A calibrated 3-D hydrodynamic and transport model for managing the salinity regime of the Indian River Lagoon

A three-dimensional hydrodynamic and transport model has been applied to the Florida's Indian River Lagoon (IRL) to develop a tool for managing salinity regime. The 3D model, known as the Environmental Fluid Dynamics Code, includes capabilities consistent with the complex estuarine environment. Thus, stratified residual flows and density stratification common estuaries can be simulated. An air-sea interaction sub-model also allows for specification of atmospheric forcing, which along with low frequency water-level oscillations from the coastal ocean, is responsible for residual circulation in the IRL. In this application, the model includes 1051 active water cells representing an area of the central IRL and a small area of the coastal ocean seaward of Sebastian Inlet. Variable sized model grid cells were used to provide higher resolution in the areas of interest. The model was driven by water level and salinity data acquired at fixed monitoring stations located at the north, south and ocean boundaries of the model domain. Calibration and validation of the model are based on comparison with measured data from four fixed stations within the IRL model domain. Results of the calibration and validation indicate that the model performs well under complex estuarine conditions and is capable of simulating the salinity and flow structure as it changes either at low frequency or abruptly due to episodic freshwater inflows. Production runs of the calibrated model demonstrated repeated patterns of salinity fluctuation. The patterns can be related to the impacts of episodic freshwater inflows coupled with residual flows forced by wind or volume exchange with the coastal ocean.