the long decay times estimated for eddies here implies that they likely interact with other headlands, unlike some previously studied examples.