Coupled Physical-biological Modelling of an Estuary


Principal Investigator

Clifford J. Hearn

Geography and Oceanography,


University of New South Wales


Barbara Robson

Geography and Oceanography


University of New South Wales


h05 - VPP

A three-dimensional model was applied to two
shallow mediterranean estuaries: Harvey Estuary
in southwestern Australia, and Tomales Bay, California. The model provided a tool which was used to compare the two systems and examine the major physical factors affecting conditions in estuaries of this class. This work also provides a basis for biological applications of the model with a view to exmining interactions between the hydrodynamics of the Harvey Estuary and severe cyanobacterial blooms that were observed in the Estuary between 1978 and 1994.


What are the results to date and the future of this work?

The model successfully reproduced observed seasonal and interannual patterns in salinity and temperature in the Harvey Estuary and in Tomales Bay over a period of several years. The model was then applied to the two systems with various forcing conditions, to allow an examination of major factors affecting the systems.

Wind was found to be a dominant forcing factor for Harvey Estuary, and tidal forcing was important in both systems, affecting the two estuaries in different ways. The effect of length on estuaries of this class was also considered. This work was described in a talk entitled "Hydrodynamics of shallow mediterranean estuaries" at the AMOS '99 conference. A paper describing these results is to be submitted to 'Estuarine, Coastal and Shelf Science' in March, 1999.

Basic oxygen and sediment-phosphorus dynamics have also been incorporated into the model. A clear relationship between wind stress in the Harvey Estuary and bottom oxygen concentrations is indicated. Work on this front continues.

A complete description of this work will be included in a PhD thesis (by Barbara Robson) to be completed by mid 1999.

Appendix B -



What computational techniques are used?

The model used is a three-dimensional, primitive equation hydrodynamic model based on the widely-used Princeton Ocean Model. This uses central differencing in time and incorporates a split time-step to allow explicit horizontal differencing and calculations in two-dimensions with a short time-step in the external mode while at the same time using implicit vertical differencing and calculation of three-dimensional variables with a longer time-step in the internal mode.

The program involves many loops to calculate values at each time-step in arrays with dimensions of approximately 47x15x7. Vectorisation in excess of 50% on the VPP considerably enhanced the speed of model runs.

- Appendix B