Simulation of tides, salinity and temperature within Chesapeake Bay

A tidal model of the Chesapeake Bay has been built using the Dartmouth FEM Quoddy programs to provide predictions of water levels for navigational use. A barotropic model will accurately simulate the tides provided the bottom bathymetry and drag coefficient have been tuned to provide the best match of tidal water level heights at a number of stations in the bay. The baroclinic model with turbulence closure decouples the bottom drag coefficient from the water column through turbulence suppression by salinity stratification. In addition it is noted that vertical diffusivities are episodically large in both time and space. The turbulence in a large tidal estuary, such as the Chesapeake Bay, is a complicated process which depends upon strain induced periodic stratification. A horizontal Richardson number is used to explain the sensitivity of the episodic mixing to the horizontal salinity gradient and tidal current magnitudes. The parameter shows that the bay dynamics are usually in the range of transition from stratification-suppressed turbulence and well mixed enhanced turbulence, fluctuating with every tidal cycle.