Flow balances in St. Andrew Bay revealed through hydrodynamic simulations

The circulation patterns in St. Andrew Bay, Florida are revealed through th e application of a well-tested, extensively used three-dimensional hydrodyn amic model. A high resolution grid resolving both the horizontal and vertic al directions is used with a systematically developed set of forcing functi ons to simulate conditions over a full year. Water levels at the three open boundaries are deduced from a year-long deployment of pressure gauges, and freshwater loadings are based upon drainage basin characteristics and prec ipitation measurements. Model validation involves comparisons with hydrogra phic casts taken at twelve stations distributed throughout the bay at month ly intervals. The relative average error between the observed and model-pre dicted salinity is 15% for the surface of the water column and 4% for the b ottom. The annual net flow balance consists of an influx of water at the tw o Intracoastal Waterway open boundaries, with that water exiting to the Gul f of Mexico. An average of about 100 m(3) s(-1) enters from East Bay and ab out 40 m(3) s(-1) enters through West Bay. On shorter time scales, the flow balance is quite variable both in terms of magnitude and direction. This s tudy also presents methods to overcome the paucity of data that is usually available for the development of such a model. These include techniques to take bottom pressure data sets with short gaps and create reliable sea surf ace elevation boundary conditions and to take precipitation data and draina ge basin characteristics and produce estimates of freshwater inflows.