Scientists at the Virginia Institute of Marine Science (VIMS), Department of Physical Sciences, have developed a general purpose, three-dimensional numerical model which is an integration of a hydrodynamic model, a sediment transport model, and a water quality (eutrophication) model. The model can be applied to a wide variety of environmental problems and can operate at a variety of temporal and spatial scales in coastal embayments, estuaries and tributaries.

The 'domain' of the model (area of coverage) can vary from entire embayments (e.g., the Chesapeake Bay and all its tributaries) to individual river estuaries (e.g., the James, York and Rappahannock Rivers in Virginia). To implement the HEM-3D model, a gridwork of 'cells' must be constructed that accurately fits the plan-view outline of the water body and a depth for each cell must be added from bathymetric surveys. Coarse-grids in large embayments use fewer cells relatively large in size to achieve low or moderate resolution. Fine-grids in small estuaries use many small cells where high resolution is important (e.g., release of point source materials).

For a given model domain, the trade-off comes in trying not to cover too large an area with too fine a grid; otherwise, days of computer time may be needed to complete one model run! VIMS plans to implement several HEM-3D model grids of varying resolution to cover a broad range of situations now anticipated by marine scientists in many disciplines. And we are always looking for faster, cheaper computers!

Applications of interest:

• Chesapeake Bay
• York River

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